Climate change a possible culprit in elevated Snake River zinc levels
Study: Earlier snow-melt ups acid rock drainage
By Janice Kurbjun
Climate change is suspected as the primary culprit of rising concentrations of zinc in the Snake River, according to a recent study from the University of Colorado.
Higher levels of zinc can affect stream ecology, including harming the survivability of microbes, algae, invertebrates and fish.
The study indicates there's a four-fold increase in dissolved zinc in the Snake River over the last 30 years during the lowest water flow months, said Caitlin Crouch, a master's degree student at CU-Boulder. She said her study focuses on climate change relating to water quality, which is different than most studies focusing on water quantity in the West.
The area's geology has naturally high mineral levels, so it's normal that a phenomenon known as acid rock drainage occurs — to a certain extent. What's unnatural is the amount of water running through the soils with snow melting early, presumably an effect of higher temperatures associated with climate change, said Jim Shaw, a Blue River Watershed Group director and the organization's treasurer. Nearby abandoned mines may also be enhancing the amount of acid rock drainage.
Nearly 2,000 miles of waterways in Colorado are affected by acid rock drainage, said Diane McKnight, who co-authored the study.
“Spring runoff is happening longer,” Shaw said, which means the water runs slowly into the ground instead of along its surface in one spring melt. It passes over mineralized rocks, leeching the minerals into the streamflow as it moves.
Crouch said the earlier snowmelt also means drier streambeds in September and October, which could increase metal concentrations. It's a smaller scale of what was observed during the 2002 drought, in which prolonged dry conditions allowed the harmful chemical reactions to occur in areas where water once was, and will be again.
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