Widespread and increasing use of road deicing salt is a major driver of increasing lake chloride concentrations, which can negatively impact aquatic organisms and ecosystems. We used a simple model to explore the controls on road salt concentrations and predict equilibrium concentrations in lakes across the contiguous United States. The model suggests that equilibrium salt concentration depends on three quantities: salt application rate, road density, and runoff (precipitation minus evapotranspiration). High application combined with high road density leads to high equilibrium salt concentrations regardless of runoff. Yet if application can be held at current rates or reduced, concentrations in many lakes situated in lightly to moderately urbanized watersheds should equilibrate at levels below currently recommended thresholds. In particular, our model predicts that, given 2010–2015 road salt application rates, equilibrium chloride concentrations in the contiguous United States will exceed the current regulatory chronic exposure threshold of 230 mg L−1in over 2000 lakes; will exceed 120 mg L−1in over 9000 lakes; and will be below 120 mg L−1in hundreds of thousands of lakes. Our analysis helps to contextualize current trends in road salt pollution of lakes, and suggests that stabilization of equilibrium chloride concentrations below thresholds designed to protect aquatic organisms should be an achievable goal.
Rising salinity from road deicing salts threatens the survival and reproduction of freshwater organisms. We conducted two experiments to address how
- PAR ID:
- 10397965
- Publisher / Repository:
- Nature Publishing Group
- Date Published:
- Journal Name:
- Scientific Reports
- Volume:
- 13
- Issue:
- 1
- ISSN:
- 2045-2322
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract Freshwater ecosystems are being exposed to increasing salinisation, often because of pollution from road deicing salts, which is becoming more widely acknowledged. To address this issue, municipalities are turning towards the sodium salt alternatives of CaCl2and MgCl2, which are marketed as being safer for the environment. However, research into the actual safety of these salts on aquatic plants is lacking.
We investigated the effects of the most common road salt (NaCl) and two alternatives (MgCl2and CaCl2) on the productivity of a common freshwater plant (i.e.,
Elodea canadensis ) under three salt concentrations (control, 250, and 1,000 mg Cl−/L). Light‐bottle/dark‐bottle trials were performed to quantify net primary productivity, respiration, and gross primary productivity. These responses were tracked over time (1 vs. 3 weeks) to assess plant acclimation and lag effects under different levels of the three salts.We discovered that NaCl and CaCl2altered these measures of plant metabolism, but MgCl2had no effects. We also observed instances of acclimation (i.e. salt effects after 1 week that disappeared after 3 weeks) and lag effects (i.e. no salt effect after 1 week, but salt effects after 3 weeks). These impacts are likely to be the results of plant responses to salt at the cell and molecular levels, including short‐ and long‐term changes in photosynthetic pigments. Therefore, the plant responses were salt‐specific, with instances of plant acclimation and lag effects.
This appears to be the first study of net primary productivity, respiration, and gross primary productivity in freshwater plants across a range of different salts, and it highlights how freshwater salinisation can have substantial effects on plant productivity. These effects will probably have an impact on the growth of macrophytes, which play key ecological roles in aquatic ecosystems.
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