Spatial-temporal Variation And Sources Of Nitrate In Surface Water Of Guanzhong Area In The Weihe River Basin

Surface water is an important material resource for human survival.The water quality of surface water has a direct impact on the safety of domestic water used by coastal residents and the health of aquatic environment.At present,with the development of industrialization and urbanization,surface water pollution is becoming more and more serious,threatening the ecological environment,human health,economic and social development.Nitrate is one of the main surface water pollutants.Nitrate contamination in rivers has raised worldwide concern in the world,especially in arid/semi-arid river basins lacking qualified water.Nitrate pollution in surface water is characterized by multi-source,randomness,complexity and uncertainty.Therefore,understanding the nitrate distribution and its pollution sources in surface water is critical to maintaining river health and ensuring the safety of drinking water.Water samples were collected from the Weihe River Basin in Guanzhong area.By combining with field experiment and lab testing,hydrochemical assessment and nitrogen isotopic measurement were used to determine the temporal-spatial distribution of nitrate and its main sources.The main conclusions of the study are as follows:1.The average concentrations of NO3--N in the spring,summer,autumn and winter were 9.1 mg/L,4.5 mg/L,8.6 mg/L and 9.3 mg/L,respectively,which were all below the national drinking water quality standard(10 mg/L).The exceeded rate of NO3--N concentration(>10 mg/L)in four seasons were 14.7%,5.9%,32.4%and 35.3%,respectively.2.According to the spatial distribution of nitrate in the basin,the nitrate content in different regions varied greatly.Nitrate contents in the main stream were obviously greater than those in the tributaries.And the nitrate pollution in the surface water around mountain areas was much lower than in other areas.Besides,nitrate pollution in some regions was serious,including the Weihe River in Baoji and Weinan,Qianhe River,Beiluo River,Shitou River and Luowen River.3.The nitrate pollution in the study area was objectively reflected by the temporal dynamic variation of nitrate.Compared the statistics from different seasons,it was obvious that the contents of nitrate in autumn,winter and spring were generally higher than that in summer.Besides,the exceeded rate of nitrate in autumn and winter was obviously higher than in spring and summer.4.The 815N-NO3-of water samples ranged from +8.3‰ to +27.0‰.No significant effect of denitrification on the shift in nitrogen isotopic values in surface water was observed by high DO values and linear relationship diagram between NO3--N and?15N-NO3-,except in the Weihe River in Huayin County and Shitou River.Analyses of hydrochemistry and isotopic compositions indicated that human and animal manure,sewage were the main sources of nitrate in the surface water.Furthermore,it was also influenced by agricultural activities,especially the utilization of nitrogen fertilizer.