Characteristics And Influential Factor Of Atmospheric Nitrogen Deposition In Urban-Rural Intersectional Areas In The Western Sichuan Plain

The transitional zone between urban and rural areas is one of the most intense areas where human activity changes the atmospheric underlying surface condition.With the development of urbanization,population,industry and land use have developed to be an ordered structure in this area.However,it is still unclear that the distribution characteristics and influence mechanism of atmospheric nitrogen（N）deposition on this structure.In this study,the temporal-spatial variation of dry and wet N deposition fluxes and the influence mechanism of meteorological factors and land use types were studied by using field location monitoring,wavelet analysis,spatial geographic information technology,grey relational analysis and path analysis according to the monitoring data of 9 sampling points in the urban,intensive agricultural area and rural area in Western Sichuan Plain during January,2015 and December,2016.The main conclusions were as follows:（1）The component,flux and spatial-temporal variation characteristics of atmospheric N deposition in urban and rural transitional zone are found out.The average annual fluxes of wet deposition of ammonium nitrogen（WNH₄⁺-N）,nitrate nitrogen（WNO₃^--N）and dissolved organic nitrogen（WDON）were 16.07±2.42,8.70±1.63 and 9.14±1.857 kg N hm^-2 yr^-1,respectively.And the average annual fluxes of dry deposition of ammonium nitrogen（DNH₄⁺-N）,nitrate nitrogen（DNO₃^--N）and organic nitrogen（DrON）were 9.24±2.01,5.32±1.26 and 5.98±1.25 kg N hm^-2 yr^-1,respectively.Their seasonal variations of wet deposition showed the highest value in summer（June to August）and the lowest value in winter（December to February）（P<0.05）,and dry deposition showed the opposite seasonal variations.The special variations of wt and dry deposition showed the similar law.Along the urban-intensive agricultural area-ordinary agricultural area transitional zone,the annual flux of NH₄⁺-N deposition first increased and then decreased;that of NO₃^--N deposition gradually decreased,indicating the significant spatial variability（P<0.05）;those of organic N and total N showed that the values in the city and intensive agricultural area were significantly higher than those in the ordinary rural areas（P<0.05）.（2）The composition characteristics of total N deposition and the input of N in the agro ecosystem.The temporal-spatial variation characteristics of total atmospheric N deposition were similar to those of wet deposition.Its composition characteristic expressed that the values of wet deposition were significantly higher than that of dry deposition（P<0.05）,and the fluxes of ammonium nitrogen（NH₄⁺-N）deposition were significantly higher than those of organic nitrogen（ON）and nitrate nitrogen（NO₃^--N）deposition（P<0.05）.If the N deposition was considered to replace a part of fertilizer in the crop growing season,the nitrogen-fertilizer replacement rates in paddy field,dry land and garden plot were 17.0%to 20.1%,11.7%to 21.6%and 10.9%to 15.1%respectively,which should be considered when designing the best fertilization amount.（3）The influence of meteorology on N deposition are clarified.It is the first time to find out the seasonal driving of N deposition by the meteorological factors based on the wavelet coherent analysis.In summer,rainfall was the greatest positive influence factor for WNH₄⁺-N in urban,WNO?^--N and WDON deposition in all areas.Temperature is the secondary positive driving factor for WDON deposition.In spring and summer,the wind speed was the forward and reverse driving factor of WNO?^--N and WNH₄⁺-N deposition in intensive agricultural area respectively,and in winter and spring was the forward and reverse driving factorofDNH₄⁺-N（urban and intensive agricultural areas）and DNO?^--N and DrON（urban）respectively.The relative humidity in spring and winter may be the reverse driving factor of the monthly flux of DNO?^--N deposition in rural area and the forward driving factor of the monthly flux of DrON deposition in all areas.（4）The influence of land use on N deposition are clarified.The spatial variation of atmospheric N deposition in the medium and small scale is explained by the use of"source"and"remittance"land use types.It was discovered for the first time that the key land use area within the range of monitoring point 4km was closely related to N deposition.Within 4km of monitoring points,annual NH??-N deposition had positive correlation with the area of paddy field,yard,facilities agricultural land and highway,and had negative correlation with the area of dry land,country road and forest and grassland.The annual flux of NO?^--N and ON deposition was positively correlated with the area of urban and highways（P<0.05）,and negatively related with paddy field,dry land and village he correlation analysis between the monthly flux of N deposition and the land use showed that the farmland with little fertilizer application and N emissions,and no hardened rural road land and forest grassland may be the sink of N deposition,which should be considered actively in urban and rural planning.（3）The key influence factors are clarified.The grey correlation analysis and path analysis were used to rank the influential factors of wet and dry deposition of atmospheric N.The results showed that the influence of meteorological factors was stronger than land use,and rainfall and wind speed had the greatest influence on N wet and dry deposition,respectively.Temperature and rainfall were the key influential factors for WNH₄⁺-N deposition;rainfall,temperature and road land forWNO₃^--N and WDON deposition;wind speed,relative humidity,facilities of agricultural land and paddy field for DNH₄⁺-N deposition;wind speed,relative humidity and road land for DNO₃^--N deposition,and wind speed,relative humidity,facilities of agricultural land and road land for DrON deposition.