Nitrification In Sediments Research Articles

Temperature dependence of oxygen respiration, nitrogen mineralization, and nitrification in Arctic sediments

Temperature dependence of oxygen respiration, nitrogen mineralization, and nitrification in Arctic sediments

Benthic Denitrification in the Gulf of Bothnia

Denitrification was measured over an 8-month period in the Bothnian Bay and the Bothnian Sea, the two northernmost basins of the Baltic Sea. The recorded rates varied between 0 and 0·94mmol N m−2day−1. In the Bothnian Sea, a seasonal pattern could be discerned with high rates in spring, no rate in summer and a moderate rate in winter. In the Bothnian Bay, no such seasonality was observed. It is suggested that denitrification in the Gulf of Bothnia is regulated by sediment nitrification. Calculation of annual mean rates of denitrification gave that the amount of nitrogen consumed by denitrification corresponded to 1·45×104tons N year−1for the Bothnian Bay and 3·45×104tons N year−1for the Bothnian Sea. A comparison with total N input (river runoff, point sources and atmospheric deposition) to the two basins showed that the proportion of N removed through denitrification amounted to 23% for the Bothnian Bay and 31% for the Bothnian Sea.

Is nitrate an oligotrophication factor in the Venice lagoon?

Approximately 30% of the area in the Venice lagoon ecosystem shows a phenomena of seasonal instability. Hypertrophic conditions caused by increased anthropic stress, particularly during the years 1987–1991, have progressively favoured massive springtime blooms (up to 20 kg/m 2 , on a wet weight basis) of some species of macroalgae ( Ulva laetevirens ). During the years 1993–1994 this phenomena has not occurred, as the same area was covered by only 3 kg/m 2 , on a wet weight basis, of Ulva laetevirens . Phosphorus measured in macroalgal tissue shows a very low concentration. This seems to indicate a low concentration of phosphorus in the water and not a great quantity of this element for the macroalgae. Since the phosphorus availability in the water comes from sediments (almost 50%), it is therefore possible to explain this condition as low release of phosphorus from the sediments. Phosphorus and nitrogen fluxes at the water-sediment interface, denitrification, and sulfate reduction probably all show a high nitrification and high nitrate uptake in the sediments. Because of this, the nitrate could play the important role of the oxidant to immobilise the phosphorus. The present work discusses the role of nitrate as an oligotrophication factor and as the immobilisation of phosphorus in sediment which is the probable cause of the limited growth of macroalgae Ulva laetevirens .

Contribution of nitrification and denitrification to the no and N 2O emissions of an acid forest soil, a river sediment and a fertilized grassland soil

Most studies determining the contribution of nitrification and denitrification to NO and N 2O emissions from soils have been performed in agricultural systems, often with homogenized soil samples. More information about the nitrifier and denitrifier contribution in non-agricultural systems nitrification and denitrification to NO and N 2O emissions from three different ecosystems: an acid forest soil; a river sediment in the intertidal zone; and a fertilized peat grassland, using intact soil cores. Samples were taken in the spring of 1993 and the autumn of 1994. Intact soil cores (5 cm deep) were incubated at field temperature in the laboratory and the accumulation of NO and N 2O during 24 h was measured. The nitrification and denitrification contribution was determined by specific inhibition of nitrification. The highest mean N 2O production was in the same range for all sites. Nitrification dominated N 2O production in spring at all sites. In contrast, denitrification was the main source of N 2O in the acid forest soil and grassland soil in the autumn. However, the tight coupling of nitrification and denitrification in the river sediment could have resulted in an over-estimation of the contribution of nitrification to N 2O and NO production. A large part of denitrified N in the acid forest soil was emitted as N 2O, whereas in the river sediment, except for the autumn, the denitrification N 2O-to-N 2 ratio was low, which coincided with a low nitrate content. Nitrification was the dominant NO source in spring at all sites. In autumn, high contributions of both nitrification and denitrification were observed.

Nitrification and denitrification in the rhizosphere of the aquatic macrophyte Lobelia dortmanna L.

