Single-species acute lethal toxicity tests are not predictive of relative population and community effects of two salinity types

Human-mediated salinity increases are occurring in freshwaters globally, with consequent negative effects on freshwater biodiversity. Salinity comprises multiple anions and cations. While total concentrations are typically used to infer effects, individual ion concentrations and ion ratios are critical in determining effects. Moreover, estimates of toxicity from single-species laboratory tests, may not accurately predict relative effects on populations and communities. Here, we compare salinity increases from synthetic marine salts and sodium bicarbonate in an outdoor mesocosm experiment in southeastern Australia. We found different effects of salt types on stream macroinvertebrates at the population and community levels, where similar effects were predicted from single-species laboratory tests. Our results caution against the use of single-species laboratoryderived toxicological data to predict both environmentally safe salinity levels and the relative effects of different salt sources on freshwater biodiversity.

Automated summary

Human-mediated salinity increases have negative effects on freshwater biodiversity globally. It is important to consider individual ion concentrations and ion ratios in addition to total concentrations when determining the effects of salinity. Single-species laboratory tests may not accurately predict the impact of different salt sources on populations and communities. This study compared the effects of synthetic marine salts and sodium bicarbonate on stream macroinvertebrates in an outdoor mesocosm experiment in southeastern Australia.