PARENT SESSION
Oral Session #42: Carbon and Nitrogen Cycling. Presiding: S. Hobbie.
Wednesday, August 8, 2001. 8:00 AM to 11:30 AM. Hall of Ideas E.
Nitrous oxide (N2O) emission from drainage waters of an intensively farmed, subtropical valley.
Harrison, John1, Matson, Pamela1, 1
ABSTRACT- Though agricultural runoff is thought to constitute a globally important source of the greenhouse gas nitrous oxide (N2O), production of N2O in polluted, freshwater systems is poorly understood, especially in non-temperate regions where the most rapid agricultural intensification and increase in N-fertilizer use is occurring. We measured N2O emissions over 2 agricultural cylces from freshwater drainage systems receiving agricultural and mixed agricultural/urban inputs from the intensively farmed Yaqui Valley of Sonora, Mexico. We also monitored factors likely to control rates of N2O production. N2O emissions in both purely agricultural and mixed urban/agricultural drainage systems were high (means: 19.6 and 25.05 ng N2O-N cm2 hr-1 respectively), and isolated measurements of N2O emissions from the mixed Urban/Agricultural drainage were extremely high (up to 166.5 ng N2O-N/cm2 hr-1). However, despite high relative fluxes, preliminary calculations of valley-wide N2O emissions from agricultural drainage indicate that N2O emissions from drainage waters are not as important as global budgets currently estimate. Under normal, non algae-bloom conditions, N2O fluxes were strongly correlated with nitrate concentrations (P=0.003). However, the highest N2O fluxes occurred during green algae blooms, when organic carbon and oxygen were more strongly correlated with N2O production than nitrate availability.
KEY WORDS: Nitrous Oxide, Nitrogen, Agricultural impacts, Subtropics