Nitrogen and O2 transformations were studied in sediments covered by Lobelia dortmanna L.; a combination of 15N isotope pairing and microsensor (O2, NO3−, and NH4+) techniques were used. Transformation rates and microprofiles were compared with data obtained in bare sediments. The two types of sediment were incubated in doublecompartment chambers connected to a continuous flow-through system. The presence of L. dortmanna profoundly influenced both the nitrification-denitrification activity and porewater profiles of O2, NO3−, and NH4+ within the sediment. The rate of coupled nitrification-denitrification was greater than sixfold higher in L. dortmnanna-vegetated sediment than in bare sediment throughout the light–dark cycle. Illumination of the Lobelia sediment reduced denitrification activity by ∼30%. In contrast, this process was unaffected by light–dark shifts in the bare sediment. Oxygen microprofiles showed that O2 was released from the L. dortmanna roots to the surrounding sediment both during illumination and in darkness. This release of O2 expanded the oxic sediment volume and stimulated nitrification, shown by the high concentrations of NO3− (∼30 µM) that accumulated within the rhizosphere. Both 15N2 isotope and microsensor data showed that the root-associated nitrification site was surrounded by two sites of denitrification above and below, and this led to a more efficient coupling between nitrification and denitrification in the Lobelia sediment than in the bare sediment.

Dynamics of nitrification and denitrification in root-oxygenated sediments and adaptation of ammonia-oxidizing bacteria to low-oxygen or anoxic habitats

Oxygen-releasing plants may provide aerobic niches in anoxic sediments and soils for ammonia-oxidizing bacteria. The oxygen-releasing, aerenchymatous emergent macrophyte Glyceria maxima had a strong positive effect on numbers and activities of the nitrifying bacteria in its root zone in spring and early summer. The stimulation of the aerobic nitrifying bacteria in the freshwater sediment, ascribed to oxygen release by the roots of G. maxima, disappeared in late summer. Numbers and activities of the nitrifying bacteria were positively correlated, and a positive relationship with denitrification activities also was found. To assess possible adaptations of ammonia-oxidizing bacteria to low-oxygen or anoxic habitats, a comparison was made between the freshwater lake sediment and three soils differing in oxicity profiles. Oxygen kinetics and tolerance to anoxia of the ammonia-oxidizing communities from these habitats were determined. The apparent K(infm) values for oxygen of the ammonia-oxidizing community in the lake sediment were in the range of 5 to 15 (mu)M, which was substantially lower than the range of K(infm) values for oxygen of the ammonia-oxidizing community from a permanently oxic dune location. Upon anoxic incubation, the ammonia-oxidizing communities of dune, chalk grassland, and calcareous grassland soils lost 99, 95, and 92% of their initial nitrifying capacity, respectively. In contrast, the ammonia-oxidizing community in the lake sediment started to nitrify within 1 h upon exposure to oxygen at the level of the initial capacity. It is argued that the conservation of the nitrifying capacity during anoxic periods and the ability to react instantaneously to the presence of oxygen are important traits of nitrifiers in fluctuating oxic-anoxic environments such as the root zone of aerenchymatous plant species.

Nitrification, denitrification, and nitrate ammonification in sediments of two coastal lagoons in Southern France

Nitrification, denitrification, and nitrate ammonification in sediments of two coastal lagoons in Southern France

Attenuation of nitrate in aquitard sediments of southern Ontario

To examine nitrate persistence, detailed geochemical profiling, using core-squeezed water and piezometer samples, was carried out at five sites in southern Ontario where groundwater is moving downward in silt-rich aquitard sediments at rates of 16 to more than 20 cm year −1. Elevated levels of NO 3 −-N (5–50 mg 1 −1) that occur in the shallow groundwater as a result of agricultural activity, were found to be consistently attenuated, generally to very low levels (< 0.05 mg 1 −1-N), at the ‘redoxcline’, the horizon marking the boundary between the surficial weathered (brown) sediments and the underlying unweathered (grey) sediments. Tritium dating suggests that groundwater at the redoxcline depths (3–5 m) was recharged between 1970 and 1980, thus the N03 depletion appears to result from biodegradation reactions since no major landuse changes have occurred during this period. The close association of the nitrate depletion zones with the redoxcline, where, in particular, sediment sulphur contents increase abruptly, and where also porewater SO 4 2− levels increase, suggests that the dominant attenuation reaction is autotrophic denitrification using reduced sulphur compounds present in the unweathered sediment as the electron donor. Mass balance calculations suggest that the increase in the downward rate of migration of the redoxcline, owing to added sulphur consumption from NO 3 − contamination, is only about 1 mm year −1 at these sites. Review of the literature indicates that most silt- and clay-rich sediments have S contents in the same range, or higher, than those investigated here, thus, in most cases where aquifers are overlain by several metres or more of unweathered confining sediments, it is likely that a high degree of protection is afforded from surficial NO 3 − contamination.

