As glaciers and permafrost melt in the mountains near Boulder, Colorado, an unexpected consequence is emerging: toxic mercury is being released into local wetlands.
This troubling discovery was made by researchers from the Cooperative Institute for Research in Environmental Sciences (CIRES) at the University of Colorado Boulder.
They found that melting ice exposes rocks containing minerals like sulfate, which flows into nearby watersheds.
This sulfate triggers a chemical reaction in wetlands, leading to the creation of methylmercury, a highly toxic form of mercury that can travel up the food chain and pose serious health risks.
Hannah Miller, a Ph.D. student at CU Boulder and the study’s lead author, explained that research on methylmercury production in high-altitude wetlands has been limited, leaving gaps in understanding its environmental impact.
This study, published in Environmental Research Letters, is the first to measure methylmercury levels in Boulder’s watershed.
According to Miller, understanding these levels is crucial for monitoring how changes in climate might affect the region’s soil, water, and wildlife.
Co-author Eve-Lyn Hinckley, a CIRES Fellow, emphasized that the research comes at a critical time as global warming and wildfires are threatening fragile mountain ecosystems.
Worldwide, mountain regions are experiencing the effects of climate change at an accelerated pace. Glaciers are melting, and streams fed by this meltwater are increasingly filled with sulfate.
In the North Boulder watershed alone, sulfate levels have risen by 200% over the last three decades. This increase is not limited to Colorado; more than 150 lakes and streams around the world are experiencing similar changes.
Miller and her team set out to understand how this surge in sulfate affects mercury in mountain wetlands.
Wetlands and large water bodies often have low oxygen levels in their soils, encouraging microbes to use elements like sulfate to grow. When sulfate interacts with mercury in these waterlogged soils, a chain reaction occurs, converting mercury into its most toxic form—methylmercury.
This process is particularly strong in peatlands, which are carbon-rich, swampy areas below the treeline where trees and plants create ideal conditions for microbial activity.
To investigate, Miller collected soil samples from the mountains about 25 miles northwest of Boulder. She then took the samples to the U.S. Geological Survey Mercury Research Lab in Wisconsin for analysis.
Her experiments showed that wetlands above the treeline had very little methylmercury, while the peatlands below the treeline had significantly higher levels. Miller also found that moderate amounts of sulfate led to the highest levels of methylmercury production.
This follows a principle known as the “Goldilocks effect,” which suggests that there is an ideal amount of sulfate that maximizes methylmercury production—too little or too much sulfate, and the effect is less dramatic.
The study is the first to establish sulfate thresholds for methylmercury production in the North Boulder Watershed. These findings could help land managers predict how climate-driven changes in sulfate runoff might increase toxic mercury levels in local water sources.
Miller emphasized that even though the region’s mountain ecosystems are semi-arid and have limited water bodies, they are still at risk for mercury contamination.
She warned that the increase in methylmercury could have serious implications for both wildlife and human communities that rely on these water sources.
The research sheds light on the hidden dangers of climate change in mountain ecosystems, revealing that melting ice not only raises water levels but also threatens to poison the very resources that sustain life.
