Metals have doubled in streams due to climate change 

A recent comprehensive study has revealed alarming increases in copper, zinc, and sulfate levels in the mountain streams of Colorado, influenced by acid rock drainage. Over the past three decades, these metal concentrations have roughly doubled in Colorado streams, endangering local ecosystems, water quality downstream, and complicating efforts in mining remediation. 

These problems are primarily caused by the natural chemical weathering of bedrock, which been intensified by ongoing climate change.

“Heavy metals are a real challenge for ecosystems,” said lead Arthur Andrew Manning, geologist at the U.S. Geological Survey in Denver. “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.”

Rusting Arctic rivers 

This study is based on previous research on the management of Earth’s water resources. The study further explores the complex relationship between rising temperatures and increased sulfide weathering, a topic that remains partially understood. 

However, recent phenomena such as the emergence of “rusting Arctic rivers,” which have begun to flow from thawing permafrost areas, suggest a similar underlying process but on a magnified scale, according to Manning.

Metal deposits in mountain streams 

Colorado’s unique geology, rich in metal sulfides like the well-known iron sulfide (fool’s gold or pyrite), as well as copper and zinc sulfides, plays a crucial role in this scenario. 

When these sulfides are exposed to air, they oxidize, a reaction that liberates metals into the groundwater. This contaminated water then surfaces in streams, leaving behind distinctive rusty red deposits indicative of iron sulfide oxidation. 

Moreover, the oxidation process acidifies the water, potentially hastening further weathering and environmental degradation. Notably, some of the alpine streams sampled exhibited extremely low pH levels, ranging from 3 to 4.

Isolating the effects of climate change

Drawing on 40 years of water chemistry data, with the latest samples collected in 2021, the researchers analyzed conditions in 22 headwater streams across 17 high-altitude watersheds. 

These areas, situated above 3,000 meters (approximately 10,000 feet) and characterized by their natural acidity and metal richness, have historically limited the presence of aquatic plants and animals. 

Importantly, these watersheds have experienced no recent mining or remediation interventions. “The key point is no recent mining or remediation work has been done,” Manning explained. “These watersheds have just been sitting there responding to nothing other than the climate.”

Initial spike of metals in streams

As these enriched streams descend into larger rivers, the metal concentrations are somewhat diluted, yet the initial spike remains a significant concern. 

“I don’t think this is a big red flag for major metropolitan or agriculture users way downstream at lower elevations but some of our mountain communities get their water only a short distance down from these mineralized streams,” Manning said. 

Broader study implications 

The data from this study are critical for water managers who need to anticipate which metals are entering the streams, and at what rate, to effectively mitigate risks and allocate resources for stream remediation and tourism development.

The broader implications of this study extend beyond local concerns, as it links similar increases in sulfate concentrations observed in mountain streams globally to climate change. 

This groundbreaking research is the first to statistically connect accelerated sulfide weathering with rising temperatures across a broad geographical area. 

A universal signal of climate change

Manning postulates that thawing underground ice at the highest, coldest mountain elevations is a major factor. 

“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,” explained Manning.

While the study did not find direct correlations with other potential factors such as falling water tables or melting rock glaciers, these could still influence other areas. 

“There’s just no other logical explanation than this is a changing climate signal. Nothing else would reach all these watersheds universally,” concluded Manning.

The study is published in the journal Water Resources Research.

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