Consultancy Ref.: AFCD/FIS/02/19 Consultancy Service
for Environmental Impact Assessment Study for Designation of New Fish Culture
Zones Environmental
Impact Assessment (EIA) Report for Establishment of Fish Culture Zone at Mirs
Bay November
2022 |
This Section
presents an evaluation of the potential water quality impacts from the
construction and operation of the Project, and the results were assessed with
reference to the relevant environmental legislation, standards and criteria.
The following
legislation and relevant guidance or non-statutory guidelines are applicable to
the evaluation of water quality impacts associated with the construction and
operation of the Project:
n
Water
Pollution Control Ordinance (WPCO);
§ Technical Memorandum for Effluents
Discharged into Drainage and Sewerage Systems, Inland and Coastal Waters
(TM- ICW);
n
Hong
Kong Planning Standards and Guidelines (HKPSG); and
n
Environmental
Impact Assessment Ordinance (EIAO) and the Technical Memorandum on EIA Process
(EIAO-TM), Annexes 6 and 14.
The Water
Pollution Control Ordinance (WPCO) is the primary legislation for the control
of water pollution and water quality in Hong Kong. Under the WPCO, Hong Kong waters are divided
into 10 Water Control Zones (WCZs). Each
WCZ has a designated set of statutory Water Quality Objectives (WQOs).
The proposed Project is located within the Mirs Bay
WCZ and close to the boundary of the Tolo Harbour and Channel WCZ. The applicable WQOs for these WCZs are
presented in Table
3.1.
All discharges
from the construction and operation phases of the proposed Project are required
to comply with the Technical Memorandum
Standards for Effluents Discharged into Drainage and Sewerage Systems, Inland
and Coastal Waters (TM-ICW)
issued under Section 21 of the WPCO.
The TM-ICW
defines acceptable discharge limits to different types of receiving
waters. Under the TM-ICW, effluents discharged into the drainage and sewerage
systems, inshore and coastal waters of the WCZs are subject to pollutant
concentration standards for specified discharge volumes. These are defined by
the Environmental Protection Department (EPD) and are specified in licence
conditions for any new discharge within a WCZ.
Mariculture
is identified as one of the sensitive uses under Section 5.3 of Chapter 9 of
the HKPSG. The HKPSG highlighted the
importance of good water quality for the mariculture environment, as well as
the potential water quality impact from mariculture operation. Limitation on new effluent within 200m of the
seaward boundaries and 100m of the landward boundaries of a marine fish culture
zone should be observed. The HKPSG also
highlighted the importance of good water circulation to allow pollutants be
readily dispersed, as well as control of other sources of pollution that could
affect water quality.
Annexes 6 and 14 of the EIAO-TM provide
general guidelines and criteria to be used in assessing water quality impacts.
The EIAO-TM recognises that, in the
application of the above water quality criteria, it may not be possible to
achieve the WQO at the point of discharge as there are areas which are
subjected to greater impacts (which are termed by the EPD as the mixing zones),
where the initial dilution of the discharge takes place. The definition of this area is determined on
a case-by-case basis. In general, the
criteria for acceptance of the mixing zones are that it must not impair the
integrity of the water body as a whole and must not damage the ecosystem.
Table
3.1 Summary of Water Quality Objectives for Mirs
Bay WCZ and Tolo Harbour and Channel WCZ
|
Water Quality Objective |
Mirs Bay WCZ |
Tolo Harbour and Channel WCZ |
A |
AESTHETIC APPEARANCE |
||
a) |
Waste discharges shall cause no
objectionable odours or discolouration of the water. |
Whole zone |
Not applicable |
b) |
Tarry residues, floating wood, articles
made of glass, plastic, rubber or of any other substances should be absent. |
Whole zone |
Not applicable |
c) |
Mineral oil should not be visible on
the surface. Surfactants should not
give rise to lasting foam. |
Whole zone |
Not applicable |
d) |
There should be no recognisable
sewage-derived debris. |
Whole zone |
Not applicable |
e) |
Floating, submerged and
semi-submerged objects of a size likely to interfere with the free movement
of vessels, or cause damage to vessels, should be absent. |
Whole zone |
Not applicable |
f) |
Waste discharges shall
not cause the water to contain substances which settle to form objectionable
deposits. |
Whole zone |
Not applicable |
g) |
Waste discharges shall
cause no noxious or offensive odour or offensive taint or colour in either
waters or edible aquatic organisms in the subzone to be present in
concentrations detectable by bioassay or organoleptic tests. |
Not applicable |
(i) Harbour subzone. (ii) Buffer subzone. (iii) Channel subzone. |
h) |
Waste discharges shall
cause no visible foam, oil, grease, scum, litter or other objectionable
matter in waters of the subzone. |
Not applicable |
(i) Harbour subzone. (ii) Buffer subzone. (iii) Channel subzone. |
B |
BACTERIA |
||
a) |
The level of Escherichia coli should not exceed 610
per 100 mL, calculated as the geometric mean of all samples collected in one
calendar year. |
Secondary Contact
Recreation Subzones and Fish Culture Subzones |
Secondary Contact
Recreation Subzones and Fish Culture Subzones |
b) |
The level of Escherichia coli should be zero per
100 ml, calculated as the running median of the most recent 5 consecutive
samples taken at intervals of between 7 and 21 days. |
Water Gathering Ground
Sub-zones |
Not applicable |
c) |
The level of Escherichia coli should not exceed 1
000 per 100 ml, calculated as the running median of the most recent 5
consecutive samples taken at intervals of between 7 and 21 days. |
Other inland waters of the Zone |
Not applicable |
C |
COLOUR |
||
a) |
Waste discharges shall not cause the colour
of water to exceed 30 Hazen units. |
Water Gathering Ground
Sub-zones |
Not applicable |
b) |
Waste discharges shall not cause the
colour of water to exceed 50 Hazen units |
Other inland waters of the Zone |
Not applicable |
D |
DISSOLVED
OXYGEN |
||
a) |
Waste discharges shall not cause the
level of dissolved oxygen to fall below 4 milligrams per litre for 90% of the
sampling occasions during the year; values should be calculated as the water
column average (arithmetic mean of at least 3 measurements at 1 metre below
surface, mid-depth, and 1 metre above seabed). In addition, the concentration
of dissolved oxygen should not be less than 2 milligrams per litre within 2
metres of the seabed for 90% of the sampling occasions during the year. |
Marine waters excepting Fish Culture Subzones |
Not applicable |
b) |
The dissolved oxygen level should not be less
than 5 milligrams per litre for 90% of the sampling occasions during the
year; values should be calculated as water column average (arithmetic mean of
at least 3 measurements at 1 metre below surface, mid-depth and 1 metre above
seabed). In addition, the concentration of dissolved oxygen should not be
less than 2 milligrams per litre within 2 metres of the seabed for 90% of the
sampling occasions during the year. |
Fish Culture Subzones |
Not applicable |
c) |
Waste discharges shall not cause the level of
dissolved oxygen to be less than 4 milligrams per litre. |
Water Gathering Ground Sub-zones and Other inland
waters of the
Zone |
Not applicable |
d) |
Waste discharges shall not cause the
level of dissolved oxygen in waters of the subzone to be less than 2
milligrams per litre within two metres of the bottom, or to be less than 4
milligrams per litre in the remainder of the water column. |
Not applicable |
Harbour subzone |
e) |
Waste discharges shall not cause the
level of dissolved oxygen in waters of the subzone to be less than 3
milligrams per litre within two metres of the bottom, or to be less than 4
milligrams per litre in the remainder of the water column. |
Not applicable |
Buffer subzone |
f) |
Waste discharges shall not cause the
level of dissolved oxygen in waters of the subzone to be less than 4
milligrams per litre at any point in the water column. |
Not applicable |
Channel subzone |
E |
pH |
||
a) |
The pH of the water should be within
the range of 6.5-8.5 units. In addition, waste discharges shall not cause the
natural pH range to be extended by more than 0.2 units. |
Marine waters |
Not applicable |
b) |
Waste discharges shall not cause the pH
of the water to exceed the range of 6.5-8.5 units. |
Water Gathering Ground
Sub-zones |
Not applicable |
c) |
The pH of the water should be within
the range of 6.0-9.0 units. |
Other inland waters of the Zone |
Not applicable |
d) |
Waste discharges shall not cause the
normal pH range of any waters of the subzone to be extended by greater than
+/- 0.5 pH units at any time. |
Not applicable |
Harbour subzone |
e) |
Waste discharges shall not cause the
normal pH range of any waters of the subzone to be extended by greater than
+/- 0.3 pH units at any time. |
Not applicable |
Buffer subzone |
f) |
Waste discharges shall not cause the
normal pH range of any waters of the subzone to be extended by greater than
+/- 0.1 pH units at any time. |
Not applicable |
Channel subzone |
F |
TEMPERATURE |
||
a) |
Waste discharges shall not cause the
natural daily temperature range to change by
more than 2.0 degree Celsius. |
Whole Zone |
Not applicable |
b) |
Waste discharges shall not cause the natural
daily temperature range in waters of the subzone to be extended by greater
than +/- 1.0℃ at any location or time. The rate of
temperature change shall not exceed 0.5℃ per hour
at any location, unless due to natural phenomena. |
Not applicable |
(i) Harbour subzone. (ii) Buffer subzone. (iii) Channel subzone. |
G |
SALINITY |
||
a) |
Waste discharges shall not cause the
natural ambient salinity level to change by more than 10%. |
Whole Zone |
Not applicable |
b) |
Waste discharges shall not cause the normal
salinity range of any waters of the subzone to be extended by greater than
+/- 3 parts per thousand at any time. |
Not applicable |
(i) Harbour subzone. (ii) Buffer subzone. (iii) Channel subzone. |
H |
SUSPENDED SOLIDS |
||
a) |
Waste discharges shall neither cause
the natural ambient level to be raised by 30% nor give rise to accumulation
of suspended solids which may adversely affect aquatic communities. |
Marine waters |
Not applicable |
b) |
Waste discharges shall not cause the
annual median of suspended solids to exceed 20 milligrams per litre. |
Water Gathering Ground
Sub-zones and Other inland waters of the Zone |
Not applicable |
I |
AMMONIA |
||
|
The un-ionized ammoniacal nitrogen
level should not be more than 0.021 mg per litre, calculated as the annual
average (arithmetic mean). |
Whole Zone |
Not applicable |
J |
NUTRIENTS |
||
|
Nutrients shall not be present in
quantities sufficient to cause excessive or nuisance growth of algae or other
aquatic plants. |
Marine waters |
Not applicable |
|
Without limiting the generality of
objective (a) above, the level of inorganic nitrogen should not exceed 0.3
milligram per litre, expressed as annual water column average (arithmetic
mean of at least 3 measurements at 1 metre below surface, mid-depth and 1
metre above seabed). |
Marine waters |
Not applicable |
K |
5-DAY BIOCHEMICAL OXYGEN
DEMAND |
||
a) |
Waste discharges shall not cause the
5-day biochemical oxygen demand to exceed 3 milligrams per litre. |
Water Gathering Ground Sub-zones |
Not applicable |
b) |
Waste discharges shall not cause the
5-day biochemical oxygen demand to exceed 5 milligrams per litre. |
Other inland waters of
the Zone |
Not applicable |
L |
CHEMICAL OXYGEN DEMAND |
||
a) |
Waste discharges shall not cause the chemical oxygen
demand to exceed 15 milligrams per litre. |
Water Gathering Ground Sub-zones |
Not applicable |
b) |
Waste discharges shall not cause the chemical
oxygen demand to exceed 30 milligrams per litre. |
Other inland waters of
the Zone |
Not applicable |
M |
TOXINS / TOXICANTS |
||
a) |
Waste discharges shall not cause the
toxins in water to attain such levels as to produce significant toxic,
carcinogenic, mutagenic or teratogenic effects in humans, fish or any other
aquatic organisms, with due regard to biologically cumulative effects in food
chains and to toxicant interactions with each other. |
Whole Zone |
Not applicable |
b) |
Waste discharges of dangerous
substances shall not put a risk to any beneficial uses of the aquatic environment. |
Whole Zone |
Not applicable |
c) |
Waste discharges shall not cause the
toxicants in waters of the subzone to attain such a level as to produce
significant toxic effects in humans, fish or any other aquatic organism, with
due regard to biologically cumulative effects in food chains and to toxicant
interactions with each other. |
Not applicable |
(i) Harbour subzone. (ii) Buffer subzone. (iii) Channel subzone. |
N |
CHLOROPHYLL-A |
||
a) |
Waste discharges shall not cause the level
of chlorophyll-a in waters of the subzone to exceed 20 milligrams per cubic
metre, calculated as a running arithmetic mean of 5 daily measurements for
any single location and depth. |
Not applicable |
Harbour subzone |
b) |
Waste discharges shall not cause the
level of chlorophyll-a in waters of the subzone to exceed 10 milligrams per
cubic metre, calculated as a running arithmetic mean of 5 daily measurements
for any single location and depth. |
Not applicable |
Buffer subzone |
c) |
Waste discharges shall not cause the
level of chlorophyll-a in waters of the subzone to exceed 6 milligrams per
cubic metre, calculated as a running arithmetic mean of 5 daily measurements
for any single location and depth. |
Not applicable |
Channel subzone |
O |
LIGHT PENETRATION |
||
a) |
No changes in turbidity, suspended
material, colour or other parameters arising from waste discharges shall
reduce light transmission by more than 20 per cent of the normal level in the
subzone at any location or any time. |
Not applicable |
Harbour subzone |
b) |
No changes in turbidity, suspended
material, colour or other parameters arising from waste discharges shall
reduce light transmission by more than 15 per cent of the normal level in the
subzone at any location or any time. |
Not applicable |
Buffer subzone |
c) |
No changes in turbidity, suspended
material, colour or other parameters arising from waste discharges shall
reduce light transmission by more than 10 per cent of the normal level in the
subzone at any location or any time. |
Not applicable |
Channel subzone |
P |
SETTLEABLE MATERIAL |
||
|
Waste discharges shall give rise to
no bottom deposits or submerged objects which adversely influence bottom
living communities, alter the basic Harbour geometry or shipping channels,
present any hazard to shipping or diving activities, or affect any other
beneficial use of the waters of the subzone. |
Not applicable |
(i) Harbour subzone. (ii) Buffer subzone. (iii) Channel subzone. |
(1) CAP358U
Statement of Water Quality Objectives (Mirs Bay Water Control Zone)
(2) CAP358B
Tolo Harbour and Channel Water Control Zone Statement of Water Quality
Objectives
In
accordance with the Study Brief, the Assessment Area for water quality impact
assessment covers the Mirs Bay Water Control Zone (WCZ) and the Tolo Harbour
and Channel WCZ. The proposed Mirs Bay
FCZ is located at the embayment southeast to the Island of Tap Mun. The embayment is generally 15 m – 20 m deep
except for the nearshore areas as well as around the island of Wong Mau
Chau. The embayment connects to the Mirs
Bay in the northeastern direction, which itself is also an embayment. Water depth for the majority of Mirs Bay is
around 15 m – 20 m.
