Atmospheric Nitrogen Deposition Associated with the Eutrophication of Taihu Lake

Abstract

Environmental effects of excessive amounts of atmospheric nitrogen (N) deposition have raised a great deal of attention. In the present study, the characteristics of N deposition and its contribution to water eutrophication were investigated in the Taihu Basin. The results showed that the annual average total deposition (TN), total wet deposition (TNW), and total dry deposition (TND) rates were 6154, 1142, and 5012 kg·km−2, respectively. Moreover, seasonal fluctuations in TN, TNW, and TND deposition were observed, with a higher N deposition rate occurring in spring and summer. Spatially, the distribution of TN and TND deposition throughout the Taihu Basin was similar. However, the TN deposition rate declined gradually from the southeast to the northwest, while the TNW deposition rate increased. A significant positive correlation was also found between the TN deposition contents with rainfall R=0.803,P=0.01, rainfall frequency R=0.767,P<0.01, and rainfall intensity R=0.659,P<0.05. The TN deposition concentration was significantly negatively correlated with rainfall R=−0.999,P<0.01, rain frequency R=−0.805,P<0.01, and rainfall intensity R=−0.783,P<0.01. The riverine input of TN was estimated to be 112,500 t·N·a−1, and the main N pollutants originated from domestic sewage (accounting for 48.88%) and agriculture (accounting for 28.17%). Livestock and aquaculture contributed 90% of the agricultural pollutants. Additionally, TN deposition contributed 14,400 t N·a−1 to the lake, which accounted for 12.36% of the annual riverine TN inputs. The TN deposition load already exceeds the eutrophication critical load in theory. Furthermore, the contribution of N deposition to the lake has been increasing in recent years, which may accelerate eutrophication of Taihu Lake.