6 MARINE ECOLOGY ASSESSMENT
6.1 INTRODUCTION
This marine ecological assessment of the gas pipelines has been based on the Consideration of Alternatives (Section 2) and on the Project Description (Section 3). This section of the report presents the findings of the marine ecological impact assessment. It summarises baseline information on the potentially affected marine ecological resources and also presents the findings of the various field surveys. Detailed information on the baseline conditions and results of the field surveys are presented in Annex C.
6.2 LEGISLATIVE REQUIREMENTS AND EVALUATION CRITERIA
The criteria for evaluating marine ecological impacts are laid out in the EIAO-TM. Annex 16 sets out the general approach and methodology for assessment of marine ecological impacts arising from a project or proposal. This assessment allows a complete and objective identification, prediction and evaluation of the potential marine ecological impacts. Annex 8 recommends the criteria that can be used for evaluating marine ecological impacts.
Other legislation which apply to marine species includes:
* The Wild Animals Protection Ordinance (Cap. 170) 1980, which protects all cetaceans and sea turtles.
6.3 EXISTING CONDITIONS
This section summarises the value of marine ecological resources along the pipelines alignment and identifies sensitive receivers. The Study Area has been defined in the EIA Study Brief as all sensitive receivers within the Tolo Harbour and Channel and Mirs Bay Water Control Zones (WCZs) (Figure 1.1a). Consequently, this assessment has focused on the marine ecological resources of this area.
The availability of literature on the ecology of the Study Area is variable. As with the majority of Hong Kong it appears that certain ecological components have been comprehensively studied whereas others have not. The list of relevant reports in the Study Brief has been reviewed along with relevant information pertaining to the ecological characteristics of the Tolo Channel and Mirs Bay areas. A detailed review of literature is presented in full in Section 2 of Annex C.
Due to the limited literature available for some components of the marine ecosystem, field surveys were considered necessary to fill the information gaps and to enable a complete and robust assessment of impacts to marine ecology to be performed. The findings of the field surveys are presented in Section 3 of Annex C. The locations of the sensitive receivers and the pipeline alignment (indicating the sections requiring jetting and dredging works) are shown in Figure 4.3a. The separation distance of individual sensitive receivers to the proposed alignment is provided in Section 4.
6.3.2 Summary of Baseline Conditions
The following presents a summary of the findings of the literature review and field surveys conducted for this EIA and detailed in full in Annex C.
Soft Substratum Habitats: Benthic studies have been undertaken at locations along the proposed alignment of the pipelines. Findings from the majority of these studies were that the benthos of the seabed in the vicinity of pipelines was dominated by polychaetes and characterised by low species diversity and low species biomass. Surveys conducted for this Study along the proposed alignment of the pipelines concluded that the assemblages were of a lower abundance than is observed in other areas in Hong Kong. The assemblages were dominated by polychaetes, all the species recorded occur frequently in Hong Kong and no rare species were observed.
Intertidal Habitats: The natural shorelines within the Study Area consist mainly of hard rocky or boulder shores, such as those along the northern and southern Tolo Channel coastlines. The only shores directly affected by the Project are the artificial seawalls at the Tai Po Landing Point. Few surveys have been conducted on the colonization of organisms on artificial seawalls in Hong Kong; however, fouling organisms have been anecdotally recorded as common on artificial seawalls, wharf files and other marine structures. Various species of algae, coelenterates, ascidians, bryozoans, sponges, crustaceans, molluscs and polychaetes are also commonly observed on these artificial structures. Surveys were conducted during the dry and wet season and animals recorded on the artificial seawall were mainly periwinkles, the predatory gastropod Thais clavigera and sessile filter-feeding organisms, such as the rock oyster and barnacles (Tetraclita squamosa). No rare or protected species were reported.
Hard Substratum Habitats: Literature reviews and dive surveys conducted along the alignment of the pipelines have revealed that the coastlines support assemblages that are composed of hard and soft coral species. The percentage of live coral cover increases with distance down the Tolo Channel. The intensive dive surveys conducted for this EIA within Inner Tolo Harbour, Tolo Channel, Mirs Bay and Tung Ping Chau revealed two main community types of high ecological value:
Hard Corals
* Shallow hard coral communities of high cover and species richness were recorded from South Wong Chuk Kok Tsui, Wong Chuk Kok Tsui, Chek Chau and Tung Ping Chau. A total of 53 scleractinian species comprising of 25 genera belonging to 11 families were recorded. Fifty-one species were hermatypic (reef-building species) and two ahermatypic species were recorded.
Soft and Black Corals
* A deeper coral community composing of dense stands of Antipathes sp. associated with sparse hard coral coverage of medium to high species richness was recorded from Wong Wan Tsui (Inner Tolo Channel) to Chek Chau and Wong Chuk Kok Tsui (Outer Tolo Channel).
