New methods and dedicated fieldwork provide good news for clearing mine pollution

Mayfly larvae feed on algae that grow on river rocks. Their presence indicates that the stream is recovering, as they are particularly sensitive to dissolved metals. Credits: Bruce Medhurst

Mining contains a large amount of rock, so some confusion is expected. However, mining operations can continue to affect the ecosystem even after the activity is over. Heavy metals and corrosive substances leach into the environment, preventing wildlife and vegetation from returning to the area.

Fortunately, this damage can be undone. A team of scientists, including Dave Herbst at the University of California, Santa Barbara, investigated how river ecosystems respond to restoration work. The team has integrated decades of data from four watersheds contaminated by abandoned mines. Creative thinking was required to simplify the complex dynamics of the nearly 12 toxins that inhabit the myriad species of each river.

Ultimately, the team’s clever methodology showed that restoration could improve some of the biggest problems with mine pollution.Their findings published in the journal Freshwater science, Revealed a strategy that worked well as a recovery pattern for the entire four channels. The results also suggest that regulations need to consider all pollutants together, rather than establishing standards individually.

“There are major problems with old mining sites not only in the United States but around the world,” said Herbst, a research biologist at the Sierra Nevada Institute for Aquatic Sciences (SNARL) at the University of Mammoth Lakes. “They are widespread, permanent and long-term problems, but the good news is that the investment and effort of programs like CERCLA Superfund can solve these problems.”

Herbst’s work focused on Leviathan Creek, a stream of the Sierra Nevada River, 25 miles southeast of Lake Tahoe. This river is the site of recovery efforts under the CERCLA (Comprehensive Environmental Response, Compensation, and Liability Act), also known as the Superfund.This area was not mined Precious metal, But to extract sulfur Sulfuric acid Process minerals from other sites. The presence of sulfur-containing minerals naturally produced slightly acidic water, but open pit mining exposed these minerals to the elements. As a result, stronger acids were generated and trace metals such as aluminum, cobalt and iron leached out of the rock into the environment. The combined effects of increased acidity and toxic metals have devastated the local aquatic ecosystem.

Selection of standards

Each mining site produces its own mixed pollutants. In addition, different rivers are home to different types of aquatic invertebrates, and each river is home to hundreds of different species, Herbst said. This variability made comparisons difficult.

So the researchers set out to establish standards and benchmarks. They decided to track the effects of contamination and restoration on kagerou, stoneflies and caddisflies. These groups are important for aquatic food webs and exhibit different resistances to different toxins. Rather than comparing closely related species, scientists have grouped animals with common characteristics such as physical characteristics and life history.

Second, the team needed to understand all the pollutants. They quickly realized that it was not enough to track the toxicity of individual metals individually, as is often the case in the laboratory. It is the complex effects that actually affect the ecosystem. In addition, scientists often measure toxicity based on lethal doses. Still, pollution can destroy ecosystems at much lower concentrations, Herbst explained. Over time, chronic effects such as reduced growth and reproduction do not actually kill individuals. Species can become extinct from the area.

Successful Recovery Mapping: New methods and dedicated fieldwork provide good news for clearing mine pollution

Containment ponds collect contaminated effluent from mines for treatment. Credits: Dave Herbst

Considering the various toxins, researchers have determined another criterion of toxicity, the reference unit. They defined one reference unit (CU) as the concentration of toxins that adversely affect the growth and reproduction of the test organism. The various responses give the CU an approximation, but proved to be a surprisingly robust metric.

The concentration of 1 CU depends on the substance. For example, researchers used a value of 7.1 micrograms of cobalt per liter of water as a toxicity threshold for aquatic organisms. Therefore, 7.1 μg / L is equivalent to 1 CU of cobalt. On the other hand, 150 μg / L of aral elements prevented invertebrates from living their best lives, so we set 150 μg / L as 1 CU of ar as elements.

This approach allowed scientists to compare and combine the effects of completely different toxins and examine how the occurrence of total toxicity in nature is expected. Therefore, 7.1 μg / L cobalt alone, or 150 μg / L arsenic alone, or even a combination of 3.55 μg / L cobalt and 75 μg / L arsenic, all produce a cumulative base unit (CCU) 1. .. , This causes similar problems for aquatic organisms, but reaches.

