7 Marine Ecological Impact Assessment
7.2 Relevant Legislations, Standards & Guidelines
7.5 Evaluation of Past Information & Identification of
Data Gap
7.6 Methodology for Intertidal Survey
7.7 Methodology for Fish Survey
7.8 Methodology for Benthic Survey (REA)
7.9 Methodology for Benthic Survey (Grab Sampling)
7.10 Results of
Intertidal Survey
7.12 Results of
Benthic Survey (REA)
7.13 Results of
Benthic Survey (Grab Sampling)
7.15 Impact Identification and Assessment
7.16 Evaluation of Ecological Impacts
7.17 Recommendations & Mitigation Measures
7.18 Evaluation of Residual Impacts
7.19 Environmental Monitoring and Audit Programme
7
MARINE ECOLOGICAL IMPACT ASSESSMENT
7.1.1
This
Chapter
presents the marine ecological
baseline condition within and in the vicinity of Po Toi O through literature
review and surveys. Potential
construction and operational impacts on the marine ecology caused by this
Project have been identified and evaluated. Mitigation measures have been
proposed to minimize the potential impacts where necessary.
7.2
Relevant Legislations, Standards & Guidelines
7.2.1
Reference has been made to the Technical Memorandum on Environmental
Impact Assessment Process of the Environmental Impact Assessment Ordinance (Cap. 499) (EIAO TM) for the criteria for evaluating
ecological impacts, i.e.:
·
Annex
8 stipulates the criteria for evaluating ecological impacts
·
Annex
16 sets out the general approach and methodology for the assessment of
ecological impacts arising from a project or proposal. It also defines
Recognized Sites of Conservation Importance and Species of Conservation
Importance.
7.2.2
The following EIAO guidance notes detail the temporal
considerations in arranging surveys, survey methodology at different habitat
types, data collection and requirements of impact assessment:
·
GN
6/2010 “Some Observations on Ecological Assessment from the Environmental
Impact Assessment Ordinance Perspective”
·
GN
7/2010 “Ecological Baseline Survey for Ecological Assessment”
·
GN
11/2010 “Methodologies for Marine Ecological Baseline Surveys”
7.2.3
Other Hong Kong ordinances and guidelines relevant to
this study for reference include:
·
Wild
Animals Protection Ordinance (Cap. 170), which protects wild mammals, avifauna,
reptiles, amphibians and insects under column 2 from hunting, possession,
trading and disturbance;
·
Marine
Parks Ordinance (Cap.
476), which designates,
controls
and manages
marine parks and marine reserves;
·
Protection
of Endangered Species of Animals and Plants Ordinance (Cap. 586), which regulates trading and possession of
endangered species in response to Convention on the International Trade in
Endangered Species of Wild Fauna and Flora (CITES);
·
Town
Planning Ordinance (Cap.
131), which stipulates the planning use of an area. Land uses related to this
chapter are coastal protection areas, sites of special scientific interest and
other specified uses that promote conservation or protection of the
environment;
·
Hong
Kong Planning Standard and Guidelines (Chapter 10), which provides principles of conservation,
policies to identify and conserve natural landscape and habitats through
legislation and administrative controls and planning.
7.2.4
This assessment made also reference to the following
international conventions where appropriate:
·
Convention
on the International Trade in Endangered Species of Wild Fauna and Flora
(CITES);
·
IUCN
Red List;
·
United
Nations Conventions on Biological Diversity (1992).
7.3.1
The
Study Area for marine ecological impact assessment shares the same Study Area as the water quality impact assessment
(covering Po Toi O bay, Clearwater Bay and waters surrounding Steep Island), as shown in Figure
5-3.
7.3.2
No
site of conservation importance as defined in Annex 16 of the EIAO-TM was
identified.
7.4.1
Baseline ecological
information had
been obtained through collection
and review of past findings from relevant studies/surveys regarding the
ecological characters of the Study Area described in Section 7.3.1.
Examples of published reference and other environmental studies carried out in
vicinity of the Study Area include:
·
AFCD
Hong Kong Biodiversity Database
·
AFCD
Monitoring of Marine Mammals in Hong Kong Waters
·
AFCD
Newsletters
·
Approved
Clear Water Bay Peninsula South OZP S/SK-CWBS/2 from Town Planning Board
·
Past
EIA studies, e.g. Hong Kong Offshore Wind Farm in Southeastern Waters
·
Porcupine!
by the University of Hong Kong
·
Other related field books
7.4.2
Coral communities are more abundant in the eastern part of Hong Kong
for the calm and clear oceanic waters. According to the approved EIA Hong Kong
Offshore Wind Farm in Southeastern Waters (BMT 2009), coral communities were
recorded at Shek Mei Tau and Clear Water Bay near Po Toi O. The coastal region
of Po Toi O is lined with rocky shore, which is favorable for coral growth.
Marine
mammal
7.4.3
Finless Porpoise (Neophocaena phocaenoides) resides in southern and eastern waters of
Hong Kong. Although no Finless Porpoise was found near Po Toi O, historical
records show that the nearest record was made between Steep Island and Ninepin
Group, which is about 4 km away from Po Toi O (BMT 2009). The latest marine mammal
study (i.e. from April 2013 – March 2014) conducted by Hung (2014) also pointed
out that Finless Porpoise was found near Ninepin Group.
Amphioxus
7.4.4
Although no study has recorded amphioxus Branchiostoma belcheri (a species of
conservation importance) near Po Toi O, the nearest record was made around
Ninepin Group (BMT 2009).
