Atmospheric Nitrous Oxide Fluxes from Mangrove Sediments

Although the marine environment is recognized as a net source of nitrous oxide to the atmosphere, current global budgets appear to underestimate the marine source of this radiatively active gas. Mangrove forests occupy a significant fraction of the tropical land/sea interface and receive high inputs of terrestrial nitrogen. Anthropogenic activities increase nitrogen input to mangrove sediments thereby enhancing microbial nitrogen metabolism. Elevated rates of nitrous oxide flux might therefore be expected. Our experimental determinations of nitrous oxide flux from mangrove sediments yield rates of between 0.12 and 7.8 μmol N2O m−2 h−1; values which are between 2 and 135 times greater than those reported previously for intertidal estuarine sediments. Nitrous oxide yield from these sediments varies greatly in response to both the magnitude and chemical nature of the sediment nitrogen source. Rates appear to be greater when reduced nitrogen is the dominant substrate and nitrification is the main source of nitrous oxide compared to sediments where nitrate and nitrite predominate and nitrous oxide arises from microbial denitrification.