Temporal And Spatial Variations Of Nitrogen And Phosphorus Fluxes And Key Driving Factors In The Yangtze And Yellow River Basins

Human activities caused over enrichment of nutrients in water and resulting eutrophication have become a global water environment problem.Understanding how different anthropogenic and natural factors affect watershed total nitrogen（TN）and total phosphorus（TP）loads at both temporal and spatial scales is critical for developing effective nutrient reduction strategies and assessing possible future water quality impacts.The Yangtze River and Yellow River basins are taken as the research objects,and systematically compiled the data of pollution load,meteorology,hydrology and water quality in the basin.The key influencing factors of the temporal and spatial changes of TN and TP fluxes were analyzed,and the main driving factors of the temporal changes of TN and TP fluxes in the basin were clarified.Provide a reference for nutrient reduction in the Yangtze and Yellow River basins.The main research conclusions are as follows:（1）Dataset of river networks,spatial attributes,pollution sources,and monitoring stations in the Yangtze and Yellow River basins were constructed,and an accounting method for TN and TP fluxes based on the RSPARROW model was established.The data of pollution load,meteorology,hydrology and water quality in the Yangtze River and Yellow River basins from 2006 to 2018 were systematically compiled,and the calculation methods of TN and TP fluxes based on the RSPARROW model were established in the Yangtze River and Yellow River basins,respectively.Verified by the measured data,the simulation accuracy of TN and TP fluxes in the Yangtze River Basin were 0.85 and 0.75,respectively,and the simulation accuracy of TN and TP fluxes in the Yellow River Basin were 0.67 and 0.63,respectively.（2）The temporal and spatial variation characteristics of TN and TP fluxes in the Yangtze and Yellow River basins were analyzed.The average TN flux in the Yangtze River Basin was 572 kg·km^-2·yr^-1,and the average TP flux was 45.3 kg·km^-2·yr^-1.The fluxes of TN and TP in the Jinsha River section were low,and increased gradually after Jinsha River section.The average TN flux in the Yellow River Basin was 134 kg·km^-2·yr^-1,and the average TP flux was 5.6 kg·km^-2·yr^-1.The TN flux was high in the southeast and low in the northwest of the Yellow River basin.The TP flux was higher in the Gansu-Ningxia section of the watershed.（3）Clarify the main driving factors for the temporal changes of TN and TP fluxes in the Yangtze and Yellow River basins.The control variable method was used to screen the main driving factors of the temporal changes of TN and TP fluxes in the Yangtze and Yellow River basins.It was found that rainfall was the main driving factor for the temporal change of TN flux in the Yangtze River Basin except for the source area,and point source emission was the main driving factor for the temporal change of TP flux in the Sichuan Basin,Hubei Province,Chang-Zhu-Tan urban agglomeration and the Yangtze River Delta urban agglomeration.Temporal changes of TP flux in other regions are driven by rainfall.Rainfall is the main driving factor for the temporal change of TN flux in Shaanxi Province,the upper reaches of the Yellow River and low-latitude regions in the middle reaches.And point source discharge is the main driving factor for the temporal change of TN flux in the Fenhe River Basin,the lower Yellow River and some upper reaches of the Yellow River.The main driving factors for the temporal change of TP flux in the basin are all point source emissions.