When winter falls in the North American Lakes region, as with much of the developed world, road salt becomes a lifesaver for those afflicted by frozen and slippy paths and roads. Since first being deployed in the 1940s, usage of sodium chloride-based road salt has continued to climb across North America, to the extent that around 23 million tonnes (around four times the weight of the Great Pyramid of Giza) is now used annually.
However, evidence from the first large-scale analysis of chloride in freshwater lakes, by a team of researchers from the Global Lake Ecological Observatory Network (GLEON) Fellowship Program, suggests that lakes and other waterways in this region – comprising such states as Connecticut, Maine, Massachusetts, Michigan, Minnesota, New Hampshire, New York, Rhode Island, Vermont, Wisconsin, and the province of Ontario in Canada – are being radically changed by salt being washed off the roads. Once in the water, extreme salinisation can radically alter the ecology of the lakes. By preventing water from mixing, it can lead to low oxygen conditions, adversely affecting the habitats of local fish, invertebrates, and plankton.
‘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 salinisation is changing across broad geographic scales,’ explains Hilary Dugan, limnologist at the University of Wisconsin-Madison, and lead author on the study. ‘The picture is sobering. For lakes, small amounts of shoreline development translate into big salinisation risks.’
The GLEON team studied a total of 371 lakes (284 of which are in the Lakes region), each covering at least four hectares, and with over ten years of collected data regarding chloride content. Road density and land cover within 100m and 1,500m of the edge of each lake was analysed, noting key sources of impervious infrastructure prone to high salt usage, such as roads, pavements, and car parks.
The results found that 44 per cent of sampled lakes are undergoing long-term salinisation, and that the presence of roads or other surfaces within 500m of a lake is a strong indicator of elevated chloride concentrations. The accumulation of chloride year-on-year means that 14 of the studied lakes look set to exceed the maximum recommended levels of 230mg/L, as set by the Environmental Protection Agency.
In the Lakes region, 70 per cent of the 134 studied lakes with more than just one per cent impervious land cover within 500m of the shore had increasing chloride trends. When extrapolated out to factor in the number of lakes across the entire region, an estimated 7,770 lakes are calculated as being potentially at risk of rising salinity.
‘In the North American Lakes region, where road salt is a reality, roads and other impervious surfaces within 500m of a lake’s shoreline are a recipe for salinisation,’ reflects co-author Kathleen Weathers, an ecosystem scientist at the Cary Institute of Ecosystem Studies, and co-chair of GLEON. ‘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.’