Divergent change patterns observed in hydrological fluxes entering China's two largest lakes

Large lakes are key components of hydrological processes and have critical ecological and economic functions. Streamflow and riverine sediment loads exported from tributary rivers to lakes provide inputs of water and nutrients and greatly impact the health of lacustrine ecosystems. Understanding the spatiotemporal patterns of water and sediment transport dynamics within the basins of large lakes is therefore required for informed management of their resources. In particular, the hydrological processes of large lake basins in western China were not fully explored yet. This study investigated changes in runoff and sediment fluxes entering the two largest lakes in China (Qinghai Lake and Poyang Lake) over the past half century. Our results showed that the regional trends of the two lake basins have changed in divergent way. The patterns of change of streamflow and sediment transport-including the trends, periodicity, and transition points as well as the relationship between streamflow and sediment flux-were quite different. The results obtained by a Sediment Identity method revealed that increases of the precipitation and runoff coefficient controlled the observed increase of streamflow and sediment flux within the Qinghai Lake basin, whereas the decrease of the sediment flux entering Poyang Lake was caused mainly by a reduction in sediment concentration. Climate change was the dominant driver influencing the recent increases in surface water resources and sediment load in the Qinghai Lake basin as well as the long-term fluctuations of streamflow within the Poyang Lake basin. In contrast, the observed abrupt reduction in total sediment flux entering Poyang Lake was due mainly to declining sediment discharge from the Gan River; this decrease is attributed primarily to human activities, especially reservoir construction and soil conservation practices. Overall, this study discovers the divergent change patterns when investigating hydrological processes, and highlights the importance of developing policies for managing soil and water resources within large lake basins to the northwest and southeast of the Hu Line. Management policies should consider the tremendous differences in geography, climate, and population across China.