西藏拉鲁湿地表层土壤重金属分布特征和风险评价

Distribution Characteristics and Risk Assessment of Heavy Metals in the Surface Soil of Lhalu Wetland,Tibet

拉鲁湿地是国家级自然保护区,具有重要的生态功能,为支撑该湿地生态修复与保护,该研究系统开展了研究区土壤环境质量调查。在拉鲁湿地采集了23个表层土壤样品,测试其理化性质和元素Cu、Zn、Ni、Cd、Cr、Pb、As的浓度,分析了重金属的分布特征,并进行风险评价。结果表明,拉鲁湿地土壤p H均值为7.05,为偏中性土壤,有机质和总氮含量均值分别为64.67、2.92 g/kg,均属于一级水平,总磷和总钾的均值分别为0.62、19.61 g/kg,均属于三级水平;元素Cr和Ni的浓度均值低于城市土壤背景值,Cu、Zn、Pb、Cd和As的平均浓度为34、94、39.9、0.25和22.3 mg/kg,分别是城市土壤背景值的1.55、1.45、1.29、2.05和1.12倍,但均低于《土壤环境质量农用地土壤污染风险管控标准(试行)》(GB 15618-2018,6.5≤pH≤7.5)中的风险筛选值;地累积指数法和潜在生态风险指数法表明Cd为主要风险因子,其风险贡献率显著高于其他6种重金属,综合潜在生态风险指数RI均值为92.49,整体为低风险区;研究区土壤中Ni、Cr和As元素的累积主要受自然因子控制,而Cu、Zn、Pb和Cd元素累积主要受到交通源的影响。拉鲁湿地整体土壤肥沃,环境质量优良,但存在重金属污染的风险,Cd元素的富集尤为突出。

Lhalu Wetland is a national nature reserve with important ecological functions.Therefore,for the ecological restoration and protection of the wetland,the soil environmental quality survey in the study area was carried out systematically.23 surface soil samples were collected in Lhalu Wetland,and the physical and chemical properties of soil and the concentrations of elements Cu,Zn,Ni,Cd,Cr,Pb,As were tested.Then,the distribution characteristics of heavy metals in soil were analyzed,and the risk assessment was carried out.The results show that the average pH value of Lhalu Wetland soil is 7.05,which is neutral soil.However,the average contents of organic matter and total nitrogen are 64.67 g/kg and 2.92 g/kg respectively,which is satisfactory to the first level.The mean values of total phosphorus and total potassium were 0.62 g/kg and19.61 g/kg respectively,which belonged to the third level.Among them,the mean concentrations of Cr and Ni are lower than the background values of urban soil.The average concentrations of heavy metals Cu,Zn,Pb,Cd and As are 34 mg/kg,94 mg/kg,39.9 mg/kg,0.25 mg/kg and 22.3 mg/kg,respectively,which are 1.55,1.45,1.29,2.05 and 1.12 times of the urban soil background values.The concentration values of heavy metals in soil are lower than the risk screening values in the Soil Environmental Quality Risk Control Standard for Soil Contamination of Agricultural Land(GB 15618-2018,6.5≤pH≤7.5).The assessment results of geo-cumulative index method and potential ecological risk index method show that Cd is the main risk factor,and its risk contribution rate is significantly higher than that of other six heavy metals.The average value of potential ecological risk index RI is 92.49,which is a low risk area as a whole.In addition,the accumulation factors of Ni,Cr and As in the soil are mainly affected by natural factors,while the accumulation factors of Cu,Zn,Pb and Cd are mainly affected by traffic sources.The overall soil of Lhalu Wetland is fertile and the environmental quality is excellent.However,affected by heavy metals,the enrichment of heavy metal Cd is particularly obvious.