Baseline
marine water quality of the Assessment Area has been determined through a
review of EPD routine water quality monitoring data collected between 1986 and
2020. This dataset provides Hong Kong’s
most comprehensive long-term water quality monitoring data and allows an indication
of temporal and spatial change in marine water quality in Hong Kong. Water quality monitoring data from EPD
monitoring stations that are located within or close to the Assessment Area
were used to provide the baseline water quality conditions of the Assessment
Area. The monitoring results from 1986
to 2020 at the selected monitoring stations are summarised in Table
3.2. Locations of these stations are presented in Figure
3.1.
According
to EPD’s Marine Water Quality in Hong
Kong in 2020, Mirs Bay attained an overall marine WQO compliance rate of
98% in 2020. The water quality was very
good with high DO, and low nutrient and E.
coli levels. For the Tolo Harbour
and Channel WCZ, the overall marine WQO compliance rate in 2020 was 93%. Tolo Harbour consistently complied with the
bacteriological WQO for secondary contact recreational uses applicable to the
entire marine waters of the WCZ. Tolo
Channel, however, was subject to a natural hydrological phenomenon of water
column stratification and associated lower bottom DO level due to restricted
water exchange with the open waters.
Compliance with the WQOs is generally observed in most parameters at the
selected monitoring stations at the two WCZs.
There have been exceedances of chlorophyll-a level at TM8 (Tolo Channel
subzone) but the situation has significantly improved since the implementation
of the Tolo Harbour Effluent Export Scheme (THEES) as well as a number of
measures under the Livestock Waste Control Scheme (LWCS). According to EPD’s Marine Water Quality in Hong Kong (various years), the percentage
of samples taken at TM8 with ≤6 µg/L level of
chlorophyll-a gradually increases from the low point of 70.7% in 1988 up to
average of around 90% in the recent 10 years from 2011-2020 (with 100% in 2020).
Table
3.2 Summary of EPD Routine Water Quality Monitoring
Data from Selected Stations of the Tolo Harbour and Channel WCZ and Mirs Bay
WCZ (1986 – 2020)
Parameters |
TM8 |
MM6 |
MM17 |
Temperature
(°C) |
22.7 |
23.1 |
23.8 |
(11.7-30.4) |
(11.1-29.9) |
(14.1-29.7) |
|
Salinity
(psu) |
32.1 |
32.2 |
32.2 |
(26.8-35.4) |
(26.8-34.3) |
(30.3-34.3) |
|
Dissolved
Oxygen (mg/L) |
6.1 |
6.5 |
6.2 |
(1.4-14.2) |
(3.6-11.3) |
(4.2-9.0) |
|
Dissolved
Oxygen (mg/L) - Bottom |
5.0 |
6.2 |
5.4 |
(0.0-19.5) |
(0.2-15.5) |
(1.1-8.6) |
|
Dissolved
Oxygen (%saturation) |
84 |
91 |
87 |
(33-167) |
(51-147) |
(63-115) |
|
Dissolved
Oxygen (%saturation) - Bottom |
68 |
85 |
75 |
(0-200) |
(3-200) |
(16-109) |
|
pH |
8.2 |
8.1 |
8.0 |
(7.5-8.9) |
(6.7-8.6) |
(7.6-8.3) |
|
Secchi
Disc Depth (M) |
3.5 |
3.8 |
3.7 |
(0.5-13.0) |
(1.0-8.5) |
(1.5-7.0) |
|
Turbidity
(NTU) |
3.9 |
4.1 |
1.4 |
(0.2-33.1) |
(0.2-32.1) |
(0.1-5.5) |
|
Suspended
Solids (mg/L) |
3.2 |
2.7 |
5.1 |
(0.5-71.2) |
(0.5-15.0) |
(0.7-16.0) |
|
5-day
Biochemical Oxygen Demand (mg/L) |
1.1 |
0.9 |
0.8 |
(0.1-5.8) |
(0.1-3.2) |
(0.2-2.0) |
|
Ammonia
Nitrogen (mg/L) |
0.044 |
0.033 |
0.029 |
(0.01-0.68) |
(0.01-0.53) |
(0.01-0.08) |
|
Unionised
Ammonia (mg/L) |
0.003 |
0.002 |
0.002 |
(0.000-0.077) |
(0.000-0.048) |
(0.000-0.003) |
|
Nitrite
Nitrogen (mg/L) |
0.013 |
0.010 |
0.011 |
(0.002-0.103) |
(0.002-0.064) |
(0.002-0.067) |
|
Nitrate
Nitrogen (mg/L) |
0.026 |
0.022 |
0.028 |
(0.002-0.609) |
(0.002-0.160) |
(0.003-0.103) |
|
Total
Inorganic Nitrogen (mg/L) |
0.07 |
0.06 |
0.06 |
(0.01-0.70) |
(0.01-0.54) |
(0.01-0.15) |
|
Total
Kjeldahl Nitrogen (mg/L) |
0.37 |
0.24 |
0.38 |
(0.08-4.79) |
(0.07-1.32) |
(0.11-0.88) |
|
Total
Nitrogen (mg/L) |
0.40 |
0.27 |
0.41 |
(0.05-4.80) |
(0.06-1.37) |
(0.12-0.89) |
|
Orthophosphate
Phosphorus (mg/L) |
0.013 |
0.009 |
0.008 |
(0.002-0.068) |
(0.002-0.035) |
(0.002-0.028) |
|
Total
Phosphorus (mg/L) |
0.05 |
0.04 |
0.04 |
(0.02-0.58) |
(0.02-0.32) |
(0.02-0.11) |
|
Silica
(mg/L) |
0.77 |
0.63 |
0.66 |
(0.05-2.00) |
(0.06-1.63) |
(0.07-1.24) |
|
Chlorophyll-a
(μg/L) |
3.4 |
2.5 |
2.1 |
(0.3-120.8) |
(0.3-14.4) |
(0.3-5.1) |
|
E. coli (cfu/100mL) |
2 |
2 |
2 |
(1-510) |
(1-570) |
(1-32) |
|
Faecal
Coliforms (cfu/100mL) |
3 |
3 |
2 |
(1-6000) |
(1-10067) |
(1-59) |
Notes:
1. Data presented are depth-averaged
values calculated by taking the means of three depths, i.e. surface (S),
mid-depth (M) and bottom (B), except as specified.
2. Data presented are annual arithmetic
means except for E. coli, which are
geometric means.
3. Shaded cells indicate
non-compliance with the WQOs.
Baseline
marine sediment quality in the Assessment Area has been determined through a review of EPD routine sediment quality
monitoring data collected between 1986 and 2020. Sediment monitoring data from relevant EPD
monitoring stations were used to represent the sediment quality adjacent to the
Project (Table
3.3). Locations of these stations
are presented in Figure
3.1.
Sediment
monitoring data from the EPD monitoring stations were compared with the
relevant sediment quality criteria specified in ETWB TC(W) No. 34/2002 Management of Dredged/Excavated Sediment. The EPD routine monitoring data indicate that
the contaminant levels in the sediments in the vicinity of the Project are all
below the Lower Chemical Exceedance Level (LCEL).
