Characteristics And Sources Of Atmospheric Nitrogen Deposition In Typical Functional Areas Of The Wanzhou Section Of The Three Gorges Reservoi

Atmospheric nitrogen deposition is an important link in the geobiochemical cycle of nitrogen,which is not only an important way to remove gas,liquid and granular nitrogen from the atmosphere,but also an important source of near-surface nitrogen.With the rapid development of the economy,human activities have led to a large amount of nitrogen emissions,and the negative ecological effects caused by nitrogen deposition have become increasingly strengthened.The topography,climatic conditions,geographical location and influence of the surrounding area of Wanzhou District make pollutants accumulate here and the environment continues to deteriorate.It is urgent to study the temporal and spatial variation characteristics and sources of nitrogen deposition in Wanzhou District,which not only provides corresponding data support for environmental governance,but also provides corresponding practical experience for the study of atmospheric nitrogen deposition characteristics in relevant regions at home and abroad.In this study,four typical functional areas and seven stations in industrial areas,commercial areas,residential areas and agricultural areas were selected to collect precipitation samples from May 2021 to April 2022 to analyze the concentrations of ammonium nitrogen（NH₄⁺-N）,nitrate nitrogen（NO₃^--N）,and dissolved total nitrogen（TDN）in nitrogen deposition.Through experimental data,the temporal and spatial variation characteristics of concentration and sedimentation amount of NH₄⁺-N,NO₃^--N and TDN were analyzed,and the main sources of pollutants were explored by various methods,and the potential ecological effects of nitrogen deposition were analyzed.The results of the study are as follows:（1）The p H-weighted mean of precipitation in the study area was 6.15 and the conductivity was 27.72μS·cm^-1.The weighted average concentrations of TDN,NH₄⁺-N and NO₃^--N during the sampling period were respectively 1.37±2.71 mg·L^-1、0.94±1.72mg·L^-1、0.34±0.54 mg·L^-1,nitrogen deposition is dominated by NH₄⁺-N.The temporal variation of NH₄⁺-N and TDN concentration was manifested as winter>autumn>spring>summer,mainly affected by the size of rainfall,and the spatial variation was manifested as industrial area>commercial area>agricultural area>residential area.NO₃^--N concentrations in winter are higher than in spring,summer and autumn,and industrial and commercial areas are higher than in residential and agricultural areas.（2）The quantitative analysis of NH₄⁺-N and NO₃^--N sources using Mixsiar model showed that the contribution size of NH₄⁺-N was biomass combustion（43.4%）>traffic movement（23.0%）>coal combustion（17.6%）>animal manure（9%）>fertilizer use（7%）.The contribution of NO3-N was biomass combustion（36.4%）>coal combustion（25.4%）>traffic movement（24.3%）>soil biological emission（13.9%）,and the contribution of combustion sources,especially biomass combustion,to nitrogen emissions was significant.The backward trajectory clustering analysis showed that the source air mass transport distance in the study area was short,concentrated in the local and surrounding areas,and most of them passed through Sichuan Province,Guizhou Province and Hubei Province,spreading from southeast and northwest directions.（3）The values of NH₄⁺-N,NO₃^--N and TDN sedimentation were 12.99±4.40kg·N·ha^-1·yr^-1,4.78±0.89 kg·N·ha^-1·yr^-1 and 19.03±4.29 kg·N·ha^-1·yr^-1,respectively.The sedimentation of NH₄⁺-N and TDN had obvious spatiotemporal variation characteristics:the temporal manifestations were autumn>spring>summer>winter,and the autumn deposition accounted for more than 30%of the annual sedimentation.Spatially manifested as industrial areas>commercial areas>agricultural areas>residential areas.The waters and forest ecosystems of Wanzhou are threatened by atmospheric nitrogen deposition.