Environmental Monitoring	Parameters	Limit Level (LL)
Air Quality	1-hr TSP	0
24-hr TSP	0
Noise	L_{eq (30 min)}	0
Water Quality	Suspended solids level (SS)	0
Turbidity level	0
Dissolved oxygen level (DO)	0

1 Introduction

1.1 Basic Project Information

1.1.1 The Hong Kong-Zhuhai-Macao Bridge (HZMB) Hong Kong Link Road (HKLR) serves to connect the HZMB Main Bridge at the Hong Kong Special Administrative Region (HKSAR) Boundary and the HZMB Hong Kong Boundary Crossing Facilities (HKBCF) located at the north eastern waters of the Hong Kong International Airport (HKIA).

1.1.2 The HKLR project has been separated into two contracts. They are Contract No. HY/2011/03 Hong Kong-Zhuhai-Macao Bridge Hong Kong Link Road-Section between Scenic Hill and Hong Kong Boundary Crossing Facilities (hereafter referred to as the Contract) and Contract No. HY/2011/09 Hong Kong-Zhuhai-Macao Bridge Hong Kong Link Road-Section between HKSAR Boundary and Scenic Hill.

1.1.3 China State Construction Engineering (Hong Kong) Ltd. was awarded by Highways Department (Heed) as the Contractor to undertake the construction works of Contract No. HY/2011/03. The Contract is part of the HKLR Project and HKBCF Project, these projects are considered to be “Designated Projects”, under Schedule 2 of the Environmental Impact Assessment (EIA) Ordinance (Cap 499) and Environmental Impact Assessment (EIA) Reports (Register No. AEIAR-144/2009 and AEIAR-145/2009) were prepared for the Project. The current Environmental Permit (EP) EP-352/2009/D for HKLR and EP-353/2009/K for HKBCF were issued on 22 December 2014 and 11 April 2016, respectively. These documents are available through the EIA Ordinance Register. The construction phase of Contract was commenced on 17 October 2012. The works area WA5 and WA7 were handed over to other party on 22 June 2013 and 28 February 2018 respectively. The works area WA3 and WA4 were handed over to Highways Department on 23 December 2019 and 14 March 2019 respectively. Figure 1.1 shows the project site boundary. The works areas are shown in Appendix O.

1.1.4 The Contract includes the following key aspects:

· New reclamation along the east coast of the approximately 23 hectares.

· Tunnel of Scenic Hill (Tunnel SHT) from Scenic Hill to the new reclamation, of approximately 1km in length with three (3) lanes for the east bound carriageway heading to the HKBCF and four (4) lanes for the westbound carriageway heading to the HZMB Main Bridge.

· An abutment of the viaduct portion of the HKLR at the west portal of Tunnel SHT and associated road works at the west portal of Tunnel SHT.

· An at grade road on the new reclamation along the east coast of the HKIA to connect with the HKBCF, of approximately 1.6 km along dual 3-lane carriageway with hard shoulder for each bound.

· Road links between the HKBCF and the HKIA including new roads and the modification of existing roads at the HKIA, involving viaducts, at grade roads and a Tunnel HAT.

· A highway operation and maintenance area (HMA) located on the new reclamation, south of the Dragonair Headquarters Building, including the construction of buildings, connection roads and other associated facilities.

· Associated civil, structural, building, geotechnical, marine, environmental protection, landscaping, drainage and sewerage, tunnel and highway electrical and mechanical works, together with the installation of street lightings, traffic aids and sign gantries, water mains and fire hydrants, provision of facilities for installation of traffic control and surveillance system (TCSS), reprovisioning works of affected existing facilities, implementation of transplanting, compensatory planting and protection of existing trees, and implementation of an environmental monitoring and audit (EM&A) program.

1.1.5 This is the 150^th Monthly EM&A report for the Contract which summarizes the monitoring results and audit findings of the EM&A programme during the reporting period from 1 to 31 March 2025.

1.1.6 BMT Hong Kong Limited was appointed by the Contractor to implement the EM&A programme for the Contract in accordance with the Updated EM&A Manual for HKLR (Version 1.0) and provided environmental team services to the Contract until 31 July 2020.

1.1.7 Meinhardt Infrastructure and Environment Limited has been appointed by the Contractor to implement the Environmental Monitoring & Audit (EM&A) programme for the Contract in accordance with the Updated EM&A Manual for HKLR (Version 1.0) and provide environmental team services to the Contract with effective from 1 August 2020. Ramboll Hong Kong Limited was employed by HyD as the Independent Environmental Checker (IEC) and Environmental Project Office (ENPO) for the Project until 30 September 2022. ANewR Consulting Limited has been appointed by HyD as the Independent Environmental Checker (IEC) and Environmental Project Office (ENPO) for the Project since 1 October 2022. The project organization with regard to the environmental works is as follows.

1.2 Project Organisation

1.2.1 The project organization structure and lines of communication with respect to the on-site environmental management structure is shown in Appendix A. The key personnel contact names and numbers are summarized in Table 1.1.

Table 1.1 Contact Information of Key Personnel

Party	Position	Name	Telephone	Fax
Supervising Officer’s Representative (Ove Arup & Partners Hong Kong Limited)	(Senior Resident Engineer, SRE)	Eddie Tsang	3968 4802	2109 1882
Environmental Project Office / Independent Environmental Checker (ANewR Consulting Limited)	Environmental Project Office Leader	Louis Kwan	9275 0975	3007 8448
	Independent Environmental Checker	James Choi	6122 5213	3007 8448
Contractor (China State Construction Engineering (Hong Kong) Ltd.)	Project Manager	S. Y. Tse	3968 7002	2109 2588
	Environmental Officer	Federick Wong	3968 7117	2109 2588
Environmental Team (Meinhardt Infrastructure and Environment Limited)	Environmental Team Leader	Claudine Lee	2859 5409	2559 0738
724 hours complaint hotline	---	---	5699 5730	---

1.3 Construction Programme

1.3.1 A copy of the Contractor’s construction programme is provided in Appendix B.

1.4 Construction Works Undertaken During the Reporting Month

1.4.1 A summary of the construction activities undertaken during this reporting month is shown in Table 1.2.

Table 1.2 Construction Activities During Reporting Month

Description of Activities	Site Area
Removal of Temporary Toe Loading Platform	Portion X

2 Air Quality Monitoring

2.1 Monitoring Requirements

2.1.1 In accordance with the Contract Specific EM&A Manual, baseline 1-hour and 24-hour TSP levels at two air quality monitoring stations were established. Impact 1-hour TSP monitoring was conducted for at least three times every 6 days, while impact 24-hour TSP monitoring was carried out for at least once every 6 days. The Action and Limit Level for 1-hr TSP and 24-hr TSP are provided in Table 2.1 and Table 2.2, respectively.

Table 2.1 Action and Limit Levels for 1-hour TSP

Monitoring Station	Action Level, µg/m³	Limit Level, µg/m³
AMS 5 – Ma Wan Chung Village (Tung Chung)	352	500
AMS 6 – Dragonair / CNAC (Group) Building (HKIA)	360	500

Table 2.2 Action and Limit Levels for 24-hour TSP

Monitoring Station	Action Level, µg/m³	Limit Level, µg/m³
AMS 5 – Ma Wan Chung Village (Tung Chung)	164	260
AMS 6 – Dragonair / CNAC (Group) Building (HKIA)	173	260

2.2 Monitoring Equipment

2.2.1 24-hour TSP air quality monitoring was performed using High Volume Sampler (HVS) located at each designated monitoring station. The HVS meets all the requirements of the Contract Specific EM&A Manual. Portable direct reading dust meters were used to carry out the 1-hour TSP monitoring. Brand and model of the equipment is given in Table 2.3.

Table 2.3 Air Quality Monitoring Equipment

Equipment	Brand and Model
Portable direct reading dust meter (1-hour TSP)	Sibata Digital Dust Indicator (Model No. LD-5R)
High Volume Sampler (24-hour TSP)	Tisch Environmental Mass Flow Controlled Total Suspended Particulate (TSP) High Volume Air Sampler (Model No. TE-5170)

2.3 Monitoring Locations

2.3.1 Monitoring locations AMS5 and AMS6 were set up at the proposed locations in accordance with Contract Specific EM&A Manual.

2.3.2 Figure 2.1 shows the locations of monitoring stations. Table 2.4 describes the details of the monitoring stations. The existing air quality monitoring location AMS6 - Dragonair / CNAC (Group) Building (HKIA) was handed over to Airport Authority Hong Kong on 31 March 2021. 1 hr and 24 hr air quality monitoring at AMS6 was temporarily suspended starting from 1 April 2021 and resumed on 7 August 2024.

Table 2.4 Locations of Impact Air Quality Monitoring Stations

Monitoring Station	Location
AMS5	Ma Wan Chung Village (Tung Chung)
AMS6	Dragonair / CNAC (Group) Building (HKIA)

2.4 Monitoring Parameters, Frequency and Duration

2.4.1 Table 2.5 summarizes the monitoring parameters, frequency and duration of impact TSP monitoring.

Table 2.5 Air Quality Monitoring Parameters, Frequency and Duration

Parameter	Frequency and Duration
1-hour TSP	Three times every 6 days while the highest dust impact was expected
24-hour TSP	Once every 6 days

2.5 Monitoring Methodology

2.5.1 24-hour TSP Monitoring

(a) The HVS was installed in the vicinity of the air sensitive receivers. The following criteria were considered in the installation of the HVS.

(i) A horizontal platform with appropriate support to secure the sampler against gusty wind was provided.

(ii) The distance between the HVS and any obstacles, such as buildings, was at least twice the height that the obstacle protrudes above the HVS.

(iii) A minimum of 2 meters separation from walls, parapets and penthouse for rooftop sampler was provided.

(iv) No furnace or incinerator flues are nearby.

(v) Airflow around the sampler was unrestricted.

(vi) Permission was obtained to set up the samplers and access to the monitoring stations.

(vii) A secured supply of electricity was obtained to operate the samplers.

(viii) The sampler was located more than 20 meters from any dripline.

(ix) Any wire fence and gate, required to protect the sampler, did not obstruct the monitoring process.

(x) Flow control accuracy was kept within ±2.5% deviation over 24-hour sampling period.

(b) Preparation of Filter Papers

(i) Glass fibre filters, G810 were labelled and sufficient filters that were clean and without pinholes were selected.

(ii) All filters were equilibrated in the conditioning environment for 24 hours before weighing. The conditioning environment temperature was around 25 °C and not variable by more than ±3 °C; the relative humidity (RH) was < 50% and not variable by more than ±5%. A convenient working RH was 40%.

(iii) All filter papers were prepared and analysed by ALS Technichem (HK) Pty Ltd., which is a HOKLAS accredited laboratory and has comprehensive quality assurance and quality control programmes.

(i) The power supply was checked to ensure the HVS works properly.

(ii) The filter holder and the area surrounding the filter were cleaned.

(iii) The filter holder was removed by loosening the four bolts and a new filter, with stamped number upward, on a supporting screen was aligned carefully.

(iv) The filter was properly aligned on the screen so that the gasket formed an airtight seal on the outer edges of the filter.

(v) The swing bolts were fastened to hold the filter holder down to the frame. The pressure applied was sufficient to avoid air leakage at the edges.

(vi) Then the shelter lid was closed and was secured with the aluminium strip.

(vii) The HVS was warmed-up for about 5 minutes to establish run-temperature conditions.

(viii) A new flow rate record sheet was set into the flow recorder.

(ix) On site temperature and atmospheric pressure readings were taken and the flow rate of the HVS was checked and adjusted at around 1.1 m³/min, and complied with the range specified in the Updated EM&A Manual for HKLR (Version 1.0) (i.e. 0.6-1.7 m³/min).

(x) The programmable digital timer was set for a sampling period of 24 hours, and the starting time, weather condition and the filter number were recorded.

(xi) The initial elapsed time was recorded.

(xii) At the end of sampling, on site temperature and atmospheric pressure readings were taken and the final flow rate of the HVS was checked and recorded.

(xiii) The final elapsed time was recorded.

(xiv) The sampled filter was removed carefully and folded in half length so that only surfaces with collected particulate matter were in contact.

(xv) It was then placed in a clean plastic envelope and sealed.

(xvi) All monitoring information was recorded on a standard data sheet.

(xvii) Filters were then sent to ALS Technichem (HK) Pty Ltd. for analysis.

(d) Maintenance and Calibration

(i) The HVS and its accessories were maintained in good working condition, such as replacing motor brushes routinely and checking electrical wiring to ensure a continuous power supply.

(ii) 5-point calibration of the HVS was conducted using TE-5025A Calibration Kit prior to the commencement of baseline monitoring. Bi-monthly 5-point calibration of the HVS will be carried out during impact monitoring.

(iii) Calibration certificate of the HVSs are provided in Appendix C.

2.5.2 1-hour TSP Monitoring

(a) Measuring Procedures

The measuring procedures of the 1-hour dust meter were in accordance with the Manufacturer’s Instruction Manual as follows:-

(i) Turn the power on.

(ii) Close the air collecting opening cover.

(iii) Push the “TIME SETTING” switch to [BG].

(iv) Push “START/STOP” switch to perform background measurement for 6 seconds.

(v) Turn the knob at SENSI ADJ position to insert the light scattering plate.

(vi) Leave the equipment for 1 minute upon “SPAN CHECK” is indicated in the display.

(vii) Push “START/STOP” switch to perform automatic sensitivity adjustment. This measurement takes 1 minute.

(viii) Pull out the knob and return it to MEASURE position.

(ix) Push the “TIME SETTING” switch the time set in the display to 3 hours.

(x) Lower down the air collection opening cover.

(xi) Push “START/STOP” switch to start measurement.

(b) Maintenance and Calibration

(i) The 1-hour TSP meter was calibrated at 1-year intervals against a Tisch Environmental Mass Flow Controlled Total Suspended Particulate (TSP) High Volume Air Sampler. Calibration certificates of the Laser Dust Monitors are provided in Appendix C.

2.6 Monitoring Schedule for the Reporting Month

2.6.1 The schedule for air quality monitoring in March 2025 is provided in Appendix D.

2.7 Monitoring Results

2.7.1 The monitoring results for 1-hour TSP and 24-hour TSP are summarized in Tables 2.6 and 2.7 respectively. Detailed impact air quality monitoring results and relevant graphical plots are presented in Appendix E. The existing air quality monitoring location AMS6 - Dragonair / CNAC (Group) Building (HKIA) was handed over to Airport Authority Hong Kong on 31 March 2021. 1-hr and 24-hr TSP monitoring at AMS6 was temporarily suspended starting from 1 April 2021 and resumed on 7 August 2024.

Table 2.6 Summary of 1-hour TSP Monitoring Results During the Reporting Month

Monitoring Station	Average (mg/m³)	Range (mg/m³)	Action Level (mg/m³)	Limit Level (mg/m³)
AMS5	100	67-122	352	500
AMS6	79	49-110	360	500

Table 2.7 Summary of 24-hour TSP Monitoring Results During the Reporting Month

Monitoring Station	Average (mg/m³)	Range (mg/m³)	Action Level (mg/m³)	Limit Level (mg/m³)
AMS5	33	18-53	164	260
AMS6	40	25-71	173	260

2.7.2 No Action and Limit Level exceedances of 1-hr TSP and 24-hr TSP were recorded at station AMS5 and AMS6 during the reporting month. The event action plan is annexed in Appendix F.

2.7.3 On-site wind meter was irreparably damaged and the wind data could not be retrieved since August 2019. As the wind data could not be monitored, the wind data during this reporting month were reference to the wind data obtained from Hong Kong Observatory’s Chek Lap Kok weather station. The wind data obtained from Chek Lap Kok weather station are shown in Appendix G.

3 Noise Monitoring

3.1 Monitoring Requirements

3.1.1 In accordance with the Contract Specific EM&A Manual, impact noise monitoring was conducted for at least once per week during the construction phase of the Project. The Action and Limit level of the noise monitoring is provided in Table 3.1.

