The application of deicing road salts began in the 1940s and has increased drastically in regions where snow and ice removal is critical for transportation safety. The most commonly applied road salt is sodium chloride (NaCl). However, the increased costs of NaCl, its negative effects on human health, and the degradation of roadside habitats has driven transportation agencies to seek alternative road salts and organic additives to reduce the application rate of NaCl or increase its effectiveness. Few studies have examined the effects of NaCl in aquatic ecosystems, but none have explored the potential impacts of road salt alternatives and additives on aquatic food webs.
In the first experiment, we assessed the effects of three road salts (NaCl, MgCl2, and ClearLane™) as well as NaCl and MgCl2 mixed with organic additives (GeoMelt™ and Magic Salt™) on aquatic food webs. In a second experiment, using higher concentrations of each salt type and additive, we tested the effects of increased salinity (MgCl2) and organic additives (GeoMelt™ and Magic Salt™) on the survival and day to emergence of mosquito larvae.
Results/Conclusions
We found few effects of NaCl on aquatic food webs. However, in the food web experiment we observed that low concentrations of MgCl2 increased amphipod abundance, and in the second experiment, higher concentrations of MgCl2reduced the survival of mosquito larvae. In both experiments, the microbial breakdown of organic additives reduced dissolved oxygen. Additionally, microbial activity likely transformed unusable phosphorus from the organic additives to usable phosphorus for algae (phytoplankton), which increased the food resources for zooplankton and mosquito larvae. The presence of organic additives increased zooplankton density in the food web experiment, and reduced the average day to emergence for mosquitos.
Our results indicate that alternative road salts and road salt additives can alter the abundance and composition of organisms in freshwater food webs at multiple trophic levels, even at low concentrations. Consequently, road salt alternatives and additives might alter ecosystem function and ecosystem services. Therefore, transportation agencies should use caution in applying road salt alternatives and additives. A comprehensive investigation of road salt alternatives and road salt additives should be conducted before wide-scale use is implemented. Further research is also needed to determine the impacts of salt additives and alternatives on higher trophic levels, such as amphibians and fish.