Vol. 1, No. 3
Headline Back Issues
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Atmospheric deposition: Researchers say more study necessary to help identify sources and effects of airborne substances on marine and coastal environments Gulf of Maine - Trying to identify the sources of airborne substances in our atmosphere and to determine their effects on our coastal watersheds can be like trying to capture a cloud with a net. You may end up with a damp net, but you won't have much of the cloud. Having entered the atmosphere, a number of substances fall to the earth in the form of rain, snow, sleet, and dust. Those receiving the most attention from researchers and regulators are sulfur dioxide, nitrogen oxide, and mercury, and their most prominent sources are automobile engine combustion, incinerators, industrial boilers, and electrical utilities. Researchers say identifying the sources of atmospherically deposited contaminants and their effects on marine ecosystems is difficult, because emissions of these substances can be produced by many different sources from a local incinerator to a boiler thousands of miles away. Once these combined emissions are atmospherically deposited on land or water, they also mix with substances from nonpoint sources, such as runoff. Challenges scientists face in tracing and quantifying atmospheric deposition, and understanding its effects on ecosystems, have prompted researchers and regulators to call for continued study of atmospheric deposition by the US and Canada. Research programs under way include the National Oceanic and Atmospheric Administration's (NOAA) Atmospheric Nutrient Input to Coastal Areas (ANICA) program, which develops methods for assessing atmospheric deposition to coastal regions; EPA's Great Waters Program, which monitors the effects of atmospheric deposition on watersheds and coastal waters including several in the Gulf of Maine; Environment Canada's (EC) efforts to monitor the levels of mercury and other toxic chemicals in seabirds in the Gulf; and the Ecological Monitoring and Assessment Network (EMAN), overseen by EC. EMAN coordinates research into atmospheric deposition of mercury in the Gulf of Maine, using the US National Atmospheric Deposition Program (NADP) and integrating physical, chemical, and biological data in an "ecosystem approach," according to Wilfred Pilgrim, air biologist and EMAN's mercury lead. Though they lack complete information, what researchers have learned so far, and what most US and Canadian regulations address, is that at least some amount of certain problematic substances is being atmospherically deposited in coastal watersheds. Sulfur dioxide: Sulfur dioxide is created when oil or coal is burned to generate power, in separating impurities from metal, and other industrial processes. In the atmosphere it converts to sulfuric acid and can increase acidity of rain, snow, sleet, fog, dew, gases, or dry particles, which fall to earth as so-called acid rain. When sulfuric acid is deposited in freshwater lakes, the resulting acidity can stimulate methylation of mercury - conversion of mercury to its most toxic form. But while sea water contains elements that buffer acidity, sulfuric acid can still cause problems in coastal marine environments, because it acidifies rainwater, which can then more easily dissolve heavy metals present in upland soils, eventually depositing these metals - including mercury - into estuaries in the form of runoff. Nitrogen oxide: Created in many of the same industrial fuel combustion processes that create sulfur dioxide, and also in automobile engine combustion, nitrogen oxide converts in the atmosphere to nitric acid, and is associated with the same acid rain effects caused by sulfuric acid, along with other problems. According to a report by the US Geological Survey (USGS) National Water-Quality Assessment Program, coal- and oil-burning electric utilities and large industries account for more than half of the country's nitrogen emissions, while motorized vehicles account for more than a third. USGS states that more than 3.2 million tons (2.9 million tonnes) of nitrogen are atmospherically deposited in the US each year. According to NOAA's Coastal Program, about a third of the total US air emissions of nitrogen are deposited to the Atlantic Ocean, most heavily in the near-shore region. Researchers say nitric acid fertilizes coastal waters, causing excess growth of algae and aquatic plants. Elements in the open sea can neutralize nitric acid, but the restricted water circulation in confined coastal areas prevents this. In a process called eutrophication the excess vegetation decomposes, consuming oxygen that fish and other animals need. Undesirable vegetation can also overtake eelgrass beds that serve as scallop habitat, and certain toxic forms of algae, such as red tides, can poison shellfish beds and marine mammals. Some researchers maintain, however, that a link between atmospherically deposited nitrogen and eutrophication is only a hypothesis. According to USGS, difficulty in identifying sources of atmospheric nitrogen deposition "has made it difficult to develop a national strategy for nonpoint source pollution prevention and control." Mercury: Problem's scope hard to define Globally, mercury emissions have increased several fold during the last century with increased industrial activity, although regional emissions have declined somewhat in recent years. Released when coal is burned and during incineration of municipal and medical waste, mercury is found in thermostats, thermometers, fluorescent light bulbs, batteries, and paint, although its use is being phased out of these last two products. After being atmospherically deposited on land, mercury can enter estuaries and oceans as a result of runoff. It can also be deposited directly into those water bodies. Mercury is toxic in any form according to some scientists, but when it mixes in certain bacteria, such as those in marine sediments, it is converted to its most toxic form, methyl mercury, which can cause nerve and developmental damage in humans and animals. Mercury bioaccumulates, which means it collects in the tissues of a plant or animal over its lifetime. It also biomagnifies, meaning its concentrations in organisms increase along the food chain. Predatory fish often contain high levels of mercury, prompting the US and Canada to issue health advisories against consumption of certain fish. In June, the governors of the US northeastern states and Eastern Canada's provincial premiers signed a mercury resolution calling for cooperative action to address the mercury issue, EMAN's Pilgrim noted. Through the United Nations' Commission for Environmental Cooper-ation, Canada, Mexico, and the US