Table
3.3 Summary
of EPD Routine Sediment Monitoring Data from Selected Stations of the Tolo
Harbour and Channel WCZ and Mirs Bay WCZ (1986 – 2020)
Parameters |
LCEL |
UCEL |
TS5 |
MS6 |
MS17 |
Arsenic (mg
kg-1) |
12 |
42 |
6.6 |
6.5 |
6.9 |
|
|
(3.2-12.0) |
(3.5-10.0) |
(2.2-11.0) |
|
Cadmium (mg kg-1) |
1.5 |
4 |
0.5 |
0.5 |
0.3 |
|
|
(0.1-7.5) |
(0.1-7.6) |
(<0.1-8.3) |
|
Chromium (mg kg-1) |
80 |
160 |
32.5 |
32.1 |
32.8 |
|
|
(11.0-85.0) |
(22.0-49.0) |
(6.0-44.0) |
|
Copper (mg kg-1) |
65 |
110 |
21.8 |
16.7 |
16.3 |
|
|
(5.0-70.0) |
(5.0-23.0) |
(<0.2-55.0) |
|
Lead (mg kg-1) |
75 |
110 |
53.1 |
41.9 |
43.9 |
|
|
(35.0-86.0) |
(32.0-57.0) |
(26.0-67.0) |
|
Mercury (mg kg-1) |
0.5 |
1 |
0.10 |
0.08 |
0.06 |
|
|
(<0.05-0.59) |
(0.05-0.40) |
(<0.05-0.55) |
|
Nickel (mg kg-1) |
40 |
40 |
23.3 |
23.3 |
23.9 |
|
|
(7.0-50.0) |
(15.0-35.0) |
(6.0-34.0) |
|
Silver (mg kg-1) |
1 |
2 |
<0.2 |
<0.2 |
<0.2 |
|
|
(<0.2-<0.2) |
(<0.2-<0.2) |
(<0.2-0.5) |
|
Zinc (mg kg-1) |
200 |
270 |
121.3 |
100.0 |
96.9 |
|
|
(64.0-220.0) |
(66.0-150.0) |
(36.0-170.0) |
|
Total
Polychlorinated Biphenyls (PCBs) (μg kg-1) |
23 |
180 |
18 |
18 |
14 |
|
|
(8-26) |
(9-18) |
(3-18) |
|
Low Molecular Weight
Polycyclic Aromatic
Hydrocarbons (PAHs) (μg kg-1) |
550 |
3,160 |
<180 |
<180 |
<180 |
|
|
(<180-<180) |
(<180-<180) |
(<180-185) |
|
High Molecular
Weight Polycyclic Aromatic
Hydrocarbons (PAHs) (μg kg-1) |
1,700 |
9,600 |
36 |
42 |
35 |
|
|
(<32-130) |
(<32-155) |
(<32-139) |
|
Chemical Oxygen Demand (mg kg-1) |
-- |
-- |
18796 |
17075 |
16266 |
|
|
(8300-40000) |
(11000-26000) |
(8400-38000) |
|
Total Kjeldahl
Nitrogen (mg kg-1) |
-- |
-- |
737.4 |
708.8 |
669.7 |
|
|
(23.0-2000.0) |
(220.0-2000.0) |
(18.0-1600.0) |
1.
Data presented are arithmetic means;
data in brackets indicate ranges.
2.
All data are on a dry weight basis
unless stated otherwise.
Figure
3.1 Location of Water Sensitive Receivers and
Nearby EPD Marine Water / Sediment Quality Monitoring Stations
The water sensitive receivers (WSRs) have been identified in
accordance with Annex 14 of the Technical Memorandum on EIA Process (EIAO, Cap.499, S.16) and Section 3.4.3.2
of the Study Brief. These WSRs are
illustrated in Figure
3.1 and listed in Table
3.4. Key
WSRs include:
n
Hoi Ha Wan Site of Special
Scientific Interest (SSSI1);
n
Hoi Ha Wan Marine Park (MP2);
n
Recreational areas, such as
secondary contact recreation subzones of WCZs ([1]);
n
Existing FCZs at Tap Mun, Kau Lau
Wan, Sham Wan and other nearby areas (F4 to F6);
n
Proposed FCZs at Wong Chuk Kok Hoi
and Outer Tap Mun (Site A and Site B);
n Ecological
habitats for marine organisms including coral, amphioxus (AM1) ([2]) and benthic communities, and
Finless Porpoise ([3]) at / near the Project site (CR3 to CR7, CR13 to CR14,
CR16, M6 to M10);
n Spawning
ground and nursery area of commercial fisheries resources ([4]);
n Artificial
reefs in Hoi Ha Wan Marine Park (MP2) and in Long Harbour (AR1 to AR6);
n Intertidal
area of Sai Kung West Country Park and Sai Kung East Country Park (M6 to M10);
and
n Non-gazetted
beaches (B2 to B5).
Table
3.4 Water Sensitive Receivers (WSRs) in the
Vicinity of the Proposed FCZ Site at Mirs Bay
WSR ID |
WSR |
Distance
to the Proposed FCZ site at Mirs Bay (km) |
B2 |
Non-gazetted beach of Nam She Wan |
0.4 |
B3 |
Non-gazetted beach of Tung Wan |
2.2 |
B4 |
Non-gazetted beach of Tai Wan |
2.9 |
B5 |
Non-gazetted beach of Ham Tin Wan and
Sai Wan |
3.5 |
CR3 |
Coral at Port Island |
3.1 |
CR4 |
Coral at Shek Ngau Chau ([5]) |
4.0 |
CR5 |
Coral at Nam She Wan |
<0.1 Note |
CR6 |
Coral at Nam She Wan |
0.2 |
CR7 |
Coral at Nam She Wan |
<0.1 Note |
CR13 |
Coral at Hoi Ha Wan Moon Island |
4.1 |
CR14 |
Coral at Hoi Ha Wan Coral Beach |
4.0 |
CR16 |
Coral at Heung Lo Kok |
4.9 |
F4 |
Tap Mun Fish Culture Zone |
1.2 |
F5 |
Kau Lau Wan Fish Culture Zone |
1.1 |
F6 |
Sham Wan Fish Culture Zone |
1.5 |
M6 |
Mangrove Stand / Intertidal at Hoi Ha
Wan |
4.5 |
M7 |
Mangrove Stand / Intertidal at Tai
Tan ([6]) |
3.7 |
M8 |
Mangrove Stand / Intertidal at To Kwa
Peng (5) |
3.9 |
M9 |
Mangrove Stand / Intertidal at Chek
Keng (5) |
3.1 |
M10 |
Mangrove Stand / Intertidal at Ham
Tin Wan (5) |
3.1 |
MP2 |
Hoi Ha Wan Marine Park and Artificial
Reef within the Marine Park |
3.2 |
AR1 |
Artificial Reef in Long Harbour |
2.5 |
AR2 |
Artificial Reef in Long Harbour |
1.8 |
AR3 |
Artificial Reef in Long Harbour |
2.9 |
AR4 |
Artificial Reef in Long Harbour |
2.1 |
AR5 |
Artificial Reef in Long Harbour |
2.5 |
AR6 |
Artificial Reef in Long Harbour |
2.6 |
SSSI1 |
Hoi Ha Wan SSSI |
3.3 |
Site A |
Proposed Wong Chuk Kok Hoi FCZ |
6.3 |
Site B |
Proposed Outer Tap Mun FCZ |
1.8 |
Site C |
Proposed Mirs Bay FCZ |
Project Site |
AM1 |
Amphioxus Habitat within and near
Proposed Site |
Within Project Site |
The
proposed establishment of new fish culture zone would result in increase of
pollution from fish farming operation.
Such pollution would increase nutrient level as well as decrease
dissolved oxygen level in surrounding water.
The relevant assessment criteria for the identified WSRs are stipulated
in the WQO and is shown below in Table
3.5.
Table
3.5 Summary of Assessment WQO Criteria
Parameters |
Mirs Bay WCZ |
Tolo Harbour and Channel WCZ |
Dissolved Oxygen (Bottom) (mg/L) |
Not less
than 2 mg/L for 90% of samples |
Not less
than 2 mg/L for the Harbour subzone. Not less
than 3 mg/L for the Buffer subzone. Not less
than 4 mg/L for the Channel subzone. |
Dissolved Oxygen (Depth-averaged) (mg/L) |
Not less
than 4 mg/L for 90% of samples |
Not less
than 4 mg/L. |
Suspended Solids (mg/L) |
Change
not more than 30% due to waste discharge |
Not applicable |
Total Inorganic Nitrogen (mg/L) |
≤ 0.3 |
Not applicable |
Unionized Ammonia (mg/L) |
≤ 0.021
mg/L |
Not applicable |
Chlorophyll-a (μg/L) |
Not applicable |
5-day running
average not more than 20 μg/L for the Harbour subzone. 5-day
running average not more than 10 μg/L for the Buffer subzone. 5-day
running average not more than 6 μg/L for the Channel subzone. |
E.coli
(no./100mL) |
≤ 610 no./100mL for the Secondary contact
recreation subzone and the Fish culture subzones |
≤ 610 no./100mL for the Secondary
contact recreation subzone and the Fish culture subzones |
In addition to the WQO criteria for various water quality parameter in two
WCZs, reference has been made to other past approved EIAs / direct-to-permit
application for applicable assessment criterion for protection of coral within
the Tolo Harbour and Channel WCZ.
Assessment criterion of 10 mg/L of total suspended solids levels would
be adopted following the approved EIA of Development of a Bathing Beach at Lung
Mei, Tai Po (AEIAR-123/2008), as well as direct-to-permit application of
Sediment Removal at Yim Tin Tsai, Yim Tin Tsai (East) Fish Culture Zones and
Shuen Wan Typhoon Shelter (DIR-191/2009).
For fish culture zone in Mirs Bay, an additional criterion for
chlorophyll-a of 20 µg/L would be adopted to
protect the fish stock from excessive algal growth based on criterion adopted
in previous Project WATERMAN Study ([7]). A summary of applicable assessment criteria
for each category of WSRs are provided below in Table
3.6.
There will be no marine dredging or other major marine works that could
cause significant sediment disturbance and the associated release of
sediment-bounded contaminants.
Therefore, assessment criteria for dissolved metals and organic
compounds are not necessary for this Study.
Table 3.6 Summary of Applicable Assessment Criterion for
Identified WSRs
Category of WSR |
ID |
WSR |
Annual |
||||||||
10th-percentile |
Mean |
||||||||||
Depth-averaged |
Bottom |
Depth-averaged |
Bottom |
Depth-averaged |
|||||||
Dissolved Oxygen |
Total Inorganic Nitrogen |
Unionized Ammonia |
Chlorophyll-a |
Suspended Solids |
E.coli Note |
||||||
(mg/L) |
(mg/L) |
(mg/L) |
(mg/L) |
(mg/L) |
(mg/L) |
(mg/L) |
(mg/L) |
(no./100 mL) |
|||
Non-gazetted
beach – Mirs Bay |
B2 |
Non-gazetted
beach of Nam She Wan |
≥4 |
≥2 |
N/A |
N/A |
≤0.3 |
≤0.021 |
N/A |
increase ≤30% baseline |
≤610 |
B3 |
Non-gazetted
beach of Tung Wan |
||||||||||
B4 |
Non-gazetted
beach of Tai Wan |
||||||||||
B5 |
Non-gazetted
beach of Ham Tin Wan and Sai Wan |
||||||||||
Coral –
Mirs Bay |
CR3 |
Coral at Port Island |
≥4 |
≥2 |
N/A |
N/A |
≤0.3 |
≤0.021 |
N/A |
increase ≤30% baseline |
≤610 |
CR4 |
Coral
at Shek Ngau Chau |
||||||||||
CR5 |
Coral
at Nam She Wan |
||||||||||
CR6 |
Coral
at Nam She Wan |
||||||||||
CR7 |
Coral
at Nam She Wan |
||||||||||
Coral –
Tolo Harbour and Channel |
CR13 |
Coral at Hoi Ha Wan Moon Island |
N/A |
N/A |
≥4 |
≥4 |
N/A |
N/A |
≤6 |
≤10 |
≤610 |
CR14 |
Coral at Hoi Ha Wan Coral Beach |
||||||||||
CR16 |
Coral at Heung Lo Kok |
||||||||||
Fish Culture
Zone – Mirs Bay |
F4 |
Tap Mun Fish Culture Zone |
≥5 |
≥2 |
N/A |
N/A |
≤0.3 |
≤0.021 |
≤20 |
increase ≤30% baseline |
≤610 |
F5 |
Kau Lau Wan Fish Culture Zone |
||||||||||
F6 |
Sham Wan Fish Culture Zone |
||||||||||
Site A |
Proposed Wong Chuk Kok Hoi FCZ |
||||||||||
Site B |
Proposed Outer Tap Mun FCZ |
||||||||||
Site C1 (Northern part of Project site) |
Proposed Mirs Bay FCZ (Northern Part) |
||||||||||
Site C2 (Southern part of Project site) |
Proposed Mirs Bay FCZ (Southern Part) |
||||||||||
Mangrove
Stand / Intertidal – Mirs Bay |
M7 |
Mangrove Stand / Intertidal at Tai Tan |
≥4 |
≥2 |
N/A |
N/A |
≤0.3 |
≤0.021 |
N/A |
increase ≤30% baseline |
≤610 |
M8 |
Mangrove Stand / Intertidal at To Kwa Peng |
||||||||||
M9 |
Mangrove Stand / Intertidal at Chek Keng |
||||||||||
M10 |
Mangrove Stand / Intertidal at Ham Tin Wan |
||||||||||
Mangrove
Stand / Intertidal – Tolo Harbour and Channel |
M6 |
Mangrove Stand / Intertidal at Hoi Ha Wan |
N/A |
N/A |
≥4 |
≥4 |
N/A |
N/A |
≤6 |
≤10 |
≤610 |
Marine
Park – Tolo Harbour and Channel |
MP2 |
Hoi Ha Wan Marine Park and Artificial Reef within
the Marine Park |
N/A |
N/A |
≥4 |
≥4 |
N/A |
N/A |
≤6 |
≤10 |
≤610 |
Artificial Reef – Mirs Bay |
AR1 |
Artificial Reef in Long Harbour |
≥4 |
≥2 |
N/A |
N/A |
≤0.3 |
≤0.021 |
N/A |
increase ≤30% baseline |
≤610 |
AR2 |
Artificial Reef in Long Harbour |
||||||||||
AR3 |
Artificial Reef in Long Harbour |
||||||||||
AR4 |
Artificial Reef in Long Harbour |
||||||||||
AR5 |
Artificial Reef in Long Harbour |
||||||||||
AR6 |
Artificial Reef in Long Harbour |
||||||||||
Amphioxus Habitat – Mirs Bay |
AM1 |
Amphioxus Habitat with and near Proposed Site |
≥4 |
≥2 |
N/A |
N/A |
≤0.3 |
≤0.021 |
N/A |
increase ≤30% baseline |
≤610 |
SSSI –
Tolo Harbour and Channel |
SSSI1 |
Hoi Ha Wan SSSI |
N/A |
N/A |
≥4 |
≥4 |
N/A |
N/A |
≤6 |
≤10 |
≤610 |
Note: WQO criterion for E.coli is only applicable to fish culture zones, bathing beaches as
well as secondary contact recreation subzone.
