Southern Waters
The Southern Waters consist of one large WCZ,
the Southern Water Control Zone, which covers an area of around
400 km² located to the south of Hong Kong Island and to the
east of Lantau Island, directly open to the South China Sea. It
is a large expanse of open sea and as such enjoys good levels of
dissolved oxygen, but parts of it are affected by the discharge
from the Pearl River further to the west, in particular during the
wet summer months when the river's fresh water flow increases. The
northern part of the WCZ is influenced by the flow from Victoria
Harbour. In recent years, the rapid economic development of the
Pearl River Delta region has led to increased urbanisation and industrialisation,
and the river has carried higher levels of nutrients and pollutants
as a result. The western part of the Southern Waters shows some
symptoms that appear to be directly related to the Pearl River's
outflow.
A number of parameters are affected by the
Pearl River, including salinity, suspended solids (SS) and total
inorganic nitrogen (TIN). Typically, higher levels of SS and TIN
are found at the western stations than at those further east, while
the situation is the reverse for salinity. This phenomenon becomes
more obvious in the summer months.
[Photo of Averaged levels
of salinity, total inorganic nitrogen
and suspended solids at four stations
across the Southern WCZ during wet season
(April - September) of 2005]
In terms of WQO compliance, as the TIN levels
at most stations in the WCZ are relatively high, especially in the
summer, they exceed the WQO for this parameter. In the 1990s, the
WQO compliance rate for TIN was consistently below 20%, and even
in 2005 the only station to comply with the TIN objective was situated
in the far eastern side of the WCZ. Because of TIN, the Southern
WCZ achieved a relatively low overall WQO compliance level of 71%
in 2005. Similar levels have been recorded since 1991.
[Photo of Deep Water Bay Beach -one
of the beautiful beaches on the southern side of Hong
Kong Island that enjoy consistently
good water quality]
E. coli levels are generally low and
stable across the WCZ, mostly below 10 cfu/100mL. In 2005, the WCZ
achieved full compliance with the E. coli WQO. This included
all the secondary contact recreation subzones (i.e. the eastern
coast of Lantau Island and the south coast of Hong Kong Island),
indicating their suitability for windsurfing, sailing and other
water sports. In addition, over 20 popular beaches located within
the WCZ (on the southern part of Hong Kong Island and the outlying
islands of Lantau, Lamma and Cheung Chau) enjoyed consistently good
water quality. All these beaches achieved either 'Good' or 'Fair'
rankings in 2005.
However, in some places the bacteriological
water quality was affected by coastal sewage discharges, with long-term
increases in E. coli levels recorded at stations near Sok
Kwu Wan and Kau Yi Chau. The first of these is apparently being
affected by pollution from Sok Kwu Wan on Lamma Island, while the
latter seems to be related to the discharge from the Stonecutters
Island Sewage Treatment Works, in connection with the implementation
of HATS Stage 1.
Most of the Southern WCZ monitoring stations
are situated in open seas well away from urban areas, so sediment
samples at these stations tend to have lower levels of heavy metals
and toxic organics than many of those closer to the city.