Nutrients in the Changjiang and its tributaries

Dissolved and particulate, organic and inorganic N, P and Si were measured in the main stream and 15 major tributaries of the Changjiang (Yangtze River) in April-May 1997. The nutrient concentrations are related to water discharge, suspended particulate matter, anthropogenic activities etc. The nutrient levels were quite low in the upper reaches, and significantly increased in the main stream in a region of 2000-3000 km inland from the river mouth. The northern tributaries contribute more nutrients to the Changjiang than the southern tributaries. Based on atomic ratios of N, P and Si, the limiting nutrient in the Changjiang drainage basin was P. The nutrient yields in the Changjiang and its major tributaries indicated high rates of transport of nutrients within the watersheds. Concentrations of nitrate in the Changjiang have increased, but there have been no systematic trends for phosphate and silicic acid since 1980. The DIN/P ratios and DIN/Si ratios increased. The DIN/P and DIN/Si ratios may be expected to continue to increase after construction of the "Three Gorges Dam", which will exercise a great deal of influence on the ecological environment of the Changjiang estuary and its adjacent sea.