Cleaning up mining pollution in rivers

Date:
June 8, 2021
Source:
University of California - Santa Barbara
Summary:
Mining involves moving a lot of rock, so some mess is
expected. However, mining operations can continue to affect
ecosystems long after activity has ended. Heavy metals and corrosive
substances leach into the environment, preventing wildlife and
vegetation from returning to the area.



FULL STORY ========================================================================== Mining involves moving a lot of rock, so some mess is expected. However,
mining operations can continue to affect ecosystems long after activity
has ended.

Heavy metals and corrosive substances leach into the environment,
preventing wildlife and vegetation from returning to the area.


========================================================================== Fortunately, this damage can be reversed. A team of scientists, including
UC Santa Barbara's Dave Herbst, investigated how river ecosystems
respond to remediation efforts. The team combined decades of data from
four watersheds polluted by abandoned mines. It took creative thinking
to simplify the complex dynamics of nearly a dozen toxins on the myriad
species in each river.

Ultimately, the team's clever methodology showed that restoration can
improve some of the biggest problems of mining contamination. Their
findings, published in the journal Freshwater Science, revealed strategies
that worked well as recovery patterns across the four waterways. The
results also suggest that regulations need to consider all contaminants together, rather than establish standards on an individual basis.

"There is a big problem that we have with legacy mine sites, not only
in the U.S. but worldwide," said Herbst, a research biologist at the university's Sierra Nevada Aquatic Research Laboratory (SNARL) in Mammoth Lakes. "They 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 fix those problems." Herbst's work focused
on Leviathan Creek, a Sierran stream 25 miles southeast of Lake Tahoe
which is the site of a restoration effort under CERCLA (the Comprehensive Environmental Response, Compensation, and Liability Act), also known also
as Superfund. The area was mined not for precious metals, but to extract
sulfur for making sulfuric acid to process minerals from other sites.

The presence of sulfur-bearing minerals made for water that was
naturally a bit acidic, but open-pit mining exposed these minerals to
the elements. The result was stronger acid that leached trace metals
like aluminum, cobalt and iron from the rock into the environment. The
combined effects of increased acidity and toxic metals devastated the
local aquatic ecosystem.

Sorting out standards Each mining site produces a unique blend of
pollutants. What's more, different rivers harbor different species of
aquatic invertebrate, with hundreds of different types in each stream,
Herbst said. This variability made comparisons a challenge.



==========================================================================
So the researchers set to work establishing standards and benchmarks. They decided to track the effect of pollution and remediation on mayflies, stoneflies and caddisflies. These groups are critical to the aquatic food
web and display a variety of tolerances to different toxins. Rather than compare closely related species, the scientists grouped together animals
with shared characteristics -- like physical traits and life histories.

Next the team had to make sense of all the pollutants. They quickly
realized it wouldn't be enough to track the toxicity of individual metals separately, as is often done in the lab. It's the combined impact that
actually affects the ecosystem. Furthermore, scientists often measure
toxicity based on a lethal dosage. And yet pollution can devastate
ecology at much lower concentrations, Herbst explained. Chronic effects,
like reduced growth and reproduction, can eliminate species from an area
over time without actually killing any individuals.

Given the variety of toxins, the researchers decided on another standard
for toxicity: the criterion unit. They defined 1 criterion unit (CU) as
the concentration of a toxin that produced adverse effects on growth and reproduction of test organisms. Although the variety of responses makes
the CU an approximation, it proved to be a surprisingly robust metric.

The concentration in 1 CU varies from substance to substance. For
instance, the researchers used a value of 7.1 micrograms of cobalt per
liter of water as a toxic threshold for aquatic life. So, 7.1 ?g/L equals
1 CU of cobalt.

Meanwhile, 150 ?g/L of arsenic kept invertebrates from living their best
lives, so 150 ?g/L was set as 1 CU of arsenic.

