Water Quality Issues

Sediment Quality Issues

Due to the enclosed nature of this zone, water quality declines from the outer areas (Channel Subzone) through the Buffer Subzone to the inner, Harbour Subzone. Widespread and significant increases in total nitrogen and total inorganic nitrogen were detected in 1997, potentially as a result of increased land run-off from unusually high rainfall. Whilst all seven monitoring stations have complied with the WQO for E. coli (from 1988 to 1997), full compliance with the WQO for DO was only achieved at 3 stations, though compliance in 1997 was improved over 1996 levels.

Detectable long term (1988-1997) trends in water quality included increasing DO levels at three monitoring locations, decreasing turbidity at one site and decreasing BOD₅ at two sites. These improvements are largely attributed to pollution reduction measures under the Tolo Harbour Action Plan.

In 1997, WQOs for DO, NH₃ -N and E. coli were all achieved although large increases in total nitrogen were observed throughout the zone and the WQO for TIN was not met at any of the 19 monitoring stations. Conversely, phosphorus levels reduced by around half compared with 1996 inputs. WQOs for DO, NH₃ -N and E. coli have all been met since 1993.

Long term water quality trends include increasing levels of E. coli at three stations in the vicinity of Lamma Island, potentially due to untreated sewage discharges. Also, ortho-phosphate levels have shown an increasing trend between 1988 and 1997 at six monitoring stations. A decreasing long term trend in BOD₅ levels has been observed at three stations between Lamma and Hong Kong Islands.

The water quality of this WCZ in 1997 was generally good, particularly in the outer part of the zone away from development inputs at Sai Kung which accounted for slightly higher levels of E. coli, faecal coliforms, and BOD₅ at two inner stations. Ammoniacal nitrogen, TIN and total N levels rose significantly at all stations in 1997, although total phosphorus levels decreased and DO levels increased at all stations compared with 1996. WQOs for DO, TIN, NH₃ -N and E. coli have all been met between 1995 and 1997.

Only temperature (increase) and pH (decrease) have shown widespread long term changes. More localised trends include increased DO at one station, decreased BOD₅ at one site and reduced turbidity at three stations.

Junk Bay is a small WCZ with only two routine monitoring stations. 1997 data show that the zone is characterised by turbid water with high levels of inorganic nutrients and sewage bacteria. Both E. coli and faecal coliform levels increased significantly from 1996, as have total nitrogen, ammoniacal nitrogen and TIN levels. The WQO for DO was complied with in 1997 (and from 1993-1995), and the WQO for NH₃ -N has been met since 1993. 1997 was the first year since 1993 that the WQO for TIN (average) was not complied with. Elevated levels of PAHs detected at the monitoring site in inner Junk Bay.

Increasing sewage inputs to Junk Bay have resulted in continued long term trend increases in E. coli and faecal coliforms. Both monitoring stations showed significant long term increases in ortho-phosphate and temperature and the outer station shows a long term increase in ammoniacal nitrogen. Marine water quality in this WCZ is therefore of concern.

Deep Bay forms a sheltered body of water between North West Hong Kong and Shenzhen with three monitoring stations in the inner subzone and two in the outer subzone. The inner subzone is heavily polluted with inorganic nutrients, E. coli and faecal coliforms from river inputs. Compared with 1996, the situation has improved with higher DO and lower E. coli, phosphorus and all forms of nitrogen. In the outer area, however, total nitrogen and ammoniacal nitrogen levels increased. Although 3 of the 5 stations complied with the WQO for DO, the average compliance for the zone was 60%. None of the stations complied with the WQO for TIN, although only one station (innermost) failed to meet the WQO for NH₃ -N (80% overall compliance).

Long term and zone-wide trends of increasing E. coli and TIN levels were observed as well as declines in DO at two stations and increases in ammoniacal and total nitrogen at two other stations. These trends in water quality are of concern in terms of their impact on the conservation value and mariculture industry of the Bay.