Given secondary contact recreation subzone covers significant area
around the Project Site and is represented by a lot of WSRs in this list, the
criterion is deemed applicable to these WSRs as well.
The
methodology employed to quantitatively assess potential water quality impacts
associated with the operation of the Project is presented in the Water Quality
Modelling Plan (Appendix 3A), which
provides full technical details of the modelling works as well as model
validation. The WSRs assessed are
presented in Figure 3.1.
For other
potential sources of water quality impact in construction and operation phase,
qualitative approach would be adopted in the assessment.
The
uncertainties associated with the operation phase water quality modelling and
carrying capacity estimation include:
n
Potential change in pollution
loading from the Guangdong side of Mirs Bay; and
n
Potential change in mariculture
practice which leads to different level of pollution loading from fish farms.
Future year of 2023 was chosen
because the future loading from the Guangdong Province of China is expected to
decrease continuously and therefore the estimated loading in 2023 would be
conservative (Section 4 of Appendix
3A referred). Model
prediction of water quality under 2016 presented in Appendix
3D compared observed and predicted water quality at EPD Marine
Water Quality Monitoring Stations.
Results indicated the model developed can generally represents key water
quality features including stratification and seasonal differences, while
providing predictions that are generally more conservative the observed
conditions. This means the model would
provide conservative estimation of water quality thus being acceptable.
In terms of change in
mariculture practice, the overall trend has been heading towards a more
environmentally friendly direction in the past decades. The wider adoption of pellet feed has reduced
wastage. Improved fish farming practice
has reduced overfeeding, disease and fish mortality. Future improvement in technology and fish
farming practice is expected to further the trend on small environmental
footprint for mariculture, and thus the current assumptions are considered
conservative and appropriate for impact assessment. In particular, the pollution loading from mariculture
operation at the Project site was based on feed conversion ratio (FCR) of 2,
whereas literatures reviewed under this Study indicated typical pellet feed
nowadays can achieve FCR of close to 1 ([8]) ([9]) ([10]). The adoption FCZ of 2 instead
of 1 means the amount of feed assumed for mariculture operation would be
doubled, and the associated wastage, leachage ([11]) of nutrient from waste would be notably higher than typical average
conditions for fish farm using pellet feeds.
This will ensure conservative estimation of pollution load from the
mariculture operation at the Project site.
It should be highlighted that
the water quality modelling exercise covered a typical annual cycle based on
typical hydrodynamic of spring neap cycle in dry and wet seasons. Extreme conditions, such as typhoon is not
expected to result in water quality conditions much worse than the typical
conditions and is typically not considered in other water quality simulation in
past EIAs. Also, in case of
deterioration of water quality, it is typical for mariculturists to move the
mariculture operation within or out of the Project site temporarily, which in
the sense of modelling exercise means moving sensitive receiver as well as
pollution source. In this Study, such
movement has not been taken into account and thus represents the worst case
scenario where avoidance is not possible.
To ensure robustness of the modelling exercise, performance of the
hydrodynamic and water quality prediction have been demonstrated to be on par
with past approved model (Annex A-B of Appendix 3A) and able to reproduce
realistic water quality conditions in the past (Appendix 3D). This shows the adopted model would be able to
predict the water quality conditions under the baseline and project scenarios
of the Project with reasonable accuracy and reliability, ensure reliable
assessment and conclusion be drawn.
The
construction for this Project will not involve civil or marine works. Most of the construction works
would involve the assembly of parts to form fish rafts for mariculture, as well
as the towing and anchoring of fish rafts from other location(s) to the new FCZ
using tug boat. Potential water quality
impact from the assembly of parts to form fish rafts would include accidental
spillage, construction waste, as well as sewage from construction
workforce. Anchoring and de-anchoring of
fish rafts may result in transient, localised elevation of suspended solids
near seabed.
Mariculture
activities at the Project site would
result in an increase in pollution loads primarily from fish feed, feed
wastage, fish excretion and, dead fish. The increase in pollution loads would
result in a change in water quality in the receiving waters, affecting the
water quality at nearby sensitive receivers, such as other existing FCZs,
marine ecological as well as fisheries resources. Other potential operation phase water quality
impacts include change in hydrology / flow regime due to the presence of fish
rafts, spillage of fish drugs, chemical and feed, wastewater from workforces
and increased marine traffic and visitor activities.
Maintenance
dredging and sediment removal were typically needed at FCZs sited at shallow
and sheltered as a result of building up of organic content at the seabed level
of the FCZs because of prolong mariculture operation. Build-up of organic content could be
contributed by fish faeces, unconsumed feed, lodged off attached growth from
cleaning, etc., and could results in deterioration of local water quality,
increased risk of local red tide and upwelling of anoxic and toxic gas ([12]). The Project
site was chosen to be deep enough to (1) allow sufficient dispersion of any mariculture
waste (fish faeces, unconsumed feed, lodged off attached growth, etc.) that
sinks could be brought away by tidal current and dispersed at a larger area of
the seabed so there is no significant build-up of the seabed, and (2) provide
sufficient distance from the seabed to the bottom level of fish cages. Specifically, at least 2 m of clearance from
the seabed would be maintained at all times, except for integrated
multi-trophic aquaculture (IMTA) that certain part of the mariculture setup
might stay at / near bottom of the water column (details are presented in Section
2.6.2.3). Maintenance dredging
and sediment removal are therefore not required for the Project and hence no
water quality impact would be expected from maintenance dredging and sediment
removal.
In case of
adverse weather / water quality conditions or approaching of harmful algal
bloom, there may be a need for mariculturists to temporarily relocate their
fish rafts (or equivalent) to safe location(s) to avoid fish kill or other damage. During the brief period of relocation, the
pollution load from the relocated mariculture operation would be released into
the relocated locations, thus affect the local water quality.
The towing
and anchoring of fish rafts is expected to have very limited impact on water
quality, as the level of sediment suspended in the water column from anchoring
will be very limited, primarily localised near the seabed and the impact will
be transient because suspended sediment will settle shortly close to the
anchor. Anchoring is routinely conducted
for all kinds of vessel activities and floating structures in the surrounding
waters and is considered to have limited level of impact on water body. The Project
site is more than 15 m in water depth such that propeller would not have
interaction with the seabed sediment and so SS elevation due to propeller wash
is not anticipated.
Depending
on the design and specifications, required works to assemble fish rafts onsite
could vary and may include tighten up connections by nuts and bolts, ropes or
equivalent, assembling parts with pre-casted grooves, etc. Modern fish rafts are available in modular
form and with appropriate surface treatment ([13]),
hence the onsite assembly can be done quicker and will require less onsite use
of equipment and materials. In general,
construction materials and tools are inert and use of these items is not
expected to result in notable changes in water quality. It is noted that wood or other structural materials
that require surface treatment (e.g. water-proofing, anti-fouling) are
generally treated offsite (in factories / workshops) instead of onsite during
assembly. The use of chemicals onsite is
expected to be minimal and no unacceptable water quality impact from the onsite
installation of fish raft would be expected.
Details of tools and materials adopted on-site would be determined by
the future licensees.
Because
of the lack of major works to be conducted, it is
unlikely there will be a significant workforce presence during construction
phase, and any sewage / wastewater generated shall be collected at the
transportation / work vessel(s) for disposal at appropriate facilities on
land. Discharge of sewage from workforce
or other wastewater should be strictly forbidden. No unacceptable water quality impact from
sewage / wastewater from workforce is anticipated.
In view of
the above, no unacceptable water quality impact is anticipated from fish raft
installation.
Mariculture
activities at the Project site would
result in an increase in pollution loads primarily from fish feed, feed
wastage, fish excretion, and dead fish.
The increase in pollution loads would result in a change in water
quality in the receiving waters, affecting the water quality at nearby
sensitive receivers, such as other existing FCZs, marine ecological as well as
fisheries resources. A carrying capacity
([14])
estimation was conducted (detailed in Appendix
3B) to determine the suitable production capacity allowed onsite to
ensure mariculture activities there would not result in, or be affected by
water quality impact from over-stocking.
The estimation of carrying capacity was conducted using the methodology
and box model developed by Project WATERMAN which was used in the carrying
capacity estimation for the existing FCZs in Hong Kong. The carrying capacity estimation took into
account various aspects affecting the water quality for mariculture operation,
including tidal flushing, loading contribution from mariculture activities, as
well as various water quality parameters interaction (e.g. nitrogen,
phosphorus, dissolved oxygen). Based on
the WATERMAN model, the carrying capacity for mariculture operation at the
Project Site is found to be limited by the criterion for total inorganic
nitrogen in both wet and dry seasons.
The carrying capacity estimation indicated the Project site can support
mariculture operation of 5683.5 ton of standing stock based on typical
mariculture practice in HK without significant deterioration of water quality
under the typical average condition. The
corresponding pollution load from such level of mariculture operation is
presented in Appendix 3B.
The
estimated loading at the Project site was taken into account in the Delft3D
model to verify the acceptability of change in water quality at the Project
site itself as well as to determine the offsite water quality impact on nearby
WSRs. Two modelling scenarios were
conducted. The baseline scenario covers
the without project condition of the Assessment Area in 2023. The project scenario has taken into account
the additional pollution load from the Project site, as well as the other
nearby proposed new fish culture zones at Outer Tap Mun and Wong Chuk Kok Hoi
(each at their carrying capacity). The
change in water quality as a result of the additional mariculture activities
were assessed according to the WQO.
Statistics of key water quality parameters are presented in Table
3.8
([15]). Contour plots showing spatial distribution of
key water quality parameters are presented in Appendix
3C.
