A Sustainable City Network article (2017-04-19) reported that many Midwestern and Northeastern lakes are seeing increases in their salt levels based on the application of road salt to nearby streets and highways. The finding is based on a recently published study in the Proceedings of the National Academy of Sciences which examined 371 freshwater lakes larger than 4 hectares and with at least 10 years of previous recorded chloride data.
The study found that 44 percent of sampled lakes are undergoing long-term salinization. The study was conducted by the Global Lake Ecological Observatory Network (GLEON) Fellowship Program. From the article:
Lead author Hilary Dugan, a limnologist at the University of Wisconsin-Madison and former Cary Institute of Ecosystem Studies Postdoctoral Fellow, explains, “We compiled long-term data, and compared chloride concentrations in North American lakes and reservoirs to climate and land use patterns, with the goal of revealing whether, how, and why salinization is changing across broad geographic scales. The picture is sobering. For lakes, small amounts of shoreline development translate into big salinization risks.” …
Since the 1940s, the use of road salt to keep winter roads navigable has been escalating. Each year, some 23 million metric tons of sodium chloride-based deicer is applied to North America’s roads to melt away snow and ice. Much of this road salt washes into nearby water bodies, where it is recognized as a major source of chloride pollution to groundwater, streams, rivers, and lakes.
To gauge road salt exposure, the research team assessed road density and land cover within a 100- to 1,500-meter buffer around each of the 371 study lakes. Roadways and impervious surfaces such as parking lots and sidewalks are reliable proxies for road salt application because as developed areas, they are susceptible to high levels of salting and runoff.
Results were clear: roads and other impervious surfaces within 500 meters of a lake’s shoreline were a strong predictor of elevated chloride concentrations. In the North American Lakes Region, 70 percent (94 out of 134) of lakes with more than 1 percent impervious land cover in their 500-meter buffer zone had increasing chloride trends. When results are extrapolated to all lakes in the North American Lakes Region, some 7,770 lakes may be at risk of rising salinity.
The article noted that high chloride levels can negatively affect a lake’s animal and plant ecosystem, resulting in a decline in species richness and abundance and also create low oxygen conditions that kill aquatic life and degrade water quality. In response to the findings, the study’s authors call for better shoreline management and lake monitoring practices:
The study’s authors recommend that best lake management practices recognize that shoreline management extends well beyond a lake’s perimeter. While many states and municipalities acknowledge the importance of shoreline management, they note that zoning regulations are often only enforced within 300 meters, and many lakes lack the monitoring programs needed to adequately track lake health.
Coauthor and Fellowship advisor Kathleen Weathers, an ecosystem scientist at the Cary Institute of Ecosystem Studies and co-chair of GLEON, comments, “In the North American Lakes Region – where road salt is a reality – roads and other impervious surfaces within 500 meters of a lake’s shoreline are a recipe for salinization. We need to manage and monitor lakes to ensure they are kept ‘fresh’ and protect the myriad of services they provide, from fisheries and recreation to drinking water supplies.”
A lake’s chloride status may also provide a window into the ecological health of its watershed. Co-author Samantha Burke, a graduate student at the University of Waterloo, adds, “Unlike flowing streams and rivers, water resides in lakes for long periods of time. This makes them vulnerable to pollution from their watersheds and good early warning indicators of environmental disruption.