Denitrification In Marine Sediments Research Articles

Influence of restored mussel reefs on denitrification in marine sediments

Globally we have lost the majority of shellfish reefs, with the concomitant loss of ecosystem services. Restoration provides opportunities to regain lost services and engage society in the wider ecosystem benefits of restoration. Previous research has demonstrated that the functional role of shellfish can be context dependent, and we therefore measured fluxes of nutrients and dissolved gases from four restored mussel reefs along a grain size gradient in New Zealand as a metric of success in ecosystem function. This globally novel research found that restored mussel reefs were successful in enhancing denitrification. Mussel reefs can therefore be important in reducing the risk of future eutrophication, but the importance of nutrient remineralisation varies in response to site conditions. These data show that mussel reef creation can quickly restore ecosystem function, but site selection to enhance specific services is important. This study provides evidence of a poorly realised ecosystem service provided by restored mussel beds that allows future restoration efforts to better target areas in order to have the largest impact on the removal of anthropogenic nitrogen.

Carbon nanotubes affect the toxicity of CuO nanoparticles to denitrification in marine sediments by altering cellular internalization of nanoparticle.

Denitrification is an important pathway for nitrate transformation in marine sediments, and this process has been observed to be negatively affected by engineered nanomaterials. However, previous studies only focused on the potential effect of a certain type of nanomaterial on microbial denitrification. Here we show that the toxicity of CuO nanoparticles (NPs) to denitrification in marine sediments is highly affected by the presence of carbon nanotubes (CNTs). It was found that the removal efficiency of total NOX−-N (NO3−-N and NO2−-N) in the presence of CuO NPs was only 62.3%, but it increased to 81.1% when CNTs appeared in this circumstance. Our data revealed that CuO NPs were more easily attached to CNTs rather than cell surface because of the lower energy barrier (3.5 versus 36.2 kT). Further studies confirmed that the presence of CNTs caused the formation of large, incompact, non-uniform dispersed, and more negatively charged CuO-CNTs heteroaggregates, and thus reduced the nanoparticle internalization by cells, leading to less toxicity to metabolism of carbon source, generation of reduction equivalent, and activities of nitrate reductase and nitrite reductase. These results indicate that assessing nanomaterial-induced risks in real circumstances needs to consider the “mixed” effects of nanomaterials.

Isotope fractionation and isotope decoupling during anammox and denitrification in marine sediments

To evaluate the relation of isotope fractionation during sedimentary nitrate reduction with sediment reactivity, we measured nitrate and nitrite reduction rates and corresponding isotope changes in marine sediments in the Skagerrak. Our sampling sites encompassed a gradient of reactivity, oxygen consumption, and manganese concentration. Anammox was the main N2-production pathway at the deepest site. For this site, we calculated the intrinsic isotope effect of nitrite consumption by anammox in marine sediments, and found that it is ∼ −20‰, in accordance with culture studies. Denitrification was dominant at shallower sites, which confirms previous studies from whole core incubations. The N-isotope effect of denitrification, 15ε, ranged from −12‰ to −16‰. Oxygen isotopes of nitrate were more variable, and the ratio of 18ε/15ε, was highly variable in all sediments we investigated. At all stations, the oxygen isotope effect was (partly or entirely) decoupled from the nitrogen isotope effect. In denitrification-dominated sediments, this decoupling of oxygen and nitrogen isotopes appeared to be driven by nitrite reoxidation in anoxic sediment incubations, either due to enzymatic reversibility of the respiratory nitrate reductase Nar, or to reversibility on the community level. In anammox-dominated sediments, this effect was also evident in N-isotope changes, likely due to net nitrate production and isotope exchange that is promoted by anammox. These findings suggest that the ratio of 18ε/15ε in marine environments is more flexible than previously assumed, because enzymatic or community-driven isotope exchange can alter both N and O isotopes, deviating from standard Rayleigh-type fractionation.

Meiofauna increases bacterial denitrification in marine sediments.

Denitrification is a critical process that can alleviate the effects of excessive nitrogen availability in aquatic ecosystems subject to eutrophication. An important part of denitrification occurs in benthic systems where bioturbation by meiofauna (invertebrates <1 mm) and its effect on element cycling are still not well understood. Here we study the quantitative impact of meiofauna populations of different abundance and diversity, in the presence and absence of macrofauna, on nitrate reduction, carbon mineralization and methane fluxes. In sediments with abundant and diverse meiofauna, denitrification is double that in sediments with low meiofauna, suggesting that meiofauna bioturbation has a stimulating effect on nitrifying and denitrifying bacteria. However, high meiofauna densities in the presence of bivalves do not stimulate denitrification, while dissimilatory nitrate reduction to ammonium rate and methane efflux are significantly enhanced. We demonstrate that the ecological interactions between meio-, macrofauna and bacteria are important in regulating nitrogen cycling in soft-sediment ecosystems.

The effect of nitrate concentration on sulfide-driven autotrophic denitrification in marine sediment

The effect of nitrate concentration on denitrification rate, microbial community and byproduct accumulation in sulfide-driven autotrophic denitrification, one of the dominant processes during anoxic marine sediment remediation, was investigated in this study. Microorganisms which were phylogenetically closely related with Sulfurimonas denitrificans of ε-Proteobacteria and Thiohalomonas denitrificans of γ-Proteobacteria were the major autotrophic denitrifiers in this study. Nitrate concentration was demonstrated to have selective effect on denitrifying microbial community as revealed by denaturing gradient gel electrophoresis. Denitrifiers enriched at 30 mM NO 3 - have higher diversity than other two groups (10, and 80 mM NO 3 - ) according to Shannon index. Denitrification showed zero-order reaction kinetics when nitrate concentration was higher than 4 mM. Neither absolute nitrate concentration nor overall nitrate/sulfide ratio acted as the determinant for denitrification byproduct ( i.e. N 2O and NO 2 - ) accumulation. The limitation of sulfide due to low mass transfer might be the reason for the byproduct accumulation.

