Simulation Study On The Influence Of Multiple Water Resources Regulation On Organic Carbon In Groundwater Of Yufu River Basin

In order to eliminate the effect of excessive exploitation of groundwater,a series of water resource regulation measures have been taken to prevent the decrease of groundwater level.However,the water chemical composition of surface water and groundwater is often very different,and the content of organic carbon has a great impact on groundwater environment.Organic carbon in groundwater can affect the potential for the production of disinfectant byproducts and the release of heavy metals,such as arsenic,in sediments,increasing the safety risk of groundwater.In the process of artificial recharge of groundwater,the increment of organic carbon in groundwater comes from surface water as the source of recharge and atmospheric precipitation,so it is difficult for traditional methods to quantitatively assess the influence level of organic carbon concentration in the process of recharge.Based on the above reasons,this study relies on the national key research and development program(No.2019YFC1804804)and Shandong Institute of Water Resources Research self-selected project(SDSKYZX202124-1),selected Jinan Yufu River groundwater as the research object,By analyzing the change of organic carbon concentration in the process of surface water conversion to groundwater,the model provides guidance for specific water resources regulation.The results are as follows:1.Construction of coupling model of surface water and groundwater in Yufu River BasinIn this study,SWAT model and MODFLOW model suitable for Jinan Yufu River Basin were established separately,and the water volume coupling between SWAT and MODFLOW model was realized by using QGIS platform.The determination coefficient(R~2)was selected to evaluate the reasonableness of the evaporation simulated by the SWAT model and the groundwater level simulated by the SWAT-Modflow coupling model.The results of water coupling model show that the simulated values of monthly evaporation and groundwater level are close to the measured results.The R2 of evaporation simulated by SWAT model is 0.74,and the R2 of groundwater level simulated by SWAT-Modflow coupling model and measured is 0.85.Combined with the reaction mechanism of organic carbon in groundwater,the code of the original SWAT-MODFLOW-RT3D model was supplemented,and the convection-diffusion-organic carbon oxidation reaction equation of organic carbon migration from surface water to groundwater was constructed.The coupling model of surface water and groundwater constructed in this study can be applied to the simulation of organic carbon in the interaction between surface water and groundwater in this basin,providing a model basis for the subsequent simulation and prediction of the change of organic carbon in groundwater under different scenarios.2.Analysis of coupling model results of surface water and groundwater quantity in Yufu River BasinBased on the above coupled model,the influence of surface water on groundwater organic carbon concentration in Yufu River Basin under water resource regulation is simulated and predicted.The simulation results show that the organic carbon concentration of groundwater near the Yufu River Basin increases under the influence of surface water infiltration and recharge.In 2018,the groundwater organic carbon concentration ranged from 0.056mg/L to 4.605mg/L,and in 2019,the groundwater organic carbon concentration ranged from 0.037mg/L to 6.528mg/L.The influence of rivers on organic carbon in groundwater increased with the increase of regulation period.3.Analysis of organic carbon transport model in Yufu River BasinBased on the above coupled model,the influence of surface water on groundwater organic carbon concentration in Yufu River Basin under water resource regulation is simulated and predicted.The simulation results show that the organic carbon concentration in groundwater near the Yufu River Basin increases due to the influence of surface water infiltration and recharge,and the distribution of organic carbon concentration in groundwater has obvious spatial differences.In 2018,the groundwater organic carbon concentration ranged from 0.056mg/L to 4.605mg/L,and in 2019,the groundwater organic carbon concentration ranged from 0.037mg/L to 6.528mg/L.The influence of rivers on organic carbon in groundwater increased with the increase of regulation period.4.Simulation and prediction of the influence of multiple regulation on organic carbon in groundwater of Yufu River BasinAccording to the established SWAT-MODFLOW-RT3D model,the present organic carbon concentration and the groundwater organic carbon concentration in2030 after removing organic carbon from the recharge water were simulated under water resource regulation only with the Yellow River water,water with the Yangtze River water and multiple water resources regulation.The results show that under the current conditions,with the increase of simulation time,the groundwater organic carbon concentration will increase to a large extent,and the groundwater organic carbon concentration in most areas of the basin will exceed 6.11mg/L.When organic carbon is removed from the recharge water,the concentration of organic carbon in groundwater near the river will be greatly reduced.For the Yellow River water,the Yangtze River water and the water resources under the regulation of multiple factors,the input of organic carbon per unit recharge to groundwater is 0.13kg/ha·mm,0.19kg/ha·mm and0.16kg/ha·mm,respectively.The use of Yangtze River water as the source of regulation has a great influence on the concentration of organic carbon in groundwater.When the Yellow River water resources regulation is adopted,the groundwater recharge is more,but the organic carbon input is less.