The impact of rainstorms on nutrient loading for a large and deep reservoir

A main cause of water eutrophication in lakes or reservoirs are nutrient enrichment, of which variations can be influenced by climatic changes and anthropogenic activities. It was reported that rainfall may lead to a short-term increase in nutrients that threaten the water quality of lakes or reservoirs. Daily meteorological data collected over the last few years in the Lake Qiandaohu basin highlight an increase in the frequency of extreme rainfall events. The relationships between nutrient (nitrogen and phosphorus) concentrations in the lake and external loading discharged into the lake during 2013-2016 were analyzed. Meanwhile, the fluid movement and the diffusion of the pollutants from the catchment were simulated by the ELCOM model. These were in order to evaluate the possible role of extreme precipitation events in affecting the nutrient availability in the lake. Our results show that, for the largest inflow (the Xinanjiang River), 32.5% of annual TN and 32.8% of annual TP were caused by rainstorm, respectively. The time of pollutant migration could be greatly shortened by heavy rains. For lakes and reservoirs, extreme precipitation will not only lead to a sharp increase in inflow but also result in a significant increase in nutrient loading in a short period of time. Therefore, rainstorms can be an important factor of climate-induced eutrophication in lakes or reservoirs.