Following
sections discuss the predicted level and change for key water quality
parameters separately at the Project site as well as major nearby WSRs.
Predicted
levels of dissolved oxygen were generally good in most identified WSRs under both
baseline and project scenarios. Typical
depth-averaged levels of dissolved oxygen were predicted to be around 5 mg/L to
7 mg/L, which were close to the observed range at EPD Marine Water Quality
Monitoring Stations (Table
3.2). Predicted levels of dissolved oxygen are
generally low in the bottom level and the predicted depth-averaged levels are
typically slightly higher than that of the bottom level. Changes in dissolved oxygen due to
mariculture production at Project site and other locations were predicted to be
limited at most locations away from these proposed new FCZ sites.
Near the
Project site, the levels of mean depth-averaged dissolved oxygen at the nearby
coral colonies at CR5, CR6 and CR7 were 6.1 mg/L, 6.0 mg/L and 6.1 mg/L
respectively for baseline scenario. The
predicted mean depth-averaged dissolved oxygen under project scenario were 6.0
mg/L, 5.8 mg/L and 6.0 mg/L respectively.
Levels of bottom dissolved oxygen at coral colonies CR5, CR6, CR7 were
predicted to be 6.0 mg/L, 5.7 mg/L and 5.9 mg/L under baseline scenario, and
those under project scenario were predicted to be 5.9 mg/L, 5.5 mg/L and 5.8
mg/L respectively. At the nearby non-gazetted
beach of Nam She Wan, the depth-averaged dissolved oxygen levels under baseline
scenario were predicted to be 6.0 mg/L and 5.8 mg/L respectively under baseline
and project scenarios. The predicted
mean bottom dissolved oxygen levels were 5.6 mg/L and 5.3 mg/L respectively
under baseline and project scenarios.
For the amphioxus habitat within or near the Project Site, the predicted
change in dissolved oxygen levels at the representative location of AM1 would
be limited under the operation phase.
The predicted mean depth-averaged and bottom dissolved oxygen are 6.1
mg/L and 5.8 mg/L respectively under baseline scenarios, and project operation
would only result in decrease by 0.1 mg/L for both depth-averaged and bottom
levels.
For the
northern part of the Project site, the predicted mean depth-averaged dissolved
oxygen levels were 6.1 mg/L for both scenarios.
The predicted mean bottom dissolved oxygen levels for the northern part
of the Project Site were 5.7 mg/L in baseline scenario and 5.6 mg/L in project
scenario. For the southern part of the
Project Site, mean depth-averaged and bottom dissolved oxygen under baseline
scenarios were 6.1 mg/L and 5.8 mg/L respectively, and project operation would
only result in reduction of 0.1 mg/L for both depth-averaged and bottom
dissolved oxygen. The predicted 10th-percentile
depth-averaged dissolved oxygen levels were 5.2 mg/L in baseline scenario and
5.1 mg/L in project scenario in the northern part of the Project Site. At the southern part of the Project Site, the
predicted 10th-percentile depth-averaged dissolved oxygen levels
were 5.2 mg/L in baseline scenario and 5.1 mg/L in project scenario and at both
parts of the Project site. For the 10th-percentile
bottom dissolved oxygen, the predicted levels were 4.2 mg/L at the northern
part of the Project Site under both scenarios.
For the southern part of the Project Site, the predicted 10th-percentile
bottom dissolved oxygen was 4.3 mg/L and 4.2 mg/L under the baseline and
project scenario respectively. This
means the predicted dissolved oxygen levels at both parts of the Project site
would comply with relevant WQO criteria under WQO stipulated in Table
3.5.
Beyond the
immediate vicinity of the Project Site, proposed new FCZ at Site A was
predicted to have low DO level, with predicted 10th-percentile
depth-averaged dissolved oxygen level below the corresponding assessment
criterion. As shown, the low dissolved
oxygen levels were predicted under baseline scenario and were not shown to
deteriorate (i.e. reduce) under the Project scenario. As such, no unacceptable change in dissolved
oxygen level is expected at this WSR. It
should be highlighted that even though the 10th-percentile
depth-averaged dissolved oxygen levels at Site A was predicted to be lower than
the corresponding assessment criterion of 5 mg/L, the dissolved oxygen levels
predicted at the upper part of the water column (where the majority of fish
stock is expected to stay) is generally higher.
Based on AFCD’s past records, dissolved oxygen levels of 4 mg/L or
higher at surface level would not cause any notable impact to mariculture operation
in general.
Overall, the mariculture operation at the Project site and other proposed
FCZs would result in limited change in dissolved oxygen and the predicted
dissolved oxygen level would comply with the corresponding WQO criterion
stipulated under Table
3.5. Also the
proposed mariculture operation at the Project site is not expected to result in
significant deterioration of dissolved oxygen levels at the surrounding waters
and identified WSRs.
Predicted
levels of total inorganic nitrogen were generally low in the assessment
area. Predicted levels at WSRs were
generally around 0.1 mg/L to 0.2 mg/L, which are lower than the WQO criterion
of 0.3 mg/L for Mirs Bay. Similar levels
were recorded at nearby EPD Marine Water Quality Monitoring Stations shown in Table
3.2. The differences between baseline and project
scenarios were predicted to be limited at WSRs away from proposed new FCZ sites
at the Project site and other locations.
The
mariculture operation at the Project site would result in slight increase in
total inorganic nitrogen at the surrounding water. As shown in Table
3.2,
the predicted levels of total inorganic nitrogen at B2 increased from 0.16 mg/L
to 0.21 mg/L. The predicted levels of
total inorganic nitrogen at CR5, CR6 and CR7 increased from 0.14 mg/L, 0.16
mg/L and 0.15 mg/L to 0.19 mg/L, 0.21 mg/L and 0.19 mg/L respectively. For the amphioxus habitat within or near the
Project Site, the predicted levels total inorganic nitrogen at the representative
location of AM1 are 0.14 mg/L and 0.17 mg/L respectively under baseline and
project scenarios. Since the predicted
levels of total inorganic nitrogen were lower than the WQO criterion of 0.3
mg/L for Mirs Bay at these nearby WSRs, no unacceptable change in levels of
total inorganic nitrogen would be expected.
At the
Project site, the predicted levels of total inorganic nitrogen increased from
0.12 mg/L to 0.15 mg/L at the northern part and from 0.14 mg/L to 0.17 mg/L at
the southern part, which are both below the corresponding assessment criterion
in WQO. No unacceptable elevation in
total inorganic nitrogen is expected from the proposed mariculture operation at
the Project site.
Overall,
the proposed mariculture operation at the Project site is not expected to
result in significant increase in total inorganic nitrogen levels at the
surrounding waters and identified WSRs.
Given the
small increase in total inorganic nitrogen level due to the operation of the
Project, the corresponding predicted increase in unionized ammonia is also
small. The increases at all WSRs between
the baseline and project scenarios in unionized ammonia levels were either
undetectable or at most 0.002 mg/L. The
predicted levels of unionized ammonia were at or below 0.010 mg/L at all
identified WSRs, which is below the assessment criterion of 0.021 mg/L. Predicted levels of unionized ammonia were
0.005 mg/L at the northern part of the Project site and 0.006 mg/L at the
southern part of the Project site in baseline scenario, and project operation
would result in increase of 0.001 mg/L.
No unacceptable elevation in unionized ammonia is expected from the
proposed mariculture operation at the Project site.
Predicted
levels of suspended solids varies spatially across the assessment area, ranging
from 1 to 6 mg/L. There is limited or no
change for the predicted levels between baseline and project scenarios at all
identified WSRs. Predicted SS level at
Project Site was 1.4 mg and 1.3 mg/L at the northern and southern parts of the
Project Site under baseline scenario scenarios.
Project operation would result in an increase of at most 0.1 mg/L only
in both parts of the Project Site. The
predicted levels of suspended solids for the nearby corals CR5, CR6, CR7 and
non-gazetted beach B2 were in the range of 1.3 mg/L to 1.4 mg/L. None of the identified WSR showed change in
SS levels that exceeded assessment criterion of 30% change level in baseline
level. No unacceptable change in
suspended solids level to the identified WSRs is expected.
Predicted
levels of chlorophyll-a also vary spatially across the assessment area, ranging
up to around 20 µg/L. Similar to the case of dissolved oxygen,
chlorophyll-a levels are generally higher at surface level and thus area with
shallower depth tends to have higher chlorophyll-a levels. The differences between baseline and project
scenarios were predicted to be limited at WSRs away from proposed new FCZ sites
at the Project site and other locations.
No exceedance of chlorophyll-a criterion was
predicted at all identified WSRs. No
unacceptable water quality impact on chlorophyll-a is expected from the
mariculture operation.
In both
baseline and project scenarios, the predicted levels of E.coli around the Project site were predicted to be very low
because of the lack of major sources of E.coli
(e.g. sewage). Since faecal pollution of
dogs/ cats is not expected within the Project site ([16]),
the operation of fish farm at the Project site will not introduce additional E.coli loading and thus the prediction
under baseline and project scenarios are the same. Further discussion on sewage and wastewater
generation from staff and visitors onsite is provided under Sections
3.8.4
and 3.8.5
below.
As
discussed under Section 2.6.2.3, subject to the mariculture proposal submitted
by future applicant and approval by AFCD, IMTA culture may be adopted at the
Project Site to (1) enhance productivity and (2) reduce environmental impact by
utilizing waste feed and other waste from the fish stock onsite. Given the uncertain nature of its
implementation (e.g. trophic levels / species involved / other designs), the
effect on the pollution loading from these non-fish secondary trophic level(s)
has not been taken into account in the pollution loading estimation for the
proposed mariculture operation at the Project Site. The following section provides a simple
analysis on the potential impact on pollution loading estimation from these
non-fish trophic level.
Deposit
feeders in IMTA typically feed on wasted feed, fecal matters and other waste
sink from the fish stock on top. This
means their presence would reduce the pollution loading from waste feed and
fish faeces from the mariculture operation.
According to the pollution loading estimation provided under Table
4.16 of Appendix 3A, the combined
contribution of these two sources of pollution from mariculture would be over
90% of all pollution from mariculture for all parameters except for ammonia-N
(which is mainly contributed from fish excretion). Since these deposit feeders will only consume
and assimilate the organic part of these waste, therefore the introduction of
deposit feeders could potential affect about 13.9% of the total nitrogen
budget, 67.4% of the total phosphorus budget and 100% of the 5-day biochemical
oxygen demand budget.
Table 3.7 Pollution Loading Contribution from Wasted Feed
and Fish Faeces for Production Level of 1 ton at Proposed FCZs
Sources |
Wasted
Feed |
%
Contribution |
Fish
Faeces |
%
Contribution |
Total %
Contribution |
Total |
Oxidized-N (g/day) |
0.0968 |
7.1% |
1.205 |
88.6% |
95.7% |
1.3597 |
Ammonia-N (g/day) |
0.0415 |
0.0% |
0.371 |
0.2% |
0.2% |
236.0373 |
Org-N (g/day) |
21.9176 |
57.4% |
16.265 |
42.6% |
100.0% |
38.1865 |
TIP (g/day) |
0.0394 |
2.3% |
1.624 |
95.7% |
98.0% |
1.6969 |
TOP (g/day) |
2.6986 |
76.8% |
0.813 |
23.1% |
100.0% |
3.5119 |
BOD (g/day) |
45.2051 |
8.4% |
495.095 |
91.6% |
100.0% |
540.3082 |
TSS (g/day) |
24.6477 |
92.2% |
- |
|
92.2% |
26.7298 |
Filter
feeders, including oysters, clams and mussels, which are commercially
cultivated feed on planktons or suspended organic matters. According to Jansen et. al. (2019) ([17]),
biodeposit represents a significant pathway in bivalve nutrient recycling. Jansen
et. al. reviewed a number of literature for mussel farming and indicated
biodeposition rate could be up to around 10% of soft body weight of the mussel
population in a culture area. The
biodeposit could constitute of 0.3% to 2.3% of nitrogen and 0.08% to 0.3%
phosphorus. Since biodeposit is solids
and could sink to the bottom, a significant portion of the nutrient would be
lock up and will not return to the water column quickly. Furthermore, the growth of fleshy tissues of
these bivalves also lock up a notable amount of organic nutrients from the
water column. For instance, Jansen et. al. reviewed a number of literature
for nutrients composition in mussel tissue, which constitutes of 33.3% to 62.3%
of organic carbon, 5.5% to 12.6% of organic nitrogen and 0.4% to 1.2% of
organic phosphorus. While these figures
are indicative of only several species covered in the review and may vary from
species, locations and cultivation method, this still support the notion of
additional cultivation of filter feeders would result in a net reduction of
pollution load from the water column, thus be beneficial to the water quality.