7.5
Evaluation of Past Information &
Identification of Data Gap
7.5.1
Information collected from literature review was
evaluated to identify any data gap. Since the literature was only able to
provide limited baseline ecological information, detailed ecological surveys
were required to obtain a comprehensive and updated baseline ecological
condition of the Study Area described in Section
7.3.1.
7.6
Methodology for Intertidal Survey
7.6.1
Intertidal surveys were conducted in accordance with the
Environmental Impact Assessment Ordinance, Cap.499, GN 11/2010 Methodologies
for Marine Ecological Baseline Surveys.
7.6.2
Intertidal surveys had been carried out near shores and vertical seawall that are likely to be affected by this Project. A
walkthrough survey was
carried out along the shoreline to identify habitat types. Representative sites
of each habitat were
selected for
detailed study by carrying out transect surveys where possible. Observation was
conducted on vertical seawall as transect cannot be laid.
Transect
surveys on
rocky shore, sandy shore and mudflat had been carried out during low tide (maximum lowest tide at
0.7 m)
when the shore is more exposed. 2
transects on rocky shore (R1 & R2), 1 transect on sandy shore (S1) and 1
transect on mudflat (M1) were surveyed. Locations of transect surveyed are presented in Figure
7-1.
7.6.3
Transects were laid perpendicular to shore line,
starting from high water mark to low water mark. Along each transect, standard
ecological sampling quadrats (0.5 m x 0.5 m) were laid at regular intervals (1 m for rocky shore and sandy shore, 2 m for mudflat). Intertidal epifauna and flora
within each quadrat were identified. Mobile organisms including snails and limpets were counted in terms
of abundance, while sessile organisms including macroalgae and lichens were estimated in
terms of percentage coverage per quadrat.
7.6.4
Crevices were searched for hiding fauna on rocky
shore. On sandy shore and mudflat, the surface 5 cm sediment was sieved (1 mm mash size) to search for hiding fauna. A core
with 10 cm
diameter and 20 cm depth
was also collected in each quadrat, and was sieved (1 mm mash size) to search for benthos.
7.6.5
All intertidal organisms were identified to species
level as far as possible.
7.6.6
Opportunistic observations of any intertidal organisms outside systematic surveys were also recorded.
7.6.7
Exact dates and the weather
condition of each systematic
survey day are shown in Table 7-1.
Table 7-1: Weather Condition during Each Intertidal Survey
Survey |
Habitat |
Date |
Weather condition |
Line transect R1 |
Rocky Shore |
02/03/2014 |
Drizzle with wind Lowest tide: 0.7 m |
Line transect R2 |
Rocky Shore |
30/05/2014 |
Sunny Lowest tide: 0.4 m |
Line transect M1 |
Mudflat |
27/08/2014 |
Cloudy & Windy Lowest tide: 0.7 m |
Line transect S1 |
Sandy Shore |
08/09/2014 |
Partly cloudy Lowest tide: 0.6 m |
Observation |
Vertical Seawall |
08/09/2014 |
Partly cloudy Lowest tide: 0.6 m |
7.7
Methodology for Fish Survey
7.7.1
Fish
surveys were conducted from April to June 2014 and April 2015. Active swimming
fishes in marine water were counted by direct sighting (and by the aid with a
pair of 8x binoculars if necessary) along the shore of Po Toi O bay.
7.8
Methodology for Benthic Survey (REA)
7.8.1
The
benthic Rapid
Ecological Assessment (REA) survey
was conducted in accordance with the
Environmental Impact Assessment Ordinance, Cap.499, GN 11/2010 Methodologies
for Marine Ecological Baseline Surveys.
Field data collection
7.8.2
Assessment
of substrate and ecological attributes had been conducted using a
semi-quantitative REA method. All field data had been collected by
marine ecologists using SCUBA (self-contained underwater breathing apparatus)
dive. Surveys were conducted on 1st,
2nd, 8th & 9th March 2014.
7.8.3
In order to assess the
substrate type and the taxonomic
composition,
surveys had been conducted at eleven subtidal sites
(T1 to T11), which
were selected because they are either near the
proposed dredging site or
near the alignment of the submarine outfall (Figure 7-2).
7.8.4
At
each selected
subtidal site, REA survey had been performed
along a 50 m
transect laid according to the contour of seabed at each subtidal site.
Substrate type along the transect was recorded
at 1 m
intervals. The benthic cover, taxon abundance, and ecological attributes along
the transect were
recorded in a swathe of 2 m
wide, 1 m
either side of the transect.
7.8.5
Location, size and health status (including percentage cover
of bleaching, mortality and sedimentation) of any corals and associated
substrates found were
recorded. Feasibility
of translocation was also
assessed.
7.8.6
Locations of the REA transects had been recorded on
site by
an handheld GPS unit. Pictures of representative taxa along the transects were taken during surveys.
7.8.7
Assessment
tables following the TM-EIAO guidance had been completed in order to assess
ecological value for each subtidal site. Two types of information were
recorded:
(1) Cover of the major benthic
groups;
(2) Inventory of sessile benthic
taxa.
These had been performed according to Tier I
and Tier II levels of information.
7.8.8
Tier
I: Categorization of ecological (benthic cover) and environmental variables.
·
To describe the benthic cover, six substrates and
seven ecological attributes (Table
7-2a) were
assigned. Each attribute was
ranked from 0 to 6 (Table
7-2b) based on the overall cover along the survey area.
7.8.9
Tier
II: Taxonomic inventories to define types of benthic communities.
·
An inventory of benthic taxa was compiled during each swim. Taxa were identified either in situ or with the aid of photos
to confirm identification afterward.
