Risk Assessment of Heavy Metals in Ganqu Wetland Based on Monte-Carlo Simulation
Ganqu Wetland is a representative valley wetland in the Lhasa River Basin.In order to understand the distribution characteristics and environmental risks of heavy metals in the wetland,a total of 22 sediment samples were collected.The contents of eight heavy metals(Cd,Hg,As,Pb,Cr,Cu,Ni and Zn)were analyzed.The geo-accumulation index and Hakan-son potential ecological risk index were used for risk assessment,and the ecological risk in the study area was quantitative-ly assessed by coupling with Monte-Carlo simulation.Absolute principal component score-multiple linear regression model(APCS-MLR)was further used to analyze the sources of heavy metals.The results showed that the contents of Cd,Hg,As,Pb,Cr,Cu,Ni and Zn in wetland sediments were 0.15,0.04,15.05,33.49,47.36,22.00,19.18 and 76.41 mg/kg,respec-tively.The contents of As,Ni and Cr were lower than the background values of Tibet,while the contents of Cd,Hg,Pb,Cu and Zn were 1.88,1.54,1.16,1.00 and 1.04 times of the background values,respectively.The geo-accumulation index showed that except for Cd(0.54),other elements were non-polluting.The comprehensive ecological risk index(RI)was 141.74,and the overall ecological risk in the study area was low.However,the results of the potential ecological risk index showed that Cd and Hg had a probability of 78.49％and 67.64％,respectively,which were medium ecological hazards and were the main factors causing ecological risks.The source apportionment of APCS-MLR model showed that the contribution rates of natural sources to Cu,Cr,Ni,Zn and Pb were 86.09％,97.08％,86.36％,74.97％and 75.42％,respectively.The contri-bution rates of agricultural sources to Cd,As and Hg were 72.07％,67.30％and 50.34％,respectively.At the same time,Hg was also contributed by 49.66％of natural sources,indicating that Hg was affected by both sources.
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