Evidence for Control of Water Quality in Channel Catfish Ictalurus punctatus Ponds by Phytoplankton Biomass and Sediment Oxygenation

AbstractA data set describing annual variation of water quality in ten commercial channel catfish Ictalurus punctatus ponds was subjected to exploratory statistical analysis to infer ecological processes affecting pond water quality. Two factors explained 67% of the variation in concentrations of water quality variables. The first factor (Factor 1) explained 49% of the variance and was associated with a large negative loading by total ammonia‐nitrogen and large positive loadings by total nitrogen, total phosphorus, chemical oxygen demand, and chlorophyll a. Factor 1 was interpreted with respect to factor loadings to represent the effect of phytoplankton biomass. The second factor (Factor 2) explained an additional 18% of the variance and was associated with a large negative loading by soluble reactive phosphorus and large positive loadings by nitrite‐nitrogen and, to a lesser extent, nitrate‐nitrogen. Factor 2 was interpreted to be related to variation in pond sediment oxygenation. Although factor analysis indicated the overwhelming effect of phytoplankton biomass on water quality, opportunities for management of phytoplankton communities in large commercial aqua‐culture ponds are limited. However, maintenance of an oxidized sediment‐water interface may improve water quality by limiting the diffusion of reductant‐soluble phosphorus from sediment to water and increasing sediment nitrification rates.

Nitrogen gas flux from sediments: insights from simulation modelling

AME Aquatic Microbial Ecology Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials AME 10:209-211 (1996) - doi:10.3354/ame010209 Nitrogen gas flux from sediments: insights from simulation modelling Blackburn TH Direct measurements of dinitrogen efflux from continental shelf sediments indicated that denitrification (mean 3.2 mmol N m-2 d-1) was very important in 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, as oxygen decreased, was unexpected as was the low ratio of oxygen consumption to denitrification (3.6:1). Simulation modelling suggests the following explanation: Most carbon is oxidised anoxically, but nitrogen (ammonium) diffuses to the oxygen zone relatively deep in the sediment, where high rates of coupled nitrification-denitrification result. As oxygen decreases, the zones of nitrification 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, its rate of denitrification remains constant. The concentration of nitrate from sediment nitrification increases in the overlying water, but due to the decreasing rates of sediment nitrification, its rate of denitrification is also constant. Nitrification . Denitrification . Model . Diffusion . Nitrate . Ammonium Full text in pdf format PreviousExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in AME Vol. 10, No. 2. Publication date: May 09, 1996 Print ISSN: 0948-3055; Online ISSN: 1616-1564 Copyright © 1996 Inter-Research.

Differential inhibition by allylsulfide of nitrification and methane oxidation in freshwater sediment

Addition of nitrapyrin, allylthiourea, C(inf2)H(inf2), and CH(inf3)F to freshwater sediment slurries inhibited CH(inf4) oxidation and nitrification to similar extents. Dicyandiamide and allylsulfide were less inhibitory for CH(inf4) oxidation than for nitrification. Allylsulfide was the most potent inhibitor of nitrification, and the estimated 50% inhibitory concentrations for this process and CH(inf4) oxidation were 0.2 and 121 (mu)M, respectively. At a concentration of 2 (mu)M allylsulfide, growth and CH(inf4) oxidation activity of Methylosinus trichosporium OB3b were not inhibited. Allylsulfide at 200 (mu)M inhibited the growth of M. trichosporium by approximately 50% but did not inhibit CH(inf4) oxidation activity. Nitrite production by cells of M. trichosporium was not significantly affected by allylsulfide, except at a concentration of 2 mM, when growth and CH(inf4) oxidation were also inhibited by about 50%. Methane monooxygenase activity present in soluble fractions of M. trichosporium was not inhibited significantly by allylsulfide at either 200 (mu)M or 2 mM. These results suggest that the partial inhibition of CH(inf4) oxidation in sediment slurries by high allylsulfide concentrations may be caused by an inhibition of the growth of methanotrophs rather than an inhibition of methane monooxygenase activity specifically. We conclude that allylsulfide is a promising tool for the study of interactions of methanotrophs and nitrifiers in N cycling and CH(inf4) turnover in natural systems.

