Scheibener Shane, Conley Justin M, Buchwalter David
Department of Biological Sciences, North Carolina State University, Raleigh, NC, USA.
Department of Biological Sciences, North Carolina State University, Raleigh, NC, USA.
Aquat Toxicol. 2017 Sep;190:62-69. doi: 10.1016/j.aquatox.2017.06.027. Epub 2017 Jul 1.
The salinization of freshwater ecosystems is emerging as a major ecological issue. Several anthropogenic causes of salinization (e.g. surface coal mining, hydro-fracking, road de-icing, irrigation of arid lands, etc.) are associated with biodiversity losses in freshwater ecosystems. Because insects tend to dominate freshwater ecology, it is important that we develop a better understanding of how and why different species respond to salinity matrices dominated by different major ions. This study builds upon previous work demonstrating that major ion toxicity to the mayfly Neocloeon triangulifer was apparently due to the ionic composition of water rather than specific conductance. Synthetic waters with low Ca:Mg ratios and high SO:Na ratios produced toxicity, whereas waters with higher Ca:Mg ratios and lower SO:Na ratios were not toxic to mayflies at comparable conductivities. Here we used a radiotracer approach to show that Mg did not competitively exclude Ca uptake at environmentally realistic ratios in 4 aquatic insect species. We characterized SO uptake kinetics in 5 mayflies and assessed the influence of different ions on SO uptake. Dual label experiments show an inverse relationship between SO and Na transport rates as SO was held constant and Na was increased, suggesting that Na (and not Cl or HCO) is antagonistic to SO transport. Based on this observation, we tested the hypothesis that increasing Na would protect against SO induced toxicity in a Na-dependent manner. Increasing Na from 0.7 to 10.9mM improved 96-h survivorship associated with 20.8mM SO from 44% to 73% in a concentration dependent manner. However, when Na reached 21.8mM, survivorship decreased to 16%, suggesting that other interactive effects of major ions caused toxicity under those conditions. Thus, the combination of elevated sulfate and low sodium commonly observed in streams affected by mountaintop coal mining has the potential to cause toxicity in sensitive aquatic insects. Overall, it is important that we develop a better understanding of major ion toxicity to effectively mitigate and protect freshwater biodiversity from salinization.
淡水生态系统的盐碱化正成为一个主要的生态问题。盐碱化的若干人为成因（如露天煤矿开采、水力压裂、道路除冰、干旱地区灌溉等）与淡水生态系统中的生物多样性丧失有关。由于昆虫往往在淡水生态中占主导地位，因此我们更深入地了解不同物种如何以及为何对以不同主要离子为主的盐分基质做出反应非常重要。本研究基于先前的工作，该工作表明水对蜉蝣Neocloeon triangulifer的主要离子毒性显然是由于水的离子组成而非电导率。钙镁比低且硫酸根与钠离子比高的合成水产生毒性，而在可比电导率下，钙镁比高且硫酸根与钠离子比低的水对蜉蝣无毒。在这里，我们使用放射性示踪剂方法表明，在4种水生昆虫物种中，镁在环境现实比例下不会竞争性地排除钙的吸收。我们表征了5种蜉蝣对硫酸根的吸收动力学，并评估了不同离子对硫酸根吸收的影响。双标记实验表明，在硫酸根保持恒定而钠离子增加时，硫酸根与钠离子的转运速率呈反比关系，这表明钠离子（而非氯离子或碳酸氢根离子）对硫酸根转运具有拮抗作用。基于这一观察结果，我们测试了增加钠离子会以依赖钠离子的方式预防硫酸根诱导的毒性这一假设。将钠离子浓度从0.7毫摩尔/升提高到10.9毫摩尔/升，以浓度依赖方式使与20.8毫摩尔/升硫酸根相关的96小时存活率从44%提高到73%。然而，当钠离子浓度达到21.8毫摩尔/升时，存活率降至16%，这表明在这些条件下主要离子的其他相互作用效应导致了毒性。因此，在受山顶煤矿开采影响的溪流中常见的硫酸盐升高和钠含量低的组合有可能对敏感的水生昆虫造成毒性。总体而言，我们更深入地了解主要离子毒性对于有效减轻和保护淡水生物多样性免受盐碱化影响非常重要。