Table 3.1 Action and Limit Levels for Noise during Construction Period

Monitoring Station	Time Period	Action Level	Limit Level
NMS5 – Ma Wan Chung Village (Ma Wan Chung Resident Association) (Tung Chung)	0700-1900 hours on normal weekdays	When one documented complaint is received	75 dB(A)

3.2 Monitoring Equipment

3.2.1 Noise monitoring was performed using sound level meters at each designated monitoring station. The sound level meters deployed comply with the International Electrotechnical Commission Publications (IEC) 651:1979 (Type 1) and 804:1985 (Type 1) specifications. Acoustic calibrator was deployed to check the sound level meters at a known sound pressure level. Brand and model of the equipment are given in Table 3.2.

Table 3.2 Noise Monitoring Equipment

Equipment	Brand and Model
Integrated Sound Level Meter	RION NL-52
Acoustic Calibrator	RION NC-74

3.3 Monitoring Locations

3.3.1 Monitoring location NMS5 was set up at the proposed locations in accordance with Contract Specific EM&A Manual.

3.3.2 Figure 2.1 shows the locations of monitoring stations. Table 3.3 describes the details of the monitoring stations.

Table 3.3 Locations of Impact Noise Monitoring Stations

Monitoring Station	Location
NMS5	Ma Wan Chung Village (Ma Wan Chung Resident Association) (Tung Chung)

3.4 Monitoring Parameters, Frequency and Duration

3.4.1 Table 3.4 summarizes the monitoring parameters, frequency and duration of impact noise monitoring.

Table 3.4 Noise Monitoring Parameters, Frequency and Duration

Parameter	Frequency and Duration
30-mins measurement at each monitoring station between 0700 and 1900 on normal weekdays (Monday to Saturday). L_eq, L₁₀ and L₉₀ would be recorded.	At least once per week

3.5 Monitoring Methodology

3.5.1 Monitoring Procedure

(a) The sound level meter was set on a tripod at a height of 1.2 m above the podium for free-field measurements at NMS5. A correction of +3 dB(A) shall be made to the free field measurements.

(b) The battery condition was checked to ensure the correct functioning of the meter.

(i) frequency weighting: A

(ii) time weighting: Fast

(iii) time measurement: L_{eq(30-minutes)} during non-restricted hours i.e. 07:00 – 1900 on normal weekdays

(d) Prior to and after each noise measurement, the meter was calibrated using the acoustic calibrator for 94.0 dB(A) at 1000 Hz. If the difference in the calibration level before and after measurement was more than 1.0 dB(A), the measurement would be considered invalid and repeat of noise measurement would be required after re-calibration or repair of the equipment.

(e) During the monitoring period, the L_eq, L₁₀ and L₉₀ were recorded. In addition, site conditions and noise sources were recorded on a standard record sheet.

(f) Noise measurement was paused during periods of high intrusive noise (e.g. dog barking, helicopter noise) if possible. Observations were recorded when intrusive noise was unavoidable.

(g) Noise monitoring was cancelled in the presence of fog, rain, wind with a steady speed exceeding 5m/s, or wind with gusts exceeding 10m/s. The wind speed shall be checked with a portable wind speed meter capable of measuring the wind speed in m/s.

3.5.2 Maintenance and Calibration

(a) The microphone head of the sound level meter was cleaned with soft cloth at regular intervals.

(b) The meter and calibrator were sent to the supplier or HOKLAS laboratory to check and calibrate at yearly intervals.

3.6 Monitoring Schedule for the Reporting Month

3.6.1 The schedule for construction noise monitoring in March 2025 is provided in Appendix D.

3.7 Monitoring Results

3.7.1 The monitoring results for construction noise are summarized in Table 3.5 and the monitoring results and relevant graphical plots are provided in Appendix E.

Table 3.5 Summary of Construction Noise Monitoring Results During the Reporting Month

Monitoring Station	Average L_{eq (30 mins)}, dB(A)	Range of L_{eq (30 mins)}, dB(A)	Limit Level L_{eq (30 mins)}, dB(A)
NMS5	66	62-69	75

*A correction factor of +3dB(A) from free field to facade measurement was included.

3.7.2 There were no Action and Limit Level exceedances for noise during daytime on normal weekdays of the reporting month

3.7.3 Other noise sources during the noise monitoring included aircraft noise and human activities nearby.

3.7.4 The event action plan is annexed in Appendix F.

4 Water Quality Monitoring

4.1 Monitoring Requirements

4.1.1 Impact water quality monitoring was carried out to ensure that any deterioration of water quality is detected, and that timely action is taken to rectify the situation. For impact water quality monitoring, measurements were taken in accordance with the Contract Specific EM&A Manual. Table 4.1 shows the established Action/Limit Levels for the environmental monitoring works. The ET proposed to amend the Acton Level and Limit Level for turbidity and suspended solid and EPD approved ET’s proposal on 25 March 2013. Therefore, Action Level and Limit Level for the Contract have been changed since 25 March 2013.

4.1.2 The original and revised Action Level and Limit Level for turbidity and suspended solid are shown in Table 4.1. The event action plan is annexed in Appendix F.

Table 4.1 Action and Limit Levels for Water Quality

Parameter (unit)	Water Depth	Action Level	Limit Level
Dissolved Oxygen (mg/L) (surface, middle and bottom)	Surface and Middle	5.0	4.2 except 5 for Fish Culture Zone
Dissolved Oxygen (mg/L) (surface, middle and bottom)	Bottom	4.7	3.6
Turbidity (NTU)	Depth average	27.5 or 120% of upstream control station’s turbidity at the same tide of the same day; The action level has been amended to “27.5 *and* 120% of upstream control station’s turbidity at the same tide of the same day” since 25 March 2013.	47.0 or 130% of turbidity at the upstream control station at the same tide of same day; The limit level has been amended to “47.0 *and* 130% of turbidity at the upstream control station at the same tide of same day” since 25 March 2013.
Suspended Solid (SS) (mg/L)	Depth average	23.5 or 120% of upstream control station’s SS at the same tide of the same day; The action level has been amended to “23.5 *and* 120% of upstream control station’s SS at the same tide of the same day” since 25 March 2013.	34.4 or 130% of SS at the upstream control station at the same tide of same day and 10mg/L for Water Services Department Seawater Intakes; The limit level has been amended to “34.4 *and* 130% of SS at the upstream control station at the same tide of same day and 10mg/L for Water Services Department Seawater Intakes” since 25 March 2013

Notes:

(1) Depth-averaged is calculated by taking the arithmetic means of reading of all three depths.

(2) For DO, non-compliance of the water quality limit occurs when monitoring result is lower that the limit.

(3) For SS & turbidity non-compliance of the water quality limits occur when monitoring result is higher than the limits.

(4) The change to the Action and limit Levels for Water Quality Monitoring for the EM&A works was approved by EPD on 25 March 2013.

4.2 Monitoring Equipment

4.2.1 Table 4.2 summarizes the equipment used in the impact water quality monitoring programme.

Table 4.2 Water Quality Monitoring Equipment

Equipment	Brand and Model
DO and Temperature Meter, Salinity Meter, Turbidimeter and pH Meter	YSI Model 6820 (V2) YSI Pro Quatro
Positioning Equipment	Garmin GPS72H
Water Depth Detector	Lowrance x-4
Water Sampler	Kahlsio Water Sampler (Vertical) 2.2 L with messenger

4.3 Monitoring Parameters, Frequency and Duration

4.3.1 Table 4.3 summarizes the monitoring parameters, frequency and monitoring depths of impact water quality monitoring as required in the Contract Specific EM&A Manual.

Table 4.3 Impact Water Quality Monitoring Parameters and Frequency

Monitoring Stations

Parameter, unit

Frequency

No. of depth

Impact Stations:
IS5, IS(Mf)6, IS7, IS8(N), IS(Mf)9 & IS10(N)

Control/Far Field Stations:
CS2(A) & CS(Mf)5,

Sensitive Receiver Stations:
SR3(N), SR4(N2), SR5(N), SR10A(N) & SR10B(N2)

· Depth, m

· Temperature, ^oC

· Salinity, ppt

· Dissolved Oxygen (DO), mg/L

· DO Saturation, %

· Turbidity, NTU

· pH

· Suspended Solids (SS), mg/L

Three times per week during mid-ebb and mid-flood tides (within ± 1.75 hour of the predicted time)

(1 m below water surface, mid-depth and 1 m above sea bed, except where the water depth is less than 6 m, in which case the mid-depth station may be omitted. Should the water depth be less than 3 m, only the mid-depth station will be monitored).

Remark:

1) Original WQM stations IS8 and SR4(N) are located within the active work area of TCNTE project and the access to the WQM stations IS8 (Coordinate: E814251, N818412) and SR4(N) (Coordinate: E814705, N817859) are blocked by the silt curtains of the Tung Chung New Town Extension (TCNTE) project. Alternative monitoring stations IS8(N) (Coordinate: E814413, N818570) and SR4(N2) (Coordinate: E814688, N817996) were proposed to replace the original monitoring stations IS8 and SR4(N). Proposal for permanently relocating the aforementioned stations was approved by EPD on 20 August 2019. The water quality monitoring has been conducted at stations IS8(N) and SR4(N2) since 21 August 2019.

2) The water quality monitoring programme was temporarily suspended during the reporting month since no marine works were scheduled or conducted, therefore no water quality monitoring was conducted.

4.4 Monitoring Locations

4.4.1 In accordance with the Contract Specific EM&A Manual, thirteen stations (6 Impact Stations, 5 Sensitive Receiver Stations and 2 Control Stations) were designated for impact water quality monitoring. The six Impact Stations (IS) were chosen on the basis of their proximity to the reclamation and thus the greatest potential for water quality impacts, the five Sensitive Receiver Stations (SR) were chosen as they are close to the key sensitive receives and the two Control Stations (CS) were chosen to facilitate comparison of the water quality of the IS stations with less influence by the Project/ ambient water quality conditions.

4.4.2 A new water quality monitoring team has been employed for carrying out water quality monitoring work for the Contract starting from 23 August 2017. Due to marine work of the Expansion of Hong Kong International Airport into a Three-Runway System (3RS Project), original locations of water quality monitoring stations CS2, SR5 and IS10 are enclosed by works boundary of 3RS Project. Alternative impact water quality monitoring stations, naming as CS2(A), SR5(N) and IS10(N) was approved on 28 July 2017 and were adopted starting from 23 August 2017 to replace the original locations of water quality monitoring for the Contract.

4.4.3 The topographical condition of the water monitoring stations SR3(N) (Coordinate: 810525E, 816456N), SR4(N) (Coordinate: 814760E, 817867N), SR10A(N) (Coordinate: 823741E, 823495N) and SR10B(N2) (Coordinate: 823686E, 823213N) cannot be accessed safely for undertaking water quality monitoring. The water quality monitoring has been temporarily conducted at alternative stations, namely SR3(N) (Coordinate 810689E, 816591N), SR4(N) (Coordinate: 814705E, 817859N) and SR10A(N) (Coordinate: 823644E, 823484N) since 1 September 2017. The water quality monitoring at station SR10B was temporarily conducted at Coordinate: 823683E, 823187N on 1, 4, 6, 8 September 2017 and has been temporarily fine-tuned to alternative station SR10B(N2) (Coordinate: 823689E, 823159N) since 11 September 2017. Proposal for permanently relocating the aforementioned stations was approved by EPD on 8 January 2018.

4.4.4 Original WQM stations IS8 and SR4(N) are located within the active work area of TCNTE project and the access to the WQM stations IS8 (Coordinate: E814251, N818412) and SR4(N) (Coordinate: E814705, N817859) are blocked by the silt curtains of the Tung Chung New Town Extension (TCNTE) project. Alternative monitoring stations IS8(N) (Coordinate: E814413, N818570) and SR4(N2) (Coordinate: E814688, N817996) were proposed to replace the original monitoring stations IS8 and SR4(N). Proposal for permanently relocating the aforementioned stations was approved by EPD on 20 August 2019. The water quality monitoring has been conducted at stations IS8(N) and SR4(N2) since 21 August 2019.

4.4.5 The access to the WQM station SR4(N2) (Coordinate: E814688, N817996) is blocked by the silt curtains of the Tung Chung New Town Extension (TCNTE) project. Water quality monitoring was temporarily conducted at alternative stations, namely SR4(N3) (Coordinate: E814779, N818032) on 1 March 2023. Proposal for permanently relocating the SR4(N2) was approved by EPD on 3 March 2023. The water quality monitoring has been conducted at stations SR4(N3) since 3 March 2023.

4.4.6 The locations of water quality monitoring stations are summarized in Table 4.4 and shown in Figure 2.1.

Table 4.4 Impact Water Quality Monitoring Stations

Monitoring Stations	Description	Coordinates
Monitoring Stations	Description	Easting	Northing
IS5	Impact Station (Close to HKLR construction site)	811579	817106
IS(Mf)6	Impact Station (Close to HKLR construction site)	812101	817873
IS7	Impact Station (Close to HKBCF construction site)	812244	818777
IS8(N)	Impact Station (Close to HKBCF construction site)	814413	818570
IS(Mf)9	Impact Station (Close to HKBCF construction site)	813273	818850
IS10(N)	Impact Station (Close to HKBCF construction site)	812942	820881
SR3(N)	Sensitive receivers (San Tau SSSI)	810689	816591
SR4(N3)*	Sensitive receivers (Tai Ho Inlet)	814779	818032
SR5(N)	Sensitive Receivers (Artificial Reef in NE Airport)	812569	821475
SR10A(N)	Sensitive receivers (Ma Wan Fish Culture Zone)	823644	823484
SR10B(N2)	Sensitive receivers (Ma Wan Fish Culture Zone)	823689	823159
CS2(A)	Control Station (Mid-Ebb)	805232	818606
CS(Mf)5	Control Station (Mid-Flood)	817990	821129
Remark: * The access to the WQM station SR4(N2) (Coordinate: E814688, N817996) is blocked by the silt curtains of the Tung Chung New Town Extension (TCNTE) project. Water quality monitoring was temporarily conducted at alternative stations, namely SR4(N3) (Coordinate: E814779, N818032) on 1 March 2023. Proposal for permanently relocating the SR4(N2) was approved by EPD on 3 March 2023. The water quality monitoring has been conducted at stations SR4(N3) since 3 March 2023.

4.5 Monitoring Methodology

4.5.1 Instrumentation

(a) The in-situ water quality parameters including dissolved oxygen, temperature, salinity and turbidity, pH were measured by multi-parameter meters.

4.5.2 Operating/Analytical Procedures

(a) Digital Differential Global Positioning Systems (DGPS) were used to ensure that the correct location was selected prior to sample collection.

(b) Portable, battery-operated echo sounders were used for the determination of water depth at each designated monitoring station.

(c) All in-situ measurements were taken at 3 water depths, 1 m below water surface, mid-depth and 1 m above sea bed, except where the water depth was less than 6 m, in which case the mid-depth station was omitted. Should the water depth be less than 3 m, only the mid-depth station was monitored.

(d) At each measurement/sampling depth, two consecutive in-situ monitoring (DO concentration and saturation, temperature, turbidity, pH, salinity) and water sample for SS. The probes were retrieved out of the water after the first measurement and then re-deployed for the second measurement. Where the difference in the value between the first and second readings of DO or turbidity parameters was more than 25% of the value of the first reading, the reading was discarded and further readings were taken.

(e) Duplicate samples from each independent sampling event were collected for SS measurement. Water samples were collected using the water samplers and the samples were stored in high-density polythene bottles. Water samples collected were well-mixed in the water sampler prior to pre-rinsing and transferring to sample bottles. Sample bottles were pre-rinsed with the same water samples. The sample bottles were then be packed in cool-boxes (cooled at 4^oC without being frozen), and delivered to ALS Technichem (HK) Pty Ltd. for the analysis of suspended solids concentrations. The laboratory determination work would be started within 24 hours after collection of the water samples. ALS Technichem (HK) Pty Ltd. is a HOKLAS accredited laboratory and has comprehensive quality assurance and quality control programmes.

(f) The analysis method and detection limit for SS is shown in Table 4.5.

Table 4.5 Laboratory Analysis for Suspended Solids

Parameters	Instrumentation	Analytical Method	Detection Limit
Suspended Solid (SS)	Weighting	APHA 2540-D	0.5mg/L

(g) Other relevant data were recorded, including monitoring location / position, time, water depth, tidal stages, weather conditions and any special phenomena or work underway at the construction site in the field log sheet for information.

