Taking Application Rates With a Grain of Salt: Uncovering the Impact of Road De-Icing Salt on Freshwaters of a Mountain Catchment in the Italian Alps

Abstract

While application of salt for de-icing purposes has been extensively studied in urban areas of North America, little attention has been paid to it in Europe, particularly in mountain areas. Here, after assessment of baseline salinity, and through applying different approaches (i.e., univariate statistical techniques, Multivariate Regression Trees, multivariate regressions), we investigated the potential changes in water chemistry and benthic macroinvertebrate community structure caused by the application of de-icing salt over an entire winter season, in a mountain catchment located in the Italian Alps (N 46°, E 11°). Concurrently, we tested and compared the application of three different benthic macroinvertebrate indices used to assess salinisation impacts. Overall, we identified a constant level of baseline salinity across a 13-year period, accompanied by a strong seasonality factor. Despite an application rate comparable to those of large North American cities, macroinvertebrate communities showed little evidence of change. However, chemical ions whose concentrations are known to be influenced by de-icing salt (e.g., Na+, Cl−) were identified as the structuring drivers of the macroinvertebrate communities, thus suggesting that the studied riverine environment show a high potential for change in relation to salinity. In conclusion, we caution against the simple evaluation of application rates to assess the risk/level of salinisation within a catchment, and encourage further specific analysis and study of salinisation in mountain areas: they appear as sensitive habitats to potential variations in salinity, and stressors such as increased urbanisation and climate change will further exacerbate the risk of increasing salinisation in mountain freshwaters.