Decadal change in dissolved silicate concentration and flux in the Changjiang (Yangtze) River

Abstract

Silicon (Si) plays an essential role in the biogeochemistry of rivers. This study explored how damming, eutrophication and climate change alters the abundance and flux of DSi in the Changjiang (Yangtze) River based on long-term observations. The results showed that Three Gorges Reservoir (TGR) could enhance DSi transfer only during low-flow time period, and a downstream DSi retention effect by the TGR was found between the Yichang and Jianli stations in the Changjiang River. This resulted in a DSi loss during March and April in the mainstream from Three Gorges Dam (TGD) to Jianli but a DSi addition during July and October along the main channel of the Changjiang River. Long-term data showed a sharp decrease in DSi abundance at the Cuntan, Hankou and Datong stations between the 1960s and 1980s, but a slight increase in DSi between the 1990s and 2010s at these stations. The decrease in DSi during the 1960s -1980s was primarily the result of a decrease trend of silicate weathering, while a slight DSi increase compared to the temperature/DSi relation after the 1990s was largely due to increased DSi retention in the basin by damming and eutrophication. Eutrophication and damming increase DSi trapping in both the river channel and reservoir systems in the low-flow period and thus enhance the nutrient distortion in the coastal ocean.