Mining involves moving a lot of rock, so damage is expected. However, mining operations can continue to affect ecosystems long after activity ceases. Heavy metals and corrosive substances seep into the environment, preventing wildlife and vegetation from returning to the area.
Fortunately, this damage can be reversed. A team of scientists, including Dave Herbst of UC Santa Barbara, studied how river ecosystems respond to remediation efforts. The team combined decades of data from four watersheds polluted by abandoned mines. It took some creative thinking to simplify the complex dynamics of nearly a dozen toxins on the myriad species of each river.
Ultimately, the team’s smart methodology showed that restoration can improve some of the biggest mining contamination issues. Their findings, published in the journal Freshwater science, revealed strategies that worked well as recovery models in the four streams. The results also suggest that regulations should consider all contaminants together, rather than setting standards on an individual basis.
“There’s a big problem we have with legacy mine sites, not just in the United States but around the world,” said Herbst, a research biologist at the university’s Sierra Nevada Aquatic Research Laboratory (SNARL) in Mammoth Lakes. “These are widespread, persistent and long-lasting problems. But the good news is that with the investment and effort of programs like CERCLA Superfund, we can solve these problems.”
Herbst’s work has focused on Leviathan Creek, a Sierrian stream 40 km southeast of Lake Tahoe, which is the site of a restoration effort under the Comprehensive Environmental Response, Compensation, and Liability Act), also known as the Superfund. The area was not mined for precious metals, but to extract sulfur to make sulfuric acid to process minerals from other sites. The presence of sulfur minerals made for naturally slightly acidic water, but surface mining exposed these minerals to the elements. The result was a stronger acid that leached traces of metals like aluminum, cobalt, and iron from the rock into the environment. The combined effects of increased acidity and toxic metals have devastated the local aquatic ecosystem.
Each mine site produces a unique mixture of pollutants. Plus, different rivers are home to different species of aquatic invertebrates, with hundreds of different types in each stream, Herbst said. This variability made comparisons difficult.
The researchers therefore set to work to establish standards and benchmarks. They decided to monitor the effect of pollution and sanitation on mayflies, sandflies and caddisflies. These groups are essential to the aquatic food web and exhibit a variety of tolerances to different toxins. Rather than comparing closely related species, scientists have grouped together animals that share common characteristics, like physical traits and life histories.
Then the team had to make sense of all the pollutants. They quickly realized that it would not be enough to monitor the toxicity of each metal separately, as is often done in the laboratory. It’s the combined impact that really affects the ecosystem. In addition, scientists often measure toxicity on the basis of a lethal dose. And yet pollution can devastate the ecology at much lower concentrations, Herbst explained. Chronic effects, such as reduced growth and reproduction, can wipe out species from an area over time without actually killing individuals.
Given the variety of toxins, the researchers opted for another standard of toxicity: the unit of criteria. They defined 1 Criterion Unit (UC) as the concentration of a toxin that produced adverse effects on the growth and reproduction of the test organisms. While the variety of responses makes CU an approximation, it has proven to be a surprisingly robust metric.
The concentration in 1 CU varies from substance to substance. For example, the researchers used a value of 7.1 micrograms of cobalt per liter of water as the toxic threshold for aquatic life. Thus, 7.1 µg / L is equivalent to 1 CU of cobalt. During this time, 150 g / L of arsenic prevented the invertebrates from living their best lives, so 150? G / L was defined as 1 CU of arsenic.
This approach allowed scientists to compare and combine the effects of completely different toxins, providing validation of how full toxicity is expected to occur in nature. So 7.1 g / L of cobalt alone, or 150? G / L of arsenic alone, or even a combination of 3.55? G / L of cobalt plus 75? G / L of arsenic all produce one unit. Cumulative Criteria (CCU) of 1, which poses similar problems for aquatic creatures regardless of how it is achieved.
This combined effect has been found to be essential in understanding the real implications of mining pollution, as animals are exposed to many toxins at once. “You have to consider these metals together, not individually, when evaluating the toxicity threshold in the field,” Herbst said.
Thus, despite the variety of metals in different places, by expressing the toxicity in units of cumulative criteria, scientists were able to compare from one river to another. When the total toxicity exceeds 1 CCU, the diversity of invertebrates crumbles.
Judge their efforts
The team now had their subjects (aquatic invertebrates) and a simple way to measure pollution (the cumulative criteria unit). They also had over 20 years of field data from four watersheds where Superfund cleanups were underway. They used unpolluted streams near each river as a benchmark to judge the progress of the restoration.
The authors found that these projects were able to restore rivers to near-nature conditions within 10 to 15 years. It was a wonderful surprise. “Regardless of the fact that there were different mining pollutants, different ways of solving the problem, and different sizes of streams, all of the projects yielded positive results,” Herbst said.
Much of the recovery occurred in the first few years of treatment, he added. Since conditions are the worst at first, even a little effort will make a big difference.
“The other surprising part was the degree of similarity in responses despite contaminants and different remediation practices,” Herbst said. The rate of recovery, the order in which the species returned (based on common traits), and even the long-term timing were similar in all four rivers. These promising results and shared pathways suggest that even the most daunting environmental problems can be solved with the right effort and investment.
Lessons and free tips
The remediation of the four sites in California, Colorado, Idaho and Montana is underway. Many interventions, such as treating acidic water with lime, require continued attention. However, efforts such as the replacement of contaminated soils, the installation of microbial bioreactors and the revegetation of excavated and riparian areas will, hopefully, make sanitation autonomous.
And a stand-alone solution is the goal, as these sites can become inaccessible at certain times of the year, resulting in varying pollution levels. For example, snow prevents access to the Leviathan mine in winter, so remediation can only take place between spring and fall. Spring snowmelt also dissolves more metals, creating worse conditions than during drier periods in early fall.
Herbst plans to revisit the seasonal aspects of sanitation in future research. For now, he believes other abandoned mines should implement remediation and monitoring practices to assess the success of the reclamation.
These exciting discoveries would have been impossible without long-term monitoring at all four sites. “You rarely get follow-up studies of restoration projects that last longer than a few years,” said Herbst, “which is a real shame because most of them don’t show any type of response in such a short period of time. “.
And the only reason Herbst and his colleagues had these datasets was because they had invested the time and resources themselves. “This is due in large part to the dedication of individual researchers to these projects,” he said. “There are other players that come and go along the way, but as long as there is a dedicated researcher collecting this data, they will be there in the future on which we will base our decisions.”
Besides the importance of long-term monitoring, the message Herbst hopes the EPA and industry will adopt is that we cannot individually enforce water quality standards for toxic metals. “We have to apply them collectively depending on how they act together,” he said.
Even if the individual contaminants are below the required limits, their combined effect could be far greater than what wildlife can withstand. The concept of cumulative criteria units provides a very simple way to account for this: if eight toxins in a stream are all at half their CU value, they still add up to 4 CCUs.
Bottom line: There are reasons to celebrate. “We are able to demonstrate through this research that these programs can be successful even for the biggest problems,” Herbst said, “which is exactly what the Superfund projects are intended to solve”.