Wellesley College, Wellesley, MA, USA.
Division of Biological Sciences, University of Montana, Missoula, MT, USA.
Sci Total Environ. 2019 May 15;665:1125-1134. doi: 10.1016/j.scitotenv.2019.02.151. Epub 2019 Feb 11.
The soils and food webs associated with mid to high elevation, forested, headwater streams in northeastern North America are potential hotspots for mercury (Hg) methylation and bioaccumulation, but are not well studied. Our goals were to quantify total Hg (THg) and methyl Hg (MeHg) concentrations in soils and terrestrial food webs associated with headwater streams of northern hardwood forests to identify predictors of small-scale spatial variation in Hg bioaccumulation. We sampled soil characteristics that promote Hg methylation including pH, sulfur and calcium content, and organic matter. To assess spatial variation, we sampled at high (700 m asl) and mid elevations (500 m asl), both adjacent to (<1 m) and away from (>75 m) three replicate headwater streams in each of two watersheds of the White Mountains region, New Hampshire, USA. Soils of these forested watersheds differed significantly in pH and the content of calcium, sulfur, organic matter and THg. Conditions for methylation were more favorable in the upland forest sites compared to streamside sites. Significant bioaccumulation of THg occurred in all measured components of the food web, including insects, spiders, salamanders, and birds. Trophic position, as determined by δN, was the best predictor of both THg and MeHg bioaccumulation across the sampled taxa and was also a better predictor than spatial location. However, the degree of bioaccumulation at which MeHg significantly affects animal behavior, reproduction or survival is unknown for most taxa in terrestrial habitats, particularly for invertebrates. These findings show that Hg methylation and bioaccumulation is not limited to areas traditionally classified as wetlands or to areas with exceptionally high THg inputs, but that it is a widespread and important phenomenon in the moist deciduous forests of eastern North America.
与北美东北部中高海拔、森林覆盖的源头溪流相关的土壤和食物网是汞（Hg）甲基化和生物积累的潜在热点，但研究并不充分。我们的目标是量化与北方硬木林源头溪流相关的土壤和陆地食物网中总汞（THg）和甲基汞（MeHg）的浓度，以确定 Hg 生物积累的小尺度空间变异的预测因子。我们采样了促进 Hg 甲基化的土壤特性，包括 pH 值、硫和钙含量以及有机质。为了评估空间变异，我们在高海拔（700 m 海拔）和中海拔（500 m 海拔）采样，两个海拔高度都靠近（<1 m）和远离（>75 m）怀特山脉地区的两个流域的三个重复源头溪流，美国新罕布什尔州。这些森林流域的土壤在 pH 值和钙、硫、有机质和 THg 的含量上有显著差异。与溪流沿岸站点相比，高地森林站点的甲基化条件更为有利。在食物网的所有测量组成部分中，包括昆虫、蜘蛛、蝾螈和鸟类，都发生了显著的 THg 生物积累。由 δN 确定的营养位置是所有采样类群中 THg 和 MeHg 生物积累的最佳预测因子，其预测能力也优于空间位置。然而，对于大多数陆地栖息地的动物，特别是无脊椎动物，MeHg 对动物行为、繁殖或生存产生显著影响的生物积累程度尚不清楚。这些发现表明，Hg 甲基化和生物积累不仅限于传统上被归类为湿地的地区，也不限于 THg 输入异常高的地区，而是在北美东部的湿润落叶林中广泛存在且非常重要的现象。
