Nutrient pollution damages streams in ways previously unknown, ecologists find

Beth Gavriles in UGA Today: An important food resource has been disappearing from streams without anyone noticing until now. In a new study published March 6 in the journal Science, a team of researchers led by University of Georgia ecologists reports that nutrient pollution causes a significant loss of forest-derived carbon from stream ecosystems, reducing the ability of streams to support aquatic life.

The findings show that the in-stream residence time of carbon from leaves, twigs and other forest matter, which provide much of the energy that fuels stream food webs, is cut in half when moderate amounts of nitrogen and phosphorus are added to a stream. "This study shows how excess nutrients reduce stream health in a way that was previously unknown," said the study's lead author Amy D. Rosemond, an associate professor in the UGA Odum School of Ecology.

Stream food webs are based on carbon from two main sources. One is algae, which produce carbon through photosynthesis. Nutrient pollution has long been known to increase carbon production by algae, often causing nuisance and harmful algal blooms. The second source is leaves and bits of wood from streamside forests. This forest-derived carbon typically persists year-round, making it a staple food resource for stream organisms.

"Most people think of nitrogen and phosphorus pollution in streams as contributing to algae blooms," said Diane Pataki, program director in the National Science Foundation's Division of Environmental Biology, which funded the research. "But streams contain a lot of leaf litter, and this study shows that nutrient pollution can also stimulate carbon losses from streams by accelerating the breakdown of that litter. That helps us better understand how fertilizer runoff affects carbon transport and emissions from streams and rivers."...

Looking east toward Haystack Butte and Haystack Creek along the Going-to-the-Sun Road. The cut of the Going-to-the-Sun Road, a National Civil Engineering Landmark, is visible in the vegetation of the mountainside. Photo: David Restivo, NPS, Wikimedia Commons via Flickr, under the Creative Commons Attribution 2.0 Generic license