Water quality responses to rainfall and surrounding land uses in urban lakes

The effect of rainfall on the water quality of urban lakes is related to the surrounding land use types. Six lakes surrounded by business units (commercial lakes) and park green spaces (park lakes) in the central area of Beijing, China, were monitored between June 2013 and October 2015. A total of 638 water samples were obtained. The results showed that the water quality was generally worse in the rainy season than in the dry season, with the mean dissolved oxygen (DO) concentration declining by 25.1 %. Compared to the rise in DO of park lakes after rainfall, commercial lakes showed a decreased DO. The nitrate nitrogen (NO₃^--N) concentration decreased after rain, and that in commercial lakes decreased more than that in park lakes. Different from DO and NO₃^--N, the ammonia nitrogen (NH₄⁺-N)), total suspended solids (TSS) and total phosphorus (TP) concentrations of the lakes increased obviously after rain. The values in park lakes increased 138 % (NH₄⁺-N)), 120 % (TSS) and 69 % (TP) more than those in commercial lakes. Principal component analysis (PCA) results illustrated that green space was the main source of TSS and TP for urban lakes. Most of the nitrogen (N) comes from artificial impervious surfaces. These results will help target pollutant control for urban lakes.