Cathie S.W. Kueh
Water Policy and Planning Group, Environmental Protection Department, the Government of the Hong Kong Special Administrative Region

Abstract

Hong Kong's coastal marine water is under the influence of nutrient-rich Pearl River flow, pollution from local sources and those from the neighbouring Shenzhen. Between 1986 and 2000, an increase in inorganic nitrogen and phosphorus was observed in Deep Bay, parts of Southern water and some urban inshore areas. A rise in sewage bacteria E. coli in Victoria Harbour and Deep Bay was also found. During this period, the chlorophyll-a level in the water remained relatively stable. Available longer term data indicate that the coastal waters of Hong Kong may have experienced two cycles of heighten algal activity in the last 20 years, one in the 80s and another in the 90s, intercepted by a period of lower activity around 1991-1993.

Since the early 90s, there has been a wide-spread increase in chlorophyll-a, occurring at over 70% of the monitoring stations in most parts of the territory. While the diatom population remained relatively stable, dinoflagellates, small flagellates and other algal groups showed a distinct rise. Statistical analyses indicate that phytoplankton density was in general positively correlated with organic matter (BOD₅), total nitrogen and negatively correlated with total phosphorus, total inorganic nitrogen, orthophosphate, silicate and salinity. Relationships between nutrient parameters and phytoplankton groups in different water bodies will be discussed.