Seasonal variation in nitrification and denitrification in estuarine sediment colonized by benthic microalgae and bioturbating infauna

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 126:111-121 (1995) - doi:10.3354/meps126111 Seasonal variation in nitrification and denitrification in estuarine sediment colonized by benthic microalgae and bioturbating infauna Rysgaard S, Christensen PB, Nielsen LP Measurements of seasonal variation in oxygen fluxes, nutrient fluxes, and denitrification were obtained in an estuarine sediment inhabited by benthic microalgae and bioturbating infauna. Oxygen dynamics in the upper sediment strata were found to be controlled by the microalgae and there was a net flux of O2 out of the sediment during spring and autumn. High assimilation by the microalgae reduced the efflux of NH4+ and PO43- from the sediment to the water column during daytime. Denitrification based on NO3- from the water column (Dw) only occurred in winter and spring, when NO3- was present in the water column, and activity was proportional to the water column NO3- concentration. The rate of Dw was reduced during daytime when the upper oxic zone of the sediment increased due to O2 production by benthic microalgae. Coupled nitrification-denitrification (Dn) in the sediment was stimulated by the O2 production during winter and spring, at which times NO3- and NH4+ were present in the water column in high concentrations. In contrast, during summer, when the concentration of NO3- and NH4+ in the water column was low, benthic microalgae inhibited Dn by competing with nitrifying bacteria for NH4+. Dw accounted for 80% of the total denitrification during winter, while on an annual basis, Dw and Dn each accounted for 50% of the total denitrification activity. Benthic infauna, such as Corophium spp., Hydrobia spp., and Nereis spp., occurred in densities of up to several thousand ind. m-2 from May to October. Oxygen consumption, Dw and Dn were linearly correlated with the density of the amphipod Corophium spp., all the processes studied being stimulated by the pumping of O2- and NO3--rich water through the burrows in the upper 2 to 6 cm of the sediment. During summer, the Dn activity was, therefore, the net result of the inhibitory effect by benthic microalgae and the stimulatory effect of the benthic infauna. However, as the concentration of inorganic nitrogen in the overlying water and the sediment nitrification potential are both low in shallow coastal waters during summer, when benthic infauna density is high, we conclude that the stimulatory effect of bioturbating infauna on both Dw and Dn is of minor importance to the annual denitrification budget. Denitrification . Nitrification . Microalgae . Bioturbation . ISN regulation Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 126. Publication date: October 05, 1995 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1995 Inter-Research.

Oxygen regulation of nitrification and denitrification in sediments

Oxygen regulation of nitrification and denitrification in sediments was investigated with 15N isotope techniques. Sediment cores were incubated in a continuous ftowthrough system in which the O2 concentration was varied in the overlying water while the NO3− concentration was kept constant. Nitrification was stimulated with increasing O2 concentrations in the overlying water from 0 to 100% of atmospheric saturation, whereas only a slight stimulation was observed above 100%. At O2 concentrations below 100% of atmospheric saturation, NO3− from the overlying water was the most important source of N for denitrification, whereas above 100% of atmospheric saturation, NO3− produced by nitrification was the main source of N for denitrification. The converse effects of the O2 levels on the source of NO3− can be explained by applying a simple one‐dimensional model: O2 in the overlying water controls the diffusional distance of NO3− to the anoxic zone of denitrification and consequently the location of NO3− vertically in the sediment as well as the magnitude of the nitrification activity. Our results suggest that in aquatic environments containing low NO3− concentrations in the overlying water (such as coastal waters), higher O2 conditions will stimulate denitrification, while the opposite will occur in systems containing high NO3−concentrations (such as eutrophic lakes and streams).

Simulation Model of the Coupling between Nitrification and Denitrification in a Freshwater Sediment

A model was constructed to simulate the results of experiments which investigated nitrification and denitrification in the freshwater sediment of Lake Vilhelmsborg, Denmark (K. Jensen, N. P. Sloth, N. Risgaard-Petersen, S. Rysgaard, and N. P. Revsbech, Appl. Environ. Microbiol. 60:2094-2100, 1994). The model output faithfully represented the profiles of O(2) and NO(3) and rates of nitrification, denitrification, and O(2) consumption as the O(2) concentration in the overlying water was increased from 10 to 600 muM. The model also accurately predicted the response, to increasing O(2) concentrations, of the integrated (micromoles per square meter per hour) rates of nitrification and denitrification. The simulated rates of denitrification of NO(3) diffusing from the overlying water (D(w)) and of NO(3) generated by nitrification within the sediment (D(n)) corresponded to the experimental rates as the O(2) concentration in the overlying water was altered. The predicted D(w) and D(n) rates, as NO(3) concentration in the overlying water was changed, closely resembled those determined experimentally. The model was composed of 41 layers 0.1 mm thick, of which 3 represented the diffusive boundary layer in the water. Large first-order rate constants for nitrification and denitrification were required to completely oxidize all NH(4) diffusing from the lower sediment layers and to remove much of the NO(3) produced. In addition to the flux of NH(4) from below, the model required a flux of an electron donor, possibly methane. Close coupling between nitrification and denitrification, achieved by allowing denitrification to tolerate some O(2) ( approximately 10 muM), was necessary to reproduce the real data. Spatial separation of the two processes (no toleration by denitrification of O(2)) resulted in too high NO(3) concentrations and too low rates of denitrification.

