by Brenda Zollitsch, Policy Analyst
A global decline in amphibians has been attributed to many different factors, including UV radiation, bacterial and fungal infections, and the most-cited culprit, habitat loss. However, amphibian abundance and diversity may also be affected by chlorides (Petranka et al, 2013; Sadowski, 2002). Multiple studies (both laboratory and field) have clearly linked salt concentration to harmful effects on the survival and/or reproduction of frogs and salamanders (Winston, Hunt, and Pluer, 2012). According to Hill and Sadowski (2015), wetland chloride levels in most developed areas have already reached or exceed chronic water quality thresholds in the US and Canada.
The problem is much broader than amphibian impacts though. A literature review conducted by researchers from the Mitchell Center for Sustainability Solutions finds that high salt concentrations impact vegetative communities by reducing native species abundance, richness, evenness and overall cover in wetlands (Maine Snow and Ice Control Best Practices Work Group, 2015). Additionally, chloride contaminated surface or groundwater results in significant loss of wetland biodiversity as native plant communities are replaced by more salt-tolerant, opportunistic and/or invasive species such as narrow-leaf cattail, common reed and purple loosestrife (ibid). This widespread replacement degrades critical nesting and breeding habitats for birds and other wildlife.
While agricultural sources of chloride (potassium fertilizer in areas of intensive crop production) and septic systems contribute to chloride concentrations, the primary source in most areas is deicing practices from snow and ice control operations (Hill and Sadowski, 2015). To protect local wetlands, road salt applications near or immediately upstream of wetlands that have high conductivity levels should be as limited as possible (Karraker, Gibbs and Vonesh, 2008).
What Can Be Done?
Removal of chlorides from wetlands and other aquatic resources is challenging. It has been found to be both technically and financially unfeasible in many areas. Thus, the most effective way to reduce chloride impacts is to improve source control and eliminate overuse of road salt in winter maintenance activities (Maine Snow and Ice Control Best Practices Work Group, 2015; Winston, Hunt, and Pluer, 2012). Here are three strategies to consider.
1) Adopt Environmental Best Practices for Chloride Use Reduction
This week, I moderated a session on the connections between chlorides and stormwater at the 2015 Maine Stormwater Conference in Portland, Maine. Maine struggles with chloride pollution in its urban impaired streams, with high conductivity readings in most, if not all of its listed streams. The lessons learned are valuable for the management of chlorides in wetlands as well (Maine Snow and Ice Control Best Practices Work Group, 2015). The session highlighted some of the regional efforts to reduce chloride input from winter maintenance operations. Over the last several years, I have been the facilitator of a stakeholder-driven process to develop a voluntary best practices manual for reducing the environmental impacts of winter maintenance activities on Maine’s aquatic resources.
Maine’s efforts have resulted in the development of a set of groundtruthed administrative and operational voluntary best management practices developed collaboratively by municipal public works directors, Maine Department of Transportation, Maine Turnpike Authority, soil and water conservation districts, private consultants, Maine Department of Environmental Protection, and other stakeholders. The voluntary BMPs include snow and ice control product selection, application process, equipment, storage, loading, washing, and location-specific BMPs, such as practices for parking lots, sidewalks and walkways.
These BMPs are designed not only to reduce the amount of chlorides entering the aquatic environment but also maintain the commitment to public safety, level of service and reduce costs. Most importantly, the guide emphasizes simple, and in some cases, small changes to the way operations look at chloride management. Examples include developing and adapting level of service plans to ensure chloride application and timing is optimal, considering adoption of pre-wetting and pre-treatment practices (which have been shown to achieve vast cost savings as well as reduce chloride pollution), as well as the all-important practice of careful calibration, loading and storage practices. At a statewide roundtable on the topic in Maine this past September, public works directors shared that these small changes have already saved thousands of dollars and made significant impacts on reducing salt use for a number of municipalities. For more information on BMPs, check out the list of resources at the end of this blog.
