Dry deposition of N has a major impact on surface water quality in the Taihu Lake region in southeast China

Human activities have greatly increased the emission of reactive nitrogen (N) to the atmosphere, leading to large increases in N deposition in sensitive ecosystems. However, few have measured both the wet and dry deposition of individual N species in southeast China and their impact on surface water quality. We investigated wet and dry deposition of N, including gaseous NH3, NO2 and HNO3, and particulate NH4+-N and NO3−-N in both the atmosphere and precipitation during a two-year period at three sites in the Taihu Lake region in southeast China. The total N deposition in this region was 64.8 kg N ha−1 yr−1 (range: 59.1-70.5 kg N ha−1 yr−1). On an annual basis, the ratio of reduced to oxidized N deposition was 1.7, suggesting that the reduced form of N dominates N deposition. Of the annual N deposition, 45.5% was deposited via precipitation, with the remaining via dry deposition. The total gaseous and particulate N deposition was 24.9 and 10.4 kg N ha−1 yr−1, respectively. The high N loading in this region has resulted in the reduction of water quality in Taihu Lake. Atmospheric N deposition accounted for 33.3 and 27.5% of the total N loading in Taihu Lake and in water bodies in the region, respectively. We conclude that dry deposition of N is one of the most important sources of surface water pollution and should be taken into account when developing strategies for mitigating water pollution.