Effects of Methane Metabolism on Nitrification and Nitrous Oxide Production in Polluted Freshwater Sediment

We report the effect of CH(4) and of CH(4) oxidation on nitrification in freshwater sediment from Hamilton Harbour, Ontario, Canada, a highly polluted ecosystem. Aerobic slurry experiments showed a high potential for aerobic N(2)O production in some sites. It was suppressed by C(2)H(2), correlated to NO(3) production, and stimulated by NH(4) concentration, supporting the hypothesis of a nitrification-dependent source for this N(2)O production. Diluted sediment slurries supplemented with CH(4) (1 to 24 muM) showed earlier and enhanced nitrification and N(2)O production compared with unsupplemented slurries (</=1 muM CH(4)). This suggests that nitrification by methanotrophs may be significant in freshwater sediment under certain conditions. Suppression of nitrification was observed at CH(4) concentrations of 84 muM and greater, possibly through competition for O(2) between methanotrophs and NH(4) -oxidizing bacteria and/or competition for mineral N between these two groups of organisms. In Hamilton Harbour sediment, the very high CH(4) concentrations (1.02 to 6.83 mM) which exist would probably suppress nitrification and favor NH(4) accumulation in the pore water. Indeed, NH(4) concentrations in Hamilton Harbour sediment are higher than those found in other lakes. We conclude that the impact of CH(4) metabolism on N cycling processes in freshwater ecosystems should be given more attention.

Diurnal variation of denitrification and nitrification in sediments colonized by benthic microphytes

Diurnal variation of denitrification in sediments with benthic microphytes was investigated by a 15N isotope-pairing technique in order to distinguish between coupled nitrification-denitrification and denitrification of nitrate supplied from the water column. Sediments were incubated in a continuous flowthrough system and exposed to diurnal light and dark cycles. Illumination of both limnetic and estuarine sediments doubled the rate of coupled nitrification-denitrification but reduced the rate of denitrification of nitrate supplied from the water column by -50%. Photosynthesis in the uppermost sediment layers during illumination led to deeper oxygen penetration and a resultant stimulation of nitrification. This stimulation may explain the increased rate of coupled nitrification-denitrification during illumination. The rate of denitrification of nitrate supplied from the water column was reduced during illumination due to a longer diffusion path between water and the anoxic denitrification zone. Denitrification, the bacterial reduction of nitrate to nitrogen gas via nitrite, is an important nitrogen sink in aquatic environments. There are two main sources of nitrate for sediment denitrification: nitrate diffusing into the sediment from the water column and nitrate produced by nitrification in the sediment (Jenkins and Kemp 1984; Seitzinger 1988). The processes of nitrification and denitrification are usually vertically separated within the sediment (Vanderborght and Billen 1975). Nitrification is strictly aerobic and therefore restricted to a thin oxic zone in the upper few millimeters of the sediment. Denitrification takes place in anoxic environments, and in many sediments, most activity is found just below the oxic-anoxic interface (Sweerts and de Beer 1989). The rates of nitrification and denitrification in the active microenvironments are controlled by the availability of substrates, which to a large extent are supplied by diffusion along

Linkages between organic matter mineralization and denitrification in eight riparian wetlands

