Distribution of nutrients and chlorophylla in the Three-Gorges Reservoir, China

The Three-Gorges Reservoir (TGR) is one of the largest water conservancy projects in the world. The status of nutrients and phytoplankton biomass has changed since the Three-Gorges Reservoir started water storage on June 1, 2003. The distribution features of nutrients and chlorophylla were determined by cruise monitoring during September 8-15, 2003. The results showed that the concentrations of dissolved total nitrogen (DTN) range from 1.01 to 1.35 mg L^sup -1^, those of dissolved total phosphorus (DTP) from 0.028 to 0.054 mg L^sup -1^. The concentrations of dissolved nitrogen and phosphorus exceed the eutrophication standards of OECD, and the ratio of DTN to DTP is over 16:1. It is shown that phosphorus is an eutrophication-limiting element in the water body. The concentrations of potassium range from 2. 80 to 3.44 mg L^sup -1^; those of total organic carbon from 1.92 to 2.59 mg L^sup -1^; those of chlorophylla from 1.58 to 7. 53 mg m^sup -3^ with an average value of 4.69 mg m^sup -3^ at surface layer. A trophic gradient could be observed from the oligotropher to the mesotropher in the flow direction. Phytoplankton biomass increased significantly in the reservoir area than before. A significant positive correlation (p < 0. 05,r = 0.728 ) between chlorophylla and NO^sub 3^-N and a significant negative correlation (p < 0. 01,r = -0.9207) between chlorophylla and turbidity were also observed. Distribution features could be well divided into three clusters in terms of systematic cluster analyses, including the upper-stream area cluster, the middlestream area cluster and the down-stream area cluster.[PUBLICATION ABSTRACT]