Simulation Of Interaction Between Surface Water And Groundwater And Evaluation Of Nitrate Load In Shaying River Basin

The interaction of water quantity and solute transport between surface water and groundwater is an important part of water cycle in nature.Huai River Basin is an important grain production area and grain yield increasing area in China.The large amount of fertilizer application caused the nitrate pollution of shallow groundwater,and the pollution from groundwater to surface water,which increased the nitrogen pollution load in surface water.This paper takes Shaying River Basin as the research object.Based on the hydrological characteristics of recharge and discharge between groundwater and surface water,a nitrogen pollution transport simulation system was constructed on a large scale by coupling a surface water model,a groundwater model and a solute transport model for recognizing the migration way of nitrogen pollutants in the process of hydrological cycle and making a quantitative contribution of nitrate pollution load.The main conclusions are as follows:1.Based on the theory of basin water cycle,water balance and solute transport,the heterogeneity and scale effect of the basin were considered.A coupled model system with a distributed hydrological model(SWAT),a groundwater flow model(MODFLOW)and a solute transport model(MT3DMS)was established.2.Based on the observation data of water quantity and water quality during 2007-2012,the model was verified by the surface water flows,groundwater levels,surface water quality and groundwater quality.The results are shown that the coefficient of determination R2 of surface water flows is greater than 0.68,and R2 of the groundwater levels and surface water quality are both greater than 0.9,and the relative error of groundwater quality Re is less than 15%.The accuracy of the model meets the requirements3.The relationship between surface water and groundwater is mainly based on groundwater recharge to surface water.The annual net recharge during 2007-2012 was 318 million m3.The relationship between surface water and groundwater in wet years mainly shows that groundwater recharges surface water,while in dry years surface water recharges groundwater.Spatially in the upper areas of Shaying River Basin,groundwater mainly recharges surface water,while in the middle and lower reaches of Shaying River Basin,surface water recharges groundwater.The nitrate flux process of the basin was mainly composed of nitrate from groundwater to surface water with 3800 tons.The annual nitrate net contribution from groundwater to surface water for autumn and winter was high.In summer surface water supplied nitrate to groundwater.Net nitrate contribution from groundwater to surface water in the upstream areas accounts for 87.4%of the total watershed,while in the lower areas of Shaying River Basin,net nitrate contribution is from surface water to groundwater.4.The recharge flux from groundwater to surface water increases with the increase of rainfall.In general,surface water recharges groundwater in the flood season,while groundwater recharges surface water in the dry season.In addition,under the influence of the dam scheduling rules with discharging water in the flood season and storing water in the wet season,groundwater can respond more changes in rainfall than surface water.The time variation characteristics of surface water are weakened.Even during the flood season,groundwater recharges surface water,while in the dry season,surface water recharges groundwaterThis study provides the basis for the scientific identification of characteristics and the spatial distribution of nitrogen source between surface water and groundwater,and enhances the comprehensive ability and quality control for nitrogen.Meanwhile,it provides effective managements for reducing agricultural non-point source nitrogen pollution load and technical supports for groundwater pollution controls.