Department of Environmental Science and Management, Portland State University, PO Box 751, Portland, OR 97201, USA.
U.S. Geological Survey, 345 Middlefield Rd. MS496, Menlo Park, CA 94025, USA.
Sci Total Environ. 2019 Jun 1;667:601-612. doi: 10.1016/j.scitotenv.2019.02.259. Epub 2019 Feb 21.
Methylmercury (MeHg) bioaccumulation in freshwater aquatic systems is impacted by anthropogenic stressors, including climate change and nutrient enrichment. The goal of this study was to determine how warmer water temperatures and excess nutrients would alter zooplankton communities and phytoplankton concentrations, and whether those changes would in turn increase or decrease MeHg concentrations in freshwater zooplankton. To test this, we employed a 2 × 2 factorial experimental design with nutrient and temperature treatments. Mesocosms were filled with ambient water and plankton from Cottage Grove Reservoir, Oregon, U.S.A., a waterbody that has experienced decades of elevated MeHg concentrations and corresponding fish consumption advisories due to run-off from Black Butte Mine tailings, located within the watershed. Treatment combinations of warmer temperature (increased by 0.7 °C), nutrient addition (a single pulse of 10× ambient concentrations of nitrogen and phosphorous), control, and a combination of temperature and nutrients were applied to mesocosms. The individual treatments altered phytoplankton densities and community structure, but alone the effects on MeHg concentrations were muted. Importantly, we found a significant interactive effect of nutrients and temperature: the nutrient addition appeared to buffer against increased MeHg concentrations associated with elevated temperature. However, there was variability in this response, which seems to be related to the abundance of Daphnia and edible phytoplankton. Nutrients at low temperature were associated with marginal increases (1.1×) in zooplankton MeHg. Our findings suggest that global change drivers that influence community composition and ecosystem energetics of both zooplankton and phytoplankton can alter MeHg pathways through food webs.
甲基汞（MeHg）在淡水水生系统中的生物积累受到人为胁迫的影响，包括气候变化和营养富集。本研究的目的是确定较高的水温和过量的营养物质将如何改变浮游动物群落和浮游植物浓度，以及这些变化是否会反过来增加或减少淡水浮游动物中的 MeHg 浓度。为了检验这一点，我们采用了 2×2 因子实验设计，包括营养和温度处理。中宇宙是用美国俄勒冈州科特格罗夫水库的环境水和浮游生物填充的，该水库经历了几十年的高 MeHg 浓度和相应的鱼类消费建议，因为位于流域内的黑巴特矿尾矿的径流。温暖温度（增加 0.7°C）、营养物添加（氮和磷浓度的 10 倍单脉冲）、对照和温度和营养物组合的处理组合被应用于中宇宙。单独的处理改变了浮游植物的密度和群落结构，但对 MeHg 浓度的影响是温和的。重要的是，我们发现了营养物质和温度的显著交互作用：营养物质的添加似乎缓冲了与升高温度相关的 MeHg 浓度的增加。然而，这种反应存在变异性，这似乎与水蚤和可食用浮游植物的丰度有关。低温下的营养物质与浮游动物 MeHg 浓度的适度增加（1.1×）有关。我们的研究结果表明，影响浮游动物和浮游植物群落组成和生态系统能量学的全球变化驱动因素可以通过食物网改变 MeHg 的途径。
