Increased Sediment Flux in the Yangtze River Headwater

Riverine sediment is not only an important pathway for nutrient and pollutant transport, but also a sensitive indicator of soil erosion and environmental changes in the river basin. Sediment flux (SF) in the Tuotuo River on the central Tibetan Plateau (TP), considered the main headwater of the Yangtze River, has significantly increased over the past three decades. Increasing SF in the upper reaches of a river is often accompanied by intensifying soil erosion, land degradation, river channel siltation and reduced operating life of downstream reservoirs. Annual time series data on hydro-meteorological variables showed significant increases in air temperature, precipitation, ground temperature, river discharge, suspended sediment concentration (SSC) and SF for the period from 1986 to 2014. Mean values were appreciably higher during 1998-2014 period as compared with 1986-1997. The increase in meltwater is attributable more to warming than an increase in precipitation. The increase in SSC mainly resulted from enhanced transport capacity and erosive power associated with precipitation and discharge. However, this increase was buffered by a decrease in sediment sources due to the shift in maximum monthly rainfall from June-July to July-August, since denser vegetation cover in July-August prevents soil erosion. In addition, increases in both discharge and SSC equally contributed to the increase of SF.