The Source Apportionment Of Riverine Nitrogen Export In Zhejiang Province And It's Control Management Research

The ecosystem nitrogen imput interfered by human activities has a crucial potential influence on water environment in recent years.The increased nutrient export to river is the main cause of eutropHication,which deteriorates the water quality and has a negative effect on the growth and reproduction of aquatic organism.The high frequency of harmful algal bloom in recent years of China has declined the water quality sharply.Nitrogen(N),as the important source of water eutropHication,has an increasingly prominent role in water improvement.So,to identify the source of riverine N export and to assess the discharge accurately is meaningful for the understand of water pollution mechanism and establishment of control strategies.However,the driving forces of riverine N export that is closely related to water N pollution are still not well understood.Based on a mass balance approach,combined with literature analysis and data mining,this study has quantified the sources of N discharge and analyzed the effect of land use composition on riverine N export from 2000 to 2015,taking Zhejiang Province,China as a case study.And Monte Carlo analysis method is introduced to evaluate the uncertainty of riverine N export in Zhejiang Province.Our results show that the total reactive N discharge to rivers in Zhejiang increased from 0.22 to 0.26 Tg yr-1 from 2000 to 2015 at an annual rate of 1.2%.At the watershed scale,our estimate of N export agrees well with the monitored riverine N concentration in the eight major watersheds in Zhejiang.Direct discharge of domestic wastewater and effluents from wastewater treatment plants are dominant sources of riverine N export,followed by agricultural non-point sources.The strength of correlation between land use composition and water quality sharply decreased with decreasing width of the buffer zone.Although riverine N export increases with the increasing proportion of urban and agricultural land uses,we did not find any relationship between land use change and changes in riverine N export.This suggests that the dominant factor affecting riverine N export should be human activities(e.g.wastewater discharge and fertilization level),while land use only mediates riverine N export.Based on the source apportionment of riverine N export,in order to improve the water quality of Zhejiang Province,in addition to control N loss from cropland and domestic wastewater discharge,it is necessary to improve the discharge criteria of wastewater treatment plants(WWTP),to accelerate the upgrading and reconstruction and heighten the environmental awareness of public as effluents from WWTP has a greater contribution to the riverine N export.