NITROUS-OXIDE EMISSIONS AND THE USE OF WETLANDS FOR WATER-QUALITY AMELIORATION

Wetlands ameliorate nitrate pollution but have also been recognized as a source of the greenhouse gas nitrous oxide. Nitrate and N2O fluxes were studied in an experimental wetland in mid-Wales. Diversion of wat er inflows caused a 200% increase in nitrate release and a >95% declin e in nitrous oxide emission over a 20-week period. The responses were attributed to the onset of drier (more aerobic) conditions causing (i) aerobic mineralization and nitrification of N-containing compounds th at had previously been immobilized within the wetlands (releasing nitr ate) and (ii) the absence of anaerobic denitrification (a potent mecha nism for nitrate elimination and source of N2O), allowing NO3-N to lea ve the wetland. The responses were instantaneously reversible upon re- initiation of the nitrate inflow, indicating a close hydrological coup ling between nitrate removal and nitrous oxide emission processes.