Distribution of soil heavy metals and ecological risk assessment of agricultural land in Nianchu River basin, Tibet
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摘要:
以西藏年楚河流域江孜县、白朗县农用地土壤为研究对象，对Hg、As、Pb、Cd、Cr、Cu、Mn、Zn和Ni 9种重金属进行调查；采用单因子指数法、内梅罗综合污染指数法等方法，结合空间插值法评价年楚河流域农用地土壤重金属污染状况，同时运用相关性和主成分分析探究土壤重金属来源。结果表明：1)农用地土壤中Hg、Cu、Mn和Ni浓度与西藏土壤环境背景值相比，均表现为不同程度的累积，与GB 15618—2018《土壤环境质量 农用地土壤污染风险管控标准（试行）》比较，As元素超标率最大；从江孜县到白朗县，农用地土壤重金属综合生态风险指数逐步增大；2)研究区的区域污染负荷指数为1.45，属低污染等级，重度污染集中在白朗县；3)主成分分析表明，9种重金属的来源可分为自然与人为源复合因子、矿山开采因子、农业因子、土壤母质因子和大气传输因子。
Abstract:Taking the cultivated soil in Bailang County and Jiangzi County of Nianchu River basin in Tibet as the research objects, the contents of 9 kinds of heavy metals, Hg, As, Pb, Cd, Cr, Cu, Mn, Zn and Ni, were investigated and analyzed. The single factor index method, Nemerow comprehensive pollution index method and other methods, combined with the spatial interpolation method were used to evaluate the heavy metal pollution of agricultural land in Nianchu River basin. Meanwhile, correlation analysis and principal component analysis were used to explore the sources of soil heavy metals. The results showed that: 1) The content of Hg, Cu, Mn and Ni in the soil of agricultural land showed different degrees of accumulation, compared with the background values of the soil environment in Tibet. Compared with Soil Environmental Quality: Risk Control Standard for Soil Contamination of Agricultural Land (GB 15618-2018), As had the highest rate exceeding the standard. From Jiangzi County to Bailang County, the comprehensive ecological risk index of soil heavy metals in agricultural land gradually increased. 2) The regional pollution load index of the study area was 1.45, which was a low pollution level. Severe pollution was concentrated in Bailang County. 3) Principal component analysis showed that the sources of 9 kinds of heavy metals could be divided into natural and anthropogenic complex factors, mining factors, agricultural factors, soil parent material factors and atmospheric transmission factors.
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Key words:
- Nianchu River basin /
- agricultural land /
- heavy metals /
- pollution assessment /
- source analysis
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图 1 年楚河流域行政区划及采样点分布
Figure 1. Administrative divisions and distribution of sampling points in Nianchu River basin
图 2 采样点农用地土壤PN空间分布
Figure 2. PN spatial distribution of soil in agricultural land at each sampling point
图 3 各采样点农用地土壤中9种重金属Igeo统计
Figure 3. Igeo distribution of 9 heavy metals in soils of agricultural land at sampling sites
图 4 各采样点农用地土壤中9种重金属Er统计
Figure 4. Er distribution of 9 heavy metals in soils of agricultural land at sampling sites
图 5 各采样点农用地土壤中Hg、Cd和Ni的Er空间分布
Figure 5. Er spatial distribution of Hg, Cd and Ni in soils of agricultural land at sampling points
图 6 研究区农用地土壤RI空间分布