Overall,
the inclusion of IMTA would result in different levels of pollution reduction
from the proposed mariculture operation at the Project Site by means of (1)
reduction of wasted feed, fecal matters and other waste, and (2) filter feeding
of plankton and biodeposition.
Table 3.8 Predicted
Water Quality under Baseline and Project Scenario
ID |
WSR |
Scn. |
Annual |
||||||||
10th-percentile |
Mean |
||||||||||
Depth-averaged |
Bottom |
Depth-averaged |
Bottom |
Depth-averaged |
|||||||
Dissolved Oxygen |
Total Inorganic Nitrogen |
Unionized Ammonia |
Chlorophyll-a |
Suspended Solids |
E.coli Note2 |
||||||
(mg/L) |
(mg/L) |
(mg/L) |
(mg/L) |
(mg/L) |
(mg/L) |
(µg/L) |
(mg/L) |
(no./100 mL) |
|||
Non-gazetted
beach – Mirs Bay Assessment Criteria |
≥4 |
≥2 |
N/A |
N/A |
≤0.3 |
≤0.021 |
N/A |
increase ≤30% baseline |
≤610 |
||
B2 |
Non-gazetted beach of Nam She Wan |
Baseline |
4.2 |
3.3 |
6.0 |
5.6 |
0.16 |
0.008 |
4 |
1.5 |
0 |
Project |
4.0 |
3.0 |
5.8 |
5.3 |
0.21 |
0.010 |
4 |
1.6 |
0 |
||
B3 |
Non-gazetted beach of Tung Wan |
Baseline |
5.2 |
5.0 |
6.1 |
6.0 |
0.18 |
0.007 |
2 |
1.2 |
0 |
Project |
5.2 |
4.9 |
6.1 |
5.9 |
0.18 |
0.007 |
2 |
1.3 |
0 |
||
B4 |
Non-gazetted beach of Tai Wan |
Baseline |
5.1 |
4.2 |
6.0 |
5.7 |
0.18 |
0.008 |
1 |
1.2 |
0 |
Project |
5.1 |
4.2 |
6.0 |
5.7 |
0.19 |
0.008 |
2 |
1.2 |
0 |
||
B5 |
Non-gazetted beach of Ham Tin Wan and
Sai Wan |
Baseline |
5.2 |
4.5 |
6.1 |
5.9 |
0.17 |
0.007 |
1 |
1.3 |
0 |
Project |
5.2 |
4.5 |
6.1 |
5.9 |
0.17 |
0.007 |
1 |
1.3 |
0 |
||
Coral
– Mirs Bay Assessment Criteria |
≥4 |
≥2 |
N/A |
N/A |
≤0.3 |
≤0.021 |
N/A |
increase ≤30% baseline |
≤610 |
||
CR3 |
Coral at Port Island |
Baseline |
5.2 |
5.1 |
6.4 |
6.2 |
0.07 |
0.003 |
4 |
1.5 |
0 |
Project |
5.2 |
5.1 |
6.4 |
6.2 |
0.08 |
0.003 |
5 |
1.6 |
0 |
||
CR4 |
Coral at Shek Ngau Chau |
Baseline |
5.2 |
5.2 |
6.2 |
6.0 |
0.15 |
0.005 |
1 |
1.3 |
0 |
Project |
5.2 |
5.2 |
6.1 |
6.0 |
0.15 |
0.006 |
2 |
1.3 |
0 |
||
CR5 |
Coral at Nam She Wan |
Baseline |
5.1 |
4.5 |
6.1 |
6.0 |
0.14 |
0.005 |
3 |
1.3 |
0 |
Project |
4.9 |
4.3 |
6.0 |
5.9 |
0.19 |
0.007 |
3 |
1.4 |
0 |
||
CR6 |
Coral at Nam She Wan |
Baseline |
4.3 |
4.2 |
6.0 |
5.7 |
0.16 |
0.007 |
2 |
1.3 |
0 |
Project |
4.2 |
3.7 |
5.8 |
5.5 |
0.21 |
0.009 |
3 |
1.4 |
0 |
||
CR7 |
Coral at Nam She Wan |
Baseline |
5.2 |
4.5 |
6.1 |
5.9 |
0.15 |
0.006 |
3 |
1.3 |
0 |
Project |
5.1 |
4.3 |
6.0 |
5.8 |
0.19 |
0.008 |
3 |
1.4 |
0 |
||
Coral
– Tolo Harbour and Channel Assessment Criteria |
N/A |
N/A |
≥4 |
≥4 |
N/A |
N/A |
≤6 |
≤10 |
≤610 |
||
CR13 |
Coral at Hoi Ha Wan Moon Island |
Baseline |
5.1 |
4.5 |
6.2 |
6.0 |
0.09 |
0.004 |
3 |
1.4 |
0 |
Project |
5.0 |
4.3 |
6.1 |
5.9 |
0.11 |
0.004 |
4 |
1.5 |
0 |
||
CR14 |
Coral at Hoi Ha Wan Coral Beach |
Baseline |
5.2 |
4.3 |
6.3 |
6.0 |
0.08 |
0.004 |
4 |
1.6 |
0 |
Project |
5.1 |
4.3 |
6.2 |
5.9 |
0.10 |
0.005 |
5 |
1.7 |
0 |
||
CR16 |
Coral at Heung Lo Kok |
Baseline |
5.1 |
4.4 |
6.2 |
6.0 |
0.09 |
0.004 |
3 |
1.4 |
0 |
Project |
5.0 |
4.3 |
6.1 |
5.9 |
0.10 |
0.004 |
4 |
1.5 |
0 |
||
Fish
Culture Zone – Mirs Bay Assessment Criteria |
≥5 |
≥2 |
N/A |
N/A |
≤0.3 |
≤0.021 |
≤20 |
increase ≤30% baseline |
≤610 |
||
F4 |
Tap Mun Fish Culture Zone |
Baseline |
5.4 |
5.2 |
6.5 |
6.4 |
0.08 |
0.003 |
4 |
1.5 |
0 |
Project |
5.4 |
5.2 |
6.5 |
6.4 |
0.10 |
0.004 |
5 |
1.6 |
0 |
||
F5 |
Kau Lau Wan Fish Culture Zone |
Baseline |
6.0 |
5.4 |
6.6 |
6.5 |
0.09 |
0.004 |
6 |
1.7 |
0 |
Project |
5.6 |
5.4 |
6.6 |
6.5 |
0.12 |
0.004 |
7 |
1.8 |
0 |
||
F6 |
Sham Wan Fish Culture Zone |
Baseline |
5.5 |
5.0 |
6.5 |
6.3 |
0.09 |
0.004 |
8 |
2.2 |
0 |
Project |
5.3 |
4.9 |
6.5 |
6.2 |
0.11 |
0.005 |
9 |
2.4 |
0 |
||
Site A |
Proposed Wong Chuk Kok Hoi FCZ Note3 |
Baseline |
4.0 |
2.9 |
5.8 |
5.2 |
0.10 |
0.006 |
6 |
2.0 |
0 |
Project |
4.0 |
2.8 |
5.8 |
5.1 |
0.13 |
0.008 |
7 |
2.1 |
0 |
||
Site B |
Proposed Outer Tap Mun FCZ |
Baseline |
5.2 |
4.2 |
6.3 |
5.8 |
0.10 |
0.004 |
3 |
1.4 |
0 |
Project |
5.2 |
4.2 |
6.2 |
5.7 |
0.12 |
0.005 |
4 |
1.5 |
0 |
||
Site C1 (Northern part of Project site) |
Proposed Mirs Bay FCZ (Northern Part) |
Baseline |
5.2 |
4.2 |
6.1 |
5.7 |
0.12 |
0.005 |
3 |
1.4 |
0 |
Project |
5.1 |
4.2 |
6.1 |
5.6 |
0.15 |
0.006 |
3 |
1.4 |
0 |
||
Site C2 (Southern part of Project site) |
Proposed Mirs Bay FCZ (Southern Part) |
Baseline |
5.2 |
4.3 |
6.1 |
5.8 |
0.14 |
0.006 |
2 |
1.3 |
0 |
Project |
5.1 |
4.2 |
6.0 |
5.7 |
0.17 |
0.007 |
2 |
1.4 |
0 |
||
Mangrove
Stand / Intertidal – Mirs Bay Assessment Criteria |
≥4 |
≥2 |
N/A |
N/A |
≤0.3 |
≤0.021 |
N/A |
increase ≤30% baseline |
≤610 |
||
M7 |
Mangrove Stand / Intertidal at Tai Tan |
Baseline |
6.0 |
5.7 |
7.0 |
6.9 |
0.04 |
0.002 |
16 |
3.1 |
0 |
Project |
6.0 |
5.6 |
7.1 |
7.0 |
0.05 |
0.003 |
19 |
3.6 |
0 |
||
M8 |
Mangrove Stand / Intertidal at To Kwa Peng |
Baseline |
5.6 |
4.8 |
6.7 |
6.5 |
0.03 |
0.002 |
19 |
4.4 |
0 |
Project |
5.5 |
4.5 |
6.8 |
6.4 |
0.04 |
0.003 |
22 |
5.0 |
0 |
||
M9 |
Mangrove Stand / Intertidal at Chek Keng |
Baseline |
4.8 |
4.2 |
6.4 |
6.2 |
0.05 |
0.004 |
24 |
5.7 |
0 |
Project |
4.4 |
3.9 |
6.4 |
6.1 |
0.06 |
0.005 |
27 |
6.5 |
0 |
||
M10 |
Mangrove Stand / Intertidal at Ham Tin Wan |
Baseline |
5.2 |
4.5 |
6.1 |
5.9 |
0.17 |
0.007 |
1 |
1.3 |
0 |
Project |
5.2 |
4.5 |
6.1 |
5.9 |
0.17 |
0.007 |
1 |
1.3 |
0 |
||
Mangrove
Stand / Intertidal – Tolo Harbour and Channel Assessment Criteria |
N/A |
N/A |
≥4 |
≥4 |
N/A |
N/A |
≤6 |
≤10 |
≤610 |
||
M6 |
Mangrove Stand / Intertidal at Hoi Ha Wan |
Baseline |
5.2 |
4.5 |
6.3 |
6.1 |
0.08 |
0.004 |
4 |
1.6 |
0 |
Project |
5.0 |
4.3 |
6.2 |
6.0 |
0.10 |
0.004 |
5 |
1.7 |
0 |
||
Marine
Park – Tolo Harbour and Channel Assessment Criteria |
N/A |
N/A |
≥4 |
≥4 |
N/A |
N/A |
≤6 |
≤10 |
≤610 |
||
MP2 |
Hoi Ha Wan Marine Park and Artificial Reef within
the Marine Park |
Baseline |
5.2 |
4.6 |
6.2 |
6.0 |
0.09 |
0.004 |
4 |
1.5 |
0 |
Project |
5.1 |
4.4 |
6.2 |
5.9 |
0.11 |
0.004 |
4 |
1.6 |
0 |
||
Artificial
Reef – Mirs Bay Assessment Criteria |
≥4 |
≥2 |
N/A |
N/A |
≤0.3 |
≤0.021 |
N/A |
increase ≤30% baseline |
≤610 |
||
AR1 |
Artificial Reef in Long Harbour |
Baseline |
5.2 |
4.4 |
6.2 |
5.9 |
0.12 |
0.005 |
3 |
1.4 |
0 |
Project |
5.1 |
4.3 |
6.1 |
5.8 |
0.15 |
0.006 |
4 |
1.5 |
0 |
||
AR2 |
Artificial Reef in Long Harbour |
Baseline |
5.2 |
4.8 |
6.3 |
6.0 |
0.11 |
0.004 |
4 |
1.5 |
0 |
Project |
5.2 |
4.4 |
6.2 |
5.9 |
0.14 |
0.005 |
4 |
1.6 |
0 |
||
AR3 |
Artificial Reef in Long Harbour |
Baseline |
5.1 |
4.2 |
6.2 |
5.8 |
0.12 |
0.005 |
3 |
1.4 |
0 |
Project |
4.7 |
4.2 |
6.1 |
5.7 |
0.15 |
0.006 |
4 |
1.5 |
0 |
||
AR4 |
Artificial Reef in Long Harbour |
Baseline |
5.2 |
4.3 |
6.3 |
5.9 |
0.11 |
0.005 |
4 |
1.6 |
0 |
Project |
5.2 |
4.2 |
6.2 |
5.8 |
0.14 |
0.005 |
5 |
1.7 |
0 |
||
AR5 |
Artificial Reef in Long Harbour |
Baseline |
5.2 |
4.2 |
6.3 |
5.7 |
0.11 |
0.005 |
5 |
1.6 |
0 |
Project |
5.1 |
4.1 |
6.2 |
5.6 |
0.14 |
0.006 |
5 |
1.8 |
0 |
||
AR6 |
Artificial Reef in Long Harbour |
Baseline |
5.1 |
4.2 |
6.2 |
5.7 |
0.11 |
0.005 |
5 |
1.8 |
0 |
Project |
4.7 |
3.7 |
6.1 |
5.5 |
0.13 |
0.006 |
6 |
1.9 |
0 |
||
Amphioxus
Habitat – Mirs Bay Assessment Criteria |
≥4 |
≥2 |
N/A |
N/A |
≤0.3 |
≤0.021 |
N/A |
increase ≤30% baseline |
≤610 |
||
AM1 |
Amphioxus Habitat |
Baseline |
5.2 |
4.3 |
6.1 |
5.8 |
0.14 |
0.006 |
2 |
1.3 |
0 |
Project |
5.1 |
4.2 |
6.0 |
5.7 |
0.17 |
0.007 |
2 |
1.4 |
0 |
||
SSSI
– Tolo Harbour and Channel Assessment Criteria |
N/A |
N/A |
≥4 |
≥4 |
N/A |
N/A |
≤6 |
≤10 |
≤610 |
||
SSSI1 |
Hoi Ha Wan SSSI |
Baseline |
5.1 |
4.3 |
6.2 |
5.9 |
0.09 |
0.004 |
3 |
1.4 |
0 |
Project |
5.1 |
4.3 |
6.1 |
5.8 |
0.11 |
0.005 |
4 |
1.5 |
0 |
||
EPD
Marine WQ Monitoring Stations Assessment Criteria |
N/A |
N/A |
N/A |
N/A |
N/A |
N/A |
N/A |
N/A |
N/A |
||
TM8 |
EPD Marine WQ Monitoring Station |
Baseline |
5.2 |
4.2 |
6.2 |
5.8 |
0.07 |
0.003 |
3 |
1.5 |
0 |
Project |
5.1 |
4.2 |
6.2 |
5.6 |
0.08 |
0.004 |
4 |
1.6 |
0 |
||
MM6 |
EPD Marine WQ Monitoring Station |
Baseline |
5.2 |
4.4 |
6.3 |
6.0 |
0.11 |
0.005 |
4 |
1.5 |
0 |
Project |
5.2 |
4.3 |
6.2 |
5.8 |
0.14 |
0.005 |
4 |
1.6 |
0 |
||
MM17 |
EPD Marine WQ Monitoring Station |
Baseline |
4.3 |
3.3 |
5.9 |
5.2 |
0.10 |
0.004 |
3 |
1.5 |
0 |
Project |
4.3 |
3.2 |
5.9 |
5.1 |
0.11 |
0.005 |
3 |
1.5 |
0 |
Note1: Values in exceedance of the corresponding assessment criteria are bold and shaded.
Note2: WQO criterion for E.coli is only applicable to fish culture zones, bathing beaches as well as secondary contact recreation subzone. Given secondary contact recreation subzone covers significant area around the Project Site and is represented by a lot of WSRs in this list, the criterion is deemed applicable to these WSRs groups as well.
