Water quality and eutrophication in the Guangzhou Sea Zone of the Pearl River estuary

To gain a better understanding of water quality and eutrophication, we investigated the seasonal and spatial distribution of water quality at 17 stations in the Guangzhou Sea Zone (GZSZ). Nutrients, chlorophyll-a (Chl-a), salinity, chemical oxygen demand, and other physical and chemical parameters were determined in February, May, August and October from 2005 to 2007. The concentrations showed ranges of 93.2-530.4 mu mol/L for dissolved inorganic nitrogen (DIN), 0.62-3.16 mu mol/L for phosphate (PO4-P) and 50-127 mu mol/L for silicate (SiO3-Si). The results indicated that DIN was strongly influenced by domestic sewage coming from Guangzhou City and NO3-N was the main form of DIN in most areas, while concentrations of phosphate and silicate were generally controlled by Pearl River runoff, land-based sources along the land or islands, and algae assimilation. N/P ratios were very high in both dry season and wet season, and varied from 57 to 667, suggesting that P was potentially the most limiting nutrient in the GZSZ. The concentrations of Chl-a were 3-96 mu g/L, and were highly correlated with the distribution characteristics of COD. The concentrations of nutrients have increased over the past two decades (1982-2007). This means it is necessary to control the input of nutrients to the GZSZ, especially that of phosphate.