4.5.3 Maintenance and Calibrations

(a) All in situ monitoring instruments would be calibrated by ALS Technichem (HK) Pty Ltd. before use and at 3-monthly intervals throughout all stages of the water quality monitoring programme.

4.6 Monitoring Schedule for the Reporting Month

4.6.1 The schedule for impact water quality monitoring in March 2025 is provided in Appendix D.

4.7 Monitoring Results

4.7.1 Impact water quality monitoring was conducted at all designated monitoring stations in March 2025 during the reporting month. Impact water quality monitoring results and relevant graphical plots are provided in Appendix E.

4.7.2 Water quality impact sources during water quality monitoring were nearby construction activities by other parties and nearby operating vessels by other parties.

4.7.3 For marine water quality monitoring, no Action Level and Limit Level exceedances of dissolved oxygen level, turbidity level and suspended solid level were recorded during the reporting month.

4.7.4 The event action plan is annexed in Appendix F.

5 Dolphin Monitoring

5.1 Monitoring Requirements

5.1.1 Impact dolphin monitoring is required to be conducted by a qualified dolphin specialist team to evaluate whether there have been any effects on the dolphins.

5.1.2 The Action Level and Limit Level for dolphin monitoring are shown in Table 5.1.

Table 5.1 Action and Limit Levels for Dolphin Monitoring

	North Lantau Social Cluster
	NEL	NWL
Action Level	STG < 4.2 & ANI < 15.5	STG < 6.9 & ANI < 31.3
Limit Level	(STG < 2.4 & ANI < 8.9) and (STG < 3.9 & ANI < 17.9)

Remarks:

1. STG means quarterly encounter rate of number of dolphin sightings.

2. ANI means quarterly encounter rate of total number of dolphins.

3. For North Lantau Social Cluster, AL will be trigger if either NEL or NWL fall below the criteria; LL will be triggered if both NEL and NWL fall below the criteria.

5.1.3 The revised Event and Action Plan for dolphin Monitoring was approved by EPD in 6 May 2013. The revised Event and Action Plan is annexed in Appendix F.

5.2 Monitoring Methodology

Vessel-based Line-transect Survey

5.2.1 According to the requirement of the updated EM&A manual, dolphin monitoring programme should cover all transect lines in NEL and NWL survey areas (see Figure 2.2) twice per month throughout the entire construction period. The co-ordinates of all transect lines are shown in Table 5.2. The coordinates of several starting and ending points have been revised due to the presence of a work zone to the north of the airport platform with intense construction activities in association with the construction of the third runway expansion for the Hong Kong International Airport. The EPD issued a memo and confirmed that they had no objection on the revised transect lines on 28 July 2017, and the revised coordinates are in red and marked with an asterisk in Table 5.2.

Table 5.2 Co-ordinates of Transect Lines

Line No.		Easting	Northing	Line No.		Easting	Northing
1	Start Point	804671	815456	13	Start Point	816506	819480
1	End Point	804671	831404	13	End Point	816506	824859
2	Start Point	805476	820800*	14	Start Point	817537	820220
2	End Point	805476	826654	14	End Point	817537	824613
3	Start Point	806464	821150*	15	Start Point	818568	820735
3	End Point	806464	822911	15	End Point	818568	824433
4	Start Point	807518	821500*	16	Start Point	819532	821420
4	End Point	807518	829230	16	End Point	819532	824209
5	Start Point	808504	821850*	17	Start Point	820451	822125
5	End Point	808504	828602	17	End Point	820451	823671
6	Start Point	809490	822150*	18	Start Point	821504	822371
6	End Point	809490	825352	18	End Point	821504	823761
7	Start Point	810499	822000*	19	Start Point	822513	823268
7	End Point	810499	824613	19	End Point	822513	824321
8	Start Point	811508	821123	20	Start Point	823477	823402
8	End Point	811508	824254	20	End Point	823477	824613
9	Start Point	812516	821303	21	Start Point	805476	827081
9	End Point	812516	824254	21	End Point	805476	830562
10	Start Point	813525	821176	22	Start Point	806464	824033
10	End Point	813525	824657	22	End Point	806464	829598
11	Start Point	814556	818853	23	Start Point	814559	821739
11	End Point	814556	820992	23	End Point	814559	824768
12	Start Point	815542	818807	24*	Start Point	805476*	815900*
12	End Point	815542	824882	24*	End Point	805476*	819100*

Note:
Co-ordinates in red and marked with asterisk are revised co-ordinates of transect line.

5.2.2 The survey team used standard line-transect methods (Buckland et al. 2001) to conduct the systematic vessel surveys, and followed the same technique of data collection that has been adopted over the last 22 years of marine mammal monitoring surveys in Hong Kong developed by HKCRP (see Hung 2021). For each monitoring vessel survey, a 15-m inboard vessel with an open upper deck (about 4.5 m above water surface) was used to make observations from the flying bridge area.

5.2.3 Two experienced observers (a data recorder and a primary observer) made up the on-effort survey team, and the survey vessel transited different transect lines at a constant speed of 13-15 km per hour. The data recorder searched with unaided eyes and filled out the datasheets, while the primary observer searched for dolphins and porpoises continuously through 7 x 50 Fujinon marine binoculars. Both observers searched the sea ahead of the vessel, between 270^o and 90^o (in relation to the bow, which is defined as 0^o). One to two additional experienced observers were available on the boat to work in shift (i.e. rotate every 30 minutes) in order to minimize fatigue of the survey team members. All observers were experienced in small cetacean survey techniques and identifying local cetacean species.

5.2.4 During on-effort survey periods, the survey team recorded effort data including time, position (latitude and longitude), weather conditions (Beaufort sea state and visibility), and distance traveled in each series (a continuous period of search effort) with the assistance of a handheld GPS (Garmin eTrex Legend).

5.2.5 Data including time, position and vessel speed were also automatically and continuously logged by handheld GPS throughout the entire survey for subsequent review.

5.2.6 When dolphins were sighted, the survey team would end the survey effort, and immediately record the initial sighting distance and angle of the dolphin group from the survey vessel, as well as the sighting time and position. Then the research vessel was diverted from its course to approach the animals for species identification, group size estimation, assessment of group composition, and behavioural observations. The perpendicular distance (PSD) of the dolphin group to the transect line was later calculated from the initial sighting distance and angle.

5.2.7 Survey effort being conducted along the parallel transect lines that were perpendicular to the coastlines (as indicated in Figure 2.2) was labeled as “primary” survey effort, while the survey effort conducted along the connecting lines between parallel lines was labeled as “secondary” survey effort. According to HKCRP long-term dolphin monitoring data, encounter rates of Chinese white dolphins deduced from effort and sighting data collected along primary and secondary lines were similar in NEL and NWL survey areas. Therefore, both primary and secondary survey effort were presented as on-effort survey effort in this report.

5.2.8 Encounter rates of Chinese white dolphins (number of on-effort sightings per 100 km of survey effort and number of dolphins from all on-effort sightings per 100 km of survey effort) were calculated in NEL and NWL survey areas in relation to the amount of survey effort conducted during each month of monitoring survey. Only data collected under Beaufort 3 or below condition would be used for encounter rate analysis. Dolphin encounter rates were calculated using primary survey effort alone, as well as the combined survey effort from both primary and secondary lines.

Photo-identification Work

5.2.9 When a group of Chinese White Dolphins were sighted during the line-transect survey, the survey team would end effort and approach the group slowly from the side and behind to take photographs of them. Every attempt was made to photograph every dolphin in the group, and even photograph both sides of the dolphins, since the colouration and markings on both sides may not be symmetrical.

5.2.10 A professional digital camera (Canon EOS 7D model), equipped with long telephoto lenses (100-400 mm zoom), were available on board for researchers to take sharp, close-up photographs of dolphins as they surfaced. The images were shot at the highest available resolution and stored on Compact Flash memory cards for downloading onto a computer.

5.2.11 All digital images taken in the field were first examined, and those containing potentially identifiable individuals were sorted out. These photographs would then be examined in greater detail and were carefully compared to the existing Chinese White Dolphin photo-identification catalogue maintained by HKCRP since 1995.

5.2.12 Chinese White Dolphins can be identified by their natural markings, such as nicks, cuts, scars and deformities on their dorsal fin and body, and their unique spotting patterns were also used as secondary identifying features (Jefferson 2000).

5.2.13 All photographs of each individual were then compiled and arranged in chronological order, with data including the date and location first identified (initial sighting), re-sightings, associated dolphins, distinctive features, and age classes entered into a computer database.

5.3 Monitoring Results

Vessel-based Line-transect Survey

5.3.1 During the month of March 2025, two sets of systematic line-transect vessel surveys were conducted on the 11^th, 12^th, 14^th and 18^th to cover all transect lines in NWL and NEL survey areas twice. The survey routes of each survey day are presented in Figures 2-5 of Appendix H.

5.3.2 From these surveys, a total of 267.00 km of survey effort was collected, with 100% of the total survey effort being conducted under favourable weather conditions (i.e. Beaufort Sea State 3 or below with good visibility) (Annex I of Appendix H).

5.3.3 Among the two survey areas, 96.80 km and 170.20 km of survey effort were collected from NEL and NWL survey areas respectively. Moreover, the total survey effort conducted on primary lines was 193.88 km, while the effort on secondary lines was 73.12 km.

5.3.4 During the two sets of monitoring surveys in March 2025, no Chinese White Dolphin was sighted at all.

5.3.5 For the March’s surveys, encounter rates of Chinese White Dolphins deduced from the survey effort and on-effort sighting data made under favourable conditions (Beaufort 3 or below) are shown in Tables 5.3 and 5.4.

Table 5.3 Dolphin encounter rates deduced from the two sets of surveys (two surveys in each set) in March 2025 in Northeast (NEL) and Northwest Lautau (NWL)

		Encounter rate (STG) (no. of on-effort dolphin sightings per 100 km of survey effort)	Encounter rate (ANI) (no. of dolphins from all on-effort sightings per 100 km of survey effort)
		Primary Lines Only	Primary Lines Only
NEL	Set 1: March 11^th / 12^th	0.0	0.0
NEL	Set 2: March 14^th / 18^th	0.0	0.0
NWL	Set 1: March 11^th / 12^th	0.0	0.0
NWL	Set 2: March 14^th / 18^th	0.0	0.0

Table 5.4 Overall dolphin encounter rates (sighting per 100 km of survey effort) from all surveys conducted in March 2025 on primary lines only as well as both primary lines and secondary lines in Northeast and Northwest Lantau

	Encounter rate (STG) (no. of on-effort dolphin sightings per 100 km of survey effort)		Encounter rate (ANI) (no. of dolphins from all on-effort sightings per 100 km of survey effort)
	Primary Lines Only	Both Primary and Secondary Lines	Primary Lines Only	Both Primary and Secondary Lines
Northeast Lantau	0.0	0.0	0.0	0.0
Northwest Lantau	0.0	0.0	0.0	0.0

5.4 Conclusion

5.4.1 During this month of dolphin monitoring, no adverse impact from the activities of this construction project on Chinese White Dolphins was noticeable from general observations.

5.4.2 Due to monthly variation in dolphin occurrence within the study area, it would be more appropriate to draw conclusion on whether any impacts on dolphins have been detected related to the construction activities of this project in the quarterly EM&A report, where comparison on distribution, group size and encounter rates of dolphins between the quarterly impact monitoring period and the 3-month baseline monitoring period will be made.

5.5 References

- Buckland, S. T., Anderson, D. R., Burnham, K. P., Laake, J. L., Borchers, D. L., and Thomas, L. 2001. Introduction to distance sampling: estimating abundance of biological populations. Oxford University Press, London.

- Hung, S. K. 2021. Monitoring of Marine Mammals in Hong Kong waters: final report (2020-21). An unpublished report submitted to the Agriculture, Fisheries and Conservation Department, 154 pp.

- Jefferson, T. A. 2000. Population biology of the Indo-Pacific hump-backed dolphin in Hong Kong waters. Wildlife Monographs 144:1-65.

6 Mudflat Monitoring

6.1 Sedimentation Rate Monitoring

Methodology

6.1.1 To avoid disturbance to the mudflat and nuisance to navigation, no fixed marker/monitoring rod was installed at the monitoring stations. A high precision Global Navigation Satellite System (GNSS) real time location fixing system (or equivalent technology) was used to locate the station in the precision of 1mm, which is reasonable under flat mudflat topography with uneven mudflat surface only at micro level. This method has been used on Agricultural Fisheries and Conservation Department’s (AFCD) project, namely Baseline Ecological Monitoring Programme for the Mai Po Inner Deep Bay Ramsar Site for measurement of seabed levels.

6.1.2 Measurements were taken directly on the mudflat surface. The Real Time Kinematic GNSS (RTK GNSS) surveying technology was used to measure mudflat surface levels and 3D coordinates of a survey point. The RTK GNSS survey was calibrated against a reference station in the field before and after each survey. The reference station is a survey control point established by the Lands Department of the HKSAR Government or traditional land surveying methods using professional surveying instruments such as total station, level and/or geodetic GNSS. The coordinates system was in HK1980 GRID system. For this contract, the reference control station was surveyed and established by traditional land surveying methods using professional surveying instruments such as total station, level and RTK GNSS. The accuracy was down to mm level so that the reference control station has relatively higher accuracy. As the reference control station has higher accuracy, it was set as true evaluation relative to the RTK GNSS measurement. All position and height correction were adjusted and corrected to the reference control station. Reference station survey result and professional land surveying calibration is shown as Table 6.1:

Table 6.1 Reference Station Survey result and GNSS RTK calibration result of Round 1

Reference Station	Easting (m)	Northing (m)	Baseline reference elevation (mPD) (A)	Round 1 Survey (mPD) (B)	Calibration Adjustment (B-A)
T1	811248.660mE	816393.173mN	3.840	3.817	-0.023
T2	810806.297mE	815691.822mN	4.625	4.653	+0.028
T3	810778.098mE	815689.918mN	4.651	4.660	+0.009
T4	810274.783mE	816689.068mN	2.637	2.709	+0.072

6.1.3 The precision of the measured mudflat surface level reading (vertical precision setting) was within 10 mm (standard deviation) after averaging the valid survey records of the XYZ HK1980 GRID coordinates. Each survey record at each station was computed by averaging at least three measurements that are within the above specified precision setting. Both digital data logging and written records were collected in the field. Field data on station fixing and mudflat surface measurement were recorded.

Monitoring Locations

6.1.4 Four monitoring stations were established based on the site conditions for the sedimentation monitoring and are shown in Figure 6.1.

Monitoring Results

6.1.5 The baseline sedimentation rate monitoring was in September 2012 and impact sedimentation rate monitoring was undertaken on 28 March 2025. The mudflat surface levels at the four established monitoring stations and the corresponding XYZ HK1980 GRID coordinates are presented in Table 6.2 and Table 6.3.

Table 6.2 Measured Mudflat Surface Level Results

	Baseline Monitoring (September 2012)			Impact Monitoring (March 2025)
Monitoring Station	Easting (m)	Northing (m)	Surface Level (mPD)	Easting (m)	Northing (m)	Surface Level (mPD)
S1	810291.160	816678.727	0.950	810291.150	816678.678	1.082
S2	810958.272	815831.531	0.864	810958.288	815831.534	0.959
S3	810716.585	815953.308	1.341	810716.575	815953.306	1.456
S4	811221.433	816151.381	0.931	811221.450	816151.390	1.121

Table 6.3 Comparison of current measurement to the baseline measurement

	Comparison of Measurement			Remarks and Recommendation
Monitoring Station	Easting (m)	Northing (m)	Surface Level (mPD)	Remarks and Recommendation
S1	-0.010	-0.049	0.132	Level continuously increased, need attention
S2	0.016	0.003	0.095	Level continuously increased, need attention
S3	-0.010	-0.002	0.115	Level continuously increased, need attention
S4	0.017	0.009	0.190	Level continuously increased, need attention

6.1.6 This measurement result was generally and relatively higher than the baseline measurement at S1, S2, S3 and S4. The mudflat level is continuously increased.