are also cooperating to address transport of mercury emissions across international borders, Pilgrim said. But some researchers say formulating public policy relating to the health effects of mercury is difficult, because much about its interactions and effects are not yet understood. US regulations getting results Although researchers in the US and Canada say there is much to learn about atmospheric deposition's sources and environmental effects, both countries are addressing components of the issue with regulations. Amendments made in 1990 to the United States' federal Clean Air Act of 1970 call for a two million ton (1.8 million tonne) reduction in nitrogen oxide emissions by the year 2000 - about a 10 percent reduction from 1980 levels of those emissions. In July, the EPA announced even tighter nitrogen oxide emission standards for new electric utility and industrial boilers, which will take effect as a final rule in September 1998. EPA estimates that the proposed limits will cut projected growth in nitrogen oxide emissions by about 42 percent from current levels. In regard to sulfur dioxide, federal regulations allow US utilities to buy and sell sulfur dioxide emissions allowances from one another, keeping total emissions under an overall limit. An allowance for emission of one ton of sulfur dioxide is worth about $100. In June, EPA announced that US utilities had cut sulfur dioxide emissions "from their largest and dirtiest electric utility boilers" by 35 percent more than what acid rain provisions of the Clean Air Act require, and reduced nitrogen oxide emissions by an average of 18 percent more than the Act's 1996 goal. "The sulfur dioxide cap and trade program has been extremely successful with getting quick early reductions, but I don't want to imply that the drastic early reductions are going to go forward indefinitely," said Linda Schoumacher of the Edison Electric Institute in Washington, DC, a trade association for shareholder utilities. The initial cost of implementing measures to reduce emissions was less than anticipated, but the industry spends $3 billion to $4 billion annually to comply with the federal regulations, Schoumacher explained. Utilities will pay whatever it takes to comply, but "will not pay extra to continue over-compliance," she said. Electrical utilities reduce emissions by using low sulfur coal, coal that is cleaner when it leaves the mine, and special equipment that cleans emissions before they leave the smokestack, among other measures. Smog reduction efforts also affect air deposition According to Sonia Hamel, Director of Air Policy and Planning for Massachu-setts' Executive Office of Environmental Affairs, the state's new nitrogen oxide reduction plan, which caps power plant emissions at 65 percent of their 1990 levels, and its low-emission vehicle program begun in 1995 "are producing significant reductions in atmospheric deposition as a side benefit." New Hampshire adopted stringent nitrogen oxide regulations in 1994, said Tom Noel, Deputy Director of the state Department of Environmental Service's Air Division. "We have, along the way, learned that this is also going to reduce airborne deposition of NOx [nitrogen oxide] into estuaries and waterways and so forth," he noted. The state's three Northeast Utilities/ Public Service Company of New Hampshire power plants have reduced their nitrogen oxide emissions by a total of 55 to 60 percent, and will achieve a 65 percent reduction by 1999, said Noel. New Hampshire had its own acid rain regulations in place before 1990 federal regulations were in place. It is also considering a motor vehicle emissions inspection program, and is adopting federal standards for mercury emissions from waste incinerators, Noel added. Maine's emission regulations were also initially designed to address federal smog reduction mandates, "But a secondary benefit is that it will reduce deposition," said Jim Brooks, director of the state Department of Environmental Protection's Air Bureau. Maine is studying how atmospheric deposition is affecting coastal ecosystems, is collaborating with other New England states on regional strategies for addressing mercury deposition, and is monitoring atmospheric deposition of mercury at several sites throughout the state, Brooks said. Canadian Fed, provinces share regulation of emissions Canada's provinces regulate sulfur dioxide emissions, according to Gerry Ternan a program engineer in Environment Canada's Atlantic Region's Air and Toxics Issues Section. "Federal jurisdiction has more to do with transboundary air pollution," he explained. Ternan said each province has negotiated a cap on sulfur dioxide emissions with Environment Canada, but decides how to allocate emissions allowances among industries and utilities. Under the Canada/US Air Quality Accord the two countries are addressing long-range transport of sulfur dioxide and nitrogen oxide, he said. Canada's commitment under the Air Quality Accord calls for nitrogen oxide emissions from factories and boilers to be reduced by 100,000 metric tons (110,230 tons) from what would have otherwise occurred in the year 2000, and also calls for additional reductions for subsequent years, noted Ternan. While the provinces regulate emissions from in-use motor vehicles, only one area of Vancouver, British Columbia currently requires auto emissions testing. The Canadian Federal government sets fuel regulations limiting sulfur in diesel and gasoline, and regulates new vehicle emissions with requirements similar to the USEPA standards, Ternan said. Canada's federal and provincial governments collaborate on developing guidelines limiting emissions of sulfur dioxide and nitrogen oxide from thermal power plants, according to Ternan. Also, Environment Canada regulates other industrial sources' airborne emissions of some specific toxic substances such as mercury emissions from certain kinds of industrial plants, he said. Canadian utilities have made rapid progress in reducing emissions, according to Pierre Guimond, Senior Advisor for the Canadian Electricity Association, which represents Canadian electrical utilities and manufacturers of electrical components and equipment. "We have reduced emissions of [sulfur dioxide] at considerable expense and continue to be prepared to do more but as long as we can do that at reasonable cost," said Guimond, noting that Canadian utilities use many of the same measures US utilities use to reduce emissions. "A lot has been accomplished - we've come a long way. We recognize that there's a lot more we can do," he said, adding that electrical utilities will be looking for guidance from the science community. |
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Gulf of Maine Council on the Marine