Soft corals, antipatharians and gorgonians were of low coverage and abundance within the Tolo locations; however, high coverage of the zooxanthellate soft coral Sansibia sp. was recorded from the northwestern location of Tung Ping Chau. This location is the only documented Hong Kong site to contain this species (1)(2). Quantitative studies of the coral communities over a twenty-year period have shown a temporal decline in hard coral cover and species richness and a restricted distribution in the upper depth zone (3)(4). The results of the present study support these previous findings with hard coral generally restricted to a shallow depth zone (0 to - 5 m) and a progressive increase in species richness from Inner Tolo Harbour to the Tolo Channel.
The surveys, however, documented a narrow fringing hard coral community of high cover and species richness at South Wong Chuk Kok Tsui. The assemblage at this location had not been documented before and was in good condition given its proximity to Fung Wong Fat; a site with reduced coral coverage, high total and partial mortality (5). The moderate tidal flushing and current regime that occurs along the northern shores of Tolo Channel have allowed for the maintenance of hard corals to deeper depths and the establishment of extensive stands of Antipathes spp.
Numerous Plesiastrea versipora and Turbinaria peltata colonies of large size were recorded within Fung Wong Fat, South Wong Chuk Kok Tsui, Wong Chuk Kok Tsui and Chek Chau. P. versipora rarely reaches such a size, although it is noted to do so in higher latitudes (6). Therefore due to the size and longevity of these colonies they are considered as key sensitive receivers.
Marine Mammals: Literature reviews on marine mammals have shown that the Indo-Pacific Humpback Dolphin, Sousa chinensis, and the Finless Porpoise, Neophocaena phocaenoides, are the only species of marine mammal regularly sighted in Hong Kong waters (7) (8) . As sightings of Sousa chinensis have mainly been in western waters of Hong Kong (near North Lantau) and no records have been reported within or close to the Study Area, this species is not under threat from impacts due to the proposed Project.
The population of Neophocaena phocaenoides is reported to occur largely in southwestern waters of Hong Kong and areas around South Lantau, Lamma, and Po Toi are an important habitat for the species (9). The marine waters in Mirs Bay appeared to be used by the Finless Porpoises throughout the year but with a much lower sighting frequency than in southern waters. The area within Tolo Harbour and Tolo Channel did not appear to be used by the species. Although Finless Porpoises have been sighted in Mirs Bay near the proposed pipelines corridor, the marine waters in Mirs Bay are not thought to represent a critical habitat for this species due to the very low sighting frequency recorded in the area. Therefore, the ecological value of the marine mammal habitat in Mirs Bay is regarded as low.
The ecological characteristics of the different habitat types within the Study Area have been compared with habitats in other areas of Hong Kong in order to establish their ecological importance (Annex C).
6.3.3 Ecological Importance
According to the EIAO-TM Annex 8, the ecological value/importance of a habitat can be evaluated using the following criteria:
- Naturalness
- Ecological Linkage
- Size
- Potential value
- Diversity
- Nursery Ground
- Rarity
- Age
- Re-creatability
- Abundance
The criteria listed above have been applied to the information gathered and/or reviewed on the marine ecology of the habitats within the Study Area in order to determine the ecological value. The application of these criteria has led the habitats to be classified as presented in Table 6.1. Complete details of how each habitat was evaluated against the criteria presented above are presented in Section 4 of Annex C. Habitats where permanent or temporary impacts are expected to occur through either direct impact associated with habitat loss or indirect impacts through perturbations to water quality parameters have been evaluated. Information on the extent and severity of water quality impacts are presented in the water quality impact assessment (see Section 4).
Table 6.1 Summary of Ecological Value of Assemblages Present along the Pipelines Alignment
|
Assemblage Type |
Shortest Separation Distance to the Pipelines (m) |
Low |
Medium |
High |
|
Finless Porpoise Habitat (Mirs
Bay)a |
N/A
|
* |
|
|
|
Subtidal Soft Benthos |
N/A |
* |
|
|
|
Artificial Seawall – Intertidal |
N/A |
* |
|
|
|
Artificial Seawall – Subtidal |
N/A |
* |
|
|
|
Subtidal Hard Surface (Pak Sha
Tau) |
520 |
|
* |
|
|
Subtidal Hard Surface (Wong Wan
Tsui) |
380 |
|
|
* |
|
Subtidal Hard Surface (Fung Wong
Fat) |
430 |
|
|
* |
|
Subtidal Hard Surface (South Wong
Chuk Kok Tsui) |
680 |
|
|
* |
|
Subtidal Hard Surface (Wong Chuk
Kok Tsui) |
550 |
|
|
* |
|
Subtidal Hard Surface (Gruff
Head) |
600 |
|
|
* |
|
Subtidal Hard Surface (Chek Chau) |
1,350 |
|
|
* |
|
Subtidal Hard Surface (Tung Ping
Chau) |
1,230 |
|
|
* |
|
Ting Kok SSSI |
2,670 |
|
|
* |
|
Kei Ling Ha Mangal SSSI |
3,200 |
|
|
* |
|
Hoi Ha Wan Marine Park |
600 |
|
|
* |
|
Yan Chau Tong Marine Park |
4,240 |
|
|
* |
|
Tung Ping Chau Marine Park |
1,200 |
|
|
* |
|
a: Although Finless Porpoises have been sighted in Mirs Bay near the
proposed pipelines corridor, the marine waters in Mirs Bay are not thought to
represent a critical habitat for this species due to the very low sighting
frequency recorded in the area.
