Denitrification in shallow, sublittoral Gulf of Mexico permeable sediments

作者：Gihring Thomas M; Canion Andy; Riggs Ashley; Huettel Markus; Kostka Joel E^*

来源：Limnology and Oceanography, 2010, 55(1): 43-54.

DOI：10.4319/lo.2010.55.1.0043

We examined nitrogen cycling over a 1-yr period in shallow, sandy sediments at two contrasting sites near a barrier island in the northeastern Gulf of Mexico, and we provide here the direct determination of dinitrogen gas (N-2) production at ambient nitrate concentrations in permeable marine sediments. Nitrogen-stable isotope tracer techniques were used to quantify N-2-production rates and pathways in sediment cores and slurries. To simulate pore-water advection, the dominant transport process in the upper layer of the permeable sand beds, intact sediment cores were perfused with aerated seawater. This perfusion increased denitrification rates up to 2-fold in Apalachicola Bay sands and up to 17-fold in Gulf of Mexico sublittoral sands, respectively, relative to static cores. Seasonal N-2-production rates were highest in spring and fall. Denitrified nitrate originated almost entirely from benthic nitrification at the exposed Gulf site, whereas water-column nitrate dominated sedimentary denitrification at the sheltered Bay site. Sediment incubations in stirred chambers were used to determine net fluxes of oxygen (O-2), N-2, nitrate, and ammonium across the sediment-water interface during varied degrees of continuous pore-water exchange. Rates of N-2 efflux correlated with rates of pore-water flow increasing from 0.12 mmol N m(-2) d(-1) under diffusion-limited transport conditions up to 0.87 mmol N m(-2) d(-1) with pore-water advection. Mineralized nitrogen was completely converted to N-2 gas in Gulf of Mexico sediments. Our results demonstrate that advective pore-water circulation will accelerate benthic N-2 production by coupled nitrification denitrification and that substantial nitrogen loss occurs from coastal permeable sediments.

• 出版日期2010-1