Effect of Soil and Water Loss on Water Eutrophication in Xiaojiang River Basin in Three Gorges Reservoir Region

Soil and water loss is an important source of water eutrophication. In this study, soil erosion were measured in the four types of cultivated lands (Paddy land, Terraced farmland, Sloping farmlands <; 25°, and Sloping farmlands ≥ 25°) in Xiaojiang River basin, Chongqing of China. In addition, water qualities were investigated in 5 reaches of Xiaojiang River (Qukou, Yanglu, Gaoyang, Huangshi, and Shuangjiang) at various times (April, June, July, and November) in 2008. The results showed that (1) Soil and water loss was mainly result from sloping farmlands in Xiaojiang River Basin; (2) Soil and water loss made major contribution to eutrophication in Xiaojiang River. In the study area, the annual losses of TN and TP through soil and water loss from farmlands accounted for 45.7 % and 40.2% of the total TN and TP import of Xiaojiang, respectively; (3) TN and TP concentrations in Xiaojiang River were seriously exceeded the criteria of eutrophication at the sampling times; (4) The phenomenon of “water blooming” occurred in June 2008, one month early when the peak TN concentrations occurred. This may be attributed to interaction of other environmental factors, such as suitable hydrological conditions, temperature and light radiation; (5) TN and TP concentrations in Xiaojiang River were mostly controlled by both soil and water loss and the Yangtze River. And TP concentrations showed obviously seasonal variations. Our study demonstrates that nutrients losses from farmland can be effectively controlled by appropriated management practices, such as the shift of the sloping farmlands to terraced farmlands, proper application of fertilizers, and so on.