·
Hard
corals
(Order Scleractinia) – to genus and species level where possible;
·
Soft
corals
(Subclass Octocorallia) – to genus level where possible;
·
Other
benthos
(such as sponges zoanthids, bryozoans, macroalgae etc) – to genus level where
possible or phylum with growth form;
·
Each taxon in the inventory was ranked (from 0 to 5) on the basis of its abundance in the community at the subtidal
site (Table 7-2c). These broad categories ranked the taxa in terms of the relative abundance of individuals, rather than
the contribution to benthic cover, at each subtidal
site.
Table 7-2: Categories of (a)
Benthic Attributes, (b) Ordinal Ranks of Percentage Cover, and (c) Ordinal Ranks
of Taxa Abundance of Substrate
a) Benthic attributes |
b) Percentage Cover |
c) Taxon abundance |
|||
Substrate |
Ecological |
Rank |
Percentage
Cover |
Rank |
Abundance |
Bedrock |
Hard Corals |
0 |
Not recorded |
0 |
Absent |
Boulders (diameter
>50cm) |
Dead Coral Skeleton |
1 |
1-5% |
1 |
Sparse |
Cobbles (diameter <
50cm) |
Soft Corals |
2 |
6-10% |
2 |
Uncommon |
Rubble (dead corals) |
Sea anemone beds |
3 |
11-30% |
3 |
Common |
Sand with gravel |
Encrusting Algae |
4 |
31-50% |
4 |
Abundant |
Mud & Silt |
Coralline Algae |
5 |
51-75% |
5 |
Dominant |
|
Erect Macroalgae |
6 |
76-100% |
|
|
7.9
Methodology for Benthic Survey (Grab Sampling)
7.9.1
The
benthic grab sampling
survey was conducted in accordance with the
Environmental Impact Assessment Ordinance, Cap. 499, GN 11/2010 Methodologies for
Marine Ecological Baseline Surveys.
Sampling
7.9.2
Benthic
surveys using grab sampling had been
carried out on 24th
July 2014 and on 6th October 2014 at
seven stations (three stations B1 – B3
on 24th July 2014, four stations A1 –
A4 on 6th
October 2014, see Figure 7-1).
Station B2 was the proposed
location of the diffuser in Option 2 (see Table
2-2 & Figure 2-2 in Chapter 2 – Project Descriptions), while stations B1 and B3 were 150 m south and 150 m north from station B2 respectively. Nevertheless,
since a species of conservation importance (Amphioxus Branchiostoma belcheri) was recorded in station B2, additional
stations (stations A1 – A4) were sampled for investigating an alternative
diffuser location (see Option 3 in Table 2-2 & Figure 2-2 in Chapter 2 – Project Descriptions) to mitigate impacts on B.
belcheri.
7.9.3
3 samples were collected at each station (i.e. three replicates for each station).
A hand held differential Global Positioning System (GPS) was used to ensure the correct sampling location.
7.9.4
For each sample,
about 0.1 m2 sediment was sampled by a modified
Van Veen grab sampler (dimensions 0.3 m x 0.32 m x 0.16 m).
7.9.5
The
sampler was
lowered slowly through the water column, preventing any disturbance to the seabed. After
sampled
from the seabed, the sampler
was
raised,
carefully retrieved and examined to determine acceptability of the sample. A sample was accepted only if it has minimal disturbance and
adequate penetration depth.
7.9.6
The
sample was then
transferred
into a large plastic bucket.
Subsequently, the sample was mixed
gently with seawater to suspend fine silt/clay and release benthic organisms. The
sample was then
washed through
a sieve table,
which comprised 1 mm and 500µm meshes. Sample was rinsed carefully with seawater to
remove as much mud as possible. Materials left on screens were washed into large, labelled
zip-lock bags. Excess seawater was drained
from the bag.
Then, 4% buffered formalin solution mixed with rose bengal stain was added to the sample. The formalin solution was used to fix and
preserve sample while the rose bengal stain was used to stain organic tissue which aids sample sorting in the laboratory.
The bag was
placed inside another labelled zip-lock bag, and placed upright into robust
plastic containers before
sending to the laboratory.
7.9.7
The
sampler and all other utensils were rinsed with seawater after each
sample had been collected to avoid cross
contamination between samples.
Sample Sorting
7.9.8
Benthic
samples were soaked in the fixing solution for a minimum
24 hours to ensure adequate fixation. Samples were
then washed
through a 500µm sieve with fresh water in order
to
remove the formalin. After re-sieving, benthic organisms, which were stained pink, were picked out and placed into a
labelled wide mouth plastic jar, which
contained
70% ethanol for preservation. Initial sorting of material was undertaken by eyes, while
assisted by hand
held lens and dissecting microscope.
7.9.9
After
rinsing with clean alcohol, small amount
of aliquots
of the sample was placed in glass dishes. All
organisms found, including anterior fragments of polychaetes, were removed from sample, and sorted to
major taxonomic categories such as polychaetes, arthropods, and mollusks by the
aid with a dissecting microscope.
7.9.10
Organisms
were then identified to the lowest
practicable level by the aid with dissecting microscope, published keys and reference
materials (e.g. Day (1967); Fauchald (1977);
Arnold and Birtles (1989), Lim (2000), Shin (1996), Chan
(2000), Ma (undated)). In case of many benthic organisms, particularly the
polychaetes, family level was
often
the lowest practicable level due to the sample condition. Where possible,
specimens were identified down to genus or
species level.
7.9.11
After
identification, abundance of each taxa was counted and recorded. For specimens
that had become fragmented, only the
anterior end of the organism was counted.
7.9.12
After
identification and counting, specimens were
transferred to vials and preserved with 70% ethanol. Station
number, replicate number and taxonomic category were labelled on each vial.
