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

Patricia L Gillis,C James Bennett,Ryan S Prosser,Karen L K Lemon,Vicki L Mckay,Joseph Salerno,Quintin J Rochfort

doi:10.1007/s00244-020-00791-2

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.

Highlights

The increase in the chloride concentration of North American surface waters over the past 30 years has been correlated with the increased application of de-icing salts on paved surfaces (Jackson and Jobbagy 2005; Kaushal et al 2005; Chapra et al 2009; Dugan et al 2017)
Todd and Kaltenecker (2012) reported that road salt is contributing to a gradual increase in baseline chloride concentrations in mussel habitats and that the chloride levels in some Ontario surface waters pose a threat to the recovery of freshwater mussel species at risk, because the elevated chloride concentrations may affect recruitment
This study focused on the Thames River watershed, the second most species-rich watershed for freshwater mussels in Canada (Cudmore et al 2004)

Summary

Introduction

The increase in the chloride concentration of North American surface waters over the past 30 years has been correlated with the increased application of de-icing salts on paved surfaces (Jackson and Jobbagy 2005; Kaushal et al 2005; Chapra et al 2009; Dugan et al 2017). Study Site-Sourced Glochidia and NaCl: In order to determine if early life stage mussels sourced from mussels living downstream of a winter runoff point source respond differently to salt than those living upstream of the bridge, glochidia from gravid L. siliquoidea that had been collected from either side of the McGregor Creek bridge were exposed to salt using the methods described above.

Results

Conclusion