Coastal eutrophication in relation to atmospheric nitrogen deposition: Current perspectives

Abstract

Nitrogen-limited estuaries, shallow coastal and continental shelf waters account for nearly half the global oceanic primary production. Accelerating primary production, or eutrophication, of these waters appears linked to increasing anthropogenic N loading. Among loading sources, atmospheric nitrogen deposition (AND) (as wet- and dryfall) is of considerable and increasing importance (100 to over 1000 mgN·m^-2·yr^-1). Current contributions of AND to total external N loading range from 10 to over 50%, AND may play a central role in mediating “new” production in coastal oceans downwind of emissions. Examples of AND-impacted waters include: US Atlantic coastal waters, where atmospheric N inputs can significantly enhance CO₂ fixation and chlorophyll a production, the Baltic and North Seas, the Canadian Atlantic seaboard, and the Western Mediterranean Sea. Recent increases in toxic and non-toxic phytoplankton blooms in these waters may be linked to accellerating nutrient loading at the land-sea interface; a significant fraction of it attributable to AND. This hitherto-neglected nutrient-production interaction requires evaluation on regional and larger synoptic scales. Aircraft and satellite-based ocean color remote sensing (i.e. SeaWiFS) will be useful in characterizing and linking the spatial-temporal interactions of this and other »new« nutrient inputs with eutrophication of estuarine and coastal waters.