Salting Our Freshwater Lakes: RBC Researcher Kait Farrell in PNAS, Washington Post

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Salting Our Freshwater Lakes: RBC Researcher Kait Farrell in PNAS, Washington Post

44% of a sample of 371 US Lakes show signs of long-term salinization, according to a new paper in the Proceedings of the National Academy of Science by Kait Farrell and 14 others. Although no agency systematically tracks the application of salt to de-ice roads, researchers across the country knew that salt was making its way into freshwater ecosystems as snowmelt and spring rains wash it into ditches, creeks, and streams. So, the study’s authors assembled a large database of lake studies that tracked chloride levels tracks for at least ten years. Among other findings, they estimate that if the trends continue, 14 of the 371 lakes would exceed the EPA’s “aquatic life criterion concentration” of 230 milligrams per liter, which borders on the EPA’s recommendation that drinking water sources not exceed 250 milligrams per liter. As the figure below shows, chloride levels were strongly related to the amount of impervious surface in a watershed, one measure of the density of roads and pavement.

Distribution of impervious land cover within a 500-m buffer of all lakes >4 ha in the lower 48 United States (n = 149,350). Black squares represent the median impervious land cover percentage in each state. Thick horizontal black lines denote the interquartile range of the distribution, and thin black lines extend to 1.5 times the interquartile range. The vertical dashed line is shown at impervious land surface = 1%. Circles represent lakes included in this study, colored by slope (yellow, negative slope; purple, zero slope; red, positive slope). Due to the frequency of zero values on the x axis, circles are spread out within the gray rectangle. Percentages following y axis labels represent the percent of lakes in that state with greater than 1% impervious land cover within a 500-m buffer. In states with >10 lakes present in the dataset, an asterisk denotes that the sampling distribution in our dataset was significantly different from statewide distribution (Mann–Whitney test, P < 0.05), and ^ denotes that the sampling distribution was not significantly different from statewide distribution. [Click image to open original at publisher’s site.]

This study was also featured in the Washington Post on April 10; read the full article here.