Dominant factors influencing changes in the water quantity and quality in the Dianshi Reservoir, East China

This study aims to identify the major factors affecting the water quality and quantity of the Dianshi Reservoir and to determine the potential risks facing the Dianshi Reservoir under the combined effects of climate and human activities. Multi-year data (2010 to 2019) were collected, and comparative analysis, trend analysis, Pearson correlation analysis, stable isotopes, and Morlet wavelet analysis were used conjunctively. The results showed that precipitation and runoff are the main recharge sources of the Dianshi Reservoir. The reservoir water level was mainly influenced by industrial and domestic water uses. Ammonia-nitrogen (NH4+-N), total phosphorus (TP), total nitrogen (TN), and chemical oxygen demand (CODMn) were the main pollution indices in the Dianshi Reservoir. Animal excrement responsible for organic pollution entered the reservoir through surface runoff, while sewage discharge, fertilizer application, and leaf decomposition were the main sources of NH4+-N, TP, and TN in the reservoir. Wavelet analysis indicated that water quality was greatly affected by the human activities before 2016, while the effects of precipitation, temperature, and evaporation gradually increased after 2016 and became the main factors after 2018. In addition, the management measures of the Dianshi Reservoir are not comprehensive, resulting in potential risks to water quantity regulation and water quality protection. It is, therefore, necessary to formulate a water regulation program and a comprehensive reservoir safety protection system.