2) Develop Chloride Application Certification Programs
New Hampshire has taken their adoption of best practices one step further and created a voluntary certification program for salt applicators in their state. Certifications can be held by either private contractors or municipal operators. The primary motivator for municipal staff is to learn how to achieve cost savings and improve environmental conditions (related to their stormwater management efforts). However, the impetus for private contractors is liability protection. Contractors that complete the certification, maintain the requirements for certification over time, and implement the best practices properly receive additional liability protections for slip and fall claims. This has proven a win-win in the state, providing a lower risk work environment for small contractors and decreasing the impacts from chlorides to New Hampshire’s aquatic resources. Other states, such as Maine, Nevada and Minnesota are also considering similar programs, based on the successes achieved in New Hampshire.
For more information about this program, check out the New Hampshire Green SnoPro certification program jointly managed by the NH Department of Environmental Services, New Hampshire Technology Transfer Center, and the University of New Hampshire here.
3) Consider Impacts of Chlorides When Planning Wetland Restoration Projects
A third consideration related to chlorides and wetlands is the impact on wetland restoration activities. Wetland restoration studies have shown that wetland restoration sites that receive high chloride concentrations in road salt runoff may develop plant assemblages that vary significantly from the target restoration species (Panno et al, 1999; Richburg et al, 2001; Miklovic and Galatowitsch, 2005). With this in mind, both taking chlorides into account when selecting restoration sites and working with the local DOT/Municipality to ensure salt-reduction BMPs have been put in place to protect the area surrounding the restoration site is advisable.
Final Thoughts: Working to Achieve the Triple Bottom Line
While the problem of chloride impacts on wetland plants and animals, especially amphibians, is a significant and challenging one, there are source control techniques that can be implemented that have been shown to not only reduce chloride contributions to aquatic environments, but also maintain high levels of public safety/service, AND produce cost-savings. With the possibility of achieving the triple bottom-line, I encourage you initiate a dialog with state and local officials to review your local snow and ice control operations and advocate for limiting the impact of chloride on your state/tribe/municipality’s wetlands.
Suggested Winter Maintenance Best Practice Resources:
Maine Environmental Best Practices Manual for Snow and Ice Control (2015)
Minnesota Winter Parking Lot and Sidewalk Maintenance Manual (2010)
Snow and Ice Control: Guidelines for Materials and Methods (National Cooperative Highway Research Program Report 526, Transportation Research Board of the National Academies, 2004)
Synthesis of Best Road Practices for Road Salt Management (Transportation Association of Canada)
Hill and Sadowski. (2015). Wetlands. November: 1-11.
Karraker and Ruthig. (2009). Effect of road deicing salt on the susceptibility of amphibian embryos to infection by water molds.
Kraaker, Gibbs and Vonesh. (2008). Impacts of road deicing salt on the demography of vernal pool-breeding amphibians. Ecological Applications. 18:724-734.
Maine Snow and Ice Control Best Practices Work Group. (2015). Maine Environmental Best Practices (BMP) Manual for Snow and Ice Control.
Petranka et al. (2013). Effects of road salts on seasonal wetlands. Environmental Science and Technology. 35(18): 3640-3645.
Sadowski. (2002). The impacts of chloride concentrations on wetlands and amphibian distribution in the Toronto Region. In B.D. Thraves (Eds): Prairie Perspectives: 144-162.
Winston, Hunt, and Pluer. (2012). Road salt and its effects on amphibians: A concern for North Carolina? North Carolina Department of Transportation technical Assistance No. TA-2012-05.
 According to Karraker and Ruthig (2009), because of their permeable skin, unprotected eggs (i.e. no shell), and aquatic larval stages, salamanders and other amphibians are intolerant to high levels of chloride in the wetlands and vernal pools they inhabit. For example, chloride concentration must be less than 945 – 1200 mg/L (depending on study) for salamander growth and survival. Additionally, 450 mg/L chloride appears to be the threshold at which half of salamander eggs become viable organisms in the laboratory (ibid).