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SECTION
5 ASSIMILATIVE CAPACITY CAPITAL STOCK
| 5.3 |
Assimilative
Capacity of Freshwater Systems |
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| 5.3.1.9 |
Another
means of addressing local, and specific
river water quality patterns is through
examination of the compliance of river systems
with WQOs. Data for 1998 (EPD 1999c) show
that for five key WQOs set by EPD for inland
waters (pH, suspended solids, DO, COD and
BOD5), the least compliant rivers were those
within the Deep Bay WCZ. Whilst compliance
with pH was generally good, a number of
river systems within this WCZ showed poor
levels of compliance with the other four
WQOs. Several of the rivers in this WCZ
in the north west New Territories continue
to receive high organic pollutant inputs
from domestic sewage, livestock waste and
industrial effluents which explains the
high levels of organic pollution present.
Despite the reductions in organic pollution
to such river systems as a result of regulatory
measures and changes in agricultural practices
(see Section 5.3.3), levels of E. coli bacteria
(indicating faecal pollution) remain comparatively
high in both the Deep Bay streams as well
as a number of other rivers in each of the
other freshwater WCZs.
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| 5.3.1.10 |
Although
the water quality index provides an overview
of the water quality of freshwaters, only
a limited number of parameters are measured.
Water quality is also influenced by a range
of inorganic parameters including nutrients
and metals. The results of long term trend
analyses undertaken by EPD are shown for
a range of water quality parameters in Table
5.3b. The figures presented are the percentage
of water quality monitoring stations showing
a significant long term trend in the parameters.
| Table
5.3b Long Term Changes in Selected River
Water Quality Parameters |
Table
5.3b Long Term Changes in Selected River
Water Quality Parameters
| Water
Quality Parameter |
No.
Stations Showing a Significant Trend
|
%
Monitoring Stations Showing Long Term
Trends :
Increasing Trend |
%
Monitoring Stations Showing Long Term
Trends :
Decreasing Trend |
| Dissolved
Oxygen |
56 |
98.2% |
1.8% |
| Suspended
Solids |
50 |
2.0% |
98.0% |
| BOD5 |
52 |
1.9% |
98.1% |
| Ammonical
Nitrogen |
50 |
6.0% |
94.0% |
| Total
Phosphorus |
68 |
0% |
100% |
| Aluminium |
27 |
63% |
37.0% |
| Copper |
36 |
2.8% |
97.2% |
| Lead |
44 |
0% |
100% |
Source:Consultants
calculations based on monitoring stations
showing long term trends in river water
quality in EPD (1999c)
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| 5.3.1.11 |
The
data indicate that for all parameters except
Aluminium, where long term trends in water
quality were identified, these were of a
positive nature at a much greater number
of stations than those showing adverse changes
for each parameter. The trend in concentrations
of Aluminium was most prevalent in the Southern
(Mui Wo River), Port Shelter (Ho Chung River),
Junk Bay (Tseng Lan Shue Stream) and Victoria
Harbour WCZs (Sam Dip Tam Stream). It appears
that the prevalence of this metal may be
due to construction activities (eg piling)
and industrial discharges.
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| 5.3.1.12 |
Previous
reports on territorial water quality (PlanD
1993a) have noted the presence of high levels
of metals in watercourses in the north west
New Territories which were associated with
industrial wastewater discharges. However,
more recent data (EPD 1999c) suggest that
the concentrations of most metals in these
watercourses have declined, except for a long
term increase in copper (at 2 monitoring stations)
and zinc (1 station) in Yuen Long Creek and
aluminium and zinc (1 station each) in the
River Ganges. |
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