Seasonal differences in chloride, conductivity, temperature
A study of changes in the Upper Ohio River Valley
Road salts in local streams
During the winter season in northern latitudes road salts are used to melt ice and snow on roadways, making roads safer for travel. But sodium chloride, the primary deicing agent in road salt, is known to corrode vehicles, contaminate drinking water supplies, and can create toxic conditions for aquatic organisms (e.g., fish and macroinvertebrates) if sodium chloride concentrations are high enough. 1,2
Chloride originating in road salts reaches streams via surface runoff, from stormwater lines, and via roadside ditches carrying the water directly into streams. Additionally, chloride can accumulate in groundwater where it may be stored for days, months or years. However, during prolonged dry periods, groundwater may be the main source of water for a stream, and stream may have little ability to dilute contaminated groundwater, ultimately leading to higher concentrations of chloride and elevated conductivity (a measure of all the dissolved salts and metals in stream water) in stream water.
In the Upper Ohio River Region of Appalachia climate change is predicted to make summers hotter, wetter, but more prone drought. 3 In 2020 the Upper Ohio River Watershed, near Wheeling, WV reported the 4th driest year on record, with rainfall between June and October 6.61 inches (16.8 cm) below average. 4 The dry summer of 2020 led to very low flow conditions in streams and creeks across the region.
Conversely, warmer winters (but still below freezing!) produce more snowfall, and the winter of 2018-2019 was relatively mild with few major snow events, compared to the winter of 2019-2020 where there was substantially more snow fall. These differences provided the opportunity to compare seasonal changes in water quality between years to better understand how local streams might respond to climate change.
Conclusion
Streams in the Upper Ohio River Valley appear to be negatively impacted by high concentrations of chloride and other dissolved salts in both the summer and winter months. In the snowy winter season, roads salts are washed into streams directly from roads and sidewalks. We infer that the increase in chloride and conductivity observed in the summer was the result of salt contaminated groundwater flowing into streams during the prolonged period of low rainfall.
While the are many sources of dissolved salts in streams (i.e., road salts, acid mine drainage, sewage inputs, agriculture, etc.) education about the proper application of road salts and regulation to reduce excess salt application on roads and sidewalks could improve both surface water and groundwater quality and aquatic resources in the Upper Ohio River Valley, and that could improve the health of the region's aquatic resources.
References
1 Pond, G. J., Krock, K. J. G., Cruz, J. v., & Ettema, L. F. (2017). Effort-based predictors of headwater stream conditions: comparing the proximity of land use pressures and instream stressors on macroinvertebrate assemblages. Aquatic Sciences, 79(3), 765–781. https://doi.org/10.1007/s00027-017-0534-3
2 Moore, J., Fanelli, R. M., & Sekellick, A. J. (2020). High-Frequency Data Reveal Deicing Salts Drive Elevated Specific Conductance and Chloride along with Pervasive and Frequent Exceedances of the U.S. Environmental Protection Agency Aquatic Life Criteria for Chloride in Urban Streams. Environmental Science and Technology, 54(2), 778–789. https://doi.org/10.1021/acs.est.9b04316