Two sites in Inner Deep Bay were found to have high levels of nutrient (total phosphorus) in the sediments.

High levels of copper and zinc were identified between 1993 and 1997 in inner Deep Bay sediment.

Elevated levels of PAHs were detected at two monitoring sites in inner Deep Bay.

Mirs Bay WCZ forms an extensive area of generally good water quality to the east of Hong Kong and includes 16 monitoring sites. The area of poorest water quality is Starling Inlet, the closest point of the zone to land, where E. coli levels in 1997 were the highest recorded since 1991. Across the zone TIN levels were much greater in 1997 than the previous year. Full compliance (all stations) with the WQO for DO was achieved in 1996 and 1997, whilst all stations have been compliant with WQOs for TIN and NH₃ -N since 1993.

No long term water quality changes have been detected on a zone-wide basis. There has been a long term increase in chlorophyll-a at five stations and an increase in sewage indicator bacteria at the station in Starling Inlet.

This WCZ lies between Lantau Island and the North Western part of Hong Kong's New Territories, and includes 5 monitoring stations. 1997 data show E. coli and faecal coliform levels to be highest near sources of sewage discharge, and the highest levels in the last 5 years. Levels of total nitrogen and total Kjeldahl nitrogen also increased significantly from those in 1996. Four of the stations complied with the WQO for DO in 1997 resulting in 80% compliance compared with 100% for the previous two years. 80% compliance with the WQO for TIN was also achieved in 1997 and full compliance with NH₃ -N has been achieved since monitoring started in 1988.

Long term nutrient inputs from the Pearl River appear to be increasing as TIN levels have risen for 3 stations from 1988-1997 to a level only just within the WQO. Increasing trends in orthophosphate levels and nitrate nitrogen levels have also been identified at two stations. E. coli and faecal coliform levels have also increased at the easternmost station close to sources of sewage inputs.

This zone, which has four monitoring stations, extends from the western coast of Hong Kong island, northwards between Victoria Harbour and Lantau Island to Tsing Yi in the north. In 1997 water quality in the south of the zone was better than in the north which is subject to more sewage inputs. Throughout the zone, there were some increases in E. coli and faecal coliform levels (particularly in the north) compared with 1996 and significant increases in nitrogen levels, due to an increase in organic nitrogen sources. Nevertheless, WQOs for DO continue to be met (as they have since 1995) and WQOs for TIN and NH₃ -N have been met since 1988.

Long term increases in sewage indicator bacteria are the most notable water quality trend throughout this zone. Three stations also show increases in depth-averaged water temperature and declines in total volatile solids between 1988 and 1997.

Victoria Harbour has fourteen monitoring stations located within the zone which occupies the marine area between Hong Kong Island and Kowloon. The zone is subject to heavy pollutant loadings from 12 sewage outfalls and water quality in 1997 was poorest near to those points. All stations recorded a large increase in nutrient levels in 1997 though all but 2 stations had reduced levels of chlorophyll-a compared with 1996. Whilst the zone was 100% compliant with the WQO for NH₃ -N (and has been since 1988), only 36% compliance with the WQO for TIN was achieved. However, there was an improvement in DO in 1997 with all but one station achieving compliance (91% overall compared with 27% in 1996).

Long term trends include a rise temperature in all but one station, increases in E. coli levels at seven stations and a decreasing trend for BOD₅ at five stations between 1988 and 1997.

High negative Eh values in sediment principally from sewage, commercial and industrial discharges. Also, high levels of ammoniacal nitrogen and total sulphide in Victoria Harbour may result in further toxicity under these anaerobic conditions.

Serious contamination of sediment with chromium and copper was found in Tsuen Wan Bay, Rambler Channel and Kwun Tong (also nickel and zinc). The likely source is waste effluents from textile, printed circuit board and electroplating industries. Elevated PAH levels at all monitoring stations were detected.