6.2 Water Quality Monitoring

6.2.1 The mudflat monitoring covered water quality monitoring data. Reference was made to the water quality monitoring data of the representative water quality monitoring station (i.e. SR3(N)) as in the EM&A Manual. The water quality monitoring location (SR3(N)) is shown in Figure 2.1.

6.2.2 Water quality monitoring in San Tau (monitoring station SR3(N)) was conducted in March 2025 as part of mudflat monitoring. The monitoring parameters included dissolved oxygen (DO), turbidity and suspended solids (SS). The water monitoring results for station SR3(N) were extracted and summarised below:

Table 6.4 Water Quality Monitoring Results (Depth Average) at Station SR3(N)

	Mid Ebb Tide			Mid Flood Tide
	DO (mg/L)	Turbidity (NTU)	SS (mg/L)	DO (mg/L)	Turbidity (NTU)	SS (mg/L)
3 Mar 2025	6.7	2.8	12.1	6.3	2.8	16.9
5 Mar 2025	6.6	2.8	4.0	6.2	2.6	4.2
7 Mar 2025	5.8	3.4	3.3	5.9	3.5	3.3
10 Mar 2025	6.2	2.3	3.1	6.6	2.4	5.2
12 Mar 2025	6.8	2.7	2.9	6.6	2.3	2.7
14 Mar 2025	6.6	2.7	3.7	6.2	2.4	3.3
17 Mar 2025	6.9	3.1	5.2	6.5	2.7	4.9
19 Mar 2025	6.3	3.2	2.8	6.1	2.9	2.7
21 Mar 2025	6.6	3.1	5.1	6.3	2.8	5.2
24 Mar 2025	6.5	3.1	2.2	6.1	2.9	1.9
26 Mar 2025	6.1	3.3	3.8	6.0	3.3	3.1
28 Mar 2025	6.0	3.4	3.3	6.2	3.3	3.3
31 Mar 2025	6.1	3.3	2.4	6.0	3.2	2.6
Average	6.4	3.0	4.1	6.2	2.8	4.5

6.3 Mudflat Ecology Monitoring Methodology

Study Site – Tung Chung Bay and San Tau

6.3.1 To collect baseline information of mudflats in the study site, the study site was divided into three sampling zones (labeled as TC1, TC2, TC3) in Tung Chung Bay and one zone in San Tau (labeled as ST) (Figure 2.1 of Appendix I). The horizontal shoreline of sampling zones TC1, TC2, TC3 and ST were about 250 m, 300 m, 300 m and 250 m, respectively, refer to photo records Figure 2.2 of Appendix I. Survey of horseshoe crabs, seagrass beds and intertidal communities were conducted in every sampling zone. The present survey was conducted in March 2025 (totally 3 sampling days, i.e., 2^nd, 3^rd and 4^th of March, when day-time low tidal levels are suitable for survey and sampling.)

6.3.2 Since the field survey of June 2016, trash including big trash (Figure 2.3 of Appendix I) were often found in sampling zones. It raised concern about the solid waste dumping and current-driven waste issues in Tung Chung Wan. Respective measures (e.g., manual clean-up) should be implemented by responsible governmental agency units.

Horseshoe Crabs

6.3.3 Active search method was adopted for horseshoe crab monitoring by two experienced surveyors in every sampling zone. During the search period, any accessible and potential area would be investigated for any horseshoe crab individuals within 2-3 hour of low tide period (tidal level below 1.2 m above Chart Datum (C.D.)). Once a horseshoe crab individual was found, the species was identified referencing to Li (2008). The prosomal width, inhabiting substratum and respective GPS coordinate were recorded. A photographic record was taken for future investigation. Any grouping behavior of individuals, if found, was recorded.

6.3.4 In June 2017, a big horseshoe crab was tangled by a trash gill net in ST mudflat (Figure 2.3 of Appendix I). It was released to sea once after photo recording. The horseshoe crab of such size should be inhabiting sub-tidal environment while it forages on intertidal shore occasionally during high tide period. If it is tangled by the trash net for few days, it may die due to starvation or overheat during low tide period. These trash gill nets are definitely ‘fatal trap’ for the horseshoe crabs and other marine life. Manual clean-up should be implemented as soon as possible by responsible governmental agency units.

Seagrass Beds

6.3.5 Active search method was adopted for seagrass bed monitoring by two experienced surveyors in every sampling zone. During the search period, any accessible and potential area would be investigated for any seagrass beds within 2-3 hours of low tide period. Once seagrass bed was found, the species, estimated area, estimated coverage percentage and respective GPS coordinates were recorded.

Intertidal Soft Shore Communities

Field Sampling

6.3.6 The intertidal soft shore community surveys were conducted in low tide period. In every sampling zone, three 100m horizontal transect lines were laid at high tidal level (H: 2.0m above C.D.), mid tidal level (M: 1.5m above C.D.) and low tidal level (L: 1.0m above C.D.). Along every horizontal transect line, ten random quadrats (0.5 m x 0.5m) were placed.

6.3.7 Inside a quadrat, any visible epifauna was collected and was in-situ identified to the lowest practical taxonomical resolution. Whenever possible a hand core sample (10 cm internal diameter ´ 20 cm depth) of sediments was collected in the quadrat. The core sample was gently washed through a sieve of mesh size 2.0 mm in-situ. Any visible infauna was collected and identified. Finally, the top 5 cm surface sediment was dug for visible infauna in the quadrat regardless of hand core sample was taken.

6.3.8 All collected fauna were released after recording except some tiny individuals that were too small to be identified on site. These tiny individuals were taken to laboratory for identification under dissecting microscope.

6.3.9 The taxonomic classification was conducted in accordance to the following references: Polychaetes: Fauchald (1977), Yang and Sun (1988); Arthropods: Dai and Yang (1991), Dong (1991); Mollusks: Chan and Caley (2003), Qi (2004), AFCD (2018).

Data Analysis

6.3.10 Data collected from direct counting and core sampling was pooled in every quadrat for data analysis. Shannon-Weaver Diversity Index (H’) and Pielou’s Species Evenness (J) were calculated for every quadrat using the formulae below,

H’= -Σ ( Ni / N ) ln ( Ni / N )(Shannon and Weaver, 1963)

J = H’ / ln S (Pielou, 1966)

where S is the total number of species in the sample, N is the total number of individuals, and Ni is the number of individuals of the i^th species.

6.4 Event and Action Plan for Mudflat Monitoring

6.4.1 In the event of the impact monitoring results indicating that the density or the distribution pattern of intertidal fauna and seagrass is found to be significant different to the baseline condition (taking into account natural fluctuation in the occurrence and distribution pattern such as due to seasonal change), appropriate actions should be taken and additional mitigation measures should be implemented as necessary. Data should then be re-assessed and the need for any further monitoring should be established. The action plan, as given in Table 6.5 should be undertaken within a period of 1 month after a significant difference has been determined.

Table 6.5 Event and Action Plan for Mudflat Monitoring

Event

ET Leader

IEC

Contractor

Density or the distribution pattern of horseshoe crab, seagrass or intertidal soft shore communities recorded in the impact or post-construction monitoring are significantly lower than or different from those recorded in the baseline monitoring.

Review historical data to ensure differences are as a result of natural variation or previously observed seasonal differences;

Identify source(s) of impact;

Inform the IEC, SO and Contractor;

Check monitoring data;

Discuss additional monitoring and any other measures, with the IEC and Contractor.

Discuss monitoring with the ET and the Contractor;

Review proposals for additional monitoring and any other measures submitted by the Contractor and advise the SO accordingly.

Discuss with the IEC additional monitoring requirements and any other measures proposed by the ET;

Make agreement on the measures to be implemented.

Inform the SO and in writing;

Discuss with the ET and the IEC and propose measures to the IEC and the ER;

Implement the agreed measures.

Notes:

ET – Environmental Team

IEC – Independent Environmental Checker

SO – Supervising Officer

6.5 Mudflat Ecology Monitoring Results and Conclusion

Horseshoe Crabs

6.5.1 Four juvenile horseshoe crabs and no adult were recorded in present surveys. Photo records of previously and currently observed horseshoe crabs are shown in Figure 3.1 and Figure 3.4 of Appendix I. The present survey results regarding horseshoe crabs are presented in Table 3.1. The complete survey records are presented in Annex II of Appendix I.

6.5.2 In the survey of March 2015, there was one important finding that a mating pair of Carcinoscorpius rotundicauda was found in ST (prosomal width: male 155.1mm, female 138.2mm). It indicated the importance of ST as a breeding ground of horseshoe crab. In June 2017, mating pairs of Carcinoscorpius rotundicauda were found in TC2 (male 175.27 mm, female 143.51 mm) and TC3 (male 182.08 mm, female 145.63 mm) (Figure 3.2). In December 2017 and June 2018, one mating pair was of Carcinoscorpius rotundicauda was found in TC3 (December 2017: male 127.80 mm, female 144.61 mm; June 2018: male 139 mm, female 149 mm). In June 2019, two mating pairs of Tachypleus tridentatus with large body sizes (male 150mm and Female 200mm; Male 180mm and Female 220mm) were found in TC3. Another mating pair of Tachypleus tridentatus was found in ST (male 140mm and Female 180mm). In March 2020, a pair of Tachypleus tridentatus with large body sizes (male 123mm and Female 137mm was recorded in TC1. Figure 3.2 of Appendix I shows the photographic records of the mating pair found. The recorded mating pairs were found nearly burrowing in soft mud at low tidal level (0.5-1.0 m above C.D.). The smaller male was holding the opisthosoma (abdomen carapace) of larger female from behind. A mating pair was found in TC1 in March 2020, it indicated that breeding of horseshoe crab could be possible along the coast of Tung Chung Wan rather than ST only, if suitable substratum was available. Based on the frequency of encounter, the shoreline between TC3 and ST should be more suitable mating ground. Moreover, suitable breeding period was believed in wet season (March – September) because tiny individuals (i.e. newly hatched) were usually recorded in June and September every year (Figure 3.3 of Appendix I). One mating pair was found in June 2022. 3 adult individuals (prosomal width >100mm) of Carcinoscorpius rotundicauda were recorded in September 2022 survey, with one alive, one dead in TC3 and one dead in TC2. In June 2022, 7 large individuals (prosomal width >100mm) of Carcinoscorpius rotundicauda were recorded (prosomal width ranged 131.4mm - 140.3mm) in TC3. In December 2018, one large individual of Carcinoscorpius rotundicauda was found in TC3 (prosomal width 148.9 mm). In March 2019, 3 large individuals (prosomal width ranged 220 – 310mm) of Carcinoscorpius rotundicauda were observed in TC2. In June 2019, there were 3 and 7 large individuals of Tachypleus tridentatus recorded in ST (prosomal width ranged 140 – 180mm) and TC3 (prosomal width ranged 150 – 220mm), respectively. In March 2020, a mating pair of Tachypleus tridentatus was recorded in TC1 with prosomal width 123 mm and 137mm. Based on their sizes, it indicated that individuals of prosomal width larger than 100 mm would progress its nursery stage from intertidal habitat to sub-tidal habitat of Tung Chung Wan. The photo records of the large horseshoe crab are shown in Figure 3.4 of Appendix I. A dead specimen of adult horseshoe crab was seen at TC3 in March 2025 (Figure 3.4 of Appendix I (Cont’d)). These large individuals might move onto the intertidal shore occasionally during high tide for foraging and breeding. Because they should be inhabiting sub-tidal habitat most of the time. Their records were excluded from the data analysis to avoid mixing up with juvenile population living on intertidal habitat.

6.5.3 Some marked individuals were found in the previous surveys of September 2013, March 2014, and September 2014. All of them were released through a conservation programme in charged by Prof. Paul Shin (Department of Biology and Chemistry, The City University of Hong Kong (City U). It was a re-introduction trial of artificial bred horseshoe crab juvenile at selected sites. So that the horseshoe crab’s population might be restored in the natural habitat. Through a personal conversation with Prof. Shin, about 100 individuals were released in the sampling zone ST on 20 June 2013. All of them were marked with color tape and internal chips detected by specific chip sensor. There should be a second round of release between June and September 2014 since new marked individuals were found in the survey of September 2014.

6.5.4 The artificial bred individuals, if found, would be excluded from the results of the present monitoring programme to reflect the changes of natural population. However, the mark on their prosoma might have been detached during molting after a certain period of release. The artificially released individuals were no longer distinguishable from the natural population without the specific chip sensor. The survey data collected would possibly cover both natural population and artificially bred individuals.

Population difference among the sampling zones

6.5.5 Figures 3.5 and 3.6 of Appendix I show the changes of number of individuals, meaning prosomal width and search record of horseshoe crabs Carcinoscorpius rotundicauda and Tachypleus tridentatus respectively in each sampling zone throughout the monitoring period.

6.5.6 To consider the entire monitoring period for TC3 and ST, medium to high search records (i.e. number of individuals) of both species (Carcinoscorpius rotundicauda and Tachypleus tridentatus) were usually found in wet season (June and September). The search record of ST was higher from September 2012 to June 2014 while it was replaced by TC3 from September 2014 to June 2015. The search records were similar between two sampling zones from September 2015 to June 2016. In September 2016, the search record of Carcinoscorpius rotundicauda in ST was much higher than TC3. From March to June 2017, the search records of both species were similar again between two sampling zones. It showed a natural variation of horseshoe crab population in these two zones due to weather condition and tidal effect. No obvious difference of horseshoe crab population was noted between TC3 and ST. In September 2017, the search records of both horseshoe crab species decreased except the Carcinoscorpius rotundicauda in TC3. The survey results were different from previous findings that there were usually higher search records in September. One possible reason was that the serial cyclone hit decreased horseshoe crab activity (totally 4 cyclone records between June and September 2017, to be discussed in 'Seagrass survey' section). From December 2017 to September 2018, the search records of both species increased again to low-moderate level in ST and TC3. From December 2018 to September 2019, the search records of Carcinoscorpius rotundicauda change from very low to low while the change of Tachypleus tridentatus was similar during this period. Relatively higher population fluctuation of Carcinoscorpius rotundicauda was observed in TC3. From March 2020 to September 2020, the search records of both species, Carcinoscorpius rotundicauda and Tachypleus tridentatus, were increased to moderate level in ST. However, the search records of both species, Carcinoscorpius rotundicauda and Tachypleus tridentatus, were decreased from very low to none in TC3 in this period. From March 2021 to September 2021, the search records of both species, Carcinoscorpius rotundicauda and Tachypleus tridentatus, were kept at low-moderate level in both ST and TC3. It is like the previous findings of June. It shows another growing phenomenon of horseshoe crabs, and it may be due to the weather variation of the start of wet season. The survey results were different from previous findings that there were usually higher search records in September. One possible reason was that September of 2021 was one of the hottest months in Hong Kong in record. As such, hot and shiny weather decreased horseshoe crab activity. In December 2021, no juvenile was recorded like previous in December due to the season. In March 2022, only juveniles recorded in both ST and TC3, no adult specimen was observed. In June 2022, total of 13 individuals of Carcinoscorpius rotundicauda and Tachypleus tridentatus were found, with 6 juveniles, 6 adults and 1 died recorded. In September 2022, total of 7 individuals of were found, with 4 juveniles, 3 adults (1 alive and 2 died) recorded. In March 2023, a total of 12 individuals of juveniles Carcinoscorpius rotundicauda and Tachypleus tridentatus were found and recorded. In June 2023, a total of 27 individuals of juveniles Tachypleus tridentatus were found and recorded. In September 2023, a total of 2 individuals of juveniles Tachypleus tridentatus were found and recorded. In December 2023, no horseshoe crab was found. In March and September 2024, Tachypleus tridentatus were found for each month. In December 2024, 2 individuals of juveniles Carcinoscorpius rotundicauda were found. Four individuals of juveniles Tachypleus tridentatus were recorded in March 2025.

6.5.7 For TC1, the search record was at a low to moderate level throughout the monitoring period. The change of Carcinoscorpius rotundicauda was relatively more variable than that of Tachypleus tridentatus. Relatively, the search record was very low in TC2. There were occasional records of 1 to 4 individuals between March and September throughout the monitoring period. The maximum record was 6 individuals only in June 2016.

