Wednesday, May 07, 2008

Stream Restoration to Reduce Nitrates

A team from the University of Maryland found a way to measure some benefits of urban stream restoration:

Using state-of-the-art techniques in a long-term study, Kaushal's team injected stable isotope tracers into restored and unrestored sections of an urban stream, and measured how microbes in the streambanks naturally absorb nitrate and convert it into inert nitrogen gas. By analyzing those samples, the team was able to determine in-the-field nitrogen reductions by stream microbes through a process known as denitrification.

The research showed that stream restoration techniques that "reconnected" the banks to the stream doubled nitrogen removal rates by microbes, and reduced nitrogen levels in ground water by 40%, contributing to significantly lower nitrogen levels in the stream compared to unrestored conditions. Getting water out of the stream channel into denitrification "hot spots" in floodplain wetlands helped improve water quality.
Reducing waterborne nitrates is particularly important in the Chesapeake Bay region. The bay suffers from large dead zones during summer months due to a lack of dissolved oxygen. Hypoxia is caused by algae that feeds on the excessive nitrates and phosphates that flow into the bay year-round. Cleanup efforts have failed to meet their goals for reducing nitrate content in the watershed because there are so many sources scattered over such a large area. Faulty sewer systems, agricultural fertilizers, and lawn fertilizers are the main culprits.

Urban stream restoration is only part of the solution to improving the health of our watersheds. It looks like one that could benefit urban wildlife, as well as ecosystems downstream.