This approach enabled the scientists to compare and combine the effects of completely different toxins, providing a validation of how total toxicity
would be expected to occur in nature. So, 7.1 ?g/L of cobalt by itself,
or 150 ?g/ L of arsenic by itself, or even a combination of 3.55 ?g/L of
cobalt plus 75 ?g/L of arsenic all produce a cumulative criteria unit
(CCU) of 1, which spells similar problems for aquatic critters however
it is reached.



==========================================================================
This combined effect proved critical to understanding the real-world implications of mining pollution because animals are exposed to
many toxins at once. "You need to consider these metals together, not individually, when evaluating the toxicity threshold in a field setting," Herbst said.

So despite the variety of metals at different locations, by expressing
toxicity in cumulative criteria units, the scientists could compare across rivers. When total toxicity tops 1 CCU, invertebrate diversity unravels.

Judging 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 clean-ups have been underway. They used
unpolluted streams near each river as a baseline to judge how well
restoration was proceeding.

The authors found these projects were able to restore rivers to
near natural conditions in 10 to 15 years. It was a wonderful
surprise. "Regardless of the fact that there were different mining
pollutants, different ways of remediating the problem and different sizes
of stream, all the projects came to successful outcomes," Herbst said.

Much of the recovery happened in the first few years of treatment,
he added.

Since conditions are at their worst in the beginning, even a small effort
will make a big difference.

"The other surprising part was the degree of commonality in the
responses despite differing contaminants and remediation practices,"
Herbst said. The rate of recovery, order in which species returned (based
on shared traits), and even the long-term timeframe was similar across
all four rivers. These promising results and shared paths suggest that
even daunting environmental problems can be solved with proper effort
and investment.

Lessons and loose ends Remediation at the four sites in California,
Colorado, Idaho and Montana is ongoing. Many interventions, like treating acidic water with lime, require continuous attention. However, efforts
like replacing contaminated soil, setting up microbial bioreactors and revegetating excavated and riparian areas will hopefully make remediation self-sustaining.

And a self-sustaining solution is the goal, because these sites can
become inaccessible at certain times of year, leading to variable levels
of pollution.

For instance, snow prevents access to the Leviathan mine in winter, so remediation can occur only between spring and fall. The spring snowmelt
also dissolves more metals, creating worse conditions than during drier
times at the beginning of autumn.

Herbst plans to revisit the seasonal aspects of remediation in future
research.

As for now, he thinks that other abandoned mines should implement
remediation and monitoring practices to evaluate the success of
restoration.

These exciting discoveries would have been impossible without long-term monitoring at the four locations. "You seldom get monitoring studies of restoration projects that last more than a couple of years," Herbst said, "which is really a shame because most of them don't show any kind of
response over that short a period of time." And the only reason Herbst
and his colleagues had these datasets was because they invested the
time and resources themselves. "A lot of it is due 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's
some dedicated researcher collecting this data then it will be there
in the future for us to base decisions on." Aside from the importance
of long-term monitoring, the message Herbst hopes the EPA and industry
embrace is that we can't apply water quality standards for toxic metals individually. "We must be applying them collectively according to how
they're acting together," he said.

Even if individual contaminants are under the required limits, their
combined effect could be well over what wildlife can handle. The concept
of cumulative criteria units provides a really simple way to account
for this: If eight toxins in a stream are all at half of their CU value,
they still add up to 4 CCUs.

Bottom line: There is reason to celebrate. "We're able to
demonstrate through this research that these programs can be
successful even for the biggest of problems," Herbst said,
"which is exactly what Superfund projects are intended to fix." ========================================================================== Story Source: Materials provided by
University_of_California_-_Santa_Barbara. Original written by Harrison
Tasoff. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. William H. Clements, David B. Herbst, Michelle I. Hornberger,
Christopher
A. Mebane, Terry M. Short. Long-term monitoring reveals convergent
patterns of recovery from mining contamination across 4 western
US watersheds. Freshwater Science, 2021; 40 (2): 407 DOI:
10.1086/714575 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/06/210608154411.htm

--- up 4 weeks, 4 days, 22 hours, 45 minutes
* Origin: -=> Castle Rock BBS <=- Now Husky HPT Powered! (1337:3/111)