Direct denitrification in mangrove sediments in Terminos Lagoon, Mexico

Rates of direct denitrification were measured using ¹⁵N isotope tchniques in intact sediment cores from fringe and basin mangroves in Terminos Lagoon, Mexico. Sediments were injected with ¹⁵NO₃^- and the distribution of ¹⁵N was measured over time in the head space, overlying water, and sediments. Experiments included an investigation of spatial variation in denitrification rates by comparing results from the fringe and basin mangroves in the rainy season (July 1991); a second experiment was to determine the effect of 3 different NO₃^- concentrations (25, 100, 200 umol core^-115N-KNO₃^-) on denitrification rates and was performed in the fringe mangrove during the 'Norte' season (January 1992). Highest ¹⁵N-N₂ fluxes were measured in the fringe mangrove at 9.4 umol m^-2 h^-1, while denitrification rates in the basin mangrove ranged from 1.9 to 4.5 umol m^-2 h^-1. ¹⁵N-N₂ fluxes in sediment cores from the fringe mangrove were significantly higher (4.5 to 7.7 umol m^-2 h^-1) in cores enriched with 200 umol core^-115N-KNO₃^- compared to cores enriched with 25 and 100 umol core^-115N-KNO₃^- (