Study On The NET Anthropogenic Nitrogen Input And The Response To Riverine Nitrogen Flux Export In Shanmei Reservoir Watershed

In recent years,nitrogen input caused by human activities such as agricultural cultivation and nitrogen fertilizer application is one of the main causes of environmental problems,which increased nitrogen concentration in rivers and eutrophication of water bodies.It is demonstrated that controlling nitrogen emissions from human activities is the key to the management of nitrogen pollution in rivers.Therefore,quantitative analysis of the anthropogenic nitrogen input source,and discussion of the response of riverine nitrogen output to anthropogenic nitrogen input has attracted widespread attention from scholars at home and abroad.Taking Shanmei Reservoir watershed as the research area,based on the net anthropogenic nitrogen input model(NANI)and the watershed distributed hydrological model(SWAT),this paper quantitatively studied the input intensity of anthropogenic net nitrogen t and the input levels of each input source in Shanmei Reservoir watershed from 2001 to 2010,and discussed the response characteristics of riverine nitrogen flux to runoff,NANI and landscape patterns.Based on land use in 1985 and 2006,the contributions of NANI,natural background source and retained nitrogen pools to the riverine nitrogen flux output at different time scales were quantitatively evaluated.The main conclusions of the study are as follows:(1)From 2001 to 2010,the net anthropogenic nitrogen input(NANI)in Shanmei Reservoir watershed showed a downward trend.Among them,the nitrogen fertilizer application rate accounted for 59.5% of the total amount of NANI,which was the largest input source of anthropogenic nitrogen input in the watershed.Only 29% of NANI was exported by rivers in the watershed.Due to the dual impact of basin scale and river runoff,there was no significant correlation between the interannual variation of NANI and the riverine nitrogen flux,and the interannual nitrogen flux of the river in the Shanmei Reservoir watershed.(2)NANI,natural background sources and retained nitrogen pools were the main sources of riverine nitrogen flux output in Shanmei reservoir watershed,with contribution rates of 52%,4%,and 44%,respectively.The anthropogenic nitrogen input,including NANI and the retained nitrogen pools,was the main input source of the riverine nitrogen flux,while the effect of the retained nitrogen pools on the river nitrogen flux decreased with the decrease of the total net anthropogenic nitrogen input.(3)The impact of the “source” landscape type on river water quality was higher than that of the “sink” landscape type.Compared with 1985,under the landscape pattern of 2006,79% of the riverine nitrogen output in the sub-basin of Shanmei Reservoir watershed decreased.From the perspective of landscape type change,areas of forest and dryland were significantly correlated with riverine nitrogen flux changes.From the perspective of changes in landscape level index,LPI,CONTAG,SHEI and SHDI were highly correlated with annual,monthly,daily and maximum one-day riverine nitrogen flux change.