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SECTION
5 ASSIMILATIVE CAPACITY CAPITAL STOCK
| 5.3 |
Assimilative
Capacity of Freshwater Systems |
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| 5.3.3 |
Impacts
and Resource Constraints |
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| 5.3.3.1 |
The
principal impact upon freshwater quality
and assimilative capacity in Hong Kong's
watercourses is pollutant loadings from
anthropogenic sources. These sources include
point discharges such as untreated sewage
discharges, dumping of waste, release of
toxic wastewaters from industrial and commercial
sources and discharges of agricultural wastes
including bacterial, organic and pesticide
chemical wastes. However, non-point discharges
also form a significant source of contamination,
both to freshwater systems which typically
receive the inputs first and then later
as pollutants are transferred to marine
waters. These discharges include run-off
from urban areas, in particular from roads,
and they typically contain toxic substances
such as PAHs and oils as well as elevated
suspended solids loadings. Without adequate
collection and treatment of run-off from
such paved areas, the growth in Hong Kong's
road system presents an increasing source
of water pollution. Other non-point sources
include leached groundwater from industrial
facilities, waste disposal areas (eg landfills)
and other contaminated sites (see discussion
on blackspots in Paragraph 3.2.2.8 - 3.2.2.9)
where spillages or historical mis-handling
of chemicals has resulted in dispersion
of pollutants into soils and surrounding
surface and groundwaters.
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| 5.3.3.2 |
The
continued growth in Hong Kong's population
is the key driver behind much of the pollution
reaching freshwater systems. This pressure
has manifested itself as new development
which has outpaced the provision of appropriate
sewage treatment (and drainage) infrastructure
resulting in large discharges of untreated
wastewaters to rivers and streams. Urbanisation
has also caused alterations to surface water
run-off patterns and increased the potential
for pollution from construction activities.
In addition, whilst measures have been taken
to control and regulate pollution from industry
and agriculture (as well as changes in agricultural
intensity - see Section 3.3 - Agriculture
and Fisheries), organic and faecal wastes
from livestock farms are still a major cause
of pollution in many rivers in the Deep
Bay area. Unregulated waste disposal in
the past (see Paragraph 3.5.3.12), and the
contamination of soils and groundwaters
from former industrial land uses also poses
a threat to the longer term maintenance
of freshwater quality.
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| 5.3.3.3 |
Although
river water quality has improved for many
pollutant parameters across the SAR (see
Section 5.3.2), organic and faecal (E. coli)
pollution is the main reason for non-compliance
with WQOs in many watercourses. The water
quality in most rivers is poorer in the
lower reaches where dilution or flushing
capacity is reduced, where wastewater discharges
are typically greatest, or where the mouth
of the watercourse reaches marine waters
which are themselves polluted eg Kai Tak
Nullah at Kwun Tong Typhoon Shelter (Victoria
Harbour WCZ) and Yuen Long Creek adjoining
Deep Bay.
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| 5.3.3.4 |
The
freshwater systems in the Deep Bay water control
zone continue to receive large inputs of pollutants
from untreated sewage and agricultural wastewaters.
The impacts of these discharges (as well as
others, eg from the Shenzhen River) not only
affects the water quality and biodiversity
of these rivers and streams but is causing
marine water pollution in Deep Bay itself,
ecological impacts and damage to mariculture
operations (see Paragraphs 4.3.4.3, 5.2.3.9
and 5.2.1.15). This interaction between freshwater
and marine waters is also of concern elsewhere
in Hong Kong. Despite major reductions in
organic loadings to freshwaters, faecal pollution
remains a problem in many rivers and the discharge
of E. coli at bathing beaches appears to be
influencing the quality of beach waters and
can also have implications for public health. |
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| 5.3.3.5 |
The
natural assimilative capacity of freshwater
systems is also affected by physical changes
to river beds including man-made modifications
to watercourses (such as culverting or channelisation)
and through abstraction of water for purposes
such as agricultural irrigation which reduces
the amount of water available for dilution
of contaminants, and results in low water
flows during dry months. Although man-made
drainage provides assimilative capacity in
terms of flood protection (see Section 5.3.2),
it has potentially differing effects on water
quality by increasing flows during peak periods.
This is because although the water is conducted
away from the land by drainage infrastructure,
this reduces the assimilative capacity of
the land to absorb or retain pollutants, and
also means that during dry seasons, many rivers
and channels have low flows, often comprising
mainly of effluents. The development of new
flood protection and drainage works also has
potential impacts on areas of ecological importance
both through loss of habitat from construction,
but more significantly through long term changes
in the hydrological regime which can alter
drainage characteristics and wetland ecosystems,
particularly in important wetland areas such
as the north west New Territories. The training
and channelling of natural watercourses also
reduces ecological diversity of the river
systems. Illegal disposal of refuse and rubbish
into freshwatercourses, drainage channels
and nullahs is also common in many rural parts
of Hong Kong and poses a hazard to health
as well as impacting upon water quality and
general amenity of the areas affected. Littering
issues are further discussed in Paragraphs
3.2.2.10 (Land Use and Land Supply) and 4.3.2.9
(Terrestrial Habitats and Species). |
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