Western Waters

[Photo of Lung Kwu Chau Marine Park]

Hong Kong's Western Waters consist of two adjoining Water Control Zones: the Deep Bay WCZ and the North Western WCZ. Deep Bay borders Shenzhen and is a shallow, sediment-laden bay into which flows the Shenzhen River. The Bay is an ecologically important one, with the Mai Po and Inner Deep Bay Ramsar site a wetland area famed for its thousands of migratory birds, and recognised as a wetland of international importance under the Ramsar Convention. Oyster culture is also a feature of Deep Bay. As for the North Western WCZ, it is heavily influenced by the outflow of the Pearl River.

 

[Photo of A Chinese white dolphin found in Hong Kong's Western Waters ]

[Photo of Construction of the Hong Kong-Shenzhen Western Corridor (a bridge across Deep Bay) ]

There is a marine park located around Lung Kwu Chau (Lung Kwu Chau Marine Park), and the WCZ is also home to the beautiful Chinese white dolphin. Dolphin-watching here has become a very popular activity in recent years.

 

 

Deep Bay WCZ

Unfortunately, rapid developments in Shenzhen and on the Hong Kong side of the northwestern New Territories have seriously affected the WCZ's water quality over the past twenty years. In the 1980s and early 1990s, monitoring stations detected rising levels of E.coli bacteria and 5-day biochemical oxygen demand (BOD5), due to sewage and livestock waste pollution. The bay began facing serious problems of increasing nutrient and organic enrichment, hypoxia, ammonia toxicity and bacterial contamination, which together threatened its sensitive ecology and oyster culture industry.

 

Pollution flows into the bay from the catchments and rivers on both the Hong Kong and Shenzhen sides. This has resulted in poor water quality especially in Inner Deep Bay, which typically records high levels of suspended solids (SS), turbidity, organic matter (BOD5 and chemical oxygen demand), nutrients (nitrogen and phosphate) and E. coli bacteria. However, the data for BOD5, SS and nitrogenous nutrients shows a distinctly decreasing gradient from Inner Deep Bay to Outer Deep Bay, indicating that pollutants are being gradually diluted as they move out to sea.

 

Following concerns arising from deteriorating water quality, in 1992 a Deep Bay (Shenzhen Bay) Action Plan was formulated by the former Hong Kong Guangdong Environmental Protection Liaison Group (EPLG) (renamed in 2000 as the Hong Kong-Guangdong Joint Working Group on Sustainable Development and Environmental Protection). The aim of this joint initiative from both sides of the border was to address the range of pollution issues that were threatening the bay's ecosystem. In 1998 the EPLG declared that one of its long-term goals would be to reduce pollution entering Deep Bay, and in 1999 a Deep Bay Water Pollution Control Joint Implementation Programme was formulated. In 2000, both parties to the Programme agreed on a 15-year plan to clean up Deep Bay which would reduce pollution loads from existing sources and control future pollution so that the water in the area could maintain its assimilative capacity by 2015. The plan would be reviewed every five years. Both sides are now jointly developing a mathematical model that will act as an analytical tool for managing the water environment of the Pearl River Estuary.

 

Most of the pollution which originates in Hong Kong is the result of discharges from livestock farms and unsewered villages. The EPD has been active in enforcing pollution control legislation in the Northwestern New Territories. Particularly important has been its implementation of the Livestock Waste Control Scheme, introduced in 1987 and amended in 1994. This Control Scheme bans the keeping of livestock in areas designated as Prohibition Areas. The Scheme has significantly reduced the number of livestock farms in the New Territories and imposed effluent treatment standards on those which remain. To further reduce pollution from livestock farms, the Government introduced the Voluntary Surrender of Poultry and Pig Farm Licence Schemes in 2005 and 2006 respectively. These provide incentives for livestock farmers to give up their farming licences, for which they will receive financial compensation. In addition, the implementation of Sewerage Master Plans for all of Hong Kong has been of benefit, as the Government has gradually extended its public sewer network to hundreds of previously unsewered villages, a scheme which will continue over the next decade.

[Photo of Decline of water quality in Deep Bay (1986-2005) ]

 

By 2005, however, the water quality of Deep Bay remained generally poor, particularly in the inner bay area. Typically it showed high levels of organic and inorganic pollutants, and low levels of dissolved oxygen. The levels of nitrogen compounds in Deep Bay remained the highest of any recorded across Hong Kong's waters.

 

WQO compliance rates in the Deep Bay WCZ over the past two decades have consistently been below 50%. In 2005, the overall compliance rate for the Deep Bay WCZ was just 33%. The entire WCZ failed to meet the total inorganic nitrogen (TIN) objective, and the two innermost stations in the bay also failed to comply with the dissolved oxygen objective. Unionised ammonia, which is toxic to marine organisms, was also recorded at above WQO levels except in the outer reaches of the bay.

 

Sediment samples for the Deep Bay WCZ show generally elevated levels of arsenic, most of which are greater than the Lower Chemical Exceedance Level (LCEL). The reasons for this may be related to the naturally high arsenic levels in the soil of the northern New Territories.

 

North Western WCZ

Due to the effect of the Pearl River, the North Western WCZ has historically experienced higher levels of TIN, particularly to the west closest to the river's outflow. In 2005, for example, TIN levels approached the WQO in the eastern parts of the WCZ, but exceeded them in other areas. In addition to this, the WCZ is affected by local discharges, in particular those from the Pillar Point Sewage Treatment Works, as well as discharges from village houses in unsewered areas.

 

Over the years that the EPD has monitored this WCZ, it has recorded long-term increases in ammonia nitrogen and TIN at its stations along the Urmston Road (the water channel between Lung Kwu Chau and Tap Shek Kok), which appear to be from a combination of local discharges and Pearl River flow. Rises in levels of E. coli have also been recorded at the two stations on the perimeter of the WCZ. The rise of E. coli on the eastern side could be the result of the station's proximity to the HATS discharge in Victoria Harbour (see Chapter Seven), while the rise on the western side was recorded near the sewage outfall at Black Point, which discharged increasing flows from the San Wai Sewage Treatment Works in recent years.

 

Hong Kong International Airport, one of the largest infrastructure projects ever undertaken in Hong Kong, was built on an island reclaimed from Chek Lap Kok and Lam Chau, both within the North Western WCZ. To reclaim the land, as much as 250 million cubic metres of material was dredged in a period of three years (1993 -1995) to create an island of 1,248 hectares. During the reclamation period, there was a not unexpected increase in suspended solids and turbidity levels in the WCZ, especially near the airport reclamation site. Normal levels resumed, however, after completion of reclamation in 1996.

[Photo of Levels of Suspended Solids at a station near the airport reclamation site]

By contrast with the Deep Bay WCZ, the North Western WCZ achieved an overall WQO compliance of 89% in 2005, having remained above 80% for most of the 1980s and 1990s. All stations complied with the dissolved oxygen and unionised ammonia WQOs. Only the two westernmost stations, closest to the Pearl River which carries high levels of nitrogen, did not comply with the WQO for total inorganic nitrogen.