Scott Johnson: Lakes Soaking up Road Salt

Ars Technica:

Road salt became common in the 1940s, and the amount used has increased over time. The US puts down around 18 million tons of salt each year. Roadsides along highways obviously get dosed with more than their fair share of salt, but salt also runs off (sometimes via storm drains) into streams and lakes where it can accumulate. That makes road salt a common target in local efforts to protect bodies of water. Although this has sometimes been studied on the local scale, there hasn’t been much big-picture analysis. A new study led by the University of Wisconsin-Madison’s Hilary Dugan works to fill in that gap by estimating how widespread salt contamination is in North America.

The researchers used data from 371 lakes that covered at least four hectares and had chloride measurements going back at least 10 years. That’s not a purely random sampling, but it’s the best way to find trends. Most are in the US Midwest and Northeast, with a handful from southern Canada and some spread over the rest of the US. One-third of the 371 lakes showed a significant upward trend in salt concentration.