What role do small dams play in pollution control?

"Small dams, reservoirs and ponds trap water pollution, which provides an important benefit to water resources," Powers said. "This is especially relevant in agricultural lands of the Midwest U.S., where there are lots of small, but aging dams."

Although small individually, the sum total of the small reservoirs and ponds have a global surface area comparable to that of all large reservoirs added together.

Powers and his fellow researchers showed in detail how a small aging dam, which was more than 100 years old and located in agricultural Wisconsin, trapped water pollutants associated with fertilizer and manure runoff. They also showed an increase in downstream transport of nutrient pollution after the dam was removed, which occurred because of concerns about the dam's safety.

"Many small dams are threatened by long-term structural decline and are also filling with sediment," Powers said. "If we don't better incorporate how small dams affect the movement of water and wastes through the environment, their benefit to downstream water quality could be lost. Meanwhile, legacy sediment and pollution currently trapped behind dams could release as dams lose their water storage capacity, fall apart, or are removed deliberately."

Powers notes that there is a crucial need to gain a better understanding of what small dams mean for our water quality before they crumble and disappear.

"I am continuing to work on the subject at a broader regional scale by looking at hundreds of stream and river monitoring stations throughout the Midwestern U.S. to detect signals of dams," he said. "One current goal is to try and figure out which regions are most vulnerable to water quality changes caused by accumulation of sediment and phosphorus behind dams."

The research paper appeared in the Journal of Geophysical Research-Biogeosciences.

Powers is conducting his research as part of the Notre Dame Environmental Change Initiative's Land Use Project. The Environmental Change Initiative conducts policy-oriented research designed to help policy-makers manage environmental changes.