Desert Research Institute, Reno, NV, USA.
Environ Sci Technol. 2011 May 1;45(9):3974-81. doi: 10.1021/es104384m. Epub 2011 Apr 7.
Results from a systematic investigation of mercury (Hg) concentrations across 14 forest sites in the United States show highest concentrations in litter layers, strongly enriched in Hg compared to aboveground tissues and indicative of substantial postdepositional sorption of Hg. Soil Hg concentrations were lower than in litter, with highest concentrations in surface soils. Aboveground tissues showed no detectable spatial patterns, likely due to 17 different tree species present across sites. Litter and soil Hg concentrations positively correlated with carbon (C), latitude, precipitation, and clay (in soil), which together explained up to 94% of concentration variability. We observed strong latitudinal increases in Hg in soils and litter, in contrast to inverse latitudinal gradients of atmospheric deposition measures. Soil and litter Hg concentrations were closely linked to C contents, consistent with well-known associations between organic matter and Hg, and we propose that C also shapes distribution of Hg in forests at continental scales. The consistent link between C and Hg distribution may reflect a long-term legacy whereby old, C-rich soil and litter layers sequester atmospheric Hg depositions over long time periods. Based on a multiregression model, we present a distribution map of Hg concentrations in surface soils of the United States.
对美国 14 个森林地点的汞 (Hg) 浓度进行系统调查的结果表明，Hg 浓度最高的是枯枝落叶层，与地上组织相比，Hg 高度富集，表明 Hg 在沉积后有大量的吸附作用。土壤中的 Hg 浓度低于枯枝落叶层，表层土壤中浓度最高。地上组织没有表现出可检测到的空间分布模式，这可能是由于不同地点存在 17 种不同的树种。枯枝落叶层和土壤中的 Hg 浓度与碳 (C)、纬度、降水和土壤中的粘土呈正相关，这些因素共同解释了浓度变化的 94%。我们观察到土壤和枯枝落叶层中的 Hg 含量随纬度呈明显增加趋势，而大气沉降测量的纬度梯度则相反。土壤和枯枝落叶层中的 Hg 浓度与 C 含量密切相关，这与众所周知的有机质与 Hg 之间的关系一致，我们提出 C 也塑造了大陆尺度上森林中 Hg 的分布。C 与 Hg 分布之间的一致联系可能反映了一个长期的遗留问题，即富含 C 的旧土壤和枯枝落叶层在很长一段时间内隔离大气 Hg 沉降。基于多元回归模型，我们提出了美国表层土壤中 Hg 浓度的分布图。
