Vermont Center for Ecostudies, Norwich, VT, USA.
Department of Biological Sciences, Dartmouth College, Hanover, NH, USA.
Ecotoxicology. 2019 Sep;28(7):717-731. doi: 10.1007/s10646-019-02068-4. Epub 2019 Jun 26.
Mercury (Hg) has accumulated in forested landscapes in the Northeastern U.S., and hotspots with enhanced deposition have been identified throughout the region. Due to a variety of favorable landscape characteristics, including relatively high dissolved organic carbon (DOC), fluctuating water levels, and low pH and dissolved oxygen, vernal pools provide ideal conditions for the conversion of Hg to its more toxic and bioavailable form, methylmercury (MeHg). Yet little is known about the concentrations, speciation, and bioavailability of Hg in vernal pools, or its bioaccumulation in vernal pool fauna and potential export into terrestrial systems. We investigated the role of forest cover type on the bioaccumulation of MeHg in wood frog (Lithobates sylvatica) and spotted salamander (Ambystoma maculatum) eggs, larvae, and adults, and investigated relationships among MeHg and water chemistry (pH, DOC). Water samples from pools located in coniferous stands had greater concentrations of THg and MeHg compared to deciduous pool water, and showed significant positive correlation to DOC (r = 0.683, P < 0.001) and correlated negatively with pH (r = -0.613, P < 0.001). Methylmercury levels in amphibian embryos were similar between the two species (L. sylvatica mean = 5.4 ng/g dw; A. maculatum mean = 3.5 ng/g dw). Concentrations of MeHg increased substantially in larvae, and were significantly greater in A. maculatum (mean = 237.6 ng/g ± 18.5 SE) than L. sylvatica larvae (62.5 ng/g ± 5.7 SE). Forest cover type did not explain variation in MeHg concentration among amphibian embryos or larvae. Methylmercury levels in adult tissue samples were significantly greater in A. maculatum (mean = 79.9 ng/g ± 8.9 SE) compared to L. sylvatica (mean = 47.7 ng/g ± 9.7 SE). This research demonstrates that vernal pools are important hotspots where amphibians bioaccumulate MeHg, which may then be transferred to terrestrial ecosystems. The abundance of amphibian larvae suggests they could be important bioindicators for monitoring MeHg loading and bioavailability.
美国东北部的森林景观中积累了汞 (Hg)，并且已经在整个地区确定了具有增强沉积作用的热点。由于各种有利的景观特征，包括相对较高的溶解有机碳 (DOC)、波动的水位以及低 pH 值和溶解氧，季节性池塘为汞转化为更具毒性和生物可利用形式的甲基汞 (MeHg) 提供了理想的条件。然而，关于季节性池塘中汞的浓度、形态和生物利用度，以及它在季节性池塘动物群中的生物积累及其潜在向陆地系统的输出，人们知之甚少。我们研究了森林覆盖类型对林蛙 (Lithobates sylvatica) 和斑点钝口螈 (Ambystoma maculatum) 卵、幼虫和成虫中 MeHg 生物积累的影响，并研究了 MeHg 与水化学 (pH 值、DOC) 之间的关系。与落叶林池塘水相比，来自针叶林林分池塘的水样中总汞和甲基汞浓度更高，并且与 DOC 呈显著正相关 (r = 0.683, P < 0.001)，与 pH 值呈负相关 (r = -0.613, P < 0.001)。两种物种的两栖动物胚胎中的甲基汞水平相似（林蛙平均值= 5.4ng/g dw；斑点钝口螈平均值= 3.5ng/g dw）。MeHg 浓度在幼虫中大幅增加，斑点钝口螈的浓度显著高于林蛙幼虫（平均值= 237.6ng/g±18.5 SE）。森林覆盖类型并不能解释两栖动物胚胎或幼虫中 MeHg 浓度的变化。成年组织样本中的 MeHg 水平在斑点钝口螈中显著高于林蛙（平均值= 79.9ng/g±8.9 SE）。这项研究表明，季节性池塘是重要的热点，两栖动物在这些热点中积累 MeHg，然后可能将其转移到陆地生态系统。大量的两栖动物幼虫表明它们可能是监测 MeHg 负荷和生物利用度的重要生物指标。
