Investigating the effects of inflow river water quality on lake nutrient-concentration variations: a case study in Gehu Lake, China

Context Controlling the inputs of nutrients, one of the main sources of lake pollution from inflow rivers, is an important way to protect lakes. Aims To obtain a whole picture of spatiotemporal variation of water quality in Gehu lake and its main inflow rivers from 2011 to 2018, and to study relationship of water quality between lake and inflow rivers. Methods We analysed the relationship by using correlation analysis and BATHTUB model and discussed the goal of collaborative control by setting up different scenarios. Key results The concentrations of total nitrogen (ρ(TN)) and total phosphorus (ρ(TP)) are the main water pollutants in Gehu Lake and it continues to maintain the middle-eutropher state. ρ(TN) and ρ(TP) in the lake have a significant negative correlation with the quantity of water inflow and a significant positive correlation with ρ(TN) and ρ(TP) in inflow rivers. Conclusions It showed that when ρ(TN) and ρ(TP) in inflow rivers decreased by 25%, ρ(TN) and ρ(TP) in Gehu Lake decreased by 21.01 and 22.64%. Furthermore, when ρ(TN) and ρ(TP) in inflow rivers decreased by 50%, they correspondingly decreased by 40 and 36.91% in the lake. Implications Our findings provide effective control of water quality in Gehu Lake and give a guide for environmental governance and water-quality improvement measures.