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SECTION
5 ASSIMILATIVE CAPACITY CAPITAL STOCK
| 5.2 |
Assimilative
Capacity of Marine Waters |
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Pressures
on Natural Assimilative Capacity
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| 5.2.3.7 |
Two
types of human modifications to natural
water bodies, other than pollutant inputs,
can result in changes to the assimilative
capacity functions of local waterbodies:
constraining water circulation (most commonly
in Hong Kong through reclamation), and reducing
flows of clean water through the system.
These modifications are discussed below
using local examples from Victoria Harbour
and Deep Bay.
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| 5.2.3.8 |
During
the past decades of reclamation the width
of the narrowest portion of Victoria Harbour
has been halved (Plan D Drawing TSR 94/1568)
yet the volume of wastewater discharges
to the harbour has increased dramatically.
The constrained nature of the waterbody
is now visually manifested in its severe
wave climate which has resulted in difficulties
in navigational usage. Water quality data
also indicate that the harbour itself and
areas of the WCZs which flank the harbour
(including parts of Junk Bay, Eastern and
Western Buffers, and Southern WCZ) have
worsening levels of faecal pollution despite
increased efforts to improve wastewater
treatment. The dispersion of over 2 million
cubic metres of sewage each day discharged
into the harbour is thus clearly limited
by the physical dimensions of the receiving
waterbody and is resulting in the consistent
recording of elevated bacterial levels.
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| 5.2.3.9 |
A
different issue is manifested in Deep Bay.
This waterbody has a naturally poor flushing
capacity which is exacerbated by heavy pollutant
inputs from agricultural and urban sources
on both sides of the bay and a reduction
in the natural freshwater flow that would
normally assist in driving water out of
the inner bay. In fact, in the dry season
when natural flows are lowest, the quantities
of discharged effluents may exceed the natural
flow volumes (Peking University 1995). As
a result of these conditions, Deep Bay experiences
significant organic, faecal pollution and
levels of ammoniacal nitrogen which may
be toxic to marine life. Continued development
in the river catchments draining to the
Bay (particularly the Shenzhen River) are
predicted to significantly increase pollutant
loadings in the next 10 years without specific
action to control, divert and treat wastewaters
(Hyder 1998). This is of particular concern
given the proximity of the Mai Po and Inner
Deep Bay Ramsar site and the presence of
shellfish culture activities in the area.
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| 5.2.3.10 |
While
these two examples are perhaps the most extreme
cases in Hong Kong, they illustrate the importance
of considering impacts to assimilative capacity
when making decisions regarding changes in
landforms or water abstraction rates. Further
discussion of the issues of reclamation/land
supply and freshwater resources can be found
in Sections 3.2 and 3.4, respectively. |
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| Pressures
on Assimilative Capacity Enhancers |
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| 5.2.3.11 |
As
discussed above, the assimilative capacity
of marine waters depends on the pollutant
inputs, the natural flushing and dispersion
of the system, and any anthropogenic enhancements
of the system through environmental infrastructure
or other programmes. With Hong Kong's large
and dense population, the provision of treatment
facilities for sewage is one of the most effective
ways of enhancing assimilative capacity features.
This provision is proceeding but is hampered
by delays in providing connections to large
treatment facilities. As a result, a number
of major flows, and many minor flows, are
discharged directly to the sea. Under the
HKSARG's High Priority Programme (HPP), 17
of 27 Sewerage Master Plan works have been
completed (the remainder are in progress),
and approximately $5.3 billion is committed
over the next five years to improve sewerage
systems not covered by the HPP (HKSARG 1999).
These actions are expected to significantly
reduce the volume of direct marine discharges
over time. |
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| 5.2.3.12 |
Perhaps
the most obvious pressure on society's ability
to enhance assimilative capacity is paying
for the cost of building and operating environmental
infrastructure. At present, Hong Kong operates
a sewage charging scheme and a trade effluent
surcharge scheme for certain industry/commercial
premises. While these schemes to a degree
implement the polluter pays principle for
wastewater, they are designed to recover only
the operating and maintenance costs of the
facilities. Under a full-cost recovery scheme,
capital costs for sewerage and sewage treatment
works, which are substantial, would also be
reflected in the charging scheme. The existing
Hong Kong scheme therefore undervalues the
true cost of wastewater collection, treatment
and disposal, such that while there is some
incentive for dischargers to reduce pollutant
flows and loads, this incentive is diluted
by the omission of capital costs and the partial
recovery of operation and maintenance costs
(ERM 1997d). |
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