Denitrification (N2 production) and oxygen consumption rates were measured at ambient field nitrate concentrations during summer in sediments from eight wetlands (mixed hardwood swamps, cedar swamps, heath dominated shrub wetland, herbaceous peatland, and a wetland lacking live vegetation) and two streams. The study sites included wetlands in undisturbed watersheds and in watersheds with considerable agricultural and/or sewage treatment effluent input. Denitrification rates measured in intact cores of water-saturated sediment ranged from ≤ 20 to 260 μmol N m-2 h-1 among the three undisturbed wetlands and were less variable (180 to 260 μmol N M-2 h-1) among the four disturbed wetlands. Denitrification rates increased when nitrate concentrations in the overlying water were increased experimentally (1 up to 770 μM), indicating that nitrate was an important factor controlling denitrification rates. However, rates of nitrate uptake from the overlying water were not a good predictor of denitrification rates because nitrification in the sediments also supplied nitrate for denitrification. Regardless of the dominant vegetation, pH, or degree of disturbance, denitrification rates were best correlated with sediment oxygen consumption rates (r2 = 0.912) indicating a relationship between denitrification and organic matter mineralization and/or sediment nitrification rates. Rates of denitrification in the wetland sediments were similar to those in adjacent stream sediments. Rates of denitrification in these wetlands were within the range of rates previously reported for water-saturated wetland sediments and flooded soils using whole core15N techniques that quantify coupled nitrification/denitrification, and were higher than rates reported from aerobic (non-saturated) wetland sediments using acetylene block methods.

Nitrification and Denitrification in Lake and Estuarine Sediments Measured by the 15 N Dilution Technique and Isotope Pairing

The transformation of nitrogen compounds in lake and estuarine sediments incubated in the dark was analyzed in a continuous-flowthrough system. The inflowing water contained NO(3), and by determination of the isotopic composition of the N(2), NO(3), and NH(4) pools in the outflowing water, it was possible to quantify the following reactions: total NO(3) uptake, denitrification based on NO(3) from the overlying water, nitrification, coupled nitrification-denitrification, and N mineralization. In sediment cores from both lake and estuarine environments, benthic microphytes assimilated NO(3) and NH(4) for a period of 25 to 60 h after darkening. Under steady-state conditions in the dark, denitrification of NO(3) originating from the overlying water accounted for 91 to 171 mumol m h in the lake sediments and for 131 to 182 mumol m h in the estuarine sediments, corresponding to approximately 100% of the total NO(3) uptake for both sediments. It seems that high NO(3) uptake by benthic microphytes in the initial dark period may have been misinterpreted in earlier investigations as dissimilatory reduction to ammonium. The rates of coupled nitrification-denitrification within the sediments contributed to 10% of the total denitrification at steady state in the dark, and total nitrification was only twice as high as the coupled process.

Rates of nitrification, distribution of nitrifying bacteria and inorganic N fluxes in northern Bering-Chukchi shelf sediments

Spatial distribution of sediment nitrification rates and fluxes of ammonium and nitrate were measured in shelf sediments of the northern Bering and Chukchi seas. The sediments could be divided into three main areas depending on macrofaunal activity and input of organic nitrogen. Sediments underlying the highly productive Bering Shelf-Anadyr water (BSAS) were characterized by a high macrofaunal biomass and a high input of nitrogen-rich organic material. Tube-dwelling amphipods dominated in the sandy sediments of the northern Bering Sea, while bivalves dominated in the fine textured sediments of the Chukchi Sea. Sediments underlying the low productive Alaska Coastal Water (ACS) were characterized by low macrofaunal biomass and an input of lower quality organic material. Generally nitrification rates and nutrification potentials (NP) were highest in BSAS and lower in ACS. Nitrification rates of surface sediment, calculated from NP, accounted for 90% of the measured rates in ACS, but only 35–75% in BSAS. These data together with the distribution patterns of NP and pore water nitrate profiles implied, that most sediment nitrification was confined to the sediment surface in ACS and in BSAS bivalve sediments, while most sediment nitrification took place in the ventilated burrow walls of BSAS amphipod sediments. The NH 4 + efflux was five-fold greater from BSAS compared to ACS, whereas the estimated sediment net NH 4 + production was three-fold greater. The increase in NH 4 + efflux relative to net NH 4 + production could mostly be attributed to macrofaunal excretion. The NO 3 − flux between sediment and water column was correlated with NO 3 − concentrations in the bottom water. At concentrations higher than 10 μM NO 3 −, the flux was directed into the sediment and at lower concentrations out of the sediment. Spatial distribution of high bottom water NO 3 − concentrations correlated with high NH 4 + fluxes out of the sediment. This resulted in a lower net efflux of inorganic nitrogen from these sediments.

Model of nitrification and denitrification in marine sediments

Model of nitrification and denitrification in marine sediments