7.9.13
Collected
benthic sediment samples were analyzed for the following parameters for each of
the sampling location:
·
Faunal abundance; &
·
Species composition.
7.9.14
Raw
abundance data were calculated for each species. Abundance summaries of the
combined dataset are given for:
·
percent contribution of each taxonomy to the overall
dataset; and
·
percent contribution of each taxonomy to the station
dataset.
7.10
Results of Intertidal Survey
7.10.1
Four habitats – rocky shore,
mudflat, sandy shore, and vertical seawall – were identified in Po Toi O. Rocky
shore dominated headlands, mudflat distributed in the bay, sandy shore was
found between rocky shore and mudflat, and vertical seawalls were found on pier
and jetty besides human settlement. Representative photos of habitats are
presented in Appendix 7.1.
7.10.2
In general, taxa recorded
outside systematic
survey (e.g. birds Egretta spp.) have
a higher mobility than taxa recorded in systematic survey (e.g. snails Cerithidea spp.). A detail list with the taxa
recorded in these habitats is presented in
Appendix 7.2.
Vertical
Seawall
7.10.3
On vertical seawall, 13
taxa were recorded in total. In terms of the taxa composition, no distinct
pattern was found. Nevertheless, taxa found in the high tidal zone had a lower density and a smaller body size
(or coverage for algae) than those occupied the low tidal zone. Commonly found species included Acanthopleura japonica (Chiton) and Saccostrea cucullata (Rock Oyster).
7.10.4
No species of conservation importance was recorded on vertical seawall.
7.10.5
No breeding behaviour, egg, or immature individual was
recorded on vertical seawall.
Rocky Shore
7.10.6
On rocky shore, 37 taxa were recorded in total. 32 of them were recorded
during systematic
surveys (12 taxa in R1 and 26 taxa in R2), while 5 extra taxa were recorded in walk-through
survey. The most abundant taxon found in systematic surveys R1 and R2 were Cellana toreuma (Limpet) and Monodonta
labio (Toothed top shell) respectively.
7.10.7
Zonation can be found from
the high tidal zone to the low tidal zone. Some taxa (e.g. Echinolittorina spp.) were only recorded in high tidal zone, while
some taxa (e.g. Cellana spp., Clibanarius sp. & Petrolishthes japonicus) were only found
from mid to low tidal zones. Nevertheless, some taxa (e.g. Ligia exotica & Monodonta
labio) were recorded from high to low tidal zones.
7.10.8
4 species with conservation
statuses were recorded in rocky shore. All of them (Eastern Cattle
Egret Bubulcus coromandus, Little
Egret Egretta garzetta, Blue Rock-thrush Monticola solitarius & White Wagtail
Motacilla alba) were avifauna species and were recorded outside systematic surveys. Nevertheless, although all wild
birds in Hong Kong are protected under the Wild Animals Protection Ordinance
(Cap. 170) (AFCD 2014), only Eastern Cattle Egret and Little Egret
which have conservation status other than Cap. 170 are considered having
conservation importance. Their conservation statuses are presented in Table 7-3.
Table 7-3: Conservation
Statuses of Taxa with Conservation Importance Recorded on Rocky Shore (AFCD
2014)
Common Name |
Conservation Status |
Eastern Cattle Egret (Bubulcus coromandus) |
1.
Listed as “Local Concern” by Fellowes et al. (2002) |
Little Egret (Egretta garzetta) |
1.
Listed as “Regional Concern” by Fellowes et al. (2002) |
* All wild birds are protected under the Wild Animals
Protection Ordinance (Cap. 170) |
7.10.9
No breeding behaviour, egg, or immature individual was
recorded on rocky shore.
Sandy shore
7.10.10 On sandy shore, 4 taxa were recorded in total. All of them were recorded during systematic survey. The recorded taxa comprised 3 sessile taxa (Chlorophyta,
Cyanobacteria & Rhodophyta) and 1 mobile taxon (Ligia exotica). All sessile taxa were having a low coverage (from 2.5%
to 15% coverage), as they were only found on rocks scattered on the shore. Only
1 mobile taxon (Ligia
exotica) with low abundance was recorded.
7.10.11 No
species of conservation importance was recorded on sandy shore.
7.10.12 No
breeding behaviour, egg, or immature individual was recorded on sandy shore.
Mudflat
7.10.13 On
mudflat, 25 taxa were recorded in total. 17 of them were recorded
during systematic
survey, while 8 extra taxa were recorded in walk-through survey. No flora taxon (e.g. algae)
was recorded in both systematic and walk-through surveys. The most abundant taxon
found in systematic
survey was Saccostrea
cucullata, which attached on scattered rocks throughout the intertidal zone.
7.10.14 Similar to rocky shore, a different taxa
composition can be found from the high tidal zone to the low tidal zone. Some
taxa (e.g. Grafrarium sp. & Batillaria spp.) were recorded from high
to low tidal zones, while some taxa (e.g. Anomalocardia
flexuosa & Cerithidea spp.)
were only found in low tidal zone.
7.10.15 3 species of conservation importance were recorded
on mudflat. All 3 species (Little Egret Egretta
garzetta,
Intermediate Egret E. intermedia & Black-crowned Night Heron Nycticorax nycticorax) were avifauna species and were recorded outside systematic survey. Their conservation
statuses are presented in Table 7-4.
