Issues in Ecology Number12 Summer 2004 Impacts of Atmospheric Pollutants on Aquatic Ecosystems b DeborahL.Swackhamer,Hans W.Paerl,StevenJ.Eisenreich,James Hurley,KeriC.Hombuckle, MichaelMcLachlan,David Mount,Derek Muir,andDavidSchindler INIRODUCTION Sinceairmovesrapidly,atmosphericpollutantscan travellong distancesquickly and be deposited on distant watersheds.The onsOver the past several decd made d forapantdoerh es.Ana efuent pipes A more been toidentify and posited in a particulr watershed (Fgure 1)Airshedsdiffer fo control environmental contaminants generated by dispersed or each form of every pollutant and are determined by modeling ombileehaustlivesokwas atmospheric deposition of each chemical.They are useful commer er travel far souroes when the倒 stem of concern or flow into riversor enter theair This report reviews three In particular,volatile chemicals- those that evaporatereadily-car or thei health of a widera can either be deposited directly including lower levels of the food nverteb dep ans The ("indirect"deposition)Deposition First semi-volatile organic of thesepollutants can occur via contaminantsoften have propertie that allow them to persist in the ouds and minute particulate matter to aquatic organisms at lower Rates of wet deposition aremost Sound and AltamahaSound (listed fromnorthtosouth)2These levels of the food web,as well as influenced by how readily th to fish and to the wildlife and olve in water,while irshedsshow the geographic area that contains the emission ans that eat fish The ratesofdr re ver rganic rom esticides and poly chlorinated biphenyls(PCBs)to which they arebeing deposited.Chemicals deposited toaquatic brominated flame-retardants,water-and stain-repellent coatings ercur can ordry d n In may also be transformed into once they are deposited on and travel through watersheds.Until recently is bioaccumulative and can harm fish,wildlife,and humans. Finally,the significance of inorganic forms of nutrients a atmospheric pollu s ha Deen gaining increa d att and dry deposition onto la sed and aquati culprit in th 2 Issues in Ecology Number 12 Summer 2004 Impacts of Atmospheric Pollutants on Aquatic Ecosystems by Deborah L. Swackhamer, Hans W. Paerl, Steven J. Eisenreich, James Hurley, Keri C. Hornbuckle, Michael McLachlan, David Mount, Derek Muir, and David Schindler INTRODUCTION Over the past several decades, the United States has made considerable progress in reducing the amount of pollutants discharged from identifiable point sources such as municipal effluent pipes. A more difficult challenge has been to identify and control environmental contaminants generated by dispersed or nonpoint sources such as automobile exhaust, livestock wastes, fertilizer and pesticide applications, and myriad commercial and industrial processes. These nonpoint pollutants can travel far from their sources when they seep or flow into rivers or enter the air. In particular, volatile chemicals – those that evaporate readily – can be carried through the atmosphere and fall on parts of the world far removed from their origins. They can either be deposited directly onto terrestrial and aquatic ecosystems (“direct” deposition) or deposited onto land surfaces and subsequently run off and be transferred into downstream waters (“indirect” deposition). Deposition of these pollutants can occur via wet or dry forms. Wet deposition includes rain, snow, sleet, hail, clouds, or fog, while dry deposition includes gases, dust, and minute particulate matter. Rates of wet deposition are most influenced by how readily the chemicals dissolve in water, while rates of dry deposition are very sensitive to the form (gas or particle) of the chemicals and the “stickiness” of the surface upon which they are being deposited. Chemicals deposited to aquatic ecosystems can re-volatilize and thus be redistributed via the atmosphere. During atmospheric transport, pollutants also can be transformed into other chemicals, some of which are of greater concern than those originally released to the atmosphere. Pollutants may also be transformed into other chemicals once they are deposited on and travel through watersheds. Until recently, however, little recognition has been given to the environmental consequences of toxic substances and nutrients that fall from the air as wet and dry deposition onto land-based and aquatic ecosystems. Since air moves rapidly, atmospheric pollutants can travel long distances quickly and be deposited on distant watersheds. The “airshed” for a particular body of water can encompass hundreds of miles. An airshed defines the geographic area that contains the emissions sources that contribute 75 percent of the pollutants deposited in a particular watershed1 (Figure 1). Airsheds differ for each form of every pollutant and are determined by modeling atmospheric deposition of each chemical. They are useful theoretical tools for explaining atmospheric transport and for illustrating the need to control emission sources far removed from the ecosystem of concern. This report reviews three categories of atmospheric pollu￾tants that we consider of greatest concern, both for their ecological effects and their impacts on the health of a wide range of biota, including lower levels of the food web (algae, macrophytes, and invertebrates), fish, wildlife, and humans. These categories include organic compounds, mercury, and inorganic nutrients. First, semi-volatile organic contaminants often have properties that allow them to persist in the environment for very long periods, to bioaccumulate (that is, build up in animal tissues), and to be toxic to aquatic organisms at lower levels of the food web, as well as to fish and to the wildlife and humans that eat fish. These persistent organic pollutants include a wide range of chemicals from pesticides and poly￾chlorinated biphenyls (PCBs) to brominated flame-retardants, water- and stain-repellent coatings, and synthetic fragrances. Second, the metal mercury can be transported in the atmosphere and fall onto terrestrial and aquatic ecosystems as precipitation or dry deposition. In aquatic systems, mercury may eventually be transformed into monomethyl mercury, a form that is bioaccumulative and can harm fish, wildlife, and humans. Finally, the significance of inorganic forms of nutrients as atmospheric pollutants has been gaining increased attention. Nutrient-laden runoff from the land has long been acknowledged as a culprit in the over-enrichment and eutrophication of coastal Figure 1 – Principal nitrogen oxide airsheds and corresponding watersheds for Hudson/Raritan Bay, Chesapeake Bay, Pamlico Sound, and Altamaha Sound (listed from north to south).2 These airsheds show the geographic area that contains the emissions sources that contribute 75 percent of the nitrogen oxide deposited in each watershed. Via atmospheric transport, pollutants such as nitrogen oxide can impact watersheds hundreds of miles away