New acid rain threat identified.

New Acid Rain Threat Identified

Acid rain's primary threat to aquatic life has generally been seen as its ability to lower the pH of water. But a study released this week by the New York City-based Environmental Defense Fund (EDF) highlights what its authors contend is an equally deadly but ignored impact of acid rain -- nitrate-induced suffocation and light starvation of aquatic species.

Though nitrates are a nutrient, when their levels become excessive they can cause "algal bloos" -- essentially an overgrowth of algae and other phytoplankton. These plants quickly consume most of the dissolved oxygen in water, suffocating other aquatic species. Algal overgrowth also clouds the water, preventing necessary light from filtering down to plants on the seafloor.

The EDF study focused on the effects of excess nitrogen on the Chesapeake Bay -- the largest U.S. estuary and a major spawning ground for East Coast fisheries from Maine to North Carolina. Until now, says Michael Oppenheimer, one of the study's authors, the Environmental Protection Agency (EPA) and others have largely ignored or greatly underestimated acid rain's role in overloading the Chesapeake and other waters with nitrogen. EDF's calculations, based on data from a range of federal and stage agencies, including the EPA's Chesapeake Bay Program, indicate that acid deposition contributes at least one-quarter of the nitrogen entering the bay as a result of human activity. That makes acid deposition second only to fertilizer runoff as a source of nitrogen pollution.

Moreover, says Diane Fisher, who led the EDF study, "Our analyses show that acid rain is a significant problem in coastal waters up and down the entire eastern seaboard." Affecting primarily brackish and salt water, it "will continue to grow until nitrogen oxides (NO.sub.x.) emissions are controlled," she adds. In fact, efforts already underway to control nitrogen emissions (from sources other than acid rain) into many waterways "could be largely negated if NO.sub.x emissions [from acid deposition] are not further reduced," her study says.

To counter the acid rain nitrate problem, EDF recommends that:

* states in the Chesapeake Bay watershed implement NO.sub.x limits for electric power plants and factories and beef up motor vehicle inspection programs. (Unlike the sulfur dioxide component of acid rain, in which electric power plants contribute 70 percent of the pollution, motor vehicles are the major source of acid rain's nitrates. However, federal law prevents states from setting motor vehicle standards for NO.sub.x.)

* the federal government adopt regulations to reduce industrial and vehicular NO.sub.x emissions by at least 40 percent -- a level that matches nitrogen reductions from other sources now being planned for the Chesapeake. (The Clean Air Act reauthorization legislation, pending in the House and Senate, would reduce allowable NO.sub.x emissions from cars by about 60 percent.) EDF particularly endorses energy-efficiency measures to reduce NO.sub.x.

* all governmental bodies acknowledge acid rain's contribution to the deteriorating quality of East Coast waters, and work at reducing nitrogen from sources besides acid rain -- especially from sewage treatment plants and fertilizer and manure storage.

The EDF study wins high praise from William C. Baker, president of the Annapolis, Md.-based Chesapeake Bay Foundation. "The Chesapeake Bay is dying," he says, and this new report not only "brings to light an important new source of nitrogen -- a major pollutant in the Chesapeake Bay" -- but also points to where those involved in saving it must direct their attentions.

Though EPA spokesman Dave Cohen says the EDF scientists "seem to [offer] fairly compelling evidence regarding nitrogen loading" into the Chesapeake from acid rain, he adds that his agency's scientists were "surprised" at the size of the nitrogen contribition being attributed to this source and will therefore begin reevaluating the data themselves. If EDF's 25 percent figure is accurate, he says, "then acid rain will be making a greater, more harmful contribution to the bay than we [at EPA] had suspected."