Table 7-4: Conservation
Statuses of Taxa with Conservation Importance Recorded on Mudflat (AFCD 2014)
Common Name |
Conservation Status |
Little Egret (Egretta garzetta) |
1. Listed as “Regional Concern” by Fellowes et al. (2002) |
Intermediate Egret (E. intermedia) |
1. Listed as “Regional Concern” by Fellowes et al. (2002) |
Black-crowned Night Heron (Nycticorax nycticorax) |
1. Listed as “Local Concern” by Fellowes et al. (2002) |
* All wild birds are protected under the Wild Animals Protection Ordinance
(Cap. 170) |
7.10.16 Patches
of eggs were found in high and mid tidal zones during systematic survey. Immature
individuals of Black-crowned Night Heron Nycticorax nycticorax were also recorded in walk-through survey.
These suggested that mudflat is a spawning and a nursery ground.
7.11.1
11 fish species were
recorded in the Study Area described in Section
7.3.1. Except 3 species – Stripey (Microcanthus strigatus), Chinese demoiselle (Neopomacentrus bankieri) & Toothed blenny (Petroscirtes breviceps) – have no rarity information in Hong Kong,
all of the species recorded are common in Hong Kong (AFCD 2014). Except the
Grass puffer (Takifugu niphobles) is
listed as “Data Deficient” by the IUCN Red List, no fish species recorded has
conservation status. However, the Grass puffer is one of the commonest puffer
fish in Hong Kong (Shao et. al. 2014).
7.11.2
Most fishes recorded, including Yellowfin seabream (Acanthopagrus latus), Mangrove snapper (Lutjanus argentimaculatus) & Grey
mullet (Mugil cephalus), were immature
individuals. This suggested that Po Toi O Bay is a nursery ground of fish.
7.11.3
A detailed list of the
species recorded in fish survey is presented in Appendix 7.3.
7.12
Results of Benthic Survey (REA)
7.12.1
Two substrate types – hard
substrate and soft substrate – were identified. Hard substrate including
bedrock, boulders and rubbles were found in shallow water (i.e. about 2.5 m
below Chart Datum), while soft substrate such as coarse sand and fine sand
dominated deeper water (i.e. deeper than 3.0 m below Chart Datum).
7.12.2
Hard substrates were
dominated by sessile plants (e.g. erect macroalgae, encrusting algae and
coralline algae) and suspension feeding sessile animals (e.g. barnacles and
tube worms). Corals communities were also found on hard substrates but only
with a low percentage cover.
7.12.3
A total of 69 hard coral
colonies were found along all 7 transects (T1-T7) on hard (i.e. rocky)
substrates (see Figure 7-2). Although coral colonies
were small to medium in size (i.e. ranged from 100 to 4800 cm2),
colonies were generally in good and healthy condition with low levels of
sedimentation, bleaching and partial mortality. Most of them were associated
with rubbles and boulders.
7.12.4
No coral was found on soft
substrates (transects T8-T11).
7.12.5
The species diversity of
coral recorded was considered as low to moderate. In total, 19 hard coral
species of 6 families including Favites
pentagona (Family: Faviidae) and Goniopora
columna (Poritidae) were recorded. All species have been recorded in Hong
Kong waters.
7.12.6
No soft coral and no other
sessile taxon of conservation importance was recorded.
7.12.7
Detail results are
presented in a detailed coral survey report, which is attached in Appendix 7.4.
7.13
Results of Benthic Survey (Grab Sampling)
7.13.1
Samples in all 7 stations
showed different substrate types: rocks with sand in A1, coarse sand in B1,
fine sand in B2 & A3, and mud in B3, A2 & A4.
7.13.2
In total, 535 individuals which comprised of 35 taxa
were recorded in the benthic survey by grab sampling. Station B1 had the
highest population (274 individuals, consisted of 12 taxa), while station B3
had the highest diversity (18 taxa, 48 individuals in total). Nevertheless, due
to the specimens’ conditions, some specimens were not able to be identified to
species level. Specimens were identified down to the lowest level (e.g. family
level) as possible. A detailed list with the taxa recorded in each
station is presented in Appendix 7.5.
7.13.3
The species (taxa) composition varied from habitat to
habitat. In terms of population, Syllidae and Branchiostoma belcheri dominated the seabed with coarse sand (i.e.
station B1) and fine sand (i.e. stations B2 & A3) respectively, while the muddy seabed (i.e. stations B3, A2 & A4) and seabed with rocks and sand (i.e. station A1) were not
dominated by any single taxon.
7.13.4
Amphioxus Branchiostoma
belcheri, a taxon of conservation importance, was found in stations B1,
B2 and A3 which had either coarse or fine sand seabed. No B.
belcheri was
recorded in stations with rocky and muddy seabeds (i.e. station A1 and stations
B3, A2 & A4 respectively). All recorded B.
belcheri were
about 25 – 35 mm in length, which suggested that all individuals were in one to
two years old (Chen 2007). In addition, since gonads (i.e. reproductive organ) were found in some
B. belcheri, recorded individuals were in reproductive stage.
7.13.5
The density of B.
belcheri individuals varied from stations to stations.
Station B2 (average 236.7 ind/m2) had the highest density, following
by A3 (average 33.3 ind/m2), and B1 (average 13.3 ind/m2)
had the lowest. As a significant amphioxus population has a density higher than
100 ind/m2 (Chen 2007), station B2 (i.e. fine sand seabed) is considered
as a major amphioxus habitat.
7.13.6
Berried females of Typhlocarcinops
denticarpes were recorded in station A4 (i.e. muddy seabed), which
suggested that the muddy seabed is a breeding ground of T. denticarpes.
7.14
Evaluation of Habitat
7.14.1
The
ecological value of the habitats have been
evaluated in accordance with EIAO-TM Annex 8 Table 2.