6.5.8 About the body size, larger individuals of Carcinoscorpius rotundicauda were usually found in ST and TC1 relative to that in TC3 from September 2012 to June 2017. But the body size was higher in TC3 and ST followed by TC1 from September 2017 to March 2020. From June 2020 to December 2020, there was no individuals of Carcinoscorpius rotundicauda recorded in TC3 but in ST. The body size of Carcinoscorpius rotundicauda in ST was recorded gradually increased (from mean prosomal width 23.6mm to 49.6mm) since March 2020 to September 2020. From December 2020 to March 2021, the body size of Carcinoscorpius rotundicauda in ST was recorded decreased (from mean prosomal width 49.6mm to 43.3mm). In March 2021, the body size of Carcinoscorpius rotundicauda in TC3 (mean prosomal width 46.2mm) was recorded larger than that in ST (mean prosomal width 43.3mm). From September 2021 to June 2022, the body size of Carcinoscorpius rotundicauda in ST was recorded increased (from mean prosomal width 39.8mm to 54.42mm). For Tachypleus tridentatus, larger individuals were usually found in ST and TC3 followed by TC1 throughout the monitoring period. In June 2019, all found horseshoe crabs were large individuals and mating pairs. It is believed that the sizes of horseshoe crabs would decrease and gradually rise afterward due to the stable growth of juveniles after the spawning season. From March 2019 to September 2021, Tachypleus tridentatus were only recorded in TC3 and ST. The body size in TC3 increased from September 2019 to December 2019 then decreased in March 2020 and no recorded species in TC3 for three consecutive quarters from June 2020 to December 2020. From March 2020 to Sep 2021, the body size of Tachypleus tridentatus in TC3 increased (from mean prosomal width 34.00mm to 38.8mm). It showed a natural variation of horseshoe crab population in TC3. Apart from natural mortality, migration from nursery soft shore to subtidal habitat was another possible cause. The body size in ST was gradually growth since December 2019 to September 2020 then slightly dropped in December 2020. In June 2022, T. tridentatus were only recorded in ST, the body size in ST decreased from mean prosomal width 77.59mm to 54.02mm in March 2022. In September 2022 T. tridentatus were only recorded in TC3. The mean prosomal was 61.09mm. In March 2023, 7 T. tridentatus were recorded in ST and TC3. The mean prosomal was 62.68mm. In March 2024, 2 T. tridentatus were recorded in ST with a mean prosomal width 70.55mm. No horseshoe crab was recorded in all sites in June 2024, and 2 T. tridentatus were recorded in ST with a mean prosomal width 40.00mm. In December 2024 2 Carcinoscorpius rotundicauda recorded with a mean prosomal width 43.00mm. In March 2025, 3 T. tridentatus were recorded in ST and 1 recorded at TC3.

6.5.9 In general, it was obvious that the shoreline along TC3 and ST (western shore of Tung Chung Wan) was an important nursery ground for horseshoe crab especially newly hatched individuals due to larger area of suitable substratum (fine sand or soft mud) and less human disturbance (far from urban district). Relatively, other sampling zones were not a suitable nursery ground, especially TC2. Possible factors were less area of suitable substratum (especially TC1) and higher human disturbance (TC1 and TC2: close to urban district and easily accessible). In TC2, large daily salinity fluctuation was a possible factor since it was flushed by two rivers under tidal inundation. The individuals inhabiting TC1 and TC2 were confined in small foraging area due to limited area of suitable substratum. Although there were mating pairs seldomly found in TC1 and TC2, the hatching rate and survival rate of newly hatched individuals were believed to be very low.

Seasonal variation of horseshoe crab population

6.5.10 Throughout the monitoring period, the search records of horseshoe crabs were fluctuated and at moderate – very low level in June (Figure 3.5 and 3.6). Low – Very low search record was found in June 2013, totally 82 individuals of Tachypleus tridentatus and 0 ind. of Carcinoscorpius rotundicauda were found in TC1, TC3 and ST. Compare with the search record of June 2013, the numbers of Tachypleus tridentatus were gradually decreased in June 2014 and 2015 (55 ind. in 2014 and 18 ind. in 2015); the number of Carcinoscorpius rotundicauda raise to 88 and 66 ind. in June 2014 and 2015 respectively. In June 2016, the search record increased about 3 times compared with June 2015. In total, 182 individuals of Carcinoscorpius rotundicauda and 47 individuals of Tachypleus tridentatus were noted, respectively. Then, the search record was like June 2016. The number of recorded Carcinoscorpius rotundicauda (133 ind.) slightly dropped in June 2017. However, that of Tachypleus tridentatus rapidly increased (125 ind.). In June 2018, the search record was low to moderate while the numbers of Tachypleus tridentatus dropped sharply (39 ind.). In June 2019, 10 individuals of Tachypleus tridentatus were observed in TC3 and ST. All of them, however, were large individuals (prosomal width >100mm), their records are excluded from the data analysis to avoid mixing up with the juvenile population living on intertidal habitat. Until September 2020, the number of Carcinoscorpius rotundicauda and Tachypleus tridentatus gradually increased to 39 ind. and 28 ind., respectively. In December 2020, the number of Carcinoscorpius rotundicauda and Tachypleus tridentatus greatly decreased to 3 ind. and 7 ind., respectively. In March 2022, the number of Carcinoscorpius rotundicauda and Tachypleus tridentatus gradually decreased to 7 ind. and 2 ind., respectively in comparing with the March of previous record. The drop of abundance may be related to the unusual cold weather in the beginning of March 2022.

6.5.11 The search record of horseshoe crab declined obviously in all sampling zones during dry season especially December (Figures 3.5 and 3.6 of Appendix I) throughout the monitoring period. Very low – low search record was found in December from 2012 to 2015 (0-4 ind. of Carcinoscorpius rotundicauda and 0 – 12 ind. of Tachypleus tridentatus). The horseshoe crabs were inactive and burrowed in the sediments during cold weather (<15 ºC). Similar results of low search record in dry season were reported in a previous territory-wide survey of horseshoe crab. For example, the search records in Tung Chung Wan were 0.17 ind. hr^-1person^-1 and 0.00 ind. hr^-1 person^-1 in wet season and dry season respectively (details see Li, 2008). Compared with the search record of December from 2012 to 2015, which of December 2016 were much higher relatively. There were totally 70 individuals of Carcinoscorpius rotundicauda and 24 individuals of Tachypleus tridentatus in TC3 and ST. Since the survey was carried in earlier December with warm and sunny weather (~22 ºC during dawn according to Hong Kong Observatory database, Chek Lap Kok station on 5 December 2016), the horseshoe crab was more active (i.e. move onto intertidal shore during high tide for foraging and breeding) and easier to be found. In contrast, there was no search record in TC1 and TC2 because the survey was conducted in mid-December with colder and cloudy weather (~20°C during dawn on 19 December). The horseshoe crab activity decreases gradually with the colder climate. In December of 2017, 2018 and 2019, very low search records were found again as mentioned above. No record of horseshoe crab was recorded in December 2022 and 2023.

6.5.12 From September 2012 to December 2013, Carcinoscorpius rotundicauda was a fewer common species relative to Tachypleus tridentatus. Only 4 individuals were ever recorded in ST in December 2012. This species had ever been believed of very low density in ST hence the encounter rate was very low. In March 2014, it was found in all sampling zones with higher abundance in ST. Based on its average size (mean prosomal width 39.28 – 49.81 mm), it indicated that breeding and spawning of this species had occurred about 3 years ago along the coastline of Tung Chun Wan. However, these individuals were still small while their walking trails were inconspicuous. Hence there was no search record in the previous sampling months. Since March 2014, more individuals were recorded due to larger size and higher activity (i.e. more conspicuous walking trail).

6.5.13 For Tachypleus tridentatus, sharp increase of number of individuals was recorded in ST during the wet season of 2013 (from March to September). According to a personal conversation with Prof. Shin (City U), his monitoring team recorded a similar increase in horseshoe crab population during wet season. It was believed that the suitable ambient temperature increased its conspicuousness. However, a similar pattern was not recorded in the following wet seasons. The number of individuals increased in March and June 2014 and followed by a rapid decline in September 2014. Then the number of individuals fluctuated slightly in TC3 and ST until March 2017. Apart from natural mortality, migration from nursery soft shore to subtidal habitat was another possible cause. Since the mean prosomal width of Tachypleus tridentatus continued to grow and reached about 50 mm since March 2014. Then it varied slightly between 35-65 mm from September 2014 to March 2017.Most of the individuals might have reached a suitable size (e.g. prosomal width 50 – 60 mm) strong enough to forage in sub-tidal habitat. In June 2017, the number of individuals increased sharply again in TC3 and ST. Although a mating pair of Tachypleus tridentatus was not found in previous surveys, there should be new round of spawning in the wet season of 2016. The individuals might have grown to a more conspicuous size in 2017 accounting for higher search record. In September 2017, moderate numbers of individual were found in TC3 and ST indicating a stable population size. From September 2018 to March 2020, the population size was low while natural mortality was the possible cause. From June 2020 to September 2020, the population size of Tachypleus tridentatus increased to moderate level in ST while the mean proposal width of them continued to grow and reach about 55mm. The population size of Tachypleus tridentatus slightly decreased in ST from March 2021 to March 2022 and the mean proposal width of them increased to about 77.59mm

6.5.14 In recent years, the Carcinoscorpius rotundicauda was a more common horseshoe crab species in Tung Chung Wan. It was recorded in the four sampling zones while most of the population located in TC3 and ST. Due to potential breeding last year, the number of Tachypleus tridentatus increased in ST. Since TC3 and ST were regarded as important nursery ground for both horseshoe crab species, box plots of prosomal width of two horseshoe crab species were constructed to investigate the changes of population in detailsBox plot of horseshoe crab populations in TC3

6.5.15 Figure 3.7 of Appendix I shows the changes of prosomal width of Carcinoscorpius rotundicauda and Tachypleus tridentatus in TC3. As mentioned above, Carcinoscorpius rotundicauda was rarely found between September 2012 and December 2013 hence the data were lacking. In March 2014, the major size (50% of individual records between upper (top box) and lower quartile (bottom box)) ranged 40 – 60 mm while only few individuals were found. From March 2014 to September 2018, the median prosomal width (middle line of whole box) and major size (whole box) decreased after March of every year. It was due to more small individuals found in June indicating new rounds of spawning. Also, there were slight increasing trends of body size from June to March of next year since 2015. It indicated a stable growth of individuals. Focused on larger juveniles (upper whisker), the size range was quite variable (prosomal width 60 – 90 mm) along the sampling months. Juveniles reaching this size might gradually migrate to sub-tidal habitats. In March 2022, 2 Carcinoscorpius rotundicauda with body size (prosomal width 52.21-54.63mm) were found in TC3. The findings were relatively lower than the previous record in March. This can be due to the natural variation caused by multi-environmental factors.

6.5.16 For Tachypleus tridentatus, the major size ranged 20-50 mm while the number of individuals fluctuated from September 2012 to June 2014. Then a slight but consistent growing trend was observed from September 2014 to June 2015. The prosomal width increased from 25 – 35 mm to 35 – 65 mm. As mentioned, the large individuals might have reached a suitable size for migrating from the nursery soft shore to subtidal habitat. It accounted for the decline in TC3. From March to September 2016, a slight increasing trend of major size was noticed again. From December 2016 to June 2017, a similar increasing trend of major size was noted with much higher number of individuals. It reflected a new round of spawning. In September 2017, the major size decreased while the trend was different from the previous two years. Such decline might be the cause of serial cyclone hit between June and September 2017 (to be discussed in the 'Seagrass survey' section). From December 2017 to September 2018, increasing trend was noted again. It indicated a stable growth of individuals. From September 2018 to that of next year, the average prosomal widths decreased from 60mm to 36mm. It indicated new rounds of spawning occurred during September to November 2018. In December 2019, an individual with larger body size (prosomal width 65mm) was found in TC3 which reflected the stable growth of individuals. In March 2020, the average prosomal width (middle line of the whole box) of Tachypleus tridentatus in TC3 was 33.97mm which is smaller than that in December 2019. It was in normal fluctuation. From June 2020 to December 2020, no horseshoe crab was recorded in TC3. In Sep 2021, only one Tachypleus tridentatus with body size (prosomal width 38.78mm) was found in TC3. The decrease in the species population was related to hot weather in September, which may affect their activity. Across the whole monitoring period, the larger juveniles (upper whisker) usually reached 60 – 80 mm in prosomal width, even 90 mm occasionally. The juveniles reaching this size might gradually migrate to sub-tidal habitats.

Box plot of horseshoe crab populations in ST

6.5.17 Figure 3.8 of Appendix I shows the changes of prosomal width of Carcinoscorpius rotundicauda and Tachypleus tridentatus in ST. As mentioned above, Carcinoscorpius rotundicauda was rarely found between September 2012 and December 2013 hence the data were lacking. From March 2014 to September 2018, the size of major population decreased, and more small individuals (i.e. lower whisker) were recorded after June of every year. It indicated a new round of spawning. Also, there were similar increasing trends of body size from September to June of next year between 2014 and 2017. It indicated a stable growth of individuals. The larger juveniles (i.e. upper whisker usually ranged 60 – 80 mm in prosomal width except one individual (prosomal width 107.04 mm) found in March 2017. It reflected that juveniles reaching this size would gradually migrate to sub-tidal habitats.

6.5.18 For Tachypleus tridentatus, a consistent growing trend was observed for the major population from December 2012 to December 2014 regardless of change of search record. The prosomal width increased from 15 – 30 mm to 60 – 70 mm. As mentioned, the large juveniles might have reached a suitable size for migrating from the nursery soft shore to subtidal habitat. From March to September 2015, the size of major population decreased slightly to a prosomal width 40 – 60 mm. At the same time, the number of individuals decreased gradually. It further indicated some large juveniles might have migrated to sub-tidal habitat, leaving the smaller individuals on shore. There was an overall growth trend. In December 2015, two big individuals (prosomal width 89.27 mm and 98.89 mm) were recorded only while it could not represent the major population. In March 2016, the number of individuals was very few in ST that no box plot could be produced. In June 2016, the prosomal width of major population ranged 50 – 70 mm. But it dropped clearly to 30 – 40 mm in September 2016 followed by an increase to 40 – 50 mm in December 2016, 40 – 70 mm in March 2017 and 50 – 60mm in June 2017. Based on the overall higher number of small individuals from June 2016 to September 2017, it indicated another round of spawning. From September 2017 to June 2018, the major size range increased slightly from 40 – 50 mm to 45 – 60 mm indicating a continuous growth. In September 2018, the decrease of major size was noted again that might reflect new round of spawning. Throughout the monitoring period, the larger juveniles ranged 60-80 mm in prosomal width. Juveniles reaching this size would gradually migrate to sub-tidal habitats.

6.5.19 As a summary for horseshoe crab populations in TC3 and ST, there were spawning ground of Carcinoscorpius rotundicauda from 2014 to 2018 while the spawning time should be in spring. The population size was consistent in these two sampling zones. For Tachypleus tridentatus, small individuals were rarely found in both zones from 2014 to 2015. It was believed no occurrence of successful spawning. The existing individuals (that recorded since 2012) grew to a mature size and migrated to sub-tidal habitat. Hence the number of individuals decreased gradually. From 2016 to 2018, new rounds of spawning were recorded in ST while the population size increased to a moderate level.

6.5.20 In March 2019 to June 2019 and Dec 2021, no horseshoe crab juveniles (prosomal width <100mm) were recorded in TC3 and ST. All recorded horseshoe crabs were large individuals (prosomal width >100mm) or mating pairs which were all excluded from the data analysis. From September 2019 to September 2020, the population size of both horseshoe crab species in ST gradually increased to moderate level while their body sizes were mostly in small to medium range (~23 – 55mm). It indicated the natural stable growth of the horseshoe crab juveniles. In December 2020, the population size of both horseshoe crab species in ST dropped to low level while their body sizes were mostly in small to medium range (~28 – 56mm). It showed the natural mortality and seasonal variation of horseshoe crabs. In June 2022, the population size of both horseshoe crab species in ST was kept as low-moderate level while their body sizes were mostly in small to medium range (~51–78mm). In September 2022, the population size of both horseshoe crab species in TC3 and ST was kept as low-moderate level while their body sizes were mostly in small to medium range (~56–62mm). In September 2023, the population size of both horseshoe crab species in TC3 and ST was kept as low-moderate level while their body sizes were mostly in small to medium range (~44-79mm).