Note3: In the EIA for the proposed new FCZ at Site A, it is assumed that measure to increase dissolved oxygen level would be taken by mariculturists as necessary. For details, Please refer to the corresponding EIA.
In
general, relocation of fish rafts adopting advanced mariculture technologies
are not necessary under adverse weather (e.g. typhoon) given the framework of
fish cages would use weather-resistant and durable materials (e.g. HDPE cages,
steel truss cages). For other potential
circumstances (e.g. red tide event, outbreak of fish disease), the licensees
will review the need of fish raft relocation and propose the fish raft
relocation plan as necessary for agreement with AFCD on a case-by-case basis,
depending on the type of algal bloom (any toxicity to fish), expected duration
of such circumstances, feasibility for early harvesting of fish stock,
feasibility of implementing onsite control measures etc. In case fish raft relocation is considered
necessary, the fish rafts will be relocated away from the areas of
circumstances, avoid marine fairways and utilities and at some distance away
from ecological and fisheries sensitive receivers (e.g. about 200 m away from
established coral communities) to minimise potential impacts to these sensitive
receivers. Such relocation will be
temporary (e.g. a few weeks) and the fish rafts will return to the Project site
upon the cease of the circumstances.
Given the temporary nature of the fish raft relocation and the
sufficient buffer distance to the ecological and fisheries sensitive receivers,
unacceptable water quality impacts to these sensitive receivers near the
relocated sites are not anticipated. In
addition, the relocated pollution load from these mariculture operation would
likely be distributed at a wider area around the proposed site. As shown in the water quality modelling
exercise, the presence of additional pollution load from the mariculture
operation at 5683.5 ton of standing stock at the proposed site would not result
in notable change in water quality. If
some of the mariculture operation is temporarily relocated, the associated
pollution load would likely to be more spread out and the potential change in
water quality would be less significant.
The relocation would involve anchoring and de-anchoring, which would
result in minor disturbance to the bottom sediment as assessed under Section
3.7. In general, the water depth
around Mirs Bay is more than 15 m. Given
the sufficient water depth at the surrounding water, sufficient clearance from
the seabed is expected from the structure of fish fam during the relocation,
and thus sediment disturbance is not expected during the relocation. Based on the above assessment, given the
temporary nature of the fish raft relocation, relocation to be sited minimising
the impacts to sensitive receivers, pollution load would spread out and
potential change in water quality would be less significant than normal
operation, the potential impacts due to temporary relocation of fish rafts
under circumstances are expected to be minor.
The
results of the water quality simulations indicated that the proposed
mariculture operation would only result in very limited and very localized
changes of water quality parameters at identified WSRs, including recreational
areas, marine parks, existing and proposed FCZs, ecological habitats (including
amphioxus), spawning ground and nursery area of commercial fisheries resources
and other fisheries sensitive receivers, artificial reefs, intertidal areas of
various country parks, and beaches. For
all WSRs identified except Site A, the water quality parameters were predicted
to be in compliance with the corresponding WQO criteria, and project operation
would not result in notable deterioration.
The low dissolved oxygen levels at Site A were predicted under baseline
scenario and were not shown to deteriorate (i.e. reduce) under the Project
scenario. Therefore, it is concluded
that the proposed mariculture operation at the carrying capacity of 5683.5 ton
of standing stock or below would not result in unacceptable change in water
quality at the nearby WSRs. The
licensees will adopt the operational measures and best practice for mariculture
activities as stated in Appendix
2A to further minimise water quality
impacts from the mariculture activities of the Project.
The
use and storage of chemicals would be limited to pharmaceuticals for fish, as
well as those required to maintain equipment for the fish farm operation. Mariculturists at the Project site would be
required to strictly observe the requirement under Cap. 529 Veterinary
Surgeons Registration Ordinance and have strict control on prescription
drugs. In addition, the mariculturists
will follow the rules for using fish drugs as described in Good Aquaculture
Practices published by AFCD ([18]) which detail the appropriate
dosage of drugs and prohibit the use any fish drugs not prescribed by AFCD or
registered veterinarian. AFCD will also
provide technical support on the use of pharmaceuticals for fish. In AFCD’s regular inspection of existing FCZs
in recent years, there was no identified case of excessive storage of drugs or
pharmaceuticals. Therefore, it is
expected that there would be very limited pharmaceuticals for fish kept onsite
and those would be stored at secured locations, and discharge of water
containing pharmaceuticals is not expected from daily operation. In view of the above, the risk of spillage of
fish drugs or pharmaceuticals is low.
Unlike
spillage of chemical, spilled/ excess fish feed with feed additives generally
does not persist for considerable amount of time as the presence of fish feed
with feed additives would attract existing fish population to feed on the spill
feed. For floating type fish feed, the
majority of feed spilled can simply be recovered by the mariculturists. Commercially available fish feed with feed
additives comes in tough fabric bags of 20-25 kg each. In case such bags of feed dropping into the
sea during storage or transportation, they will be recovered by the crew. Even if not recovered, the bag would limit
the exchange materials such that the nutrient content would unlikely be
released all at once and result in significant water quality impact. In view of this, together with the adoption
of the operational measures and best practice for mariculture activities as
stated in Appendix 2A,
the risk and consequence of such scenario are deemed minimal and no
unacceptable impact on water quality is expected.
Disinfection
of culture gears (primarily nets and cages) is required for disease control on
regular basis (e.g. once a year prior to the start of fish farming cycle). According to AFCD’s recommendation for good
practice ([19]), disinfection could be done via
steaming, or submerge under water dosed with formaldehyde or bleach within
enclosed containers. For any fishing
gears that need to be disinfected onsite, solution of any chemical used will be
required to be stored properly onsite and disposed of by licensed contractor
and no onsite disposal would be allowed.
It should be noted that disinfection under
sunlight is considered more effective and practical option for cultural gears
of large size and chemicals are not necessary to be dosed. In addition, based on the past experience of
existing FCZs, it is not necessary to store and use a large amount of chemicals
during FCZ operation. Therefore, it is
not anticipated a large amount of chemicals would be stored and disposed during
the operation of the Project.
Deep
water mariculture operation at the Project site is typically manned minimally
onsite and relies mostly on automated / remote control. Therefore, generation of sewage by staff and
visitors onsite would be limited. Sewage
shall be stored on vessels or at the mariculture facilities and be regularly
disposed by licensed contractor, and no sewage from
staff and visitors will be discharged into the sea.
Storage of chemicals / lubricant oil onsite would be
maintained at minimal level. If
maintenance of gears or machineries onsite is needed, technicians / relevant
staff should be brought to the site together with the necessary tools and
chemicals. Remaining chemicals, together
with any chemical waste generated from the maintenance process should be taken
away by the same crew for disposal to appropriate facilities or licensed
contractor when the crew leave the site.
Given the limited exposure period as well as proper storage and control, together
with the adoption of the operational measures and best practice for mariculture
activities as stated in Appendix
2A,
no unacceptable change in water quality associated with the storage of
chemicals onsite is expected.