Table 7-5: Ecological Value of
Intertidal Zones within 500 m from the Project
Criteria |
Rocky Shore |
Sandy Shore |
Mudflat |
Vertical Seawall |
Naturalness |
Natural |
Natural |
Natural |
Artificial |
Size |
≈ 2.3 km |
≈ 0.02 km |
≈ 0.7 km |
≈ 0.5 km |
Diversity |
Low |
Low |
Low |
Low |
Rarity |
Common habitat in
Hong Kong, Although no marine
species of conservation importance recorded, 2 and 3 avifauna species of
conservation importance were recorded in Rocky Shore and Mudflat respectively |
|||
Recreatability |
Not recreatable |
Not recreatable |
Not recreatable |
Recreatable |
Fragmentation |
Low |
Un-fragmented |
Low |
|
Ecological linkage |
Linked with marine
water with different coastal habitats |
|||
Potential value |
Low |
|||
Breeding / Nursery
ground |
No breeding or nursery ground identified |
Spawning and nursery ground identified |
No breading or nursery ground identified |
|
Age |
N.A. |
N.A. |
N.A. |
15-52 years |
Abundance/ Richness of Wildlife |
Low |
Low |
Low |
Low |
Ecological value |
Low |
Low |
Low |
Low |
Table 7-6: Ecological Value of
Subtidal Habitats
Criteria |
Rocky Seabed |
Sandy Seabed
(Coarse sand) |
Sandy Seabed (Fine sand) |
Muddy Seabed |
Naturalness |
Natural |
Natural |
Natural |
Natural |
Size |
N.A. |
|||
Diversity |
Low |
Low |
Low |
Low |
Rarity |
Low - moderate
diversity (19 species) of healthy hard coral colonies recorded |
Amphioxus B. belcheri recorded |
Significant population of amphioxus B. belcheri recorded |
N.A. |
Recreatability |
Difficult to recreate |
Recreatable |
Recreatable |
Recreatable |
Fragmentation |
N.A. |
|||
Ecological linkage |
Linked with
adjacent seabed habitats |
|||
Potential value |
Low |
|||
Breeding / Nursery
ground |
No breeding or nursery ground identified |
Breeding ground of
1 crustacean species |
||
Age |
N.A. |
|||
Abundance/ Richness of Wildlife |
Low |
Low – Moderate |
Low |
Low |
Ecological value |
Moderate |
Moderate |
Moderate – High |
Low |
7.15
Impact Identification and Assessment
7.15.1
The
pipeline of the submarine outfall will be drilled underground by horizontal
directional drilling without damaging the intertidal area. At the end of the
385 m
pipeline, the diffuser will emerge from the seabed and the area will be
dredged.
Direct Impact – Habitat loss
7.15.2
Although
about 750 m2
of rocky shore above high water mark will be temporarily occupied for the
installation of submarine outfall by horizontal
directional drilling (HDD), it will not encroach any
intertidal zone. Therefore, no intertidal habitat will be lost. After
completion of the
submarine outfall, the rocky shore will be reinstated.
7.15.3
A
fully-enclosed sheet pile cofferdam with an area of 10 m x 50 m (i.e. 500 m2) will be
installed on muddy seabed for the diffuser installation. Seabed within the
cofferdam will be dredged to ensure the seabed stability for installing a
diffuser with 5 m2 in size. Therefore, about 500 m2 of muddy seabed will
be lost during construction phase.
7.15.4
However,
except the area occupied by the diffuser, all dredged seabed will be backfilled
to the original
seabed level with rockfill. The cofferdam will also be removed after the
completion of backfilling. Therefore, the installation of diffuser will lose 5
m2 seabed permanently, and 495 m2 seabed temporarily.
7.15.5
As
the direct impacts identified are expected to be localized, largely temporary
and reversible, and not directly affecting any species of conservation
importance, the overall direct impact on marine ecology will be insignificant.
Indirect Impact – Water Quality Deterioration
Construction
phase
7.15.6
Both
land based and marine based construction activities are expected to deteriorate the water
quality via surface runoff, waste water generated, accidental leakage of
chemicals, and release of suspended solids (SS) during installing and
extracting the sheet pile cofferdam.
7.15.7
Increased
in SS, hence sedimentation rate, could bring negative impact on marine ecology.
Past studies verified that certain levels of SS and sedimentation rates would
depress both health and survival rate of fish (Binnie 1994), coral communities
(Pastorok & Bilyard 1985; Hawker & Connell 1992; Erftemeijer et al.
2012) and amphioxus (Chen 2007).
7.15.8
Nevertheless,
according to the assessment in Chapter 5
– Water Quality Impact Assessment, the water quality impact due to
land-based construction works would be minimized to acceptable level if
mitigation measures were implemented properly (e.g. placement of sandbag along
watercourse near Fairway Vista and rocky shore where excavation will be carried
out).
7.15.9
Chapter 5 – Water Quality Impact
Assessment also pointed out that the
marine-based construction works (i.e. installation & extraction of sheeting
pile cofferdam by vibratory action) would only cause minor displacement of
marine sediment. With erection and maintenance of silt curtain, the displaced
sediment will settle quickly and will not significantly increase the SS level in water column. In addition,
dredging and backfilling works will be confined within fully enclosed cofferdam
(see Section 7.15.3). The dredger barge will be
anchored outside the cofferdam for dredging and backfilling operation as well
as storage of marine sediment in sealed compartment. No opening of cofferdam will be required and thus
there will be no release of sediment into water bodies.
Therefore, these works are not expected to impact on the water quality.
7.15.10
The
overall indirect impact on marine ecology is expected to be insignificant.
