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A team of researchers led by Old Dominion University oceanographer Margaret Mulholland has advised the U.S. Environmental Protection Agency (EPA) to be wary of proposals that would allow some industries and utilities in Virginia to meet more stringent nitrogen discharge standards simply by changing their bookkeeping.

Inorganic nitrogen in treatment facility discharges and in runoff from fertilized lawns and croplands was long ago identified as a cause of excess algal growth and even harmful algal blooms in waters such as the Chesapeake Bay. Now, the researchers have raised a red flag about organic nitrogen.

As caps on nitrogen discharges are being lowered, industries and utilities are arguing that discharge allowances should include some organic nitrogen because a large fraction of it is not "bioavailable" to organisms in the environment; that is, most algae cannot use organic nitrogen to grow and bacteria cannot use much of the organic nitrogen found in treated effluent.

Mulholland and her collaborators determined that even though organic nitrogen may not be bioavailable in freshwater, it is or may become available in saltwater, including estuaries such as the Chesapeake Bay. The findings are reviewed in an EPA's Chesapeake Bay Program Scientific and Technical Advisory Committee (STAC) report released earlier this month.

An associate professor of oceanography and an expert in nitrogen cycling in aquatic systems, Mulholland was first author on the report and chaired the committee as a member of STAC.

While in freshwater, algal growth tends to be limited by phosphorus. Nitrogen limits growth in saltier water. In fact, nitrogen is known to fuel excess algal growth in estuaries and the resulting algal decay leads to oxygen depletion and other environmental concerns in the Chesapeake Bay.

Efforts to reduce nitrogen in discharges from wastewater treatment facilities have focused on inorganic nitrogen because organic nitrogen, or at least a portion of it, was thought to be unusable to many bacteria and algae.

By reviewing published research and contributing results from their own research efforts, the STAC experts concluded that nitrogen discharges previously thought to be inert are either directly available or likely become bioavailable to estuarine microbes and algae as a result of the effects of salt on the chemical characteristics of organic nitrogen and the differences in microbial communities in freshwater versus saltwater.

The STAC subcommittee suggested that additional tests of bioavailability along salinity and biotic gradients and better characterization of the organic nitrogen compounds discharged from treatment facilities are necessary before discharge allowances can be reduced without detrimentally impacting the Chesapeake Bay. Previous wastewater allocations have been made based on conditions known to impact nutrient bioavailability in freshwater.

If organic nitrogen presents previously unforeseen threats to the health of the bay, then total nitrogen allowances and discharge caps cannot be increased without impacting the bay, the researchers argued. They noted decreases in the allowed nitrogen discharges greatly increase the cost of wastewater treatment.

As a STAC member for the Chesapeake Bay Program, Mulholland employs her expertise in nutrient cycling, algae blooms, and other aspects of biological oceanography toward management efforts. The program is a joint project encompassing Virginia, Maryland, Pennsylvania, Delaware, New York and West Virginia, as well as the District of Columbia, the Chesapeake Bay Commission and the EPA.

An ODU faculty member since 2000, Mulholland was granted a doctorate in biological oceanography by the University of Maryland in 1998.

This article was posted on: March 21, 2007

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