A recent study conducted in Colorado mountain streams has shown that the concentrations of copper, zinc, and sulfate have doubled in the waters over the past 30 years due to warming temperatures caused by climate change. Lead author Andrew Manning, a geologist with the U.S. Geological Survey in Denver, highlighted the impact of heavy metals on ecosystems and downstream water quality, emphasizing the need for concern and remediation efforts in the mining industry. The study, published in Water Resources Research AGU’s journal, found that the source of the rising acidity and metals is natural chemical weathering of bedrock.
The study focused on the exposure of rock once sealed away by ice as a key suspect in the increased sulfide weathering that is leading to higher metal concentrations in the streams. The prevalence of metal sulfides in Colorado bedrock, such as pyrite, copper, and zinc, oxidizes when exposed to air, releasing the metals into groundwater and ultimately into surface streams. The acidic water resulting from sulfides accelerates weathering, causing further concerns for the health of aquatic plants and animals in the affected streams.
A total of 22 headwater streams in 17 watersheds were analyzed as part of the study, utilizing 40 years of water chemistry data and final sampling in 2021. These naturally acidic and metal-rich streams spanned elevations above 3,000 meters and included both pristine areas and those with historical mining activity. The reduction in stream flow volumes due to warmer temperatures and decreasing snowpacks was identified as a contributing factor to the increased metal concentrations, along with accelerated sulfide weathering.
The impact of metal-rich mountain streams on downstream water quality was noted as potentially affecting communities that source their water from these areas. The researchers emphasized the need for managers to have advanced knowledge of the metals entering the streams and their rates of increase to mitigate risks to water quality. Additionally, decisions regarding remediation efforts in historically mined areas and stocking fish for tourism could be influenced by the rising metal concentrations in these mountain streams.
While Colorado presents a unique case due to its high abundance of bedrock metal sulfides, scientists are observing similar trends in rising sulfate concentrations in mountain streams globally. This study is the first to statistically link accelerated sulfide weathering to rising temperatures on a large scale regionally. The melting of underground ice, potentially exposing fresh rock to air, has been identified as the main driver of increased metal concentrations in cold, high mountain streams in Colorado, pointing to the consequences of climate change on aquatic ecosystems.
