The relative role of denitrification and immobilization in the fate of inorganic nitrogen in mangrove sediments (Terminos Lagoon, Mexico)

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Abstract
Rates of direct and coupled nitrification‐denitrification were measured with 15N isotope techniques in intact sediment cores from fringe, basin, and riverine mangroves in Terrminos Lagoon, Mexico. We used intact sediment cores to evaluate differences in denitrification rates. The lack of 15N2 production in all cores amended with 200 (or 100) µmol core‐1 15NH4+ and the high recovery of 15N in the sediment in five of eight such experiments indicate that coupled nitrification‐denitrification was riot important to nitrogen transformation during the 8–10‐d incubations. However, when we added 450 µmol core−1 15NH4+ and 15NO3− to cores from the riverine mangrove, N2 production rates ranged from 28.9 to 221.1 µmol N m−2 h−1 for each nutrient. We compare coupled nitrification‐denitrification rates among different types of mangrove forests under natural conditions in the neotropics. Our results with nitrogen isotopes suggest that the uptake of inorganic N from tidal waters within mangrove ecosystems does not necessarily represent a nitrogen sink via denitrification, but rather a retention of nitrogen in mangrove sediments.

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