Study On The Heavy Metal Pollution And Environment Capacity In Water?Surface Sediments And Riparian Soils Of Qinggeda Lake

In recent years,lakes have experienced ecological and environmental problems in China such as lake shrinkage,water quality deterioration,heavy metal pollution,and ecological function degradation,which seriously restrict the full play of lake ecological functions.Though the governance of lakes in China has been intensified since the 18th National Congress,the decline trend of the whole water environment quality of lakes across the country has not been fundamentally changed.The development and utilization level of some lake have reached the ecological limit and threatened regional ecological security.Qinggeda Lake is undertaking irrigation of the Urumqi vegetable basket base and 500,000 mu farmland,the tourism development activities of the waters and shoreline of Qinggeda Lake have increased,the improper management and protection tends to raise disorderly development,and be harmful to the water environment quality and ecological functions of Qinggeda Lake.Therefore,it is urgent to carry out research on environmental pollution investigation and assessment of Qinggeda Lake to provide scientific guidance for lake water environment safety and management in arid areas.We conducted our research in the Qinggeda Lake,collected samples and measured the contents of eight heavy metals?Pb,Cu,Cr,Ni,Zn,Mn,V and As?and main physicochemical characteristics;The geographical weighted regression model,environmental risk assessment model,environmental capacity estimation and prediction model were developed with multi-variate statistics analysis methods,Kriging interpolation,Redundancy analysis to evaluate the contents of the eight heavy metals in the Lake water–sediments–riparian soil system,reveal the spatial distribution characteristics,assess the contamination degree and resolve the sources of heavy metals.explore the spatial dependency relationship between environmental factors and heavy metals,assess environmental risks and estimate environmental capacity.This study expects to provide scientific guidance for lake water environment safety and management in arid areas,scientific basis for prevention and control of heavy metals pollution and sustainable development of the ecological environment in the Qinggeda Lake Basin,and have certain application value for promoting the pace of the autonomous region to win the fight against pollution.The main results are as follows:?1?The Qinggeda Lake was alkaline with average pH of 8.85;the average dissolved oxygen was over 5 mg.L^-1,and conductivity varied from 598?S?cm^-1 to1028?S?cm^-1.The four water environmental factors?pH,EC,DO and water temperature?were closely correlated to water heavy metal concentration.The water temperature?T?had the least influence on the concentration of each heavy metal,while the conductivity has the greatest influence.The concentrations of six heavy metals?Cu,Cr,As,Cd,Pb,and Ni?were lower,and could meet the water body functional requirements of agricultural irrigation,aquaculture,and recreation.The concentration of As showed a decreasing trend from southwest to northeast in spatial distribution,and Pb showed a decreasing trend from west to east,while Cu showed a gradual increase from north to south.The highest concentration mainly appeared in the southwest riparian of the lake.Human activities such as the afflux of industrial wastewater into the lake were the main input sources for heavy metals in Qinggeda Lake.The total risk of human health in the water environment of Qinggeda Lake was only 1/2 of the maximum acceptable risk level 5.0×10^-5 a^-1 recommended by ICRP.The water ecological environment was good.?2?The riparian soils was alkaline,and the average and maximum values of eight heavy metal elements?Mn,As,Ni,Cu,Pb,Cr,Zn and V?did not exceed the national limit of soil quality standards and agricultural land risk control standards?GB15618-2018?,however,Cu,Cr and V were generally higher than the value of Xinjiang Soil Background.The eight heavy metals showed higher content in the eastern regions than other regions in spatial distribution,its content increased with the increase of the offshore distance,and the paddy field was the high point of accumulation of heavy metals.The riparian soils around the lake were generally free of pollution.Cr,Mn,Cu,and Zn were the main factors affecting the environmental characteristics of riparian soils such as pH,conductivity and organic matter.Among them,As had the greatest influence on conductivity,Zn on organic matter,and Cu on pH.These heavy metals showed a low accumulation capacity,and they were mainly from anthropogenic sources such as domestic sewage,agricultural production waste discharge and transportation.The contents of heavy metals such as Zn,Mn and Ni decreased gradually with the increase of soil depth,showing vertical migration.The average content of As,Cu,V and Cr showed a vertical migration characteristics of“low-high-higher”,but the overall migration ability of heavy metals was not high and have no obvious difference.The carcinogenic risk index?CR?of As was 10^-5orders of magnitude in different soil layers,and there was a certain risk of cancer.The non-carcinogenic risk index?HI?of three heavy metals?Pb,Zn and Cu?was less than 1 in different soil layers,and there was no risk of non-carcinogenic health.The ecological risk factors?E_rⁱ?of eight heavy metals?Pb,As,Zn,Cu,Ni,Cr,Mn and V?were all lower than 10,and the comprehensive potential ecological risk index?RI?was 28.43.Generally speaking,the potential ecological hazard of heavy metals was lower,and the riparian soil ecological environment was in good condition.?3?The average values of six heavy metals such as As,Cu,Pb,Cr,Zn and V in the surface sediments of the lake exceeded the Xinjiang Sediments Background.The eight target heavy metals decreased from the center of the lake to the shore similarly in spatial distribution.Cr,As,Pb,Cu,and Zn were the main factors affecting the environmental characteristics of surface sediments.Among them,As had the greatest influence on conductivity,while Zn on organic matter,and Cu on pH.As in general was moderately enriched,and the point with the largest enrichment coefficient was located in the center of the lake;Ni was the sensitive pollution factor in the study area.The average value of the accumulation index(I_geo)of Zn,Cu,Mn and V was less than 0,and was in a non-polluting state.As reached a moderate pollution level at77.78%of the sample,the comprehensive pollution load index?PLI?was 1.284.In General,the degree of potential ecological hazard was lower,and it would not pose a threat to the ecological environment for the time being.?4?The total environmental capacity of heavy metals in riparian soils was Cr?paddy field?>Zn>Pb?paddy field?>>Cr?dry land?>Ni>Pb?dry land?>Cu>As?dry land?>As?paddy field?.The environmental capacity of heavy metals in soil was affected by various factors such as pH,organic matter,conductivity,land use type and so on.The existing environmental capacity of Cr was most affected by organic matter and had the largest environmental capacity in urban land.Ni was mostly affected by pH and had the largest environmental capacity in farmland.As was mostly affected by conductivity and had the largest environmental capacity in farmland.The environmental capacity of heavy metal in different soil layers had medium-high capacity levels,and heavy metal carrying capacity was large in all.It was predicted that the time period of the six target heavy metal soil environmental capacity reaching the critical mass capacity was As?30 years?>Cu?15 years?>Cr?8years?>Zn?5 years?>Ni?4 years?>Pb?2 years?,where Pb was a heavy metal element with a focus on control.The time period for the same heavy metal to reach critical risk capacity was different in different soil layers,and was the shortest in the 0²0cm soil layer.the implementation of total control was effective measures to achieve sustainable development of soil ecological environment.