Spatio-temporal Variations Of The Net Anthropogenic Nitrogen And Phosphorus Inputs(NANI/NAPI) Into The Dongting Lake Basin

A large amount of nitrogen(N)and phosphorus(P)nutrients of human activities into the aquatic ecosystem has been keeping on increase substantially since 1980s,resulting in the continuous increase of nitrogen and phosphorus concentrations in the rivers,lakes,costal area as well as other waterbodies.In this study,the Dongting Lake basin was selected as the research area,the Net Anthropogenic Nitrogen Input(NANI)and the Net Anthropogenic Phosphorus Input(NAPI)developed by Cornell University were quantitatively studied to analyze the impact of human activities on the Dongting Lake watershed ecosystem,the main sources and driven factors of NANI/NAPI in the Dongting Lake basin is estimated The main conclusions are as follows(1)The NANI value of the Dongting Lake basin incresaed from 1985-2005 and then slightly decreased from 2005-2015.The NANI value in the basin were 53.1±4.6,75.7±6.5,91.3±8.0 and 88.6±7.9 kg·hm-2·a-1 in 1985,1995,2005 and 2015 respectively.Nitrogen fertilizer application is the largest component of its composition,followed by net food and feed import.The nitrogen fixation in the basin is relatively stable over the years,but the contribution rate to NANI had been decreasing year by year.The contribution rate of atmospheric nitrogen deposition to NANI has increased year by year,and its contribution rate even surpassed nitrogen fixation in 2015(2)The NAPI value of the Dongting Lake basin increased at first and then decreased.The NAPI in the basin were 7.0±1.0.9.2±1.6,10.3±2.0,10.0±2.0 kg·hm-2·a-1 in 1985,1995,2005 and 2015,respectively.The largest contribution to NAPI value was the net food and feed import in 1985,while the largest contribution to NAPI was phosphorus fertilizer application from 1995 to 2015,the minimum input item is non-food P(3)From the spatial distribution of NANI/NAPI values in the sub-basins,the annual average NANI intensity in each basin is totally as follows:Dongting Lake area,Xiangjiang River downstream,Zijiang River upstream,Xiangjiang River upstream,Lishui River area,Zijiang River downstream,Yuanjiang River downstream,Yuanjiang River upstream;the annual average NAPI intensity in each basin is as follows:Dongting Lake area,Xiangjiang River downstream,Zijiang River upstream,Xiangjiang River upstream,Lishui River area,Yuanjiang River upstream,Yuanjiang River downstream,Zijiang River downstream.(4)As spatial distribution in the Dongting Lake area,the highest NANI and NAPI values were found in the northeastern part of the lake region and west part of the lake basin for the concentrated agricultural activies.Higher NANI and NAPI values were found in the around Dongting Lake in the northeast.The results show that agricultural production and population growth are the main reasons leading to the increasing inputs of anthropogenic nitrogen and phosphorus,and the negative ecological effects cannot be ignored.