Figure 6. RI spatial distribution in soils of agricultural land in the study area
图 7 农用地土壤9种重金属主成分载荷
Figure 7. Principal component loading of nine heavy metals in soils of agricultural land
表 1 单因子指数法与内梅罗指数法评价标准
Table 1. Evaluation criteria of single-factor index method and Nemerow index method
Pi PN 数值 污染等级 数值 污染等级 <1 清洁 <0.7 清洁 1~2 轻度 0.7~1 警戒 2~3 中度 1~2 轻度 ≥3 重度 2~3 中度 ≥3 重度 
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表 2 潜在生态风险指数法评价标准
Table 2. Evaluation standard of potential ecological risk index method
Er RI 风险等级 <40 <150 低风险 40~80 150~300 中等风险 80~160 300~600 重度风险 160~320 ≥600 较重度风险 ≥320 严重风险
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表 3 农用地采样点土壤中重金属浓度统计结果
Table 3. Statistical results of heavy metal concentrations in the soil of sampling sites in agricultural land
重金属 浓度/(mg/kg) 变异系数 西藏土壤环境背景值[18]/(mg/kg) 超标采样点数量占比/% 最大值 最小值 平均值 Hg 0.16 0.03 0.06 0.54 0.026 100 As 34.10 8.09 20.96 0.38 18.70 68.8 Pb 30.90 14.50 22.84 0.23 28.90 12.5 Cd 0.18 0.08 0.12 0.20 0.08 100 Cr 516.00 69.20 161.63 0.86 77.40 87.5 Cu 52.10 29.50 39.18 0.16 21.90 93.8 Mn 1 287.88 666.67 903.88 0.19 626.00 93.8 Zn 148.00 67.70 93.22 0.20 73.70 87.5 Ni 583.33 38.89 117.69 1.43 32.10 93.8
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表 4 农用地土壤各采样点Igeo和PLI统计结果
Table 4. Statistical results of Igeo and PLI at each sampling point of agricultural land soil
样点编号 Igeo PLI Hg As Pb Cd Cr Cu Mn Zn Ni 1 0.65 −1.61 −1.58 −0.58 −0.10 −0.04 −0.05 −0.13 −0.17 1.14 2 0.11 −1.79 −1.46 0.12 0.69 0.32 −0.05 0.42 0.39 1.36 3 1.20 −0.23 −0.49 0.32 −0.06 0.67 −0.17 −0.09 −0.05 1.63 4 0.14 −0.14 −0.73 0.12 −0.40 0.28 −0.49 −0.39 −0.31 1.29 5 0.56 −0.84 −0.82 0.12 −0.20 0.62 −0.17 −0.13 0.00 1.40 6 0.79 0.09 −0.61 0.58 −0.10 0.34 −0.17 −0.16 −0.07 1.58 7 0.05 0.20 −0.88 0.00 −0.34 0.12 −0.40 −0.39 −0.25 1.30 8 −0.28 0.03 −0.79 0.00 −0.45 0.23 −0.05 −0.35 −0.20 1.30 9 −0.35 −0.47 −0.53 0.32 −0.75 0.27 0.37 −0.14 −0.28 1.33 10 0.47 0.28 −0.63 0.12 −0.46 0.10 0.46 −0.21 −0.14 1.50 11 0.27 −1.50 −1.39 −0.26 0.92 0.29 −0.05 −0.52 1.62 1.43 12 0.59 −0.55 −1.05 0.12 −0.36 0.03 −0.35 −0.36 −0.07 1.29 13 2.05 −0.16 −0.89 0.00 −0.38 0.10 −0.17 −0.07 0.41 1.60 14 −0.17 −0.53 −1.08 −0.13 0.39 0.42 −0.17 −0.55 0.95 1.40 15 0.80 −0.56 −1.17 −0.55 2.07 −0.16 0.18 −0.71 3.60 1.96 16 0.28 −0.85 −1.25 0.00 2.15 0.24 0.07 −0.53 3.37 1.96
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表 5 研究区农用地土壤中重金属元素之间相关系数
Table 5. Correlation coefficients of heavy metal elements in the soil of agricultural land in the study area
重金属 Hg As Pb Cd Cr Cu Mn Zn Ni Hg 1 As 0.125 1 Pb 0.103 0.750** 1 Cd 0.022 0.453 0.745** 1 Cr −0.61 −0.357 −0.480 −0.414 1 Cu −0.67 −0.057 0.406 0.519* −0.242 1 Mn −0.142 0.018 0.125 −0.057 0.235 −0.229 1 Zn 0.174 −0.226 0.020 0.364 −0.380 0.268 0.034 1 Ni −0.002 −0.243 −0.384 −0.437 0.976** −0.326 0.276 −0.480 1 注：*表示在0.05水平上显著相关；**表示在0.01水平上显著相关。
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