Impact of the HKLR project

6.5.21 It was the 51^st survey of the EM&A programme during the construction period. Based on the monitoring results, no detectable impact on horseshoe crab was revealed due to HKLR project. The population change was mainly determined by seasonal variation, no abnormal phenomenon of horseshoe crab individual, such as large number of dead individuals on the shore had been reported.

Discussion

6.5.22 There are 4 juvenile horseshoe crabs recorded in March 2025. The population of horseshoe crabs recorded in recent years has been in a decreasing trend since 2021, referring to Figure 3.5. It is noted that the inter-tidal habitat for the juvenile horseshoe crabs within the monitoring sites is become smaller in area due to increased seagrass colonization as indicated by seagrass monitoring results, i.e. seagrasses cover area increased in recent years (refer to Figure 3.11). The juvenile horseshoe crabs prefer open soft mud/sand habitat as they can easily burrow in the mud/sand to hide themselves when the habitat exposed during low tide. When the mud/sand habitat was colonized by seagrasses, the roots of seagrasses made it difficult for horseshoe crab to burrow and hide. In this situation, horseshoe crabs may avoid habitat or being easily predated by predators such as birds. All seagrasses disappeared as observed during monitoring in December 2024, and one of the two seagrasses is observed in March 2025 re-generated at a small area along mangal edge. Attention will be given to subsequent monitoring, if it will affect the breeding activities of the horseshoe crabs.

Seagrass Beds

6.5.23 All seagrasses were observed disappeared within monitoring areas of Tung Chung and San Tau during the last quarterly ecological monitoring in December 2024. However, one of the two seagrass species, i.e., Zostera japonica is re-generated during the survey in March 2025. It is likely that the underground roots of this seagrass maintained alive when the above ground plant part died during last season, i.e., December 2024. Zostera japonica was found only in ST. At close vicinity to mangrove, one small sized 25 square meter) of Zostera japonica beds were observed at tidal zone 2.0m above C.D in ST. The widely distributed seagrass, Halophila ovalis in recent years totally disappeared in December 2024 and did not observe re-generation in March 2025. Table 3.2 of Appendix I summarizes the results of the present seagrass beds survey, and the photograph records of the seagrass bed are shown in Figure 3.9 of Appendix I. The complete record throughout the monitoring period is presented in Annex III of Appendix I.

6.5.24 Since the commencement of the EM&A monitoring programme, two species of seagrass and Zostera japonica were recorded in TC3 and ST (Figure 3.10 of Appendix I). In general, Halophila ovalis was occasionally found in TC3 in few small to medium patches. But it was commonly found in ST in medium to large seagrass bed. Moreover, it had sometimes grown extensively and had covered significant mudflat area at 0.5 – 2.0 m above C.D. between TC3 and ST. Another seagrass species Zostera japonica was found in ST only. It has restricted distribution in a few locations with small vegetation coverage, and it partially co-existed with Halophila ovalis near the edge of the mangrove strand at 2.0 m above C.D.

6.5.25 According to the previous results, majority of seagrass bed was confined in ST, while it increasingly established at TC3 in recent years, and the temporal change of both seagrass species was investigated in detail:

Temporal variation of seagrass beds in ST

6.5.26 Figure 3.11 of Appendix I shows the changes of estimated total area of seagrass beds in ST along the sampling months. For Zostera japonica, it was not recorded in the 1^st and 2^nd surveys of monitoring programme. Seasonal recruitment of few, small patches (total seagrass area: 10 m²) was found in March 2013 that grew within the large patch of seagrass Halophila ovalis. Then, the patch size increased and merged gradually with the warmer climate from March to June 2013 (15 m²). However, the patch size decreased and remained similar from September 2013 (4 m²) to March 2014 (3 m²). In June 2014, the patch size increased obviously again (41 m²) with warmer climate followed by a decrease between September 2014 (2 m²) and December 2014 (5 m²). From March to June 2015, the patch size increased sharply again (90 m²). It might be due to the disappearance of the originally dominant seagrass Halophila ovalis resulting in less competition for substratum and nutrients. From September 2015 to June 2016, it was found coexisting with seagrass Halophila ovalis with steady increasing patch size (from 44 m² to 115 m²) and variable coverage. In September 2016, the patch size decreased again to (38 m²) followed by an increase to a horizontal strand (105.4 m²) in June 2017. And it did no longer co-existed with Halophila ovalis. Between September 2014 and June 2017, an increasing trend was noticed from September to June of next year followed by a rapid decline in September of next year. It was possibly the cause of heat stress, typhoon and stronger grazing pressure during the wet season. However, such increasing trend was not found from September 2017 to March 2021, while no patch of Zostera japonica was found. From June 2021, the species was recorded again with a coverage of 45m²in area. The recorded area of the seagrass bed in September 2021 survey was slightly decreased to 15m². The Z. japonica was consistently present at the monitoring site still September 2024, it disappeared in December 2024 and regenerated in the present survey.

6.5.27 For Halophila ovalis, it was recorded as 3 – 4 media to large patches (area 18.9- 251.7 m²; vegetation coverage 50 – 80%) beside the mangrove vegetation at tidal level 2 m above C.D. in September 2012. The total seagrass bed area grew steadily from 332.3 m² in September 2012 to 727.4 m² in December 2013. Flowers were observed in the largest patch during its flowering period. In March 2014, 31 small to medium patches were newly recorded (variable area 1 – 72 m² per patch, vegetation coverage 40-80% per patch) in lower tidal zone between 1.0 and 1.5 m above C.D. The total seagrass area increased further to 1350 m². In June 2014, these small and medium patches grew and extended to each other. These patches were no longer distinguishable and were covering a significant mudflat area of ST. It was generally grouped into 4 large patches (1116 – 2443 m²) of seagrass beds characterized of patchy distribution, variable vegetable coverage (40-80%) and smaller leaves. The total seagrass bed area increased sharply to 7629 m². In September 2014, the total seagrass area declined sharply to 1111m². There were only 3-4 small to large patches (6 – 253 m²) at high tidal level and 1 large patch at low tidal level (786 m²). Typhoons or strong water current was a possible cause (Fong, 1998). In September 2014, there were two tropical cyclone records in Hong Kong (7^th – 8^thSeptember: no cyclone name, maximum signal number 1; 14^th – 17^thSeptember: Kalmaegi, maximum signal number 8SE) before the seagrass survey dated 21^stSeptember 2014. The strong water current caused by the cyclone Kalmaegi especially might have damaged the seagrass beds. In addition, natural heat stress and grazing force were other possible causes reducing seagrass beds area. Besides, very small patches of Halophila ovalis could be found in other mud flat areas in addition to the recorded patches. But it was hardly distinguished due to very low coverage (10 – 20%) and small leaves.

6.5.28 In December 2014, all the seagrass patches of Halophila ovalis disappeared in ST. Figure 3.12 of Appendix I shows the difference of the original seagrass beds area nearby the mangrove vegetation at high tidal level between June 2014 and December 2014. Such rapid loss would not be a seasonal phenomenon because the seagrass beds at higher tidal level (2.0 m above C.D.) were present and normal in December 2012 and 2013. According to Fong (1998), similar incident had occurred in ST in the past. The original seagrass area had declined significantly during the commencement of the construction and reclamation works for the international airport at Chek Lap Kok in 1992. The seagrass almost disappeared in 1995 and recovered gradually after the completion of reclamation works. Moreover, incident of rapid loss of seagrass area was also recorded in another intertidal mudflat in Lai Chi Wo in 1998 with unknown reason. Hence, Halophila ovalis was regarded as a short- lived and r- strategy seagrass that could colonize areas in short period but disappears quickly under unfavorable conditions (Fong, 1998).

Unfavourable conditions to seagrass Halophila ovalis

6.5.29 Typhoon or strong water current was suggested as one unfavorable condition to Halophila ovalis (Fong, 1998). As mentioned above, there were two tropical cyclone records in Hong Kong in September 2014. The strong water current caused by the cyclones might have caused damage to the seagrass beds.

6.5.30 Prolonged light deprivation due to turbid water would be another unfavorable condition. Previous studies reported that Halophila ovalis had little tolerance to light deprivation. During experimental darkness, seagrass biomass declined rapidly after 3-6 days, and seagrass died completely after 30 days. The rapid death might be due to shortage of available carbohydrate under limited photosynthesis or accumulation of phytotoxic end products of anaerobic respiration (details see Longstaff et al., 1999). Hence the seagrass bed of this species was susceptible to temporary light deprivation events such as flooding river runoff (Longstaff and Dennison, 1999).

6.5.31 To investigate any deterioration of water quality (e.g. more turbid) in ST, the water quality measurement results at two closest monitoring stations SR3 and IS5 of the EM&A programme were obtained from the water quality monitoring team. Based on the results from June to December 2014, the overall water quality was in normal fluctuation except there was one exceedance of suspended solids (SS) at both stations in September. On 10^th September 2014, the SS concentrations measured during mid-ebb tide at stations SR3 (27.5 mg/L) and IS5 (34.5 mg/L) exceeded the Action Level (≤ 23.5 mg/L and 120% of upstream control station’s reading) and Limit Level (≤ 34.4 mg/L and 130% of upstream control station’s reading) respectively. The turbidity readings at SR3 and IS5 reached 24.8 – 25.3 NTU and 22.3 – 22.5 NTU, respectively. The temporary turbid water should not be caused by the runoff from upstream rivers. Because there was no rain or slight rain from 1^st to 10^th September 2014 (daily total rainfall at the Hong Kong International Airport: 0 – 2.1 mm; extracted from the climatological data of Hong Kong Observatory). The effect of upstream runoff on water quality should be neglectable in that period. Moreover, the exceedance of water quality was considered unlikely to be related to the contract works of HKLR according to the ‘Notifications of Environmental Quality Limits Exceedances’ provided by the respective environmental team. The respective construction of seawall and stone column works, which possibly caused turbid water, was carried out within silt curtain as recommended in the EIA report. Moreover, there was no leakage of turbid water, abnormity or malpractice recorded during water sampling. In general, the exceedance of suspended solids concentration was attributed to other external factors, rather than the contract work.

6.5.32 Based on the weather condition and water quality results in ST, the co-occurrence of cyclone hit and turbid waters in September 2014 might have combined the adverse effects on Halophila ovalis that leaded to disappearance of this short-lived and r-strategy seagrass species. Fortunately, Halophila ovalis was a fast-growing species (Vermaat et al., 1995). Previous studies showed that the seagrass bed could be recovered to the original sizes in 2 months through vegetative propagation after experimental clearance (Supanwanid, 1996). Moreover, it was reported to recover rapidly in less than 20 days after dugong herbivory (Nakaoka and Aioi, 1999). As mentioned, the disappeared seagrass in ST in 1995 could recover gradually after the completion of reclamation works for international airport (Fong, 1998). The recovery of seagrass beds of Halophila ovalis in the mudflat of ST was observed in the continuous monitoring years.

Recolonisation of seagrass beds

6.5.33 Figure 3.12 of Appendix I shows the recolonization of seagrass bed in ST from December 2014 to September 2024. From March to June 2015, 2 – 3 small patches of Halophila ovalis were newly found co-inhabiting with another seagrass species Zostera japonica. But the total patch area of Halophila ovalis was still very low compared with previous records. The recolonization rate was low while cold weather and insufficient sunlight were possible factors between December 2014 and March 2015. Moreover, it would need to compete with seagrass Zostera japonica for substratum and nutrient, because Zostera japonica had extended and covered the original seagrass bed of Halophila ovalis at certain degree. From June 2015 to March 2016, the total seagrass area of Halophila ovalis had increased rapidly from 6.8 m² to 230.63 m². It had recolonized its original patch locations and covered its competitor Zostera japonica. In June 2016, the total seagrass area increased sharply to 4707.3m². Like the previous records of March to June 2014, the original patch area of Halophila ovalis increased further to a horizontally long strand. Another large seagrass beds colonized the lower tidal zone (1.0 – 1.5 m above C.D.). In September 2016, this patch extended much and covered significant soft mud area of ST, resulting in sharp increase of total area (24245 m²). It indicated the second extensive colonization of this r-selected seagrass. In December 2016, this extensive seagrass patch decreased in size and had been separated into few, undistinguishable patches. Moreover, the horizontal strand nearby the mangrove vegetation decreased in size. The total seagrass bed decreased to 12550 m². From March to June 2017, the seagrass bed area remained generally stable (12438- 17046.5 m²) but the vegetation coverage fluctuated (20 – 50% in March 2017 to 80 – 100% in June 2017). The whole recolonization process took about 2.5 years.

Second disappearance of seagrass bed

6.5.34 In September 2017, the whole seagrass bed of Halophila ovalis disappeared again along the shore of TC3 and ST (Figure 3.12 of Appendix I). Like the first disappearance of seagrass beds that occurred between September and December 2014, strong water current (e.g. cyclone) or deteriorated water qualities (e.g. high turbidity) was the possible cause.

6.5.35 Between the survey periods of June and September 2017, there were four tropical cyclone records in Hong Kong (Merbok in 12- 13^th, June; Roke in 23^rd, Jul.; Hato in22 – 23^rd, Aug.; Pakhar in 26 – 27^th, Aug.) (Online database of Hong Kong Observatory) All of them reached signal 8 or above, especially Hato with highest signal 10.

6.5.36 According to the water quality monitoring results (July to August 2017) of the two closest monitoring stations SR3 and IS5 of the respective EM&A programme, the overall water quality was in normal fluctuation. There was an exceedance of suspended solids (SS) at SR3 on 12 July 2017. The SS concentration reached 24.7 mg/L during mid-ebb tide, which exceeded the Action Level (≤ 23.5 mg/L). But it was far below the Limit Level (≤ 34.4 mg/L). Since such exceedance was slight and temporary, its effect to seagrass bed should be minimal.

6.5.37 Overall, the disappearance of seagrass beds in ST has believed the cause of serial cyclone hit in July and August 2017. Based on previous findings, the seagrass beds of both species were expected to recolonize in the mudflat if the vicinal water quality was normal. The whole recolonization process (from few, small patches to extensive strand) would gradually last at least 2 years. From December 2017 to March 2018, there was still no recolonization of few, small patches of seagrass at the usual location (Figure 3.12). It was different from the previous round (March 2015 – June 2017). Until June 2018, the new seagrass patches with small-medium size were found at the usual location (seaward side of mangrove plantation at 2.0 m C.D.) again, indicating the recolonization. However, the seagrass bed area decreased sharply to 22.5 m² in September 2018. Again, it was believed that the decrease was due to the hit of the super cyclone in September 2018 (Mangkhuton 16^th September, highest signal 10). From December 2018 to June 2019, the seagrass bed area increased from 404 m² to 1229 m² while the vegetation coverage is also increased (December 2018: 5– 85%; March 2019: 50 – 100% and June 2019: 60 – 100%). Relatively, the whole recolonization process would occur slower than the previous round (more than 2 years). From September 2019 to March 2021, the seagrass bed area in ST slightly decreased from 1200 m²to 942.05 m²,which were in normal fluctuation. From March 2021 to December 2021, the seagrass bed area in ST decreased from 942.05 m²to 680m²,which were in normal fluctuation. In March 2022, the seagrass bed area in ST increased significantly to approximately 2040 m^2,which believed to be related to more rain in current dry season. It was observed that the brown filamental algae bloom occurred at ST site in March 2022. Distribution of the algae was overlapped with seagrass beds, mainly the species Halophila ovalis and the algae was grown over the top of the seagrass. In some areas, the brown filamental algae fully covered the seagrass bed, referring to Figure 3.9. The seagrass was still alive when checked during the field survey. Whether the algae bloom will kill seagrass in longer period time is unknown. The seagrass distribution and health condition should be checked in the coming June monitoring. The algae bloom of the brown filamental algae at the seagrass bed disappeared as observed in June 2022, referring to Figure 3.9. Seagrass in December 2022 and September 2022 have decreased compared to June 2022 due to normal seasonal change. Seagrass in March 2023 have increased compared to the previous quarter due to normal seasonal change. Seagrass in June 2023 have further increased around 20% compared to the previous period. Seagrass in September and December 2023 have decreased compared to previous quarter due to normal seasonal change. In March 2024, seagrass increased compared to the previous quarter. In September 2024, seagrass coverage increased compared to the previous quarter.

