Nitrification and dissimilatory ammonium production and their effects on nitrogen flux over the sediment-water interface in bioturbated coastal sediments

Abstract

Nitrification and dissimilatory reduction of nitrate to ammonium were measured concomitantly with nitrogen release from marine coastal sediment samples from 2 fjord sill stations. Dissimilatory ammonium production (DAP) and nitrification were measured using core injections of "NO; and H1"CO;, respectively. DAP was detected in all segments of the cores by tracing "NH: evolved from the added "NO;. 15NH: recovery increased with increasing core depth, ranging from 1.6 to 10 % for Stn H and from 0.3 to 2.9 % for Stn L. Nitrification activity at Stn L was in the order of 10 nmol cm-3 h-' in the upper 2 cm but was not demonstrated in deeper strata. Consequently, DAP was most pronounced in the upper few centimeters although it was anticipated that more than 97 % of the nitrate produced was denitnfied. Mean fluxes of ammonlum out of the sediment were 24 and 12 pm01 m-2 h-' for Stns H and L, respectively, and corresponding nitrate fluxes were 2 and -24 pm01 m-2 h-'.The sum of ammonium and nitrate release in the individual cores did not reach the rates expected from their oxygen consumption rates, which implies that inorganic nitrogen was lost, probably due to coupled nitrification and denitrification. This estimated loss was about half of the obtained nitrification rate at Stn L. Furthermore, the estimated loss was larger in cores with a rich macrofauna and especially with high numbers of Arnphiura spp. (brittlestars). It is suggested that these animals stimulate both nitrification and dissimilatory nitrate reduction.

Sediment mineralization, nutrient fluxes, denitrification and dissimilatory nitrate reduction to ammonium in an estuarine fjord with sea cage trout farms

“…The present study thus confirms earlier observations that extremely high organic matter loading can reduce the importance of the denitrification process and stimulate nitrate reduction to ammonium (Kaspar et al 1988, Gilbert et al 1997). The DNRA rates reported here are high compared to other studies (Enoksson & Samuelsson 1987, Binnerup et al 1992, Sloth et al 1995, and the process may therefore be of quantitative importance in sediment below the fish cages during periods of high water column nitrate concentrations.…”

Nitrogen cycling in sediments with different organic loading

“…The time-succession of the bacterial processes, including population development, were not measured in detail, but could perhaps be modelled based on the present data. In natural systems, with bioturbation (Enoksson & Samuelsson 1987, Kristensen 1988, anthropogenic influence, benthic micro-and macrophytes (Sundback et al 1991) and structurally much more complex substrates for mineralization, the response to organic loading is obviously more complex. The organic substrate would be expected to be transformed in food chains in the sediment, or to be resuspended and partially degraded before being mineralized in the sediment (Floderus & Hgkanson 1989).…”

Impact of bioroughness on interfacia solute exchange in permeable sediments

“…In contrast to muddy sedirnents where diffusion acts mainly in a vertical direction (Berner 1976), pressure-driven porewater flows in permeable sediments have an equally important horizontal component since the same volume of water intruding into the porespace has to leave the sediment elsewhere. While transport of oxygen and sulfate into the sediment enhances organic matter decomposition and nitrification (Jergensen & Sarensen 1985, Enoksson & Samuelsson 1987, shifts in redox potential and pH associated with upwelling anoxic porewater cause release of redox-sensitive substances such as phosphate and heavy metals (Balzer 1986). The 3-dimensional pattern of the advective porewater flows increases the surface area of the redox-potentialdiscontinuity (RPD) layer (Berner 1980.…”