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

Abstract

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-1, those of dissolved total phosphorus (DTP) from 0.028 to 0.054 mg L-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-1; those of total organic carbon from 1.92 to 2.59 mg L-1; those of chlorophylla from 1.58 to 7. 53 mg m-3 with an average value of 4.69 mg m-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 NO3-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.