Therefore, the ecological value of the marine waters in Mirs Bay is
regarded as low. |
||||
6.4 ASSESSMENT METHODOLOGY
A desktop literature review and supporting field surveys (summarised in Section 6.3 and detailed in full in Annex C) were conducted in order to establish the ecological profile of the area within and surrounding the Study Area. The importance of potentially impacted ecological resources identified within the Study Area was assessed using the EIAO-TM. The potential impacts due to the construction and operation of the pipelines and associated developments were then assessed (following the EIAO-TM Annex 16 guidelines) and the impacts evaluated (based on the criteria in EIAO-TM Annex 8).
6.5 POTENTIAL SOURCES OF IMPACT
6.5.1 Construction Phase
Impacts to marine ecological resources arising from the construction works may be divided into those due to direct disturbances to that habitat and those due to perturbations to key water quality parameters.
Direct Impacts
No long term direct impacts are expected to occur though the installation of the gas pipelines. Short term impacts are predicted to occur as a result of the jetting and dredging operations associated with the deployment of the pipelines
Soft Substratum Habitats: Short term impacts are predicted to occur as a result of the jetting and dredging operations associated with the deployment of the pipelines, although once these operations have ceased marine ecological resources in the affected area are expected to return due to recolonisation of the seabed by benthic fauna. The width of the jetted area is approximately 2 to 5 m and the dredged trench is 35 m and the pipelines will be laid in soft seabed habitats that are regarded to be of low ecological value.
Intertidal Habitats: The construction of the landing point at Tai Po will result in the permanent loss of 5 m of intertidal hard surface habitats. The intertidal assemblages will be lost during the landing of the pipelines at the Tai Po seawall as the rubble mound will be removed and then replaced on top of the pipelines. It is anticipated that assemblages will settle on and recolonise the newly constructed seawalls, as environmental conditions of that area would be similar to existing conditions.
Subtidal Hard Surface Habitats: The construction of the landing point at Tai Po will result in the permanent loss of 5 m of subtidal hard surface habitats. The subtidal assemblages will be lost during the landing of the pipelines at the Tai Po seawall as the rubble mound will be removed and then replaced on top of the pipelines. It is expected that assemblages will settle on and recolonise the newly constructed seawalls, as environmental conditions of that area would be similar to existing conditions.
Hard Coral Habitats and, Soft and Black Coral Habitats: The results obtained from dive surveys, geophysical and geotechnical surveys showed that coral habitats (including hard, soft and black corals) of ecological importance were not identified within or in the immediate vicinity of the proposed pipelines corridor. Therefore, direct impacts to coral habitats as a result of the proposed construction works are not anticipated.
Marine Mammals: Direct impacts to the Finless Porpoise habitat in Mirs Bay are not expected as the pipelines construction works would not cause any direct loss of the marine water habitats in the area. In addition, the marine waters near the proposed pipelines alignment are not a critical habitat for the species.
Indirect Impacts
Indirect impacts to marine ecological resources during the construction phase include sediment release associated with the jetting and dredging works. Potential impacts to water quality from sediment release are listed below:
* increased concentrations of suspended solids (SS);
* a resulting decrease in DO concentrations; and,
* an increase in nutrient concentrations in the water column.
Sensitive receivers for the marine ecological impact assessment are identified to assess the potential impacts to resources along the pipelines alignment as a result of perturbations to water quality (Figure 4.3a). Information presented in the review has indicated that the Study Area contains the following marine ecology sensitive receivers:
* Subtidal Hard Surface (Wong Wan Tsui)
* Subtidal Hard Surface (Fung Wong Fat)
* Subtidal Hard Surface (South Wong Chuk Kok Tsui)
* Subtidal Hard Surface (Wong Chuk Kok Tsui)
* Subtidal Hard Surface (Gruff Head)
* Subtidal Hard Surface (Chek Chau)
* Subtidal Hard Surface (Tung Ping Chau)
* Ting Kok and Kei Ling Ha Mangal SSSIs
* Hoi Ha Wan, Yan Chau Tong and Tung Ping Chau Marine Parks
It is considered important to the environmental acceptability of the Project that construction activities do not unacceptably impact these sensitive receivers. The following sections discuss and evaluate the potential impacts to marine ecological habitats focusing mainly on those listed as being of high ecological value in Table 6.1.
Suspended Solids (SS)
Subtidal Hard Surface Habitats: Soft corals, gorgonians, black corals, hard corals and anemones may be injured by both high suspended sediment concentrations and high deposition rates. Damage (sublethal effects) or mortality (lethal effects) can result from a reduction in light penetration which kills the photosynthesising symbiotic algae associated with the hard corals, and also from the deposition of sediment onto the coral's surface which physically blocks the respiratory and feeding apparatus.
