GLOBAL DISTRIBUTION OF NITROUS-OXIDE PRODUCTION AND N INPUTS IN FRESH-WATER AND COASTAL MARINE ECOSYSTEMS

This study examines N2O emissions from aquatic environments globally, particularly as they are affected by anthropogenic activity. The globa l distribution of N2O production in rivers and estuaries was modeled a s a function of nitrification and denitrification rates, which were re lated to external nitrogen (N) inputs. N loading rates were estimated as a function of environmental parameters in the watersheds using two existing models that we adapted for global databases. Model estimated export of dissolved inorganic nitrogen (DIN) by world rivers to estuar ies in 1990 is 20.8 Tg N yr(-1); approximately 75% is estimated to be anthropogenic. DIN export to the Atlantic and Indian Oceans is similar (5.4 Tg N yr(-1) and 4.6 Tg N yr(-1), respectively); inputs to the Pa cific are approximately 50% greater. China and southeast Asia account for over 50% of DIN export by world rivers. Globally, anthropogenic DI N export is predominately attributed to fertilizer N, followed by sewa ge and atmospheric deposition. About 8% of the total N inputs to the t errestrial environment can be accounted for as DIN export by rivers. W orldwide N2O emissions from rivers (55%), estuaries (11%), and contine ntal shelves (33%) are calculated to be 1.9 Tg N yr(-1). For rivers an d estuaries, approximately 90% of N2O emissions are in the northern he misphere in line with the regional distribution of DIN export by river s. China and India account for about 50% of N2O emissions from rivers and estuaries. About 1% of the N input from fertilizers, atmospheric d eposition, and sewage to watersheds is lost as N2O in rivers and estua ries. Globally, rivers and estuaries could account for approximately 2 0% of the current global anthropogenic N2O emissions and are similar i n magnitude to a number of previously identified sources including dir ect emissions of N2O from soils induced by anthropogenic N inputs.