Operational Phase – Normal operation
7.15.11
In
addition to SS and sedimentation rate, change in concentrations of total
inorganic nitrogen (TIN), unionized ammonia (UIA) and dissolved oxygen (DO) can
affect health and survival of marine wildlife. TIN is a plant nutrient that
encourages algal growth. High UIA concentration is toxic to fish. DO is
essential for survival of marine organisms. During normal operation, the sewage
collected will be treated before being discharged at the diffuser. Referring to
Chapter 5 – Water Quality Impact
Assessment, the water quality model predicted no substantial change in
concentrations of water quality parameters listed above in the Study Area described in Section
7.3.1.
7.15.12
Both coral and amphioxus
are sensitive to salinity. The diffuser will be installed at a location with
more than 10 m water depth and is far from the major Amphioxus habitat and the
rocky shore where coral grows (>100 m). The peak flow rate of the effluent
discharge during normal operation is only at about 7 L/s. The change in
salinity at these habitats arising from discharge of low salinity effluent is
expected to be negligible.
7.15.13
Therefore,
no adverse indirect impact on marine ecology is expected during normal
operation.
Operational Phase – Emergency Plant Breakdown
7.15.14
The Po Toi O Sewage Treatment
Plant (PTO STP) cannot operate in case of power or equipment failure. The Supervisory
Control and Data Acquisition (SCADA) system in the PTO STP will signal to the operation
and maintenance personnel for emergency attendance. Standby pump and screen
will be provided at the PTO STP. According to the performance pledge of CLP,
electricity provision will be restored within 2 hours after fault outage. Also,
emergency generator will be delivered to PTO STP within 4 hours by future term
contractor in case of plant failure where necessary.
7.15.15
As the average dry weather flow (ADWF) of PTO STP would be small (about 139 m3/day), it would be
possible to deploy tankers to transport away the sewage to Tseung Kwan O
Preliminary Treatment Works (TKO PTW) (or other nearby sewage
treatment works (STW)) for treatment in case the PTO STP cannot be recovered in
a short period of time.
7.15.16
Emergency storage of 4-hour ADWF (23.19 m3)
will be provided in the PTO STP. In case of plant failure, three 12 m3
sewage tankers will be called in to transport the sewage from PTO STP to TKO
PTW. Tankers will take different travel routes to reduce the risk of delay due
to traffic jam. The tanker arrangement is as follows:
Table
7-7: Tanker Away Arrangement
Tanker |
Source |
Potential Route |
Arrival Time |
Duty |
A |
DSD’s tanker which stationed at Sai Kung Sewage Treatment Works |
Sai Kung STW |
1.5 hours from plant
failure |
Transport sewage from PTO STP to TKO PTW |
B |
DSD Sewage Treatment Division Term Contractor, required to arrive in 2
hours in contract |
Shatin STW* |
2.5 hours from plant
failure |
Transport sewage from PTO STP to TKO PTW |
C |
DSD District Term Contractors (any 1 of the 3 districts), required to arrive in 1.5 hours in contract |
Kwun Tong Preliminary
Treatment Works* |
2.5 hours from plant
failure |
Standby at PTO STP, to be on duty if Tanker A/B breaks down or encounters
traffic delay |
*
Typical location where term contractor’s tankers are stationed
7.15.17
The distance between PTO STP and TKO PTW is about 12.1 km
or 18-minute travel distance. Including sewage loading and unloading time, each
tanker is assumed to take 2 hours round trip. Tankers A and B will work in
shift to continuously remove sewage from PTO STP. If one of the tankers fails
to arrive at PTO STP on time, Tanker C will come in to ensure that at least two
tankers will be operating.
An operation drill prior to
future operation will be conducted to confirm the time estimates achievable at
peak hours.
7.15.18
Appendix 5.5 shows the fluctuation of sewage volume in PTO STP in
case plant failure occurs during peak sewage flow (6pm). With continuous
removal of sewage by tankers in rotation, the highest quantity stored in the
plant will be 17.24 m3, which is well below the emergency storage
capacity (23.19 m3). With about additional 6 m3 storage
buffer, the chance of having sewage
volume exceeding the storage capacity is very low. No overflow of sewage from the PTO STP is anticipated.
7.15.19
Each tanker will deliver 12 m3 sewage from PTO
STP to TKO PTW. Based on DSD’s past experience, it takes 15 minutes to unload
all sewage. The average flow rate will be 12 m3/15 minutes/60
seconds = 0.013 m3/s, which is far below the design capacity of TKO
PTW (5.55 m3/s [1]). No overloading of TKO PTW is anticipated.
·
Delivery of an emergency generator to the PTO STP
within 4 hours from plant failure;
·
Provision of dual power by CLP;
·
Provision of a supervisory control and data
acquisition system (SCADA), which signals to the operation and maintenance
personnel for emergency attendance in case of plant failure;
·
Provision of a standby pump and screen at the PTO STP;
·
Provision of emergency storage of 4-hr ADWF sewage
retention time;
·
Arrangement of tankers for continuous removal of
incoming sewage to other sewage treatment plants for treatment to ensure a
sufficient buffer for emergency storage.
Cumulative Impact
7.15.21
Currently,
there is one planned project, maintenance dredging of Po Toi O Fish Culture
Zone, located within the Study Area. However, there is no solid plan on when
the works will be carried out. Therefore, it is assumed that it will not be
carried out concurrently with the construction work of the Project, and hence,
no cumulative impact is expected.
7.16
Evaluation of Ecological Impacts
7.16.1
The significance of ecological impacts have been
evaluated in accordance with EIAO-TM Annex 8 Table 1.
