三峡库区典型农田小流域土壤汞的空间分布特征

Spatial Distribution of Mercury in Soils of a Typical Small Agricultural Watershed in the Three Gorges Reservoir Region

为了解三峡库区农田流域汞污染现状及其生态风险,以三峡库区腹心地带的涪陵王家沟典型农田小流域为调查对象,基于Arc GIS地统计模块研究流域内不同土地利用类型(旱地、田地、林地和居民点)土壤汞(Hg)含量及其分布特征,并对其汞污染程度和生态风险进行评价.结果表明,流域内土壤Hg含量范围为9.47~94.57μg·kg-1,均值为(34.23±16.23)μg·kg-1,不同土地类型表层土壤Hg含量高低顺序为林地、田地、居民点、旱地;表层土壤出现明显汞累积现象,土壤Hg含量变化与土壤深度呈极显著负相关关系.地统计分析结果表明,流域土壤中的汞呈现出较弱的空间相关性,说明流域内土壤汞的空间分布主要受大气干湿沉降、植被覆盖和地形等自然因素影响,人为等外源干扰影响弱.流域土壤总体上虽未表现出明显的汞污染现象(污染指数为-0.08),但具有中度的汞潜在生态风险(生态风险指数为57),其中以林地较为严重.流域土壤汞承载量约为25.39 kg,旱地约占69%.

To understand the mercury( Hg) pollution level and the corresponding ecological risk in agricultural watershed of the Three Gorges Reservoir region,a typical watershed,Wangjiagou,located in Fuling,where is in interior zones of the Three Gorges Reservoir region,was selected as the study object. Meanwhile,Arc GIS geo-statistics module was conducted for investigation of the Hg contents and distribution characteristics in soils of different land use types including dry land,farmland,woodland and settlements. Also the corresponding Hg pollution level and ecological risk were assessed. The results suggested that soil Hg contents in this watershed ranged from 9. 47 to 94. 57 μg·kg-1,and the mean value was( 34. 23 ± 16. 23) μg·kg-1. Higher Hg contents in surfaces of soils were observed in woodland,followed by farmland and settlement. The lowest was found in dry land. Surfaces of soils significantly showed Hg accumulation,and an obvious inverse correlation between soil Hg contents and soil depths was also observed in this study.Additionally,geo-statistics analysis showed a weak spatial correlation of soil Hg contents in this watershed,indicating the spatial distribution of soil Hg in this watershed was mainly influenced by several natural factors such as atmospheric wet-dry deposit,vegetation coverage and topography,instead of anthropogenic interference. Overall confirmative soil Hg pollution was not found in this watershed,which showed a very low pollution index(-0. 08),but a moderate potential ecological risk still existed( the ecological risk index was57),of which woodland had the highest potential risk. The total capacity of Hg in this watershed was 25. 39 kg,among which dry land accounted for 69%.