Magnesium (Mg) is a mining‐related contaminant in the Alligators Rivers Region of tropical northern Australia. A mesocosm experiment was used to assess Mg toxicity to aquatic freshwater assemblages. Twenty‐five 2700‐L tubs were arranged, stratified randomly, on the bed of Magela Creek, a seasonally flowing, sandy stream channel in the Alligator Rivers Region of northern Australia. The experiment comprised 5 replicates of 4 nominal Mg treatments, 2.5, 7.5, 23, and 68 mg L⁻¹, and a control. Phytoplankton biomass, and diatom, zooplankton, and macroinvertebrate assemblages present in the treatment tubs were sampled before and after Mg addition. A significant negative relationship between phytoplankton biomass and Mg was observed 4 wk after Mg addition as measured by chlorophyll a concentrations (r² = 0.97, p = 0.01). This result was supported by reductions in some major phytoplankton groups in response to increasing Mg concentrations, in the same experiment and from independent field studies. There was a significant negative relationship between zooplankton assemblage similarity (to control) and Mg concentrations (r² = 0.96, p = 0.002). Seven weeks after Mg addition, macroinvertebrate assemblages were dominated by 3 microcrustacean groups (Ostracoda, Cladocera, and Copepoda), each reaching maximum abundance at intermediate Mg concentrations (i.e., unimodal responses). The responses of phytoplankton and zooplankton were used to derive assemblage effect concentrations (Mg concentrations resulting in x% of the assemblage change [ECx]). Magnesium concentrations resulting in assemblage EC01 values were <3 mg L⁻¹. Together with candidate guideline values from other laboratory‐ and field‐based lines of evidence, the mesocosm EC01 values were incorporated into a weight‐of‐evidence framework for a robust regulatory approach to environmental protection. Environ Toxicol Chem 2020;39:1973–1987. © 2020 Commonwealth of Australia. Published by Wiley Periodicals LLC on behalf of SETAC.

中文翻译：

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在中观实验中，升高的镁浓度改变了淡水的组装结构。

镁（Mg）是澳大利亚北部热带地区的鳄鱼河地区与采矿有关的污染物。介观实验用于评估镁对水生淡水组合物的毒性。在澳大利亚北部鳄鱼河地区季节性流动的沙质河流麦哲拉溪的河床上随机布置了25个2700升的桶，进行了分层。该实验包括4次标称Mg处理，2.5、7.5、23和68 mg L ^-1和对照的5次重复。在添加镁之前和之后，对处理盆中存在的浮游生物量，硅藻，浮游动物和大型无脊椎动物组合进行采样。通过叶绿素a浓度的测定，添加镁后4周浮游植物生物量与镁之间存在显着负相关（r²  = 0.97，p  = 0.01）。在同一实验和独立的田间研究中，响应于增加的Mg浓度，一些主要的浮游植物种群减少也证明了这一结果。浮游动物的组装相似性（与对照相比）与Mg浓度之间存在显着的负相关关系（r ²  = 0.96，p  = 0.002）。添加镁后七周，大型无脊椎动物群以3个微甲壳类动物群（Ostracoda，Cladocera和Copepoda）为主，每个群体在中等Mg浓度下达到最大丰度（即单峰响应）。浮游植物和浮游动物的反应被用来推导组合效应浓度（产生的Mg浓度X组合变化的百分比[EC x ]）。导致组合物EC01值的镁浓度为<3 mg L ^-1。将中观EC01值与其他基于实验室和现场的证据线的候选准则值一起，纳入了证据权重框架，以采取强有力的环境保护措施。环境毒性化学2020; 39：1973–1987。©2020澳大利亚联邦。由Wiley Periodicals LLC代表SETAC发布。