典型红壤区不同用地类型土壤重金属污染水平分析及生态风险评价

Soil heavy metal pollution levels and ecological risk under different land use types in a typical red soil region

  • 摘要: 光泽县位于武夷山脉北段, 是江南丘陵山区典型的红壤分布区, 区内涵盖山水林田湖草等各类自然资源, 同时也是福建省的省定产粮大县, 农业利用使土壤受到不同程度影响。为探究光泽县不同土地利用类型土壤重金属污染现状, 选取县域范围内不同纬度的旱地(SC)、水田(SD)、杉木林地(SM)、次生阔叶林地(KY)和竹林地(ZL)土壤共75个样本, 测定土壤镉(Cd)、铅(Pb)、锌(Zn)、铜(Cu)、铬(Cr)、镍(Ni)、汞(Hg)和砷(As) 8种重金属的含量, 并采用单因子污染指数、内梅罗综合污染指数、地累积指数、潜在生态危害指数法评价其污染风险。结果显示, 光泽县典型红壤区不同用地类型土壤Cd、Pb、Hg、Zn平均含量均有超过福建省土壤重金属元素背景值的情况, 且土壤Cd和Pb含量超标水平较高, 超过农用地土壤污染风险控制标准(2018年)筛选值的点位比例率分别为9%和25%。土壤Pb的单因子污染指数较其他重金属高; 土壤Pb和Cd的地累积指数较高, 平均处于无-中度污染等级。研究区土壤Cd含量与pH极显著正相关(P<0.01), 而土壤Pb含量与海拔极显著正相关(P<0.01)。SC、SD土壤Cd含量显著高于同纬度其他非农业用地类型土壤(P<0.05), 且有27%和20%的点位超过2008年农用地土壤污染风险筛选值标准; 土壤重金属潜在生态风险属于中度风险等级, 明显高于KY、SM、ZL。农用地和非农用地土壤Pb含量差异不显著, 单因子污染指数和地累积指数差异不显著, 但均有不同比例轻微潜在生态风险。因此, 农业利用是光泽县土壤Cd污染的主要来源, 可采取针对性的农业改良措施(如提高土壤pH、增施有机肥等)进行防治, 而土壤Pb的污染源可能涉及自然源、农业源等综合因素。

     

    Abstract: Guangze County is situated in the northern section of the Wuyi Mountains, a typical red soil distribution area within the hilly and mountainous regions south of the Yangtze River. This county has abundant natural resources, including mountains, rivers, forests, farmlands, lakes, and grasslands. Additionally, it serves as a major grain-producing county at the provincial level in Fujian Province. Agricultural activities affect the soil quality of agricultural land to varying degrees. To investigate the current status of heavy metal pollution in soils across different land use types in Guangze County, 75 soil samples were collected from five land use types within the county: vegetable field (SC), paddy field (SD), Chinese fir forestland (SM), secondary broad-leaved forestland (KY), and bamboo forestland (ZL). The contents of eight heavy metals — cadmium (Cd), lead (Pb), zinc (Zn), copper (Cu), chromium (Cr), nickel (Ni), mercury (Hg), and arsenic (As) — were analyzed. Pollution risks were assessed using several indexes: single-factor pollution index, Nemero comprehensive pollution index, geoaccumulation index, and potential ecological risk index. The results indicated that the average soil contents of Cd, Pb, Hg, and Zn across different land use types in Guangze County exceeded the background values of these elements in Fujian Province. Notably, high levels of Cd and Pb were observed, with 9% and 25% sampling points, respectively, exceeding the screening values set by the GB 15618—2018 (Soil Environmental Quality — Risk Control Standard for Soil Environment of Agriculture Land). The single-factor index (Pi) of Pb in the soil was higher than those of the other heavy metals, and the geoaccumulation indexes (Igeo) of Pb and Cd in the soil were relatively high, indicating an average pollution level ranging from none to moderate. The Cd content in the soil of the study area exhibited a significantly positive correlation with soil pH (P<0.01), whereas the Pb content showed a significantly positive correlation with altitude (P<0.01). The Cd contents in the soils of SC and SD was significantly higher than that in non-agricultural land types at the same latitude (P<0.05), with 27% and 20% of the sampling points exceeding the screening values set by the GB 15618—2018 (Soil Environmental Quality — Risk Control Standard for Soil Environment of Agriculture Land). The potential ecological risk of heavy metals in the soil of SC and SD was classified as moderate risk, which was obviously higher than that for KY, SM, and ZL. No significant difference was found in the Pb content between agricultural and non-agricultural soils or in the Pi or Igeo values. However, different proportions of slight potential ecological risks were noted. Therefore, agricultural utilization is likely the primary source of Cd pollution in the soil of Guangze County. Targeted agricultural improvement measures, such as increasing soil pH and applying organic fertilizers, should be implemented for prevention and control. The sources of Pb pollution in soil may involve a combination of natural and agricultural origins.

     

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