As discussed in Section 4, a tolerant criterion of 10 mg L-1 is adopted in this EIA for hard corals. Soft corals are often found in turbid, high-nitrate areas in canals, harbours, intertidal areas and reefs and thus appear to be fairly tolerant to waters of high turbidity and nutrients (10). Black corals are considered to be more tolerant to increased sedimentation than hard corals due to their perceived higher tolerance to turbidity and their optimal conditions for growth and survival include greatly reduced light levels (11). Soft and black corals are therefore expected to be comparatively less sensitive to and have a higher tolerant level to suspended solids and sediment deposition than hard corals. For this reason, the threshold values adopted for hard corals (ie depth averaged SS elevation of 10 mg L-1 and sediment deposition rate of 100 g m-2 day-1) are applicable to soft and black corals.
* Hard Corals
The modelling works indicate that the bed layer of the water column experiences higher elevations of suspended sediment than the middle and surface layers. Of the nine sensitive receivers identified above, only Fung Wong Fat and Wong Chuk Kok were predicted to show a maximum depth averaged SS elevation of up to 3 mg L-1 whereas the others were all below 1.2 mg L-1 (see Section 4 and Annex B).
* Fung Wong Fat: Fung Wong Fat is located at a distance of > 430 m from the pipelines alignment. The depth averaged SS elevations were recorded as 3 and 1 mg L-1 in the wet and dry seasons respectively. At the bed layer of the water column the SS elevations were reported as 8.7 mg L-1 in the wet season whereas in the dry season the elevations were below 2.7 mg L-1.
* Wong Chuk Kok: The shortest separation distance between Wong Chuk Kok and the pipelines route was found to be 550 m. The depth averaged SS elevations were recorded as 3 and 1 mg L-1 in the wet and dry seasons respectively. At the bed layer of the water column the SS elevations were reported as 5 mg L-1 in the wet season. In the dry season the SS elevations were reported as 6 mg L-1.
It is noted from the graphs of SS variation over time that the elevations occur over a very short period of less than a few hours at each location (Figure 2.1e-h Annex B). The temporal nature of the elevations is reflected by the depth averaged compliance with the criterion.
Elevations of SS in the water column at the sensitive receiver locations are very small and within the tolerance level of the hard corals. However, the water quality assessment predictions will be verified in the field during construction using the environmental monitoring and audit programme (EM&A). Should the EM&A show unacceptable impacts (with reference to exceedances of the WQO) to the hard corals, then mitigation measures such as a further reduction in jetting/dredging rates will be employed. Based on these conditions, adverse impacts to the hard corals are not predicted to occur.
* Soft and Black Corals
Negative impacts to soft and black corals may arise from increased levels of SS in the water column. The soft and black coral habitats were represented in the water quality modelling and the maximum depth averaged elevations of SS at these locations were predicted to be less than the 10 mg L-1 criterion discussed in Section 4 and compliant with the WQO allowable elevations of 1.2 mg L-1 in Mirs Bay. There is no WQO for SS in Tolo Harbour & Channel.
The level of SS elevations in the water column at the sensitive receiver locations are very small and within the tolerance level of the soft and black corals. However, the water quality assessment predictions will be verified in the field during construction using the EM&A programme. Should the EM&A show unacceptable impacts (with reference to exceedances of the WQO) to the soft and black corals, then mitigation measures such as a further reduction in jetting/dredging rates will be employed. Based on these conditions, unacceptable impacts to the soft and black corals are not anticipated.
Sediment Deposition
* Hard Corals
Impacts to the hard corals at all the high ecological value sensitive receiver locations are unlikely to occur as sediment deposition rates from the pipelines installation works are predicted to be less than 100 g m-2 day-1 (see water quality assessment in Section 4), which is below the threshold value for hard corals. Consequently, impacts are predicted to be within environmentally acceptable levels.
* Soft and Black Corals
The results of water quality modelling show that under the proposed jetting and dredging rates, the sediment deposition rate at all the coral sensitive receivers are well below the threshold tolerance level of 100 g m-2 day-1 (see water quality assessment in Section 4). The soft and black coral habitats found along the Tolo Channel are, therefore, not predicted to be affected by sedimentation, given the low sediment deposition predicted and that soft and black corals do not contain photosynthetic algae which depend on clear waters to allow penetration of sunlight. The closest coral sensitive receiver, Fung Wong Fat (430 m from the pipelines), that supports a large population of the black corals, Antipathes spp, is unlikely to be severely affected by SS deposition as a result of the jetting operations in the Tolo Channel.
Subtidal Soft Benthos: Sessile organisms within the benthos will be susceptible to the effects of increased sediment loads. Effects can be lethal or sub lethal (eg reduction in reproductive potential due to stress incurred by constantly having to flush out the depositing material). The effects of sedimentation on organisms will also depend on other factors, such as an organism's tolerance, growth orientation of sessile organisms and water movement. Infaunal benthic assemblages in Hong Kong are located in soft muds and sands which are frequently disturbed by storms, seabed currents and constant trawling activity which reworks the sediments creating high suspended sediments loads in the water column. Benthic invertebrates are, therefore, not likely to be adversely affected by the jetting and dredging operations with respect to sediment suspension and settlement but more so from any direct habitat loss within the pipelines alignment (see above for discussion).
