Published on April 12th, 2017 | by James Ayre0
Many US Freshwater Lakes Could Surpass “Safe” Chloride Levels Within 50 Years
April 12th, 2017 by James Ayre
Owing to growing development levels in surrounding areas and the widespread use of road salt, the freshwater lakes of much of North America are getting saltier by the year, according to new research conducted as part of the Global Lake Ecological Observatory Network Fellowship Program.
Around 44% of the lakes sampled in the Midwest and the Northeast (out of a total of 371 lakes sampled) show long-term salinization trends, the research found.
To put that another way, if current salinization trends continue, then many North American lakes will surpass EPA-recommended chloride levels within 50 years. And, as the press release put it: “Within this study, 14 North American Lakes Region lakes are expected to exceed the EPA’s aquatic life criterion concentration of 230 mg/L by 2050, and 47 are on track to reach chloride concentrations of 100 mg/L during the same time period.”
Why does this matter? Because lake, ground, and reservoir water is used as drinking water, irrigation water, and to support fisheries in many regions. And, notably, these findings are likely an underestimate of the problem, as noted by the researchers.
Co-author of the new study, Sarah Bartlett of the University of Wisconsin-Milwaukee, noted: “These results are likely an underestimation of the salinization problem, as a number of regions with heavy road salt application, such as Quebec or the Maritime Provinces of Canada, had no long-term lake data available.”
The press release provides more:
Chloride trends in 371 freshwater lakes were analyzed. Each lake was larger than 4 hectares in size with at least 10 years of recorded chloride data. The majority of the lakes (284) were located in a North American Lakes Region that includes Connecticut, Maine, Massachusetts, Michigan, Minnesota, New Hampshire, New York, Ontario, Rhode Island, Vermont, and Wisconsin.
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 1500-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% (94 out of 134) of lakes with more than 1% 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.
As mentioned above, that could impact drinking and irrigation water supply/costs in the regions in question. In addition, rising salinity levels can impact local aquatic food webs — causing declines and/or crashes in some species. In extreme cases, anoxic events greatly reduce water quality and cause mass kills.
The study findings are detailed in a paper published in journal the Proceedings of the National Academy of Sciences.