LAUSR

The net sediment flux in Poyang Lake, the largest freshwater lake in China, converted from positive to negative after 2000. Whether the effect of the Three Gorges Dam (TGD) or sand mining caused this change was disputed. We analyzed the trend of sediment input and output in Poyang Lake from 1956 to 2014, determined the annual numbers of sand dredgers by interpreting Landsat ETM + images, and calculated the changes to the annual net sediment flux (Sedimentdiff) after 2000. The decreased sediment input was mainly caused by decreased sediment concentrations in the five tributaries. The increased sediment output was caused by increased sediment concentrations, which was not related to the operation of the TGD, but strongly related to sand mining activities in the northern parts of the lake. The Sedimentdiff variation in different operational periods of the TGD showed that the TGD was not the main driver of the change to the net sediment flux trend in Poyang Lake. The strong positive correlation between the number of sand dredgers and Sedimentdiff indicated that sand mining activities in the northern parts of the lake were important drivers of the changes in the net sediment flux trend in Poyang Lake after 2000. It was sand mining activities, rather than the TGD, that altered the trend of the net sediment flux in Poyang Lake after 2000.