Impacts to benthic assemblages immediately outside of the pipelines trenches are expected to occur temporarily as deposition rates are predicted to be < 200 g m-2. The area is expected to be small, as sediment will be deposited within a short distance of the jetting and dredging works (Figures 2.2a - 2.2f Annex B). The predicted deposition rates are not likely to impact the natural benthic assemblages as Tolo Harbour and Channel, and Mirs Bay are often disturbed by demersal trawling (and the latter by storms); the organisms present are thus considered to be adapted to seabed disturbances. As the affected areas will be recolonised by fauna typical of the area, the temporary loss of these low ecological value assemblages is deemed acceptable.
Intertidal Habitats: Intertidal habitats within the Study Area, which may be affected by the jetting and dredging works, include the rocky shores located along the coastlines of Tolo Channel. Scouring, due to very high SS levels (eg > 100 mg L-1) may inhibit the survival of algae, thereby reducing the food supply to the numerous rocky shore herbivores and causing intolerant or less competitive species to become locally extinct. Sediment dispersion results predict that SS concentrations will not exceed 10 mg L-1 at these shores. It is thus expected that unacceptable impacts to these intertidal assemblages arising from elevated SS levels will not occur.
Marine Mammals: Mobile animals such as marine mammals have the ability to avoid areas where SS levels have increased, thus avoiding any impacts. Impacts can occur to these mammals as an indirect result of increased SS levels. Elevation in SS may cause mobile fishes to move out of the area thus interfering with the normal feeding patterns of marine mammals.
The Finless Porpoise, Neophocaena phocaenoides, is thought to be an opportunistic feeder with known prey including crustaceans (shrimps and prawns), cephalopods (squid and octopus) and small pelagic fish of low commercial value (anchovies, croakers and sardines). They are thus likely to be affected by any significant changes in key water quality parameters (such as SS and DO) arising from the project works. A deterioration in water quality is likely to cause these mobile fish to move out of the area thus interfering with the porpoises normal feeding patterns. Information from the fisheries impact assessment (Section 7) indicates that indirect impacts due to the deployment of the pipelines are not predicted to impact fisheries in Mirs Bay due to the low levels of water quality perturbations as a result of the jetting and dredging operations. The consequences of this are that impacts to marine mammals through loss of food supply (fisheries resources) are not predicted to occur as impacts to fisheries resources are regarded as of low severity and acceptable.
As mentioned in Section 4 and above, the predicted elevations of SS in Mirs Bay where the Finless Porpoise has been recorded to occur are small and within environmentally acceptable levels (as defined by the WQO's). It is thus expected that unacceptable impacts to the species arising from elevated SS levels will not occur.
Dissolved Oxygen
The relationships between SS and DO are complex, with increased SS in the water column combining with a number of other factors to reduce DO concentrations in the water column. Elevated SS (and turbidity) reduces light penetration, lowers the rate of photosynthesis by phytoplankton (primary productivity) and thus lowers the rate of oxygen production in the water column. This has a particularly adverse effect on the eggs and larvae of fish, as at these stages of development, high levels of oxygen in the water are required for growth due to their high metabolic rate. DO depletions are most likely to affect sessile organisms as they cannot move away from areas where DO is low (unlike mobile species such as fish). Depletions of DO as a result of the jetting and dredging activities have been predicted to be undetectable and compliant with the relevant WQOs. It is thus expected that unacceptable impacts to the marine ecological habitats and populations present in the vicinity of the pipelines alignment, including habitats that support growth of corals (hard coral, soft and black corals), are not expected to occur.
Nutrients
High levels of nutrients (total inorganic nitrogen - TIN and ammonia) in seawater can cause rapid increases in phytoplankton often to the point where an algal bloom occurs. An intense bloom of algae can lead to sharp increases in DO levels in surface water. However, at night and when these algae die there is usually a sharp decrease in the levels of dissolved oxygen in the water, as dead algae fall through the water column and decompose on the bottom. Anoxic conditions may result if DO concentrations are already low or are not replenished. This may result in mortality to marine organisms due to oxygen deprivation. The modelling results have indicated that the levels of Chlorophyll a, TIN and ammonia do not change appreciably from background conditions during the Project works. It is thus expected that unacceptable impacts to the marine ecological habitats and populations present in the vicinity of the pipelines alignment, including habitats that support corals (hard coral, soft and black corals), will not occur.
Impacts to Marine Parks
The Study Area contains three Marine Parks, which are located at Hoi Ha Wan, Yan Chau Tong and Tung Ping Chau, with a respective minimum separation distance of 600 m, 4,240 m and 1,200 m to the pipelines alignment. The locations and sea boundaries of the Marine Parks are shown on Figure 4.3a (Section 4). As discussed in Section 4 the Marine Parks have been considered as sensitive receivers for this project due to their high ecological value and were explicitly included in the water quality modelling works.