Latest mariculture operation often
rely on renewable sources of energy (solar and wind), supplemented by minor
backup generator for prolonged cloudy / windless period. Limited amount of fuel may be stored onsite. To minimize potential risk of fuel spillage,
fuel should be stored at sheltered and secure location for each mariculture
operation. Excessive storage of fuel
should be prohibited onsite as a risk control measure. Given the limited storage as well as other
safety measures regarding proper storage, together with
the adoption of the operational measures and best practice for mariculture
activities as stated in Appendix
2A,
no unacceptable change in water quality associated with the storage of fuel
onsite is expected.
Increased
marine traffic would be anticipated at the Project site for moving of staff and
visitors and goods (fish feed and gears, waste and produced fish etc.). Such marine traffic activities would not
result in notable change in water quality.
To ensure no sewage from staff and visitors be discharged into the sea,
sewage should be stored on vessels or at the mariculture facilities and be
regularly disposed by licensed contractor.
Littering in the sea is an offence under Cap. 228 Summary Offences Ordinance and all staff and visitors
should be warned against littering in the sea.
Unacceptable water quality impacts due to the increased marine traffic,
boating and visitor activities are not anticipated.
No marine
work or other major source of pollution is expected from the construction phase
of the Project. It is unlikely there
will be a significant workforce presence during construction phase (because of
the lack of major works to be conducted), and any sewage / wastewater generated
should be collected at the transportation / work vessel(s) for disposal at
appropriate facilities on land.
During
operation, the licensees will adopt the operational measures and best practice
for mariculture activities as stated in Appendix
2A. Apart from these
measures, the following precautionary/ mitigation measures should be
implemented to minimize water quality impact from the proposed mariculture
operation at the Project site:
n
Standing stock should not exceed
5683.5 ton of standing stock at any given time.
AFCD will ensure the production scale of the Project site will not
exceed the maximum standing stock level by controlling the mariculture
production scale permitted under individual license.
n
Only pellet feed or alternative
feed with better feed conversion ratio will be permitted within the proposed
FCZ.
n
No chemically-laden solution from
culture gears disinfection should be discharged into the sea.
n
Onsite storage of chemicals should
be controlled and minimized as far as practicable. Excess chemicals as well as chemical waste
generated should be removed from the site at appropriate facilities by licensed
contractor as soon as possible.
n
Fuel storage onsite should be
minimized, and if needed, be located at sheltered and secure location.
n
Littering of the sea should be
prohibited.
No marine
work or other major source of pollution is expected from the construction phase
of the Project. No unacceptable
construction phase water quality impact is expected.
Modelling
results indicated that compliance with WQO criterion is achieved at most of the
water sensitive receivers, and no project contribution to exceedance in
baseline scenario would be expected from the operation phase of the
Project. No unacceptable operation phase
water quality impact is expected.
No marine
work or other major source of pollution is expected from the construction phase
of the Project. No unacceptable
cumulative construction phase water quality impact is expected.
For
operation phase, the water quality modelling assessment has already taken into
account the following sources of pollution:
n
mariculture operation at the Project
site;
n
mariculture operation at existing
FCZs within Mirs Bay and Tolo Harbour and Channel ([20]);
n
proposed mariculture operation at
Site A (Wong Chuk Kok Hoi) and Site B (Outer Tap Mun);
n
dry weather flow (i.e. pollution
load from land drainage) within Mirs Bay and Tolo Harbour and Channel;
n
rainfall-related load within Mirs
Bay and Tolo Harbour and Channel;
n
treated sewage effluent from the
Sha Tau Kok Sewage Treatment Works; and
n
other sources including pollution
load from the Guangdong side of Mirs Bay.
The
assessment confirmed that no unacceptable cumulative water quality impact is
expected.
With the
implementation of proposed mitigation / precautionary measures, the
construction and operation of the Project would not result in unacceptable
change water quality at and around the Project site. Environmental monitoring is considered not
necessary for construction of the Project.
For project operation, water quality monitoring is recommended when the
standing stock is expected to achieve 75% of the
carrying capacity ([21]) (i.e. 5683.5 ton x 75% =
4262.6 ton) or when the standing stock is expected to
achieve 95% of the carrying capacity (i.e. 5683.5 ton x 75% = 5399.3 ton) for at least a month in a fish farming cycle to ensure no unacceptable change in water quality at the nearby water
sensitive receivers. Detailed
recommendations would be provided in the stand-alone Environmental Monitoring
and Audit Manual of this EIA.
In
additional to the standard EM&A exercise under EIAO, AFCD will conduct regular water quality
monitoring within and outside the Project site during Project operation to
check the water quality (e.g. suspended solids and
nutrients) for detection of abnormality and issuance of alerts to
mariculturists as part of the management measures for the Project. Real
time water quality monitoring stations will also be installed by AFCD at the
Project site, and notification to mariculturists for the Project site will be
implemented to ensure timely actions be taken.
With reference to AFCD’s previous installation of real time water
quality monitoring stations at the other existing FCZs including Tung Lung Chau
FCZ, Sok Kwu Wan FCZ and Lo Tik Wan FCZ, mariculturists there will be alerted
in case of substantial deterioration of water quality (e.g. red tide, low
dissolved oxygen level). Monitoring
parameters would include temperature, salinity, and dissolved oxygen (level and
saturation).
No marine
work or other major source of pollution is expected from the construction phase
of the Project. No unacceptable
construction phase water quality impact is expected.
Carrying
capacity estimation at the Project site has been conducted to determine the
production scale that would not result in an unacceptable change in water
quality. The carrying capacity
estimation indicated the Project site can support mariculture operation of
5683.5 ton of standing stock based on typical mariculture practice in HK
without significant deterioration of water quality under the typical average
condition. Accordingly, the
corresponding pollution load generated is calculated for subsequent Delft3D
modelling.
Delft3D
water quality modelling has been conducted to predict the potential change in
water quality at the WSRs of the Assessment Area. Compliance with WQO criterion is achieved at
most of the identified water sensitive receivers, and no project contribution
to exceedance in baseline scenario is expected from the proposed mariculture
operation at the Project site. The
results indicated project operation would not result in a significant change in
water quality with 5683.5 ton of standing stock. Unacceptable water quality impact from
Project operation is not anticipated.
Other
potential sources of water quality impacts from operation have been identified
and assessed. Appropriate precautionary
and mitigation measures have been recommended to minimise the potential water
quality impact from these sources. The
licensees will also adopt the operational measures and best practice for
mariculture activities as stated in Appendix
2A. No unacceptable adverse
impact on water quality is expected from Project operation.
([1]) The entirety of the Tolo Harbour and Channel WCZ as well as the nearshore waters of the Mirs Bay are categorized as Secondary Contact Recreation Subzone. The predicted water quality at these area are represented by other WSRs and thus do not have the respective WSRs for Secondary Contact Recreation Subzone only. Specifically, all WSRs identified under this Study except Site C, CR3, CR4 and AM1 are located within Secondary Contact Recreation Subzone.
([2]) Amphioxus is commonly found in the eastern water of Hong Kong and is considered an areal WSR like Secondary Contact Recreation Subzone and some others. As stated in S.3.4.3.2(vii) of the Study Brief, amphioxus habitat to the east of Ko Lau Wan should be considered as WSR under this Study. To identify the location of amphioxus habitat, benthic survey was conducted under this Study and identified the species’s presence in some locations within and around the proposed site. For modelling assessment, one observation point AM1, located close to benthic survey location MB9 which is the only station with amphioxus presence recorded in both seasons, was chosen as representative location for detailed assessment. This point is also located within the project boundary, and thus would provide conservative representation of potential impact for other amphioxus habitat locations at further away.
([3]) Similar to the case of Secondary Contact Recreation Subzone, ecological habitat for finless porpoise is an areal WSR with wide coverage. The predicted water quality at these areas are represented by other WSRs and thus do not have the respective WSRs for ecological habitat for finless porpoise only. Note that according to the latest AFCD Marine Mammal Monitoring Report 2021/22, no records of finless porpoise were recorded in the assessment area.
([4]) Similar to the case of Secondary Contact Recreation Subzone and ecological habitat for finless porpoise, spawning ground and nursery area of commercial fisheries resources is an areal WSR with wide coverage. The predicted water quality at these areas are represented by other WSRs and thus do not have the respective WSRs for spawning ground and nursery area of commercial fisheries only. Specifically, WSRs located within nursery area of commercial fisheries resources include CR3, CR13-CR14, CR16, AR1-AR6, F4, F5, F6, Site A, Site B, M6-M9, MP2 and SSSI1. Only one WSR (Site A) is located within spawning ground of commercial fisheries resources.
([5]) Chan, A.L.K, Choi, C.L.S., McCorry, D.,
Chan, K.K., Lee, M.W. and Ang, P. (2005) Field Guide to Hard Corals of Hong
Kong. 1st edition (Eds. Chan, W.C. and Stokes, E.). Friends of the
Country Parks and Cosmos Books Ltd, Hong Kong. 373 pp.
([6]) AFCD (2013) Distribution. Available at: https://www.afcd.gov.hk/english/conservation/con_wet/con_wet_man/con_wet_man_dis/con_wet_man_dis.html
[accessed on 12-07-2022]
([7]) Wong et.al. (2012).
Project WATERMAN Carrying Capacity of Fish Culture Zones in Hong Kong –
Technical Note TN-2012-02
([8]) Sim SY, Rimmer MA, Toledo JD, Sugama
K, Rumengan I, Williams KC, Phillips MJ (2005). A Practical Guide to Feeds and
Feed Management for Cultured Groupers. NACA, Bangkok, Thailand. 18pp.
([9]) FAO (2012). Transition from
low-value fish to compound feeds in marine cage farming in Asia. Fisheries and
Aquaculture Technical Paper No. 573
([11]) “Leachage” refers to the release
of dissolvable content from materials passing through the water column.
([12]) DIR-191/2009 Sediment Removal at
Yim Tin Tsai, Yim Tin Tsai (East) Fish Culture Zones and Shuen Wan Typhoon
Shelter.
([13]) Surface treatment like waterproofing and rush
control is typically necessary for floating facilities such as fish rafts. By using material with surface treatment
completed offsite (e.g. in a factory or workshop), the time required for onsite
works can be reduced.
([14]) Carrying capacity is defined as the maximum
standing stock of a FCZ without significant
deterioration of water quality under the typical average condition. It is a measurement of standing stock, i.e.
amount of biomass of fish being kept on site.
([15]) Table 3.8 also include prediction at nearby EPD Marine Water Quality Monitoring Stations for reference. These EPD Marine Water Quality Monitoring Stations are not WSRs.
([16]) The service provided by dogs and
cats in traditional fish rafts is expected to be no longer needed in the more
modern mariculture operations. Also,
these new mariculture operation is not expected to be manned continuously, thus
no longer suitable for keep dogs and cats onsite.
([17]) Henrice Maria Jansen, Řivind Strand,
Wouter van Broekhoven, Tore Strohmeier, Marc C. Verdegem, and Aad C. Smaal
(2019) Feedbacks from Filter Feeders: Review on the Role of Mussels in Cycling
and Storage of Nutrients in Oligo- Meso- and Eutrophic Cultivation Areas.
([20]) Note that other mariculture
operation outside of Mirs Bay and Tolo Harbour and
Channel are also taken into account indirectly through model nestling for
generation of boundary condition of water quality boundary.
([21]) From the modelling results, the 95th-percentile safety margin
of the carrying capacity, which is a conservative estimate taking into account
possible fluctuations in the weather, hydrodynamic and environmental conditions
as well as the farming practices, is about 75% of the estimated carrying
capacity under typical average condition.
Therefore, it is considered representative to
conduct operational water quality monitoring at 75% of the maximum allowable
standing stock level to monitor potential water quality at the
surrounding sensitive receivers during project operation.