Table 7-8: Evaluation
of the Significance of Ecological Impact on Intertidal Zones within 500 m from the Project
Criteria |
Rocky Shore |
Sandy Shore |
Mudflat |
Vertical Seawall |
Habitat quality |
Low |
Low |
Low |
Low |
Species |
2 avifauna species of conservation importance |
No species of conservation
importance |
3 avifauna species of conservation importance |
No species of conservation
importance |
Impact Size /Abundance |
Impacted indirectly (water quality deterioration) Low number of fauna |
|||
Impact Duration |
- Short term
construction impact - Long term
operational impact during normal operation |
|||
Impact
Reversibility |
Reversible |
|||
Impact Magnitude |
Minor |
Insignificant |
||
Overall Impact |
Minor |
Insignificant |
Table 7-9: Evaluation
of the Significance of Ecological Impact on Subtidal Habitats
Criteria |
Rocky Seabed |
Sandy Seabed (Coarse sand) |
Sandy Seabed (Fine
sand) |
Muddy Seabed |
Habitat quality |
Moderate |
Moderate |
Moderate – High |
Low |
Species |
Coral communities (19 hard coral species) |
Amphioxus B. belcheri |
Significant
population of amphioxus B. belcheri |
No species of conservation
importance |
Impact Size /Abundance |
Impacted indirectly (water quality deterioration) Moderate number of fauna. |
5 m2
lost permanently, 495 m2
will be backfilled. Low number of fauna. |
||
Impact Duration |
- Short term
construction impact - Long term
operational impact during normal operation |
|||
Impact
Reversibility |
Reversible |
Irreversible
for the diffuser footprint, reversible for
remaining area |
||
Impact Magnitude |
Insignificant |
Small |
||
Overall Impact |
Insignificant |
Minor |
7.17
Recommendations & Mitigation Measures
7.17.1
The location of the diffuser has undergone several rounds of site selection (as detailed in Chapter 2) to minimize the ecological
impacts. Recommendations
and mitigation measures have been proposed to minimize the ecological impacts to acceptable levels based on the
following hierarchy: avoidance, minimization and compensation.
7.17.2
Avoidance
·
To avoid impact on habitat with high
ecological value and/or where species of conservation importance inhabits, the
location of diffuser has been moved to muddy
seabed (A4) to avoid disturbance on subtidal rocky shore and sandy seabed (B2),
where coral and
amphioxus inhabits
respectively.
·
Avoiding impact on intertidal habitats,
Horizontal Directional Drilling (HDD) will be adopted above high water mark to
install the submarine outfall underground.
·
Avoid discharging any raw or partly
treated sewage into waterbodies when the STP cannot operate normally due to
power or equipment failure.
7.17.3
Minimization
·
To minimize the disturbance on benthic
habitats by dredging, HDD will be adopted for the installation of submarine outfall.
·
Backfill
the dredged seabed, except where the diffuser is located, to original seabed
level
·
Minimizing
the water quality impact by implementing mitigation measures such as dredging
within sheet pile cofferdam. Details of mitigation measures for water quality
impact were presented in Chapter 5 –
Water Quality Impact Assessment.
7.18
Evaluation of Residual Impacts
7.18.1
With proper
implementation of mitigation measures on water quality, the impact on marine
ecology is anticipated to be acceptable during construction and operational
phases.
7.19
Environmental Monitoring and Audit Programme
7.19.1
Since
the impact on marine ecology will be depended on water quality, regular water quality monitoring and audit
programme proposed in
the EM&A Manual
will be sufficient. No specific monitoring and audit programme on marine
ecology is required.
7.20.1. Coral communities were recorded in past study, while 4
avifauna, 1 amphioxus and 19 hard coral species of conservation importance were found in recent surveys. Besides, a major amphioxus habitat was recorded in recent surveys.
7.20.2.
Although the muddy seabed where the
diffuser will be located on will be lost during construction phase, no species of conservation importance will be directly affected. There
will be a permanent loss of 5 m2 in area at the diffuser location. However, impact
on the remaining works area (495 m2) would be reversible. Indirect
impact due to water deterioration will be minimal as dredging works will be
confined within fully enclosed cofferdam. No sediment release into water bodies
is anticipated. No cumulative impact is expected as no project is known to be
carried out concurrently with this Project. The overall construction phase
impact is considered as low and
acceptable.
7.20.3. As sewage
will be collected and treated before discharge, modelling results predicted
that no significant change in water quality is expected for normal operation of
the Project.
7.20.4. Considering
the project scale, risk of emergency condition, construction difficulties and
cost, the following provisions are the most appropriate and practical
mitigation measures in case of emergency
plant breakdown:
·
Delivery of an emergency generator to the PTO STP
within 4 hours from plant failure;
·
Provision of dual power by CLP;
·
Provision of a supervisory control and data
acquisition system (SCADA), which signals to the operation and maintenance
personnel for emergency attendance in case of plant failure;
·
Provision of a standby pump and screen at the PTO STP;
·
Provision of emergency storage of 4-hr ADWF sewage
retention time;
·
Arrangement of tankers for continuous removal of
incoming sewage to other sewage treatment plants for treatment to ensure a
sufficient buffer for emergency storage.
7.20.5.
With these
provisions, emergency discharge of
untreated sewage will not be required, and
thus no adverse impact on water quality and marine ecology due to emergency plant breakdown is
anticipated.
7.20.6.
In
summary, no adverse impact on marine
ecology is expected in operational phase.
7.20.7. With
proper implementation of mitigation measures on water quality, the residual
impact on marine ecology is expected to be acceptable. No specific monitoring
and audit programme is required for marine ecology.
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