The information from the modelling (presented in Section 4 Table 4.6) indicates that none of the WQOs are exceeded as a result of the jetting and dredging operations with very small temporary elevations of SS at 1.2 mg L-1 for Hoi Ha Wan and <0.1 mg L-1 for Yan Chau Tong and Tung Ping Chau. Depletions of DO and elevations of nutrients and Chlorophyll a levels as a result of the project were reported as undetectable and compliant with the relevant WQOs.
As the SS elevations at the Tung Ping Chau Marine Park due to the dredging and jetting operations were predicted to be temporary and small (<0.1 mg L-1), unacceptable SS impacts to the marine life within the marine park are not anticipated. The elevation in SS was predicted to be much lower than the 10 mg L-1 criterion for corals (including hard corals, soft and black corals) and the sediment deposition rates were found to be well below the tolerance level 100 g m-2 day-1, no adverse impacts to the coral habitats (including the extensive soft coral assemblages found in the northwest side of the marine park) are expected. In addition, the depletion in DO levels and the elevation of nutrients and Chlorophyll a levels as a result of the project were reported as undetectable and compliant with the relevant WQOs, the marine habitats of high ecological importance within the marine park are unlikely to be affected by the proposed construction works.
Impacts to the SSSIs
As discussed above, there are two SSSIs in the Study Area, namely Ting Kok and Kei Ling Ha, both of which are mangroves. Kei Ling Ha SSSI is located at approximately 3,200 m from the pipelines and Ting Kok SSSI is over 2.5 km from the route alignment. As these two SSSIs are of high ecological value they were represented as sensitive receivers in the water quality model. The information from the modelling (presented in Section 4 Table 4.7) indicates that depletions of DO and elevations of SS, nutrients and chlorophyll a levels as a result of the project were reported as undetectable and compliant with the relevant WQOs.
6.5.2 Operation Phase
As discussed in Section 3.2.2 and Section 4.6.3, the pipelines are designed to be maintenance free and should they require inspection this will be done using a remotely operated intelligent pipe inspection gauge (PIG). This type of maintenance will occur once every ten years and will be within the gas pipes. Consequently, there will be no need to disturb the seabed sediments during inspection and therefore water quality will not be affected.
The only operational impacts from the gas pipelines would be if repairs were required. The impacts from this would be of reduced severity that those during the construction phase as the work would take place in a specific and confined small area. Therefore, unacceptable impacts to marine ecological sensitive receivers, including habitats that support growth of corals (hard corals, soft and black corals), during the operational phase of the Project are not envisaged.
6.6 ASSESSMENT OF MARINE ECOLOGICAL IMPACTS
The following section discusses and evaluates the impacts to marine ecological habitats as a result of the installation of the pipelines. From the information presented above, the marine ecological impact associated with the Project has been evaluated in accordance with the EIAO-TM (Annex 8, Table 1) as follows.
* Habitat Quality: Impacts are predicted to occur only to the low ecological value benthic habitats identified during the field surveys along the pipelines route. The selection of the route for the pipelines has avoided as far as possible habitats of high ecological value.
* Species: Organisms of ecological interest recorded during the field surveys and reported from the literature were hard, soft and black corals along the coastlines of Tolo Channel and Mirs Bay. The corals will only be affected through minor perturbations to water quality that are within the coral tolerance criteria. The Finless Porpoise, Neophocaena phocaenoides was reported to occur in Mirs Bay but unacceptable impacts to the species are not anticipated as the marine waters in Mirs Bay are not a critical habitat for the species and the water quality perturbations are predicted to be compliant with the WQOs.
* Size: The total length of each gas pipeline is 28.5 km in Hong Kong waters, running across Mirs Bay, Tolo Channel and Tolo Harbour to Tai Po. The width of the jetted trench is approximately 2 to 5 m and that of the dredged trench approximately 35 m. The low ecological value benthic assemblages within the pipelines jetting/dredging areas will be directly lost as well as a small area of low ecological value habitat (artificial seawall) at the landing point.
* Duration: The works operations for the jetted areas of the pipelines alignment are predicted to last for 2 to 3 months, whereas the dredging works will take place approximately 20 days, including 11 days in Hong Kong water and 9 days for LNG terminal. The forward speed of the jetting machine will be limited to a maximum of 1.08 km day-1 (67.5 m hr-1 for 16 hours per day) in Tolo Harbour and Channel (as defined by the Tolo Harbour and Channel Water Control Zone) and 1.62 km day-1 in Mirs Bay (67.5 m hr-1 for 24 hours per day) (as defined by the Mirs Bay Water Control Zone). The dredging rate in Mirs Bay will be approximately 11,880 m3 hr-1. Increases in SS levels in the vicinity of sensitive receivers are expected to be low and temporary, and within environmentally acceptable limits (as defined by the WQOs and tolerance criteria).
* Reversibility: Impacts to the benthic assemblages inhabiting the soft bottom habitats along the pipelines alignment are expected to be relatively short term and recolonisation of the sediments is expected to occur. Similarly the low ecological value assemblages present on the artificial seawall can be expected to recolonise the seawall once reinstated.
