Analyzing factors driving of eutrophication of river-type urban landscape lakes

The eutrophication of river-type urban landscape (RTUL) lakes is different from that of natural lakes. In this study, Xiaofu Lake, a typical RTUL lake with high anthropogenic interference, was used as the study area. Monitoring data from 2018 to 2020 were used to analyze the temporal and spatial distribution characteristics of chlorophyll a (Chl-a) concentrations with meteorological, hydrodynamic, and nutrient factors. Correlation and regression analyses were used to identify the relationship between the factors influencing eutrophication and the Chl-a. The MIKE21 model is used to simulate changes in water quality indicators. The study determined the relationship between river water quality and environmental factors and explored the causes of eutrophication in the water bodies of Xiaofu Lake. The results showed that from 2018 to 2020, the water quality showed seasonal variation and differences in spatial distribution. Except for total nitrogen, which remained at a high level (average 8.23 mg/L), other water qualities remained between classes II and IV. The proportions of mild, moderate, and severe eutrophication in the study area were 25%, 69%, and 6%, respectively. Indicators that were highly correlated with water eutrophication were turbidity, water temperature, total phosphorus, and permanganate index. The contribution of water temperature, ammonia nitrogen, and permanganate index to eutrophication was 30.5%, 22.6%, and 20.9%, respectively. The high proportion of sewage in the source of recharge water is one of the reasons for the deterioration of water quality. In addition, the change in water eutrophication was closely related to the gate operation in the region. PRACTITIONER POINTS: There are differences between river-type urban landscape (RTUL) lakes and natural lakes, and the conditions that cause eutrophication are different. RTUL are subject to strong human interference and rely on water transfer and gate scheduling to maintain water quantity. The high proportion of sewage treatment plant tailwater in upstream water is the main reason for the long-term pollution of RTUL. The indicators highly correlated with water eutrophication are turbidity, water temperature, total phosphorus, and permanganate index.