Colorado’s mountain streams are facing a “real challenge” from a rising concentration of heavy metal levels. These rising levels are only worsening with climate change, a new study found. The amount of copper, zinc and sulfate has doubled in the alpine streams flowing from the mountains over the past three decades, according to the study published in by scientists at the U.S. Geological Survey. Bedrock full of metal sulfides is common. The metals enter streams by oxidizing in the air, trickling down into groundwater, which eventually finds its way into surface streams. It is not uncommon for the state’s streams to appear rusty red, which is a sign of iron sulfide deposits accumulating in the streambed. These metals can be a problem for the surrounding ecosystem, and climate change is only making it worse. The new findings suggest that as temperatures warm, there is an increase in sulfide weathering, leading to more metals entering the streams. The exact reasons why remain a mystery; however, researchers believe it could be linked to exposure of rock due to thawing permafrost. “Heavy metals are a real challenge for ecosystems,” lead author Andrew Manning, a geologist with the U.S. Geological Survey in Denver, said in a statement. “Some are quite toxic. We are seeing regional, statistically significant trends in copper and zinc, two key metals that are commonly a problem in Colorado. It’s not ambiguous and it’s not small.” The highest amount of metals was found in streams with the coldest temperatures, which could link the increase to permafrost. The elevations where these streams are found can reach freezing temperatures of 32 degrees Fahrenheit. However, the permafrost formed in these areas has been thawing due to global warming. “Ice is like armor. Melt it and you create windows for groundwater to get into rock that has not seen water and oxygen for millennia, and it will begin to oxidize quite quickly,” Manning said. To reach their findings, scientists looked at 40 years of water chemistry data, with final samples collected in 2021. The data had been taken from 33 streams in 17 watersheds above 10,000 feet in elevation, meaning they had been pristine and untouched for the last 50 to 100 years. “The key point is no recent mining or remediation work has been done,” Manning said. “These watersheds have just been sitting there responding to nothing other than the climate.” The researchers focused on samples from mid-July to November. They found that stream flows had been shrinking due to an increase in temperature and in the surrounding mountains. This has been an ongoing problem in the western U.S. for a while, as the region faced severe drought conditions not long ago, which caused intense pressure on the water supply. The scientists suggest that this could be contributing to the increase in metals they observed; however, there must be other factors at play, too. This is because the metal levels were so high in the water that something else had to be putting them there at a quicker rate. The research could help inform public health efforts as there are communities living in these mountain environments. “I don’t think this is a big red flag for major metropolitan or agriculture users way downstream at lower elevations,” Manning said. “but some of our mountain communities get their water only a short distance down from these mineralized streams.” Although this is a particularly severe case, Colorado streams are not the only ones experiencing these high metal concentrations. Scientists are noticing an increase in metals in other streams across the globe. But this new study is the first to link the phenomenon with rising temperatures across a whole area.
Colorado’s Mountain Streams Face Mounting Challenge from Heavy Metals Amidst Climate Change
