The Effects of Road De-icing Salts on Water Quality and Macroinvertebrates in Australian Alpine Areas.

The application of road de-icing salts has the potential to salinize fresh waters and degrade habitat for aquatic organisms. In the Australian Alps, the ecological effects of even small salinity increases from de-icing may be different than in North America and Europe because of (1) differences in the evolutionary history, and (2) areas with de-icing in Australia are not located in urbanized landscapes where de-icing has been largely studied elsewhere. In this study, we tried to determine the salinity increases attributable to de-icing in Australia and the effects of this increase in salinity to stream macroinvertebrates. We observed increased salt concentrations (as measured by continuous measurements of electrical conductivity (EC) and periodic measurements of chloride concentrations) in streams near two Australian ski resorts, during the snow seasons (June to September) of 2016 to 2018. The maximum EC observed in streams in salted sites near Perisher, New South Wales, was 390 µS cm-1 compared with a maximum of 26.5 µS cm-1 at unsalted sites. Lower EC values (i.e., maximum 61.1 µS cm-1) and short durations of salinity increases in streams near Falls Creek, Victoria, were not expected to cause an adverse biological response. Salt storage in the landscape was evident at salted sites near Perisher where EC was above background levels during periods of the year when no salt was applied to roads. Stream macroinvertebrate community composition differed at sites receiving run-off from road salting activities near Perisher. Abundances of Oligochaeta (worms) (up to 11-fold), Dugesiidae (flat worms) (up to fourfold), and Aphroteniinae (chironomids) (up to 14-fold) increased, whereas Leptophlebiidae (mayflies) decreased by up to 100% compared with non-salted sites. The taxa that were less abundant where de-icing salts were present tended to be the same taxa that toxicity testing revealed to be relatively salt sensitive species. This study demonstrates a causal link between de-icing salts, elevated stream salinity, and altered macroinvertebrate community composition in streams that received run-off from road de-icing activity in the Australian Alps.

Do magnesium and chloride ameliorate high sodium bicarbonate concentrations? A comparison between laboratory and mesocosm toxicity experiments.

Increasing salinity is a concern for biodiversity in many freshwater ecosystems globally. Single species laboratory toxicity tests show major differences in freshwater organism survival depending on the specific ions that comprise salinity types and/or their ion ratios. Toxicity has been shown to be reduced by altering ionic composition, despite increasing (total) salinity. For insistence, single species tests show the toxicity of sodium bicarbonate (NaHCO3, which commonly is a large proportion of the salts from coalbeds) to freshwater invertebrates is reduced by adding magnesium (Mg2+) or chloride (Cl-). However, it is uncertain whether reductions in mortality observed in single-species laboratory tests predict effects within populations, communities and to ecosystem processes in more complex multi-species systems both natural and semi-natural. Here we report the results of an outdoor multi-species mesocosm experiment to determine if the effects of NaHCO3 are reduced by increasing the concentrations of Mg2+ or Cl- on: a) stream macroinvertebrate populations and communities; b) benthic chlorophyll-a and; c) the ecosystem process of leaf litter decomposition. We found a large effect of a high NaHCO3 concentration (≈4.45 mS/cm) with reduced abundances of multiple taxa, reduced emergence of adult insects and reduced species richness, altered community structure and increased leaf litter breakdown rates but no effect on benthic chlorophyll-a. However, despite predictions based on laboratory findings, we found no evidence that the addition of either Mg2+ or Cl- altered the effect of NaHCO3. In semi-natural environments such as mesocosms, and natural environments, organisms are subject to varying temperature and habitat factors, while also interacting with other species and trophic levels (e.g. predation, competition, facilitation), which are absent in single species laboratory tests. Thus, it should not be assumed single-species tests are good predictors of the effects of changing ionic compositions on stream biota in more natural environments.