Regional Groundwater Environment Evolution And Partition The Prevention-control In Urban Agglomeration Around Poyang Lake

The area around Poyang Lake is characterized by complex geological and geochemical structures,including quaternary pore water,red clastic rock fissure pore water,bedrock fracture water and carbonate karst cave water and other types,while the densely distributed surface water in the region has interactive effects with groundwater;As the main engine of rapid economic development in Jiangxi Province,a large number of domestic sewage and industrial and agricultural potential pollution sources lead to prominent environmental problems in inland water in the region.I take the urban agglomeration region around Poyang Lake as the research area,based on the theories of hydrogeology,geochemistry and environmental science,analyzing the environmental chemical indexes of groundwater in multiple multi-stage river basins in 1979-1980,2012-2013,2018-2019,using statistical analysis and graphical methods to elaborate the types of groundwater chemistry and the variations and spatial variability of groundwater quality change pattern and spatial distribution law,and further illustrated by Gibbs diagram,Main ion correlation analysis and isotope changes elaborate the source of groundwater hydrochemical components and formation mechanism of hydrochemical characteristics;Based on the water quality evaluation method,the key factors affecting the quality of groundwater in the study area were analyzed,and the spatial distribution characteristics of groundwater quality were further analyzed.The driving factors of groundwater environmental evolution were discussed by analyzing the spatial distribution characteristics and genesis of typical indexes such as p H value,iron,manganese and trinitrogen.The distribution characteristics of pollution sources,groundwater pollution load and anti-pollution performance of groundwater were analyzed,and pollution prevention zoning in the study area is superimposed and mapped,and targeted groundwater pollution prevention and control strategies are put forward.Based on this,this paper mainly draws the following conclusions:（1）The Shukalev classification method is used to classify 7 groundwater environmental units in the study area.Overall,the groundwater in the study area is mainly bicarbonate water,accounting for 75%.Chlorinated water,sulphuric acid water and nitric acid water occur in some areas（mainly in pore water of valley plain）,accounting for 8%,6%and 11%respectively.Among them,the proportion of nitric acid water increases,mainly distributed in wuhe River valley plain,Poyang lakeside plain,Hilly fissure pore water area,Gaoan-Leping depression hilly fissure karst water subarea,Jiuling-Gaotaishan Taigong hilly fissure water subarea,and Guanmaoshan Taigong hilly fissure water subarea;In general,the cation content has little change,the anion is mainly HCO₃^-,while the content of SO₄^2-,Cl^-and NO₃^-has a trend of relative increase.（2）On the whole,the hydrochemical genesis of pore diving,pore confined water,fissure water and karst water groundwater is mainly influenced by rock weathering,and atmospheric precipitation also influences them to a certain extent,but evaporation has no obvious effect.The chemical composition of groundwater is affected by water-rock interaction,cation exchange,evaporation and concentration and other natural factors and human activities,in which Ca²⁺+Mg²⁺and HCO₃^-are mainly derived from carbonate dissolution,followed by Ca²⁺and Mg²⁺are also affected by silicate and evaporite dissolution.Na⁺and K⁺in groundwater mainly come from rock salt process,in which pore diving and dissolution of karst water salt rock and feldspar minerals（silicates）are the main sources of Na⁺and K⁺.Variations of stable isotopes D and ¹⁸O of surface and groundwater indicate that groundwater and surface water are supplied by evaporation and precipitation to some extent.Pore water in the study area is mainly related to feces and domestic sewage,possibly because the pore water area is mainly urban aggregation area,while the nitrate of karst water is most affected by chemical fertilizers,and the fissure water is generally affected by chemical fertilizers,feces and domestic sewage.In general,the chemical characteristics of groundwater in the study area are mainly affected by the natural environment and human activities,but due to the distribution difference of human activities,different types of groundwater are affected differently.