Study Finds Salinity Of Lakes In Region Increasing

Apr 26, 2017

A report issued this month assesses the changing salinity of freshwater lakes.  It finds increased sodium chloride in the North American lakes studied, most likely caused by using salt to de-ice roadways.

The study “Salting Our Freshwater Lakes” was conducted by researchers from the GLEON, or Global Lake Ecological Observatory Network, fellows program.  Lakes across the U.S. and Canada were tested for salt levels. 44 percent of the 371 tested were found to be experiencing long-term salinization.

This is first large-scale analysis of chloride trends in freshwater lakes, most located in  New England,  New York, Ontario, Michigan, Minnesota, and Wisconsin.  Researchers found that roads within 500 meters of a shoreline were strong predictors of elevated chloride in lakes due to road salt runoff in winter.  

Lake Champlain was the largest tested in this region.  Researchers measured a mean chloride level of 11.528 milligrams per liter.  Co-author Mindy Morales-Williams is a postdoctoral researcher at the University of Minnesota and a research affiliate at UVM’s Rubenstein School of Environment and Natural Resources.  “Champlain relative to other parts of the country has relatively low concentrations but it is showing a long-term increasing trend. So we should be concerned that it’s a very clear long-term increasing trend in Champlain.  But it’s not at the point where yet it’s severely impacting the ecosystem functions.”

Ecosystem Ecologist Dr. Kathleen Weathers of the Cary Institute of Ecosystem Studies is a co-author and co-fellowship advisor.  She says although the study assessed a small number of lakes overall, trends indicate that lake salinity increases when road salt is applied to nearby impervious surfaces.   “The challenge is that out of the 4,000 plus lakes in New York we only had data for 100 or so. So what our study says is in areas where we apply salt to keep the roads safe there is a lot of concern for lakes that have impervious surface, those surfaces over which water and salt can run into lakes, that’s even as much as 1 percent is the concern. So I suspect that we would see much saltier lakes if we were to measure or if we had data from lakes that have 1 percent impervious surface surrounding them.”

Lake Champlain International Executive Director James Ehlers was not involved with the study but monitors pollutants affecting the lake.  He calls the salinization of lakes a reflection of a larger problem.   “Salt represents just yet another contaminant to our freshwater system. And our fresh water is literally our most fundamental necessity for life. So yeah I’m concerned but I’m more concerned with the attitude, the culture that allows for this to happen.”

The study concludes that if current trends continue by 2050, 14 of the 371 lakes studied will exceed  EPA aquatic life criteria of 230 milligrams per liter and 47 more will measure over 100 milligrams per liter.

Interactive map:
http://poseidon.limnology.wisc.edu:3838/LakeChlorideViewer/

Report:
http://www.pnas.org/content/114/17/4453.full