* Magnitude: The impacts to the ecologically sensitive habitats defined in this assessment will be of low magnitude during the jetting and dredging operations associated with the laying of the gas pipelines.
6.7 SUMMARY OF MITIGATION MEASURES
In accordance with the guidelines in the EIAO-TM on marine ecology impact assessment, the general policy for mitigating impacts to marine ecological resources, in order of priority, are:
* Avoidance: Potential impacts should be avoided to the maximum extent practicable by adopting suitable alternatives;
* Minimisation: Unavoidable impacts should be minimised by taking appropriate and practicable measures such as constraints on the intensity of works operations (eg dredging rates) or timing of works operations; and
* Compensation: The loss of important species and habitats may be provided for elsewhere as compensation. Enhancement and other conservation measures should always be considered whenever possible.
Impacts to marine ecological resources have largely been avoided during the installation of the pipelines through the following measures:
* Pipelines Alignment: A number of alternative pipeline routes were studied and the preferred alignment avoids direct impacts to ecologically sensitive habitats and species.
* Bundle Configuration: As the pipelines will be bundled together and laid in the same trench the area of direct impact has been reduced and consequently the magnitude of potential impacts to ecological resources reduced.
* Reduction in Indirect Impacts: The alignment chosen for the two pipelines is located at a sufficient distance from ecological sensitive receivers so that the temporary dispersion of sediment from the installation works does not affect the receivers at levels of concern (as defined by the WQO and tolerance criteria). By laying the pipelines in the same trench, the horizontal spread of suspended sediment is restricted to a confined area in the centre of the Tolo Channel. Should the pipelines have been laid in separate trenches the horizontal spread of suspended sediment would have been much larger.
* Installation Equipment: The use of injection jetting along the majority of the route has minimised the severity of perturbations to water quality and hence allowed compliance with the WQOs at the sensitive receivers. This careful selection of installation equipment has helped avoid impacts to sensitive ecological receivers such as corals.
* Adoption of Acceptable Working Rates: The modelling work has demonstrated that the selected working rates for the dredging and jetting works will not cause unacceptable impacts to the receiving water quality. Consequently, unacceptable indirect impacts to marine ecological resources have been avoided.
6.8 RESIDUAL ENVIRONMENTAL IMPACTS
Taking into consideration the ecological value of the habitats discussed in the previous sections and the resultant mitigation requirements, the residual impacts can be determined. The residual impacts occurring as a result of the laying of the gas pipelines are the loss of the low ecological value subtidal assemblages present within the jetting/dredging areas and the loss of those on the artificial seawall at Tai Po. The residual impacts are considered to be acceptable as the habitats are of low ecological value and because infaunal organisms and epibenthic fauna are expected to recolonise the sediments after the pipelines have been laid. It has been demonstrated that marine organisms have recolonised seawalls after construction (12). It is anticipated that intertidal and subtidal assemblages similar to those recorded in the field surveys, will settle on and recolonise the newly constructed seawall at the landing point.
6.9 CUMULATIVE IMPACTS
At present there are no planned marine projects that could have cumulative impacts with the construction of the pipelines. The dredging works at the Cheng Tou Jiao LNG terminal and the installation of the Hongkong Electric pipeline are unlikely to be carried out concurrently with the construction works of the Towngas pipelines. ERM has, however, conducted an assessment of the water quality impacts of the two projects being constructed simultaneously. The findings indicated that no adverse impacts would be expected to water quality sensitive receivers including hard, soft and black corals (see Section 4.5.3 and Annex B for details).
The Civil Engineering Department is also planning minor reconstruction works for a public ferry on the island of Tung Ping Chau. However, this is not expected to cause a cumulative impact as the pier reconstruction works are minor in scale and are expected to cause minimal disturbance to water quality that will not extend far beyond the specific works area.
Therefore, unacceptable cumulative impacts as a result of concurrent project construction activities are unlikely to occur and hence cumulative impacts to marine ecology are not anticipated.
6.10 ENVIRONMENTAL MONITORING AND AUDIT
The jetting and dredging operations have been shown to proceed at rates that maintain environmental impacts to within acceptable levels. Actual impacts during the installation of the pipelines will be monitored by recording impacts to water quality. Monitoring and audit activities designed to detect and mitigate any unacceptable impacts to water quality will serve to protect against unacceptable impacts to marine ecological resources.
The water quality monitoring programme will provide management actions and supplemental mitigation measures to be employed should impacts arise, thereby ensuring the environmental acceptability of the project. Despite these measures a specific proactive marine ecology EM&A programme has been developed and is detailed in full in the EM&A Manual.
6.11 CONCLUSIONS
The alignment for the submarine pipelines was studied in detail through a route options assessment in order that a preferred alignment was selected that avoided direct impacts to habitats or species of high ecological value.
