Temproal Distribution of Nitrogen in Precipitation in Agricultural Zone,Pudong,Shanghai

In order to investigate change in nitrogen concetration in precipitation in the agricultural zone of Pudong,Shanghai,its law and affectiong factors,and N deposition flux,rains were sampled monthly over a year(2008)for analysis of nitrate(NO₃^--N)and ammonia nitrogen(NH₄⁺-N)concentrations.Results show that nitrogen concentration in rain water and annual N deposition flux were both quite high in the zone,with the mean concentration of NO₃^--N being 0.44 mg·L^-1 and of N being 1.36 mg·L^-1,and the annual deposition flux of NO₃^--N being 5.19 kg·hm^-2·a^-1 and of NH₄⁺-N,being 15.91 kg·hm^-2·a^-1 ,making the annual deposition flux of TN up to 21.10 kg·hm^-2·a^-1,of which NH₄⁺-N accounted for 75.4%.The concentrations of NO₃^--N and NH₄⁺-N in rain water were lower in the main growig season(April-October)than in the main non-growing season(November-March).However,in terms of deposition flux,NH₄⁺-N was higher in the former than in the latter,while NO₃^--N did not differ much between the two,which was attributed to the comprehensive effect of human activities,number of raing days,rainfall,wind direction,etc..Generally speaking,the nitrogen input with precipitation is of some positive significance to the primary productivity in the study zone,the nitroggen concentrations in rainfall have exceeded the threshold value of water eutrophication,which may intensify eutrophication of the aquatic systems in the zone.