Nitrogen gas flux from sediments: insights from simulation modelling

Abstract

Direct measurements of dinitrogen efflux from continental shelf sediments ~ndicated that denltnflcation (mean 3.2 mm01 N m-2 d-l) was very important ~n nitrogen cycling. Most dinitrogen came from sediment-nitrate. All ammonium produced in these sediments was probably nitrified and then denitrified. In a closed incubation, the linear production of dinitrogen, a s oxygen decreased, was unexpected as was the low rat10 of oxygen consumption to denitrification (3.6:l). Sin~ulation modelling suggests the following explanation: Most carbon IS oxidised anoxically, but mtrogen (ammonium) diffuses to the oxygen zone relatively deep in the sediment, where hlgh rates of coupled nltrif~cat~on-denitrification result. As oxygen decreases, the zones of nltrification and denitrification move upward. The nitrate initially present In the enclosed overlying water decreases, but due to the decreasing diffusional path to the zone of denitrification, ~t s rate of denitrification remains constant. The concentration of n~trate from sediment nitrification increases in the overlylng water, but due to the decreasing rates of sediment nitrification, its rate of denitrlficatlon is also constant.To construct a model which simulates a particular sediment, a variety of factors must be known: quantity of degradable organic matter, its C/N ratio, its distribution in the sediment and the extent to which the reduced products of anoxic respiration are free to diffuse (Blackburn & Blackburn 1993a, b. c, Blackburn et al. 1994). In addition, the rate constants for the oxidation of carbon by 02, NOs-and SO4'-, and for the oxidation of NH4+ and SH-must be known. The values of the variables, outlined in the legend to Fig. 1, gave quite a close representation of the data for a continental shelf sediment (Devol 1991). Dinitrogen was produced at a Linear rate (Fig. 1A). The total denitrification rate of -3.7 mm01 N m-' d-' was similar to that reported (mean 3.2 mm01 N n1r2 d-l). In the simulation (Fig. lB), -'E-mall: henry@pop.bio aau.dk there was a slight increase in No3-concentration, compared to the actual slight decrease (mean 1.3 mm01 m-2 d -l ) . Fine tuning of the nitrification and denitrification rates would correct this difference. During the time of N2 linear production (2 d), there was a fall in oxygen concentration from 200 to 20 FM. The initial rate of oxygen uptake was 11.9 mm01 m-' d-', very close to the reported value (11.4 mm01 m-2 d-l). As O2 decreased, accumulation of NH,' increased, due to the sediment becoming less oxidised (Fig. 1C). The model predicted a time-dependent decrease in the rate of nitrification from -4.5 mmol N m-' d-', but denitrification (Ds) of sediment-NO3-(N03s) was relatively constant at -3 mmol N m-' d-' (Fig. ID). Denitrification (Dw) of NO3-originally in the water (N03w), was also relatively constant at -1 mm01 N mY2 d-l, even though N03w decreased from 30 to < l 0 FM.The movement of the zone of denitrification closer to the sediment surface, as the depth of 0, penetration decreased with time ( Fig. 2), ...

Organic-N loss by efflux and burial associated with a low efflux of inorganic N and with nitrate assimilation in Arctic sediments (Svalbard, Norway)

“…Because of this deficiency, the estimated ratios may be too large. Urea effluxes can be quite high in Arctic sediments (Lomstein et al 1989); and under certain circumstances, coupled nitrificationdenitrification is predicted to be high (Blackburn 1996). As the relevance of the citations in Table 4 to the present situation is doubtful, they will not be discussed in detail, but the deep-sea sediments tend to b e most similar to ours.…”

Differential Effects of Bivalves on Sediment Nitrogen Cycling in a Shallow Coastal Bay

“…However, high SOM, and subsequent increase in SOD, can lead to oxygen limitation for nitrification and the highest rates of nitrification occur at intermediate concentrations of both ammonium and oxygen (Caffrey et Last Updated: 26 October 2017al. 1993, Sloth et al 1995, Blackburn 1996. Alternatively, carbon can affect nitrification if ammonium-oxidizing archaea (AOA), which are mixotrophs that require a carbon source, rather than ammonium-oxidizing bacteria (AOB).are responsible for nitrification (Qin et al 2014).…”

Impact of clam and mussel farming on benthic metabolism and nitrogen cycling, with emphasis on nitrate reduction pathways

“…Model and microcosm studies indicate that nitrification and coupled nitrificationdenitrification rates are highest at moderate organic matter loads, as at low loads nitrification is limited by ammonium availability and at high loads by competition for oxygen with aerobic heterotrophs and other chemoautotrophs (Blackburn & Blackburn 1993a,b, Caffrey et al 1993, Sloth et al 1995, Blackburn 1996. Thus, at the mussel farm site, which receives very high inputs of organic matter, nitrification rates and consequently nitrate reduction coupled to nitrification would be expected to be low due to competition for oxygen.…”