Literature reviews of existing information coupled with extensive field surveys of marine ecological resources have been undertaken for this impact assessment. The information gathered on baseline conditions has identified the following marine sensitive receivers of high ecological value:
* Subtidal Hard Surface (Wong Wan Tsui)
* Subtidal Hard Surface (Fung Wong Fat)
* Subtidal Hard Surface (South Wong Chuk Kok Tsui)
* Subtidal Hard Surface (Wong Chuk Kok Tsui)
* Subtidal Hard Surface (Gruff Head)
* Subtidal Hard Surface (Chek Chau)
* Subtidal Hard Surface (Tung Ping Chau)
* Ting Kok and Kei Ling Ha SSSIs
* Hoi Ha Wan, Yan Chau Tong and Tung Ping Chau Marine Parks
Potential impacts to marine ecological resources and the above sensitive receivers may arise from direct disturbances to habitats, or through changes to key water quality parameters. The loss of the low ecological value subtidal assemblages present within the jetting/dredging areas and the loss of those on the artificial seawall at Tai Po are considered to be acceptable as the habitats are of low ecological value. Infaunal organisms and epibenthic fauna are expected to recolonise the sediments after the pipelines have been laid.
Impacts arising from the proposed jetting and dredging works are predicted to be largely confined to the pipelines alignment, they are not expected to cause adverse impacts to marine sensitive receivers of high ecological value (habitats or species). Jetting and dredging working practices are predicted to ensure that water quality impacts are within acceptable levels (as defined by the WQOs and tolerance criteria) and also to mitigate impacts to marine ecological resources. The marine ecological sensitive receivers listed above are all located at sufficient distances (> 380 m) from the pipelines alignment so that impacts from the jetting/dredging operations are predicted to be of small magnitude, of very short duration and within the relevant standards and criteria. The criteria utilised in the assessments have been applied in previous EIAs in Hong Kong. EM&A results from projects that have adopted the criteria have indicated that no adverse impacts to corals have occurred.
Based on the ecological value of the habitats discussed in the previous sections and the resultant working practices, the residual impacts can be determined. The residual impacts occurring as a result of the laying of the gas pipelines are the loss of the low ecological value subtidal assemblages present within the jetting/dredging areas and the loss of those on the artificial seawall at Tai Po. The residual impacts are considered to be acceptable as the habitats are of low ecological value and because infaunal organisms and epibenthic fauna are expected to recolonise the sediments and seawall after the pipelines have been laid.
To protect against unacceptable impacts to marine ecological resources, an EM&A programme has been designed to specifically detect and mitigate any unacceptable impacts to marine ecology.
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(1) Fabricius KE (2001) Identification and documentation of octocorals from Hong Kong waters. Unpublished report for the Agriculture, Fisheries and Conservation Department.
(2) Fabricius KE and McCorry, D in prep. Octocoral coral communities of Hong Kong.
(3) Scott, P.J.B. and M. Cope. 1990. Tolo revisited: a resurvey of the corals in Tolo Harbour and Channel six years and half a million people later. In The Marine Flora and Fauna of Hong Kong and Southern China II (ed. B. Morton), 1203-20. Proceedings of the Second International Marine Biological Workshop: The Marine Flora and Fauna of Hong Kong and Southern China, Hong Kong 1986. Hong Kong: Hong Kong University Press.
(4) McCorry D. and Blackmore G. (2000). Tolo revisited: a resurvey of the corals and their metal burdens in Tolo Harbour and Channel twelve years and one million people later. In The Marine Flora and Fauna of Hong Kong and Southern China (ed. B. Morton), 453-82. Proceedings of the Fifth International Marine Biological Workshop: The Marine Flora and Fauna of Hong Kong and Southern China, Hong Kong 1998. Hong Kong: Hong Kong University Press.
(5) McCorry D and Blackmore G. (2000). Op cit..
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(7) Jefferson TA and Leatherwood S (1997) Distribution and abundance of Indo-Pacific hump-backed dolphins (Sousa chinensis Osbeck, 1765) in Hong Kong waters. Asian Marine Biology 14:93-110.
(8) Jefferson TA (2000) Conservation Biology of the Finless Porpoises (Neophocaena phocaenoides) in Hong Kong Waters. Final Report Submitted to the Agricultural, Fisheries and Conservation Department, December 2000.
(9) Jefferson TA, Hung SK, Law L, Torey M and Tregenza, N (2002) Distribution and abundance of Finless Porpoises in Hong Kong and adjacent waters of China. The Raffles Bulletin of Zoology Supplement No. 10: 43-55.
(10) http://www.animal-world.com.encyclo/reef/zoanthids/zoanthid.htm
(11) Asiatic Marine Limited (2002) Proposed Submarine Gas Pipelines from Cheng Tou Jiao LNG Receiving Terminal Shenzhen to Tai Po Gas Production Plant, Hong Kong Front End Engineering Design (FEED) and Environmental Impact Assessment (EIA) Study. Final Dive Survey Report, November 2002.
(12) Binnie Consultants Ltd (1997) Chek Lap Kok Qualitative Survey Final Report. For the Geotechnical Engineering Office, Civil Engineering Department, December 1997.