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, communities and ecosystems. Here we compare salinity increases from synthetic marine salts (SMS) and sodium bicarbonate (NaHCO3) in an outdoor mesocosm experiment in south-eastern Australia. We found different effects of salt types on stream macroinvertebrates at the population, community, and ecosystem function levels, where similar effects were predicted from single species laboratory tests. Our results caution against the use of single species laboratory derived toxicological data to predict both environmentally safe salinity levels and the relative effects of different salt sources on freshwater biodiversity.

We conducted an outdoor experiment using mesocosms holding ~900 L of water. This experiment was conducted at the same location, using identical methods to previous experiments in these mesocosms. Two salinity type treatments were used: NaHCO₃ or synthetic marine salt (SMS) dissolved in dechlorinated Canberra tap water. For both there were low and high levels (see papaer for details); plus a control (no salts added). All treatments including the control were replicated in four independent mesocosms (i.e. 20 mesocosms). Each mesocosm was stocked with macroinvertebrates, leaf packs (to measure decomposition) and emergent insect traps.

There are three datasets from this mescosm experiment:

1. Benthic macroinvertebrates

2. Emergent adult insects

3. Leaf decomposition