Analysis of phosphorus import characteristics of the upstream input rivers of Three Gorges Reservoir

Abstract

The phosphorus import of upstream rivers of Three Gorges Reservoir (TGR) significantly affects water environment of TGR. To recognize phosphorus import characteristics of the Yangtze River, the Jialing River, and the Wu River, the accumulated 10-year statistic data (2004–2013) of total phosphorus concentration were analyzed. Two water sampling campaigns at the critical sites in three upstream rivers were carried out in October 2014 and January 2015 to determine phosphorus fractions in water and suspended particulate. The results showed that there were different import characteristics of phosphorus component in three upstream rivers. The phosphorus concentration in water of Wulong site in the Wu Rivers exhibited a sharply increasing trend from 2004 to 2011, and it was much higher than that in the Yangtze River and the Jialing River after 2005. Besides agricultural nonpoint pollutions, these were greatly attributed to phosphorus mine exploitations in the upstream basin of Wu River. In addition, the import of phosphorus fractions from three upstream rivers also showed significant temporal variations. During impounding stage of TGR (October 2014), total particulate phosphorus in water accounted for more than 50 % of total phosphorus (TP); meanwhile, 51 % of phosphorus in suspended particulate were in the form of bioavailable phosphorus, meaning that the potential impact of inputted particulate phosphorus from three upstream rivers on the water environment of TGR cannot be ignored. However, total dissolved phosphorus was the predominant phosphorus fractions in water which accounted for more than 61 % of TP during high water level stage of TGR (January 2015). During this period, large amount of reservoir backwater would flow into the tributaries of TGR; consequently, the inputted dissolved phosphorus could be accumulated in the tributaries and then may provide sufficient nutrients for algal bloom in spring.