（3）From the analysis of the influence of groundwater indexes on water quality and the spatial distribution of water quality,it can be seen that there were more than10 different types of exceedance factors in the study area during 1979-1980,among which p H,Zn,Mn,Fe,NH₄⁺,SO₄^2-,F^-and COD_Mnwere more serious exceedance factors.In the 2018-2019m,the groundwater in the study area exceeded the standard of p H value,manganese,sulfide,etc.22 indicators,including organic exceeded the standard of 3.Class IV and class V groundwater are only affected by inorganic chemical indicators,the contribution rate is 82.51%and 90.52%,respectively.The most influential indicators are p H,manganese,sulfide,iron,nitrate.After evaluation of all indexes except p H,Fe,Mn and sulfide,the groundwater quality in the study area is mainly of class III.Part of class IV and V water is mainly distributed in densely populated urban areas or around pollution sources such as industry,and Class I water is distributed in Nanchang,Fengcheng,Zhangshu,Yujiang and Linchuan.The groundwater IV and V in the region are mainly affected by p H value,iron,manganese and sulfide,which may be caused by the combined influence of the original environment and human activities.（4）According to the entropy weight water quality index（EWQI）method,92.05%of the groundwater in the study area was above"medium"in 2012-2013.During the period of 2018-2019,the proportion of the water quality of the diving medium and above was 92.65%.During 1979-1980,the water quality of the groundwater diving and confined water in the study area was good,and the water quality grade was mainly excellent,while other grades accounted for less.The poor and extremely poor water quality of diving was significantly lower than that of confined water,and the proportion of good and medium increased in 2018-2019 and2012-2013 periods,both of which accounted for no less than 30%.Stepwise linear regression analysis was used to identify that Mn,TDS,NO₃^-,Fe and I^-had a strong contribution to EWQI,and the optimization model EWQI_mincomposed of them could reflect EWQI to a greater extent.At the same time,the acidic characteristics of regional groundwater were considered comprehensively.Therefore,The monitoring indexes of groundwater in the study area can optimize p H value,Mn,TDS,NO₃^-,Fe and I^-.（5）Weak acid groundwater accounts for a large proportion in the study area,which is mainly influenced by acid rain,topography,aerated zone soil and surface water.Groundwater p H value less than 6.5 is widely distributed around the Poyang Lake.Fe and Mn in groundwater are over-standard distributed in Gan-Fu alluvial plain area,coastal area around Poyang Lake,Changjiang coastal area,De’an County town,Fengcheng city and other places.Mn in different groundwater types is over-standard,and the excessive Fe content was mainly the pore water,which is mainly caused by joint influence of Holocene（Q₄）and Middle Pleistocene（Q₂）reductive sedimentary environment and human activities.Ammonia nitrogen and nitrate in trinitrogen exceed the standard most seriously in the field and plain,and nitrate water accounted for the largest proportion in the plain dominated by pore water,which was mainly caused by human activities such as domestic sewage and agricultural non-point source in the study area.The excessive lead,arsenic,mercury and cadmium in the underground water were mostly concentrated in the surrounding areas of Nanchang City,and some of them are blocky and banded,with a certain zonality.The main reason is that industrial enterprises are densely distributed in such areas,and such areas also belong to areas with high background values of lead and cadmium such as Poyang Lake,Nanchang-Xingan Ganjiang River Basin.（6）According to the human health risk evaluation of diving around Poyang Lake,As and Cr⁶⁺are carcinogenic substances for adults and children in diving.Fuzhou,Jingdezhen and Jiujiang are different with As carcinogenic risk for adults and children,while Jiujiang is the only city with Cr⁶⁺carcinogenic risk.Most cities in the study area have non-carcinogenic risk,and the main route of exposure to human body is through oral drinking.The non-carcinogenic risks of diving for both adults and children include Mn,NO₃^-,F-and NO₂^-,among which Mn and NO₃^-contribute the most to the non-carcinogenic risks.Compared with adults,the groundwater around Poyang Lake area has a greater risk of carcinogenesis and non-carcinogenesis in children,and the main exposure route is oral intake,while transdermal intake has little effect.As a result,part of the groundwater in the region is not directly drinkable for long periods of time to prevent risks to human health.（7）Combined with the distribution characteristics of pollution sources and hydrogeological conditions of urban agglomeration around Poyang Lake,analyze and evaluate the regional inland sewage pollution load and groundwater anti-pollution performance,calculate the prevention and control values of different regions in the study area,and determine groundwater protection areas.As for the distribution of prevention and control areas and control areas,the protected area is determined to be about 1619.19km²,accounting for 3.16%of the total area,the prevention and control area is about 48812.15km²,accounting for 95.31%of the total area,and the control area is about 784.31km²,accounting for 1.53%of the total area.Finally,the groundwater pollution prevention and control zoning map of urban agglomeration around Poyang Lake is drawn as follows It provides scientific basis for regional groundwater quality improvement and pollution prevention。...