Insects Key Indicators of Water Health, Experts Say

John Roach
for National Geographic News
February 1, 2007
Sometimes it's good to have bugs in your water.

An increase in the diversity and size of water insects is heralding an improvement in the environmental quality of streams that flow into the Carson River in northern California and Nevada.

The streams run below an abandoned sulfur mine high in the Sierra Nevada mountain range that runs along the border between the two states (California map).

For decades a toxic soup of acids and heavy metals leaked from the mine, coloring the water and rendering the streams nearly lifeless.

In 2000 the U.S. Environmental Protection Agency (EPA) designated the mine as a Superfund site, one of the most polluted spots in the United States.

"The water quality was awful," said Kevin Mayer, the EPA project manager for the mine cleanup.

"And unlike most sites where I work, where groundwater and soil contamination can't be visibly seen, it was extraordinarily disheartening to see the bright orange streams going down miles away from the mine."

But since then cleanup activities have led to a "dramatic improvement" in the streams' habitats, said David Herbst, a biologist with the Sierra Nevada Aquatic Research Laboratory in California.

Herbst studies insects to monitor stream health throughout the Sierra Nevada region, including the waterways downstream from the sulfur mine.

Some waters still have an orange tinge and contain toxic metals, but his monitoring results indicate the return of algae, insects, and fish to the watershed.

Insects and Health

Insects and other invertebrates are central to stream life, Herbst said by email.

They eat algae and other organic matter and in turn are food for fish and birds (related news: "Insects Key to Rain Forest Diversity, Study Shows" [March 10, 2005]).

"Different invertebrates may live from months to years, so the types present reflect what has happened in a stream over that span of time."

When Herbst inspects a stream, he looks for things like insect diversity and size.

He asks, Do only hardy, tolerant insects thrive in the water or are there ecologically sensitive insects too? Does the stream contain only insects that eat algae or also insects that prey on other insects—an indication of a healthier ecosystem?

All the details, he said, provide more information than the snapshots of a single time and place gleaned from water quality tests.

EPA's Mayer said information from standard water-quality tests is helpful for monitoring contaminant levels for people.

"But the question is, Is that clean enough for the health of the ecosystem?" he said.

"The critters living in these mountain stream ecosystems can be extraordinarily sensitive to small changes in chemistry."

Standard Setting

Herbst tries to answer this question by developing reference standards, which are compiled from studies of streams within watersheds that have experienced little human impact.

The standards become benchmarks for projects such as the mine cleanup.

Herbst then studies the insect community after each cleanup project Mayer and his team implement.

In one case, he found that insect diversity improved after the cleanup team built ponds to capture summertime runoff from snowmelt and rain. Neutralizing chemicals added to the ponds strip pollutants from the water, creating cleaner runoff.

Diversity also improved after construction of a rocky wetland full of bacteria that reduce the acidity of the mine's sulfuric waters. Contaminated waters enter the wetland at one end and come out clean on the other side.

"That project resulted in a huge improvement in the condition of one stream over a single summer," Herbst said.

"We would not have known the ecological success had we not been monitoring before and after."

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