Data from: Salinization triggers a trophic cascade in experimental freshwater communities with varying food-chain length

The application of road deicing salts in northern regions worldwide is changing the chemical environment of freshwater ecosystems. Chloride levels in many lakes, streams, and wetlands exceed the chronic and acute thresholds established by the United States and Canada for the protection of freshwater biota. Few studies have identified the impacts of deicing salts in stream and wetland communities and none have examined impacts in lake communities. We tested how relevant concentrations of road salt (15, 100, 250, 500, and 1000 mg Cl− L–1) interacted with experimental communities containing two or three trophic levels (i.e. no fish vs. predatory fish). We hypothesized that road salt and fish would have a negative synergistic effect on zooplankton, which would then induce a trophic cascade. We tested this hypothesis in outdoor mesocosms containing filamentous algae, periphyton, phytoplankton, zooplankton, several macroinvertebrate species, and fish. We found that the presence of fish and high salt had a negative synergistic effect on the zooplankton community, which in turn caused an increase in phytoplankton. Contributing to the magnitude of this trophic cascade was a direct positive effect of high salinity on phytoplankton abundance. Cascading effects were limited with respect to impacts on the benthic food web. Periphyton and snail grazers were unaffected by the salt-induced trophic cascade, but the biomass of filamentous algae decreased as a result of shading effects from phytoplankton. We also found direct negative effects of high salinity on the biomass of filamentous algae and amphipods (Hyalella azteca) and the mortality of banded mystery snails (Viviparus georgianus) and fingernail clams (Sphaerium simile). Clam mortality was dependent on the presence of fish, suggesting a non-consumptive interactive effect with salt. Our results indicate that globally increasing concentrations of road salt can alter community structure via both direct and indirect effects.全球北部地区道路融雪盐的施用正在改变淡水生态系统的化学环境。当前诸多湖泊、溪流与湿地中的氯化物浓度，已超出美国与加拿大为保护淡水生物群落设定的慢性与急性暴露阈值。目前鲜有研究探明道路融雪盐对溪流与湿地生物群落的影响，更无相关研究针对湖泊生物群落展开评估。 我们设置了梯度浓度的道路融雪盐（15、100、250、500及1000 mg Cl− L–1），以此与包含2至3个营养级的实验群落（即无鱼组与掠食性鱼类组）开展交互作用实验。我们提出假说：道路融雪盐与鱼类会对浮游动物（zooplankton）产生负面协同效应，进而引发营养级联效应。 我们在包含丝状藻类（filamentous algae）、周丛藻类（periphyton）、浮游植物（phytoplankton）、浮游动物（zooplankton）、多种大型无脊椎动物（macroinvertebrates）与鱼类的室外中宇宙实验系统（mesocosms）中验证了该假说。实验结果显示，鱼类存在与高盐浓度会对浮游动物（zooplankton）群落产生负面协同效应，进而导致浮游植物（phytoplankton）生物量上升；而高盐度对浮游植物（phytoplankton）丰度的直接促进作用，进一步放大了该营养级联效应的强度。 就底栖食物网的影响而言，营养级联效应较为有限：周丛藻类（periphyton）与螺类牧食者并未受融雪盐引发的营养级联效应影响，但丝状藻类（filamentous algae）的生物量因浮游植物（phytoplankton）的遮阴效应出现下降。我们同时发现，高盐度会对丝状藻类（filamentous algae）与端足类（amphipods，Hyalella azteca）的生物量产生直接负面影响，并会提升带纹田螺（Viviparus georgianus）与相似球蚬（Sphaerium simile）的死亡率。球蚬的死亡率与鱼类存在与否相关，这表明融雪盐与鱼类间存在非消耗性交互作用。 本研究结果表明，全球范围内道路融雪盐浓度的持续升高，可通过直接与间接效应改变淡水生物群落结构。