Salt-Laden Winter Runoff and Freshwater Mussels; Assessing the Effect on Early Life Stages in the Laboratory and Wild Mussel Populations in Receiving Waters

Abstract

The widespread use of road salt for winter road maintenance has led to an increase in the salinity of surface water in many seasonally cold areas. Freshwater mussels have a heightened sensitivity to salt, which is a concern, because many Canadian mussel species at risk have ranges limited to southern Ontario, Canada’s most road-dense region. This study examined the effect of winter road runoff on freshwater mussels. The impact of two bridges that span mussel habitat in the Thames River watershed (Ontario, Canada), the second most species-rich watershed for mussels in Canada, were studied. During a winter melt event, bridge runoff, as well as creek surface water surrounding the bridges were collected. Chloride concentrations in samples from bridge deck and tile drains varied (99–8250 mg/L). In general, survival of Lampsilis fasciola glochidia exposed to those samples reflected chloride levels (e.g. 84% at 99 mg/L; 0% at 8250 mg/L), although potassium (60 mg/L) may have at least contributed to toxicity in one sample. Serial dilution exposures with the two most toxic runoff samples revealed 48-h glochidia EC50s of 44% (McGregor Creek Tile Drain) and 26% (Baptiste Creek Deck Drain). During the melt event, the chloride concentrations in creek surface waters downstream of the bridges ranged from 69 to 179 mg Cl−/L; effects on glochidia (viability 77–91%) exposed to those waters was minimal. There were no live mussels surrounding one bridge (Baptiste Creek), likely due to poor habitat. At the other targeted bridge (McGregor Creek), fewer mussels were found close (< 100 m up- or downstream) to the bridge than further (> 200 m) away. However, other contributing factors, including agriculture, were present at both study areas.

Environmental Fate and Effects of Road Run-Off

“…Three other studies demonstrated negative effects of salt laden winter runoff on invertebrates, both in the laboratory and in their natural habitats. Gillis et al ( 2022 ) reported that the acute toxicity of road runoff collected from a bridge during the winter to mussel larvae in the laboratory was consistent with reduced wild mussel abundance in the river under that highway bridge. Shenton et al ( 2022 ) reported differences between the stream macroinvertebrate community composition in Australian sub-alpine habitats that receive salt inputs from road runoff and the areas that do not receive salt.…”

“…Izzo et al ( 2022 ) illustrated the seasonal differences in chloride levels in streams managed with storm water retention ponds compared to those without, and Zhang et al ( 2022 ) recommended that SVOC-impacted runoff from some land uses such as gas stations and roads be collected in pipes for treatment rather than being allowed to travel overland to receiving waters. Finally, Gillis et al ( 2022 ) reported that runoff from a bridge directed through a tile drain contained lower levels of chloride and was less toxic to mussels than runoff that flowed directly from a bridge deck drain into the receiving environment.…”

The Relative Toxicity of Road Salt Alternatives to Freshwater Mussels; Examining the Potential Risk of Eco-Friendly De-icing Products to Sensitive Aquatic Species

“…Potassium was also suspected to have contributed to the toxicity of L. fasciola glochidia exposed to diluted winter road runoff, as viability fell below 50% in exposure solutions ≥ 35 mg K + /L. 13 While information is limited, potassium is suspected to play a role in freshwater mussel distribution. Imlay 38 observed that 72% of the studied rivers with potassium < 4 mg/L supported freshwater mussels, but only 20% of rivers with potassium > 4 mg/L supported mussels.…”

“…10,11 Early life stage mussels experience acute toxicity when exposed to salt-laden winter road runoff, and reduced wild mussel abundance has been observed in the receiving environment. 12,13 The gradual increase in baseline chloride concentrations is expected to continue to have negative effects on freshwater biota including the recovery of mussel species at risk. 14 To mitigate the effect of salinization on freshwater biota, best management practices have been developed to reduce road salt use, and there has been growing interest in alternative de-icing products.…”

“…The salinization of freshwater has been correlated with the increased application of road salt for winter road maintenance. − Negative impacts of the increasing salt load on freshwater ecosystems have been observed across a wide range of biota and geographic regions . Changes in macroinvertebrate and amphibian community composition as well as reductions in diatom diversity and immune response in invertebrates have been reported in road salt-impacted surface waters. − Freshwater mussels (Unionidae), one of the world’s most imperiled groups, have a heightened sensitivity to salt. , Early life stage mussels experience acute toxicity when exposed to salt-laden winter road runoff, and reduced wild mussel abundance has been observed in the receiving environment. , The gradual increase in baseline chloride concentrations is expected to continue to have negative effects on freshwater biota including the recovery of mussel species at risk …”