Shallow Groundwater Quality Characteristics And Influenced Factors In Bali River Catchment

Bali River catchment is located in the lower reaches of Shaying River,a tributary of Huai River,with an area of 480 km2,.which is highly intensive agriculture.Planting and vermicelli processing industry are its main industries.Exceedingly using fertilizers and pesticides and starch wastewater reinjection become its important pollution sources.Therefore,agricultural non-point source pollution constitutes an important form,leading to the rapid deterioration to the local surface water environment,which not only affects the water environment quality in the Shaying River Basin,but also may form a certain threat to the quality of shallow groundwater for residents to live and drink.In order to investigate the current situation of the water environment of the surface water and shallow groundwater in Bali River catchment,and to study the main factors affecting the water quality characteristics,so as to provide some basis for the water environment control in the basin.This paper takes Bali River catchment,located in the lower reaches of Shaying River,as a studied object.Based on the investigation of the current situation of water environment and the distribution of pollution sources in the basin,through field sampling,indoor test and analysis(15 conventional indicators and 6 pollution indicators).Using the methods of multivariate statistical analysis,hydrochemical component analysis and numerical simulation calculation,the water quality characteristics of surface water and shallow groundwater are systematically analyzed,the influence of starch wastewater irrigation on shallow groundwater and the main factors affecting the quality characteristics of shallow groundwater in Bali River catchment are discussed.The main results are as follows:(1)The nitrogen,phosphorus and COD of the surface water in Bali River catchment are seriously exceed the standard,among which Liugou is the worst tributary with the most serious pollution.It is mainly affected by starch wastewater,livestock breeding wastewater,chemical fertilizers and pesticides,and domestic sewage,etc.(2)The shallow groundwater in Bali River catchment belongs to neutral weak alkaline water.The content of Ca2+,Mg2+ and bicarbonate in the groundwater is relatively large.The hydrochemical type is mainly HCO3-Ca+Mg.The content of "three nitrogen" and CODMn is relatively low.The concentration of "three nitrogen" is within the class ? standard.Only the concentration of CODMn of a few of the water samples exceeds the class ? standard.Therefore,the shallow groundwater quality is relatively good,basically meet the standard of drinking water.(3)Through the monitoring of the shallow groundwater quality near the irrigation area--Gengpeng Town,it was found that the content of nitrate nitrogen and nitrite nitrogen did not exceed the class ? standard,and the content of ammonia nitrogen is near the class ?(?0.10 mg/L),but the content of CODMn exceeded the class ? standard(? 3.0mg/L).Therefore,the irrigation discharge of high concentration starch wastewater will have a certain impact on the water quality of shallow groundwater in some sections.(4)Taking the reinjection of starch wastewater in Gengpeng Town as an example,the starch test site is a typical pollution area,simulating the migration process of pollutants from the surface aeration zone aquifer.It was found that the wastewater diffuses to 4.03 km2,the center concentration reaches 31.0 mg/L,the horizontal migration distance of pollution halo is 2.40 km,and the vertical migration distance is 0.017 km.It reveals the existence of the middle weak permeable layer,which to some extent blocks the migration speed and diffusion ability of pollutants from the phreatic aquifer to the lower micro-confined aquifer.(5)In addition to the hydrogeological conditions,the agricultural irrigation also has a certain impact on groundwater quality in Bali River catchment.Figure[49]table[17]reference[90].