Integrated mean concentration and integrated export coefficient and their application in Hong Kong

Red tides and eutrophication have been frequently observed over the past two decades in costal waters around Hong Kong, which are caused by many factors. More researches and control programs in the past are performed on the point source pollution, while few on the nonpoint source pollution (NSP) in Hong Kong due to the lack of NSP data and information. By making use of monthly river water quality measurements, precipitation and runoff data, and other related information, the characteristics of NSP and the nutrient concentration and export coefficient were investigated and estimated for Hong Kong region. First, through analyzing the observed data from 11 hydrological stations in Hong Kong in 1997 and 1998, it shows that there are very distinct wet and dry seasons in Hong Kong region, the average annual runoff coefficient is 0.66. Then, the mean concentration and export coefficient of pollutants for different land uses of Hong Kong region are determined. Because of the fact of the rivers in Hong Kong are short, small and plenty, the integrated mean concentration and integrated export coefficient, which can reflect the influence of mixed land uses, are proposed and applied to each Hong Kong Water Control Zone (WCZ) and the entire Hong Kong region. The results show that the river water quality is better during flood, middle in wet season, and worst in dry season; and the mean concentration can better reflect the basic characteristics of NSP than export coefficient does in Hong Kong.