Third disappearance of seagrass bed

6.5.38 All seagrass beds were observed disappeared at the monitoring sites during the December monitoring event in 2024. There were two typhoon/cyclone events that occurred during November 2024 which was an unusual local weather condition, and it may cause the disappearance of the seagrasses.

Impact of the HKLR project

6.5.39 It was the 51^st survey of the EM&A Programme during the construction period. Throughout the monitoring period, the disappearance of seagrass beds in three occasions was believed to be the cause of cyclone hits rather than impact of HKLR project. The seagrass bed was recolonized since there had been a gradual increase in size and number from December 2018 to September 2024 after the hit of the super cyclone in September 2018. The seagrass bed area decreased from March 2021 to December 2021, which was in normal fluctuation. It is observed that the seagrass Halophila ovalis covered a larger area than before. Total seagrass bed area significantly increased from March 2022 to June 2022 and slightly reduced in September 2022. Seagrass in September and December 2023 have decreased compared to previous quarter and increased in March, June, and September 2024. The third time seagrass bed disappearance was observed during quarterly monitoring in December 2024 and one of the two seagrass species regenerated in March 2025 in ST.

Intertidal Soft Shore Communities

Substratum

6.5.40 Table 3.3 and Figure 3.13 of Appendix I show the substratum types along the horizontal transect at every tidal level in all sampling zones. The relative distribution of substratum types was estimated by categorizing the substratum types (Gravels & Boulders / Sands / Soft mud) of the ten random quadrats along the horizontal transect. The distribution of substratum types varied among tidal levels and sampling zones:

· In TC1, high percentages of ‘Gravels and Boulders’ (80%) were recorded at a high tidal level. At mid tidal level, ‘Gravels and Boulders’ were comprised of 10%, following by ‘Sands’ (85%) and ‘Soft mud’ (5%). At low tidal level, ‘Soft mud’ was the main substratum type (90%), followed by ‘Sands’ (10%).

· In TC2, the high percentages of ‘Gravels and Boulders’ (85%) were recorded at high tidal level, following by ‘Sands’ (10%). At mid tidal levels, Gravels and Boulders’ was approximately 10%), following by ‘Sands’ (85%) and ‘Soft mud’ (5%). At low tidal level, ‘Soft mud’ covered 95%, ‘Gravels and Boulders’ and ‘Sands ’ covered the remaining 5% of the transect.

· In TC3, the higher percentage of ‘Gravels and Boulders’ was recorded at high tidal level (90%), following by ‘Sands’ and Soft mud covered remaining 10%. At mid tidal level, ‘Gravels and Boulders’ contributed 10% to the substratum, following by ‘Sands’ (10%) and ‘Soft mud’ 80%). At low tidal level, ‘Soft mud’ covered 95% of the transect, and ‘Sands’ and ‘Gravels’ covered 5% of the seabed.

· In ST, ‘Gravels and Boulders’ was the main substratum type (90%) at high tidal level, followed by ‘Sands’ and ‘Soft mud’ (10%). At mid tidal levels, Gravels and ‘Boulders’ were the minor substratum type (10%), following by ‘Sands’ (85%) and ‘Soft mud’ (5%). At low tidal level, ‘Soft mud’ was the main substratum type (90%), ‘Sands’ covered 8% of the transect, ‘Gravels and Boulders’ covered 2% of the transect.

6.5.41 There was neither consistent vertical nor horizontal zonation pattern of substratum type in all sampling zones. Such heterogeneous variation should be caused by different hydrology (e.g. wave in different direction and intensity) received by the four sampling zones.

Soft shore communities

6.5.42 Table 3.4 of Appendix I lists the total abundance, density and number of taxa of every phylum in this survey. A total of 7,401 individuals were recorded. Mollusca was the most abundant phylum (total abundance 6,485 ind., density 216 ind. m^-2, relative abundance 87.6%). The second and third were Arthropoda 519 ind., 17 ind. m^-2, 7%) which was followed by Sipuncula (173 ind., 6 ind. m^-2, 2.3%) and Annelida (98 ind., 3 ind. m^-2, 1.3%), respectively. The fifth was Cnidania with total abundance 65 ind., density 2 ind.m^-2and relative abundance 0.9%. The sixth was Nemertea with total abundance 46 ind., density 2 ind.m^-2and relative abundance 0.6%. Platyhelminthes was very low in abundances (density 1 ind. m^-2, relative abundance 0.2%). Moreover, the most diverse phylum was Mollusca (32 taxa) followed by Arthropoda (6 taxa). Annelida (3 taxa) and Sipuncula (2 taxa). There was 1 taxon for Nemertea, Cnidaria and Platyhelminthes.

6.5.43 The taxonomic resolution and complete list of recorded fauna are shown in Annex IV and V of Appendix I respectively. As reported in June 2018, taxonomic revision of three potamidid snail species was conducted according to the latest identification key published by Agriculture, Fisheries and Conservation Department (details see AFCD, 2018), the species names of following gastropod species were revised:

· Cerithidea cingulata was revised as Pirenella asiatica

· Cerithidea djadjariensis was revised as Pirenella incisa

· Cerithidea rhizophorarum was revised as Cerithidea moerchii

Moreover, taxonomic revision was conducted on another snail species while the specie name was revised:

· Batillaria bornii was revised as Clypeomorus bifasciata

6.5.44 In March 2021, an increased number of sea slugs and their eggs were observed in all sampling zones. It may due to the breeding season of sea slug and the increased of algae on the intertidal.

6.5.45 Table 3.5 shows the number of individuals, relative abundance and density of each phylum in every sampling zone. The total abundance (1,772 – 1,959 ind.) varied among the four sampling zones while the phyla distributions were similar. In general, Mollusca was the most dominant phylum (no. of individuals: 1,496 – 1,755 ind.; relative abundance 84.4% - 89.6%; density 199-234 ind. m^-2). Other phyla were much lower in number of individuals. Arthropoda (85 to 208 ind.; 4.3% - 11.7%; 11 - 28 ind. m^-2) was common phyla relatively. Other phyla, including Annelida (0–40 individuals; 0.0%–2.1%; 0–5 ind. m⁻²), Sipuncula (23–65 individuals; 1.3%–3.5%; 3–9 ind. m⁻²), Nemertea (0–27 individuals; 0.0%–1.4%; 0–4 ind. m⁻²), Cnidaria (0–32 individuals; 0.0%–1.8%; 0–4 ind. m⁻²), and Platyhelminthes (0–15 individuals; 0.0%–0.8%; 0–2 ind. m⁻²), were very low in abundance in all sampling zones.

Dominant species in every sampling zone

6.5.46 Table 3.6 of Appendix I lists the abundant species in every sampling zone. In the present survey, most of the listed abundant species were of low to moderate densities (42 – 95 ind. m^-2). Few of the listed species were of high or very high density (>100 ind. m^-2), which were regarded as dominant species. Other listed species of lower density (<42 ind. m^-2) were regarded as common species.

6.5.47 In TC1, the substratum was mainly ‘Gravels and Boulders’ at high and mid tidal levels. At high tidal level, the rock oyster Saccostrea cucullata (mean density 106 ind. m⁻²; relative abundance 39%) was the dominant species found at high density, and the gastropod Monodonta labio (56 ind. m⁻²; relative abundance 21%) was of low to moderate density. At mid tidal level, the rock oyster Saccostrea cucullata (79 ind. m⁻², 32%) was the dominant species with low to moderate density. The gastropod Monodonta labio (48 ind. m⁻², 19%) was at low to moderate densities, followed by Batillaria zonalis (32 ind. m⁻², 13%) at low density. At low tidal level (main substratum type ‘Soft mud’), Batillaria multiformis (41 ind. m⁻², 21%) was the dominant species with low to moderate density, while Nodilittorina radiata (38 ind. m⁻², 19%) and Barbatia virescens (36 ind. m⁻², 18%) were of lower density, regarded as common species.

6.5.48 In TC2, the substratum types were mainly 'Gravels and Boulders' at a high tidal level. The rock oyster Saccostrea cucullata (97 ind. m⁻², 35%) was the dominant species found at high density. The gastropod Monodonta labio (57 ind. m⁻², 21%) was dominant at low to moderate density, and Batillaria multiformis (40 ind. m⁻², 14%) was at lower density. At mid tidal level (main substratum types ‘Soft mud’ and ‘Gravels and Boulders’), the rock oyster Saccostrea cucullata (76 ind. m⁻², 33%), gastropods Monodonta labio (40 ind. m⁻², 16%), and Batillaria zonalis (34 ind. m⁻², 14%) were dominant at low density. Substratum types ‘Soft Mud’ were mainly distributed at low tidal level, where Barbatia virescens (44 ind. m⁻², 23%) was dominant at low densities, and Batillaria multiformis (31 ind. m⁻², 16%) were of lower densities, regarded as common species.

6.5.49 In TC3, the substratum type was mainly ‘Gravels and Boulders’ at high tidal level. The rock oyster Saccostrea cucullata (112 ind. m⁻², 40%) was the dominant species at high density, and the gastropod Monodonta labio (58 ind. m⁻², 21%) was of low to moderate density. At mid tidal level (main substratum types ‘Gravels and Boulders’), the rock oyster Saccostrea cucullata (102 ind. m⁻², 39%) was the dominant species at low to moderate density. The gastropod Monodonta labio (51 ind. m⁻², 19%) was at low density level. At low tidal level, the major substratum type was ‘Soft mud’. Barbatia virescens (58 ind. m⁻², 25%) was at low to moderate density, while Lunella granulata (33 ind. m⁻², 14%) and Batillaria multiformis (34 ind. m⁻², 14%) were dominant at low densities.

6.5.50 In ST, the major substratum type was ‘Gravels and Boulders’ at high tidal level. At high tidal level, the rock oyster Saccostrea cucullata (96 ind. m⁻², 32%) was at low to moderate densities. The gastropod Monodonta labio (52 ind. m⁻², 17%) was at low to moderate densities. At mid tidal level (main substratum types ‘Gravels and Boulders’), the gastropod Monodonta labio (45 ind. m⁻², 18%) was at low to moderate densities, and the rock oyster Saccostrea cucullata (84 ind. m⁻², 34%) was the dominant species at high densities. At low tidal level (major substratum: ‘Soft mud’), Batillaria zonalis (55 ind. m⁻², 27%) was at low to moderate densities, and Lunella granulata (38 ind. m⁻², 18%) was at low density.

6.5.51 In general, there was no consistent zonation pattern of species distribution across all sampling zones and tidal levels. The species distribution was determined by the type of substratum primarily. In general, rock oyster Saccostrea cucullata (752 ind.), gastropods Monodonta labio (400 ind.) and Batillaria multiformis (146 ind.) were the most common species on gravel and boulders substratum. Batillaria zonalis (126 ind.) was the most common species on sands and soft mud substrata.

Biodiversity and abundance of soft shore communities

6.5.52 Table 3.7 of Appendix I shows the mean values of species number, density, and biodiversity index H’and species evenness J of soft shore communities at every tidal level and in every sampling zone. As mentioned above, the differences among sampling zones and tidal levels were determined by the major type of substratum primarily.

6.5.53 Among the sampling zones, the mean species number varied from 15 to 17 spp. 0.25 m⁻² across the four sampling zones. The mean densities of ST (258 ind. m⁻²) and TC3 (243 ind. m⁻²) were higher than those of TC1 (227 ind. m⁻²) and TC2 (226 ind. m⁻²). The higher densities in ST and TC3 are attributed to the relatively high number of individuals in each quadrat. The mean H’ for TC2 was 2.20, while the mean H’ for TC1, TC3, and ST were 2.17. The mean J for TC1 was 0.83, slightly higher than TC2 (0.80), followed by TC3 and ST (0.77). This can be attributed to the relatively uneven distribution of taxa across the sampling zones.

6.5.54 In the present survey, no clear trend of mean species number, mean density, H’ and J observed among the tidal level.

6.5.55 Figures 3.14-3.17 of Appendix I show the temporal changes of mean species number, mean density, H’ and J at every tidal level and in every sampling zone along the sampling months. In general, all the biological parameters fluctuated seasonally throughout the monitoring period. Lower mean species number and density were recorded in dry season (December) but the mean H' and J fluctuated within a limited range.

6.5.56 From June to December 2017, there were steady decreasing trends of mean species number and density in TC2, TC3 and ST regardless of tidal levels. It might be an unfavorable change reflecting environmental stress. The heat stress and serial cyclone hit were believed to be the causes during the wet season of 2017. From March 2018 to December 2024 (present survey), generally increases of mean species number and density were observed in all sampling zones. It indicated the recovery of intertidal community.

Impact of the HKLR project

6.5.57 It was the 51^st survey of the EM&A programme during the construction period. Based on the results, impacts of the HKLR project were not detected on intertidal soft shore community. Abnormal phenomena (e.g. rapid, consistent or non-seasonal decline of fauna densities and species number) were not recorded.

6.6 Reference

6.6.1 AFCD, 2018. Potamidid Snails in Hong Kong Mangrove. Agriculture, Fisheries and Conservation Department Newsletter - Hong Kong Biodiversity Issue #25, 2-11

6.6.2 Chan, K.K., Caley, K.J., 2003. Sandy Shores, Hong Kong Field Guides 4. The Department of Ecology & Biodiversity, The University of Hong Kong. pp 117.

6.6.3 Dai, A.Y., Yang, S.L., 1991. Crabs of the China Seas. China Ocean Press. Beijing.

6.6.4 Dong, Y.M., 1991. Fauna of ZheJiang Crustacea. Zhejiang Science and Technology Publishing House. ZheJiang.

6.6.5 EPD, 1997. Technical Memorandum on Environmental Impact Assessment Process (1^st edition). Environmental Protection Department, HKSAR Government.

6.6.6 Fauchald, K., 1977. The polychaete worms. Definitions and keys to the orders, families and genera. Natural History Museum of Los Angeles County, Science Series 28. Los Angeles, U.S.A..

6.6.7 Fong, C.W., 1998. Distribution of Hong Kong seagrasses. In: Porcupine! No. 18. The School of Biological Sciences, The University of Hong Kong, in collaboration with Kadoorie Farm & Botanic Garden Fauna Conservation Department, p10-12.

6.6.8 Li, H.Y., 2008. The Conservation of Horseshoe Crabs in Hong Kong. MPhil Thesis, City University of Hong Kong, pp 277.

6.6.9 Longstaff, B.J., Dennison, W.C., 1999. Seagrass survival during pulsed turbidity events: the effects of light deprivation on the seagrasses Halodule pinifolia and Halophila ovalis. Aquatic Botany 65 (1-4), 105-121.

6.6.10 Longstaff, B.J., Loneragan, N.R., O’Donohue, M.J., Dennison, W.C., 1999. Effects of light deprivation on the survival and recovery of the seagrass Halophila ovalis (R. Br.) Hook. Journal of Experimental Marine Biology and Ecology 234 (1), 1-27.

6.6.11 Nakaoka, M., Aioi, K., 1999. Growth of seagrass Halophila ovalis at dugong trails compared to existing within-patch variation in a Thailand intertidal flat. Marine Ecology Progress Series 184, 97-103.

6.6.12 Pielou, E.C., 1966. Shannon’s formula as a measure of species diversity: its use and misuse. American Naturalist 100, 463-465.

6.6.13 Qi, Z.Y., 2004. Seashells of China. China Ocean Press. Beijing, China.

6.6.14 Qin, H., Chiu, H., Morton, B., 1998. Nursery beaches for Horseshoe Crabs in Hong Kong. In: Porcupine! No. 18. The School of Biological Sciences, The University of Hong Kong, in collaboration with Kadoorie Farm & Botanic Garden Fauna Conservation Department, p9-10.

6.6.15 Shannon, C.E., Weaver, W., 1963. The Mathematical Theory of Communication. Urbana: University of Illinois Press, USA.

