Hong Kong

Abstract

The Hong Kong Special Administrative Region of southeast China has a total land area of 1042 km2 and encompasses 235 islands of varying sizes. It is affected by an unusual combination of water masses which not only keeps the coastal waters of Hong Kong warm and maintains the local sub-tropical/tropical biotic communities, but also allows temperate species to survive. It is greatly affected by freshwater dilution from both heavy rainfall during monsoons, and from the Pearl River which has an annual flow of 308 billion m3, from a drainage area of 228,000 km2. These may lower the salinity of the western and northwestern approaches to 1 to 7‰, while the eastern and northeastern waters remain virtually unaffected. These conditions create sheltered, estuarine environments to the west, exposed, oceanic environments to the east, and a transitional zone in the middle, typified by the Victoria Harbour region. Species surviving are both euryhaline and eurythermal, and able to tolerate highly sedimented waters. These natural stresses also make the marine fauna and flora much more susceptible to pollution stresses. Nevertheless, there is considerable plant life, including mangroves, and the bird life associated with sheltered shore and mangroves is of considerable international significance. There is heavy use of the marine environment. A pronounced decline in demersal fish stocks in the South China Sea due to over-fishing has occurred. The sea receives over 2 million m3 of waste water per day, and at present about 80% of Hong Kong's sewage is largely untreated. About 75% enters Victoria Harbour directly, representing a daily BOD loading of over 300 tonnes. As a result, many of Hong Kong's beaches are contaminated, especially along the western shores of the New Territories. There are some signs of a trend of improving beach water quality in general, but there are also increasing signs of harmful algal blooms. The huge volume of sea traffic in Hong Kong, with considerable paint stripping and painting, results in the release of chemical contaminants and biocides, e.g. tributyltin (TBT); the latter leading to concentrations of 53,000 and 18,300 ng Sn g-1 in sediments, which exceed typical levels recorded elsewhere. Farming practices have become more specialized, resulting in large increases in application of chemical fertilizers and pesticides. Crop and livestock farms are large sources of nutrient-rich and pesticide-laden run-off, the former being considered the culprit in an increasing number of red tides. Some pesticides include compounds that have been banned in Hong Kong (e.g. DDT), which are attributable to contamination sources in the Chinese mainland. Indeed, the annual discharge of the Pearl River accounts for over 85% of the total nutrient input to the local waters of Hong Kong. Rapid urban development has exerted an unprecedented pressure on the local marine environment. Large-scale reclamation has altered current patterns, reduced tidal flushing and caused hypoxia/anoxia in many areas. During 1991 to 1999, a total of 366 million m3 of dredged spoil was disposed into coastal waters, and the new port and airport development involved the dredging of 880 million m3 of fill materials, and the dumping of 380 million m3 of dredged materials within a very small coastal area, affecting fisheries resources, coral, seagrass, benthos and water quality. Health issues, including PSP and ciguatera intoxication are a problem, and some 3 to 7% of shellfish samples contain unacceptably high levels of PCB and Σ DDT. Some important wildlife areas are now protected. Habitats such as mudflats are increasingly scarce in south China; there are only 23 remaining sites with intertidal mudflat habitats within 800 km of Hong Kong. The large Mai Po/Deep Bay Ramsar site is one such, and is described.