Distribution characteristics and source analysis of heavy metals in surface sediments of Chabalang wetland in Xizang based on APCS-MLR model
Wetlands,serving as the third ecosystem situated between water bodies and land,possess significant ecological functions. Due to its unique geographical location and natural environmental conditions,Xizang has formed numerous distinctive natural plateau wetlands. In the Lhasa River basin,the phenomenon of wetland ag-gregation is particularly pronounced,with the Chabalang wetland being a crucial member of this basin. In recent years,the vigorous development of urban tourism,agriculture,and animal husbandry has led to varying degrees of degradation in wetland area,biodiversity,and wetland functions. To understand the distribution characteris-tics and pollution status of heavy metals in the surface sediments of the Chabalang wetland in Xizang,19 sam-ples of wetland surface sediments were collected in August 2021. The concentrations of heavy metals in these sediment samples were determined,and the Nemerow Pollution Index and Potential Ecological Risk Index were employed to evaluate heavy metal pollution in the study area. Additionally,the Absolute Principal Component Scores-Multiple Linear Regression model (APCS-MLR) was utilized for source apportionment of heavy metals. The results revealed that the concentrations of Cu,Cr,Ni,Zn,Pb,Cd,As,and Hg in the surface sediments of the Chabalang wetland were 1.71,0.56,0.65,1.02,1.31,1.52,0.92,and 1.48 times the background val-ues in Xizang,respectively,but significantly lower than the screening values in the Soil Environmental Quality Standards for Agricultural Land (GB 15618—2018). Compared with other plateau wetlands in Xizang,the en-richment level of heavy metals in the sediment was relatively low. The average Nemerow Pollution Index in the study area was 1.68,indicating a mild pollution level,and the average Potential Ecological Risk Index (RI) was 134.45,representing a slight ecological risk. The APCS-MLR results indicated that Cu,Zn,Pb,and Hg in the sediments of the Chabalang wetland originated from a mixed source of transportation and agricultural activi-ties,while Cr and Ni originated from the soil parent material source,As originated from the geothermal source,and Cd originated from both the geothermal source and a mixed source of transportation and agricultural activi-ties. The primary pathway for sediment pollution in the study area was identified as a mixed source of transporta-tion and agricultural activities. This study elucidates the current status of heavy metal elements in the sediment of the Chabalang wetland,including their occurrence,spatial distribution characteristics,ecological risk levels,and possible sources. It provides an objective understanding of the current environmental quality of the wetland,offering scientific evidence and theoretical support for pollution prevention,control efforts,and sustainable de-velopment in the Chabalang Wetland and other similar high-altitude wetlands.
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