6.6.16 Shin, P.K.S., Li, H.Y., Cheung, S.G., 2009. Horseshoe Crabs in Hong Kong: Current Population Status and Human Exploitation. Biology and Conservation of Horseshoe Crabs (part 2), 347-360.

6.6.17 Supanwanid, C., 1996. Recovery of the seagrass Halophila ovalis after grazing by dugong. In: Kuo, J., Philips, R.C., Walker, D.I., Kirkman, H. (eds), Seagrass biology: Proc Int workshop, Rottenest Island, Western Australia. Faculty of Science, The University of Western Australia, Nedlands, 315-318.

6.6.18 Vermaat, J.E., Agawin, N.S.R., Duarte, C.M., Fortes, M.D., Marba. N., Uri, J.S., 1995. Meadow maintenance, growth and productivity of a mixed Philippine seagrass bed. Marine Ecology Progress Series 124, 215-225.

6.6.19 Yang,. D.J, Sun, R.P., 1988. Polychaetous annelids commonly seen from the Chinese waters (Chinese version). China Agriculture Press, China

7 Environmental Site Inspection and Audit

7.1 Site Inspection

7.1.1 Site Inspections were carried out on a weekly basis to monitor the implementation of proper environmental pollution control and mitigation measures for the Project. During the reporting month, four site inspections were carried out on 5, 12, 19 and 28 March 2025.

7.1.2 A summary of observations found during the site inspections and the follow up actions taken by the Contractor/ recommendation are described in Table 7.1.

Table 7.1 Summary of Environmental Site Inspections

Date of Audit	Observations	Actions Taken by Contractor / Recommendation	Date of Observations Closed
5 March 2025	No particular environmental issue was recorded during the site inspection.	N.A.	N.A.
12 March 2025	No particular environmental issue was recorded during the site inspection.	N.A.	N.A.
19 March 2025	No particular environmental issue was recorded during the site inspection.	N.A.	N.A.
28 March 2025	No particular environmental issue was recorded during the site inspection.	N.A.	N.A.

7.2 Advice on the Solid and Liquid Waste Management Status

7.2.1 The Contractor registered as a chemical waste producer for the Contract. Sufficient numbers of receptacles were available for general refuse collection and sorting.

7.2.2 Monthly summary of waste flow table is detailed in Appendix J.

7.2.3 The Contractor was reminded that chemical waste containers should be properly treated and stored temporarily in designated chemical waste storage area on site in accordance with the Code of Practice on the Packaging, Labelling and Storage of Chemical Wastes.

7.3 Environmental Licenses and Permits

7.3.1 The valid environmental licenses and permits during the reporting month are summarized in Appendix L.

7.4 Implementation Status of Environmental Mitigation Measures

7.4.1 A summary of the Implementation Schedule of Environmental Mitigation Measures (EMIS) is presented in Appendix M. Most of the necessary mitigation measures were implemented properly.

7.4.2 Regular marine travel route for marine vessels were implemented properly in accordance to the submitted plan and relevant records were kept properly.

7.4.3 Dolphin Watching Plan was implemented during the reporting month. No dolphins inside the silt curtain were observed. The relevant records were kept properly.

7.5 Summary of Exceedances of the Environmental Quality Performance Limit

7.5.1 For air quality, no Action and Limit Level exceedances of 1-hr TSP and 24-hr TSP were recorded at station AMS5 and AMS6 during the reporting month.

7.5.2 For construction noise, no Action and Limit Level exceedances were recorded at station NMS5 during the reporting month.

7.5.3 For marine water quality monitoring, no Action Level and Limit Level exceedances of dissolved oxygen level, turbidity level and suspended solid level were recorded during the reporting month.

7.6 Summary of Complaints, Notification of Summons and Successful Prosecution

7.6.1 There was no complaint received in relation to the environmental impacts during this reporting month.

7.6.2 The details of cumulative statistics of Environmental Complaints are provided in Appendix K.

7.6.3 No notification of summons and prosecution was received during the reporting period. Statistics on notifications of summons and successful prosecutions are summarized in Appendix N.

8 Future Key Issues

8.1 Construction Programme for the Coming Months

8.1.1 As informed by the Contractor, the major construction activities for April 2025 are summarized in Table 8.1.

Table 8.1 Construction Activities for April 2025

Site Area	Description of Activities
Portion X	Removal of Temporary Toe Loading Platform

8.2 Environmental Monitoring Schedule for the Coming Month

8.2.1 The tentative schedule for environmental monitoring for April 2025 is provided in Appendix D.

9 Conclusions

9.1 Conclusions

9.1.1 The construction phase and EM&A programme of the Contract commenced on 17 October 2012. This is the 150^th Monthly EM&A report for the Contract which summarizes the monitoring results and audit findings of the EM&A programme during the reporting period from 1 to 31 March 2025.

Air Quality

9.1.2 For air quality, no Action Level and Limit Level exceedances of 1-hr TSP and 24-hr TSP were recorded at station AMS5 and AMS6 during the reporting month.

Noise

9.1.3 For construction noise, no Action and Limit Level exceedances were recorded at station NMS5 during the reporting month.

Water Quality

9.1.4 For marine water quality monitoring, no Action Level and Limit Level exceedances of dissolved oxygen level, turbidity level and suspended solid level were recorded during the reporting month.

Dolphin

9.1.5 During this month of dolphin monitoring, no adverse impact from the activities of this construction project on Chinese White Dolphins was noticeable from general observations.

9.1.6 Due to monthly variation in dolphin occurrence within the study area, it would be more appropriate to draw conclusion on whether any impacts on dolphins have been detected related to the construction activities of this project in the quarterly EM&A report, where comparison on distribution, group size and encounter rates of dolphins between the quarterly impact monitoring period (December 2024 – February 2025) and the 3-month baseline monitoring period will be made.

Mudflat

9.1.7 This measurement result was generally and relatively higher than the baseline measurement at S1, S2, S3 and S4. The mudflat level is continuously increased. The March 2025 survey results indicate that impacts of the HKLR project were not detected on intertidal soft shore community. Based on the monitoring results, no detectable impact on horseshoe crab was revealed due to HKLR project. The population change was mainly determined by seasonal variation, no abnormal phenomenon of horseshoe crab individual, such as large number of dead individuals on the shore had been reported. Throughout the monitoring period, the disappearance of seagrass beds in three occasions was believed to be the cause of cyclone hits rather than impact of HKLR project. The seagrass bed was recolonized since there had been a gradual increase in size and number from December 2018 to September 2024 after the hit of the super cyclone in September 2018. The seagrass bed area decreased from March 2021 to December 2021, which was in normal fluctuation. It is observed that the seagrass Halophila ovalis covered a larger area than before. Total seagrass bed area significantly increased from March 2022 to June 2022 and slightly reduced in September 2022. Seagrass in September and December 2023 have decreased compared to previous quarter and increased in March, June, and September 2024. The third time seagrass bed disappearance was observed during quarterly monitoring in March 2025. The re-colonization of seagrass at the monitoring sites will be reported in subsequent mudflat monitoring. Based on the results, impacts of the HKLR project were not detected on intertidal soft shore community. Abnormal phenomena (e.g. rapid, consistent or non-seasonal decline of fauna densities and species number) were not recorded.

Environmental Site Inspection and Audit

9.1.8 Environmental site inspections were carried out on 5, 12, 19 and 28 March 2025. Most of the necessary mitigation measures were implemented properly.

1-hr TSP Monitoring at AMS5	3, 7, 13, 19, 25 and 31 March 2025
1-hr TSP Monitoring at AMS6	3, 7, 13, 19, 25 and 31 March 2025
24-hr TSP Monitoring at AMS5	6, 12, 18, 24 and 28 March 2025
24-hr TSP Monitoring at AMS6	6, 12, 18, 24 and 28 March 2025
Noise Monitoring	3, 13, 19, 25 and 31 March 2025
Water Quality Monitoring	3, 5, 7, 10, 12, 14, 17, 19, 21, 24, 26, 28 and 31 March 2025
Chinese White Dolphin Monitoring	11, 12, 14 and 18 March 2025
Site Inspection	5, 12, 19 and 28 March 2025
Mudflat Monitoring (Ecology)	3 and 4 March 2025
Mudflat Monitoring (Sedimentation Rate)	28 March 2025
The existing air quality monitoring location AMS6 - Dragonair / CNAC (Group) Building (HKIA) was handed over to Airport Authority Hong Kong on 31 March 2021. 1-hr and 24-hr TSP monitoring at AMS6 was temporarily suspended starting from 1 April 2021 and resumed on 7 August 2024.

Ramboll Hong Kong Limited was employed by HyD as the Independent Environmental Checker (IEC) and Environmental Project Office (ENPO) for the Project.

1.1.4 The Contract includes the following key aspects:

1.1.6 BMT Hong Kong Limited was appointed by the Contractor to implement the EM&A programme for the Contract in accordance with the Updated EM&A Manual for HKLR (Version 1.0) and provided environmental team services to the Contract until 31 July 2020.

1.2.1 The project organization structure and lines of communication with respect to the on-site environmental management structure is shown in Appendix A. The key personnel contact names and numbers are summarized in Table 1.1.

1.3 Construction Programme

1.3.1 A copy of the Contractor’s construction programme is provided in Appendix B.

1.4 Construction Works Undertaken During the Reporting Month

1.4.1 A summary of the construction activities undertaken during this reporting month is shown in Table 1.2.

2 Air Quality Monitoring

2.1 Monitoring Requirements

2.3.1 Monitoring locations AMS5 and AMS6 were set up at the proposed locations in accordance with Contract Specific EM&A Manual.

2.4.1 Table 2.5 summarizes the monitoring parameters, frequency and duration of impact TSP monitoring.

2.5.1 24-hour TSP Monitoring

2.5.2 1-hour TSP Monitoring

2.6.1 The schedule for air quality monitoring in March 2025 is provided in Appendix D.

2.7 Monitoring Results

2.7.2 No Action and Limit Level exceedances of 1-hr TSP and 24-hr TSP were recorded at station AMS5 and AMS6 during the reporting month. The event action plan is annexed in Appendix F.

3.1.1 In accordance with the Contract Specific EM&A Manual, impact noise monitoring was conducted for at least once per week during the construction phase of the Project. The Action and Limit level of the noise monitoring is provided in Table 3.1.

3.3 Monitoring Locations

3.3.1 Monitoring location NMS5 was set up at the proposed locations in accordance with Contract Specific EM&A Manual.

3.3.2 Figure 2.1 shows the locations of monitoring stations. Table 3.3 describes the details of the monitoring stations.

3.4.1 Table 3.4 summarizes the monitoring parameters, frequency and duration of impact noise monitoring.

3.5.1 Monitoring Procedure

3.5.2 Maintenance and Calibration

3.6.1 The schedule for construction noise monitoring in March 2025 is provided in Appendix D.

3.7 Monitoring Results

3.7.1 The monitoring results for construction noise are summarized in Table 3.5 and the monitoring results and relevant graphical plots are provided in Appendix E.

*A correction factor of +3dB(A) from free field to facade measurement was included.

3.7.2 There were no Action and Limit Level exceedances for noise during daytime on normal weekdays of the reporting month

3.7.3 Other noise sources during the noise monitoring included aircraft noise and human activities nearby.

3.7.4 The event action plan is annexed in Appendix F.

4 Water Quality Monitoring

4.1.2 The original and revised Action Level and Limit Level for turbidity and suspended solid are shown in Table 4.1. The event action plan is annexed in Appendix F.

4.2.1 Table 4.2 summarizes the equipment used in the impact water quality monitoring programme.

4.3.1 Table 4.3 summarizes the monitoring parameters, frequency and monitoring depths of impact water quality monitoring as required in the Contract Specific EM&A Manual.

4.4.6 The locations of water quality monitoring stations are summarized in Table 4.4 and shown in Figure 2.1.

4.5 Monitoring Methodology

4.5.1 Instrumentation

4.5.2 Operating/Analytical Procedures

4.5.3 Maintenance and Calibrations

(a) All in situ monitoring instruments would be calibrated by ALS Technichem (HK) Pty Ltd. before use and at 3-monthly intervals throughout all stages of the water quality monitoring programme.

4.6.1 The schedule for impact water quality monitoring in March 2025 is provided in Appendix D.

4.7 Monitoring Results

4.7.1 Impact water quality monitoring was conducted at all designated monitoring stations in March 2025 during the reporting month. Impact water quality monitoring results and relevant graphical plots are provided in Appendix E.

4.7.2 Water quality impact sources during water quality monitoring were nearby construction activities by other parties and nearby operating vessels by other parties.

4.7.3 For marine water quality monitoring, no Action Level and Limit Level exceedances of dissolved oxygen level, turbidity level and suspended solid level were recorded during the reporting month.

4.7.4 The event action plan is annexed in Appendix F.

5 Dolphin Monitoring

5.1 Monitoring Requirements

5.1.1 Impact dolphin monitoring is required to be conducted by a qualified dolphin specialist team to evaluate whether there have been any effects on the dolphins.

5.1.2 The Action Level and Limit Level for dolphin monitoring are shown in Table 5.1.

5.1.3 The revised Event and Action Plan for dolphin Monitoring was approved by EPD in 6 May 2013. The revised Event and Action Plan is annexed in Appendix F.

Vessel-based Line-transect Survey

5.2.5 Data including time, position and vessel speed were also automatically and continuously logged by handheld GPS throughout the entire survey for subsequent review.

Photo-identification Work

5.2.12 Chinese White Dolphins can be identified by their natural markings, such as nicks, cuts, scars and deformities on their dorsal fin and body, and their unique spotting patterns were also used as secondary identifying features (Jefferson 2000).

5.2.13 All photographs of each individual were then compiled and arranged in chronological order, with data including the date and location first identified (initial sighting), re-sightings, associated dolphins, distinctive features, and age classes entered into a computer database.

Vessel-based Line-transect Survey

5.3.1 During the month of March 2025, two sets of systematic line-transect vessel surveys were conducted on the 11th, 12th, 14th and 18th to cover all transect lines in NWL and NEL survey areas twice. The survey routes of each survey day are presented in Figures 2-5 of Appendix H.

5.3.2 From these surveys, a total of 267.00 km of survey effort was collected, with 100% of the total survey effort being conducted under favourable weather conditions (i.e. Beaufort Sea State 3 or below with good visibility) (Annex I of Appendix H).

5.3.3 Among the two survey areas, 96.80 km and 170.20 km of survey effort were collected from NEL and NWL survey areas respectively. Moreover, the total survey effort conducted on primary lines was 193.88 km, while the effort on secondary lines was 73.12 km.

5.3.4 During the two sets of monitoring surveys in March 2025, no Chinese White Dolphin was sighted at all.

5.3.5 For the March’s surveys, encounter rates of Chinese White Dolphins deduced from the survey effort and on-effort sighting data made under favourable conditions (Beaufort 3 or below) are shown in Tables 5.3 and 5.4.

5.4.1 During this month of dolphin monitoring, no adverse impact from the activities of this construction project on Chinese White Dolphins was noticeable from general observations.

6.3.9 The taxonomic classification was conducted in accordance to the following references: Polychaetes: Fauchald (1977), Yang and Sun (1988); Arthropods: Dai and Yang (1991), Dong (1991); Mollusks: Chan and Caley (2003), Qi (2004), AFCD (2018).

Seasonal variation of horseshoe crab population

Impact of the HKLR project

Discussion

Third disappearance of seagrass bed

6.5.38 All seagrass beds were observed disappeared at the monitoring sites during the December monitoring event in 2024. There were two typhoon/cyclone events that occurred during November 2024 which was an unusual local weather condition, and it may cause the disappearance of the seagrasses.

6.5.41 There was neither consistent vertical nor horizontal zonation pattern of substratum type in all sampling zones. Such heterogeneous variation should be caused by different hydrology (e.g. wave in different direction and intensity) received by the four sampling zones.

5.3.1 During the month of March 2025, two sets of systematic line-transect vessel surveys were conducted on the 11^th, 12^th, 14^th and 18^th to cover all transect lines in NWL and NEL survey areas twice. The survey routes of each survey day are presented in Figures 2-5 of Appendix H.