The shape of riverbeds may affect how streams combat excess nitrogen that depletes oxygen levels and chokes aquatic life, hurting water bodies, drinking water supplies and potentially tourism around the world, said a Colorado State University professor who recently received a National Science Foundation grant to study the issue.
Most scientists studying how streams process excess nitrogen have studied the biology, not the physical form and hydraulics of the streambed, said Brian Bledsoe, civil engineering assistant professor in Colorado State’s College of Engineering. He argues that channel form could be just as important in determining stream health.
In fact, knowing how the forms of small streams help manage pollutants could help increase the cost effectiveness of stream and watershed restoration, he said.
"Excess nitrogen is a serious problem around the world because it degrades water quality in a lot of important aquatic systems," said Bledsoe. "We want to learn what it is about some streams that makes them more effective at storing or removing nitrogen. What are some characteristics that we can build into restoration strategies that are likely to enhance nutrient uptake and water quality further downstream?"
Bledsoe received a $450,000 NSF CAREER Award for the project over the next five years.
"This research will be extremely beneficial in improving our understanding of how to restore ecological functions in impaired rivers," said Greg Jennings, professor of biological and agricultural engineering at North Carolina State University who has worked with Bledsoe for more than a decade on river assessment and restoration.
Bledsoe’s research will include creating new outdoor laboratories for graduate and undergraduate students in and around Fort Collins to study Spring Creek, Sheep Creek, the Little Snake River and the North St. Vrain River. Bledsoe and his team will inject tiny amounts of nitrogen isotopes into the streams and track them to monitor how the profiles of the riverbeds and flow conditions affect nutrient retention.
He plans to conduct his research in streams in a variety of geographic areas. The tiny tributaries that fan out from headwaters, for example, are the most critical in filtering out pollutants before they get further downstream.
"Rivers are dynamic, not static," Bledsoe said. "As opposed to just building habitat, we want to learn how to restore the physical processes that give streams the capacity to perform ecological functions."
Many coastal areas in the United States including the Gulf of Mexico have seasonal dead zones that are virtually devoid of life because oxygen levels are so low.
"We’re breathing air that’s about 78 percent nitrogen gas. Streams and wetlands receive nitrogen as nitrate, a form that stimulates plant growth. Microbes in streams can turn nitrate into the gaseous form of nitrogen we’re breathing. As a result, the nitrate has less impact on water quality."
Plants and algae can help filter some pollutants in streams to a point, but excess nitrogen – caused by many factors including fertilizers – can result in excess algal growth. Dying and decomposing algae remove oxygen from the water.
"Then fish kills may occur and that can have severe economic consequences for commercial fishing, recreation and tourism," Bledsoe said. The excess nitrogen can also make drinking water more difficult to treat. "This is a big issue all over the world. In the Mississippi River basin, we put the same amount of nitrogen into the watershed that Mother Nature does on her own."
Bledsoe also plans to work with the city of Fort Collins to create opportunities for students to study the city’s stormwater ponds. The city is a national leader in K-12 education about stormwater.