This combined effect has proven important in understanding the real-world impact of mining pollution, as animals are exposed to many toxins at once. “When assessing toxicity thresholds in field settings, these metals should be considered together rather than individually,” Herbst said.

As a result, scientists could compare rivers across rivers by expressing toxicity in cumulative criteria, despite the presence of different metals in different locations. When total toxicity exceeds 1 CCU, invertebrate diversity is disrupted.

Evaluation of effort

The team now has an easy way to measure subject (aquatic invertebrates) and contamination (cumulative unit of measure). We also had more than 20 years of field data from four watersheds where superfund cleanup was underway. They used an unpolluted stream near each river as a baseline to determine how well the recovery was progressing.

The authors found that these projects could bring rivers closer to nature in 10 to 15 years. It was a wonderful surprise. “Every project was successful, despite different mined pollutants, different ways of solving problems, and different river sizes,” says Herbst.

He added that most of the recovery happened in the first few years of treatment. It’s the worst at first, so even a small effort can make a big difference.

“Another surprise is the high commonality of responses, despite the different pollutants and repair methods,” Herbst said. Recovery rates, the order in which species returned (based on common characteristics), and even long-term timeframes were similar in all four rivers. These promising results and shared paths suggest that even difficult environmental problems can be solved with proper effort and investment.

Successful Recovery Mapping: New methods and dedicated fieldwork provide good news for clearing mine pollution

Leviathan Creek 20 years after the restoration began. Credits: Dave Herbst

Lessons and loose end

Restoration is underway at four sites in California, Colorado, Idaho, and Montana. Many interventions require continuous attention, such as treating acidic water with lime. However, we hope that the restoration will become self-sustaining through efforts such as the replacement of contaminated soil, the installation of microbial bioreactors, and the restoration of vegetation in the excavated riverbank areas.

A self-sustaining solution is the goal, as these sites become inaccessible at certain times of the year and can lead to varying levels of pollution. Restoration occurs only between spring and autumn, for example, in winter when snow blocks access to the Leviathan mine. Spring thaw also melts more metal, creating worse conditions than in the dry season of early autumn.

Herbst will review the seasonal aspects of restoration in future research. For now, he believes that other abandoned mines should carry out restoration and surveillance practices to assess the success of the restoration.

These exciting discoveries would not have been possible without long-term surveillance at four locations. “We rarely monitor restoration projects that last more than two years,” Herbst said. “This is really disappointing, as most projects show no reaction in a short period of time.”

The only reason Herbst and his colleagues had these datasets was because they themselves invested their time and resources. “Most of it is due to the dedication of individual researchers to these projects,” he said. “There are other players coming and going along the way, but as long as there are enthusiastic researchers collecting this data, we will be the basis for decision making in the future.”

Aside from the importance of long-term monitoring, the message Herbst expects from EPAs and industry is that water quality standards for toxic metals cannot be applied individually. “Depending on how they work together, we need to apply them together,” he said.

Even if individual pollutants are below the required limits, the combined effects can far exceed the amount wildlife can handle. The concept of cumulative base units provides a very easy way to explain this. If all eight toxins in the stream are half the CU value, they will still be up to four CCUs.

Conclusion: There’s a reason to celebrate. “Through this research, we can demonstrate that these programs can succeed even on the biggest problems,” Herbst said. “This is exactly what the Super Fund project is aiming to fix.”

Long-term monitoring shows successful recovery of mining-contaminated streams

For more information:
William H. Clements et al, long-term monitoring reveals a convergence pattern of recovery from mining pollution across four watersheds in the western United States. Freshwater science (2021). DOI: 10.1086 / 714575

Quote: Successful Recovery Mapping: New methods and dedicated fieldwork provide good news for clearing mine pollution (June 8, 2021) Obtained from 06-successful-recovery-methods- on June 8, 2021 Dedicated fieldwork.html

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New methods and dedicated fieldwork provide good news for clearing mine pollution

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