Effects of Specific Inhibitors on Anammox and Denitrification in Marine Sediments

The effects of three metabolic inhibitors (acetylene, methanol, and allylthiourea [ATU]) on the pathways of N2 production were investigated by using short anoxic incubations of marine sediment with a 15N isotope technique. Acetylene inhibited ammonium oxidation through the anammox pathway as the oxidation rate decreased exponentially with increasing acetylene concentration; the rate decay constant was 0.10+/-0.02 microM-1, and there was 95% inhibition at approximately 30 microM. Nitrous oxide reduction, the final step of denitrification, was not sensitive to acetylene concentrations below 10 microM. However, nitrous oxide reduction was inhibited by higher concentrations, and the sensitivity was approximately one-half the sensitivity of anammox (decay constant, 0.049+/-0.004 microM-1; 95% inhibition at approximately 70 microM). Methanol specifically inhibited anammox with a decay constant of 0.79+/-0.12 mM-1, and thus 3 to 4 mM methanol was required for nearly complete inhibition. This level of methanol stimulated denitrification by approximately 50%. ATU did not have marked effects on the rates of anammox and denitrification. The profile of inhibitor effects on anammox agreed with the results of studies of the process in wastewater bioreactors, which confirmed the similarity between the anammox bacteria in bioreactors and natural environments. Acetylene and methanol can be used to separate anammox and denitrification, but the effects of these compounds on nitrification limits their use in studies of these processes in systems where nitrification is an important source of nitrate. The observed differential effects of acetylene and methanol on anammox and denitrification support our current understanding of the two main pathways of N2 production in marine sediments and the use of 15N isotope methods for their quantification.

海洋における生元素の循環と微生物代謝の相互作用

Use of a stable isotope 15N to study microbial processes associated with nitrogen dynamics in marine environments has several advantages including estimates of in situ rates of nitrogen metabolisms and of transfer of nitrogen within ecosystem. First part of this review summarizes application of 15N methodology to evaluate microbial processes of ammonification, ammonium assimilation, nitrification, and denitrification in marine sediment as well as in water column. 15N nitrate isotope dilution was successfully applied to show the coupling between sedimentary nitrification and denitrification, which occurs efficiently in the aerobic-anaerobic micro-sites in the vicinity of organic detritus deposition. In global scale, the amount of denitrified nitrogen in coastal sediments estimated by 15N method is comparable to that in the whole water column, indicating its global importance as the oceanic sink of available nitrogen. Microbial populations in the upper ocean also play a significant role on nitrogen dynanics including ammonium regeneration and its assimilation. In Antarctic coastal waters of spring bloom condition, bacterial net production of ammonium was observed, although they also assimilated ammonium simultaneously. High concentration of amino acids possibly supplied from spring bloom would support this bacterial metabolism. At the later part, I describe our recent finding of non-living organic particles of sub-micron size range (0.38&sim;1.0 μm) in the ocean, abundance of which is in the order of 10 million per ml at the surface layer. Since the abundance of those particles is positively correlated with chl a and other biological parameters, we assume its biological origin. Laboratory experiments and field observations show several biological processes of their production including grazing of micro flagellates on bacteria, lysis of bacteria by viral infection and exudates of bloomphytoplankton. Also, flexible and fragile natures of those particles suggest that they are marine snow type organic aggregates of submicron seze. This finding fulfills the previous gap between dissolbed and particulate organic materials in the ocean, and suggests an importance of "detritus ladder" in marine ecosystem.

Denitrification in marine sediments: A model study

The rate and factors controlling denitrification in marine sediments have been investigated using a prognostic diagenetic model. The model is forced with observed carbon fluxes, bioturbation and sedimentation rates, and bottom water conditions. It can reproduce rates of aerobic mineralization, denitrification, and fluxes of oxygen, nitrate, and ammonium. The globally integrated rate of denitrification is estimated by this model to be about 230–285 Tg N yr−1, with about 100 Tg N yr−1 occurring in shelf sediments. This estimate is significantly higher than literature estimates (12–89 Tg N yr−1), mainly because of a proposed upward revision of denitrification rates in slope and deep‐sea sediments. Higher sedimentary denitrification estimates require a revision of the marine nitrogen budget and lowering of the oceanic residence time of nitrogen down to about 2×103 years and are consistent with reported low N/P remineralization ratios between 1000 and 3000 m. Rates of benthic denitrification are most sensitive to the flux of labile organic carbon arriving at the sediment‐water interface and bottom water concentrations of nitrate and oxygen. Denitrification always increases when bottom water nitrate increases but may increase or decrease if oxygen in the bottom water increases. Nitrification is by far the most important source of nitrate for denitrification, except for organic‐rich sediments underlying oxygen‐poor and nitrate‐rich water.

Evidence for denitrification in marine sediment highly contaminated by petroleum products

Denitrifying activity was measured in marine sediment (mediterranean coast of France) sampled near a petroleum refinery heavily contaminated by hydrocarbons (31 g kg −1 of sediment). Results provided evidence that in Lavera Bay sediment chronically polluted by petroleum products, denitrification (potential and estimated activities) was not affected by petroleum input and was comparable to those obtained in unpolluted sediments. However, due to low nitrate concentration natural denitrifying activity is not detectable. The dominant denitrifying bacteria (85% of the isolates) belonged to the genus Pseudomonas and four groups of bacteria could be discriminated. The growth pattern on nitrate was different for each isolate and one strain was not capable of nitrous oxide production.

Model of nitrification and denitrification in marine sediments

Model of nitrification and denitrification in marine sediments

Model of