The impact of climate change on the water quality of Baiyangdian Lake (China) in the past 30 years (1991-2020)

Climate change significantly influenced the water quality of lakes in recent decades. This study investigated the effects of climate change on the water quality of Baiyangdian Lake (China) in the past 30 years (1991-2020) using correlation analysis, regression analysis, and the generalized additive model (GAM). The results show that water quality grade, chemical oxygen demand (COD), total phosphorus (TP) concentrations, and annual average and minimum air temperatures of the lake showed significant differences (p < 0.05) in the one-way ANOVA during the studied period. The concentration of dissolved oxygen (DO) and TP, annual average and minimum air temperatures, and annual precipitation decreased, while the COD and total nitrogen (TN) concentration, annual maximum temperature, and monthly maximum precipitation increased. The annual average and minimum air temperature affected all water quality variables and explained 12.3 %-54.5 % of variation deviation in correlation and GAM analyses, indicating that the changes of air temperature influenced the water temperature, which then affected the biochemical reaction rates leading to changes in water quality. The precipitation factors explained 10.5 % (TN) to 54.8 % (TP) of variation deviation, implying that the increase in precipitation improved water quality by diluting the COD concentration. However, excessive precipitation also accelerated the endogenous release of phosphorus in sediments by increasing the TP concentration. Additionally, extreme climate factors correlated with some water quality variables and explained 57.7 %-95.9 % of the total variances in correlation and regression analyses, suggesting that the extreme temperatures changed the nitrogen and DO concentration to aggravate lake pollution. However, the extreme precipitation purified the water through dilution. This study will facilitate to understand the impacts of climate change on water quality and find appropriate adaptation measures for ecosystem management of shallow lakes.