The Most Limiting Nutrient (Phosphorus) and Eutrophication in the Pearl River Estuarine Coastal Waters.
Kedong Yin1,3 and Paul J. Harrison2
1Department of Biology, 2AMCE (Atmospheric, Marine and Coastal Environment Program), Hong Kong University of Science and Technology, Kowloon, Hong Kong
3South China Institute of Oceanology, Chinese Academy of Science, Guangzhou, China
The Pearl River in southern China is ranked the second largest in China and 13th largest in the world by discharge volume. Since 1980th the Pearl River delta has gone through rapid population increase and economic growth. Time series of monitoring data showed periodic peaks of chl a and NO3 in summer in the estuarine coastal plume south of Hong Kong. Those peaks in chl a are relatively low (<20 µg l-1), but NO3 is relatively high (>20 µg l-1). The time series showed no increasing trend in NO3 and chl a over the past decade, although at present, NO3 from the Pearl River is very high, reaching 100 µM. Some historical data indicated that nitrogen loading in the coastal waters may have more than doubled since 1970. However, dissolved oxygen has not shown any decrease in the past few decades. Hypoxia appears to local and episodic, not region wide. A review of historical data revealed that PO4 concentrations have remained relatively low, below 1 µM over the past few decades. Low phosphorus concentrations might have been responsible for controlling eutrophication conditions in spite of high nitrogen loading. It appears that the most limiting nutrient concept can be expanded to the estuarine coastal ecosystem in terms of eutrophication status including not only algal biomass, but also dissolved oxygen or even phytoplankton species composition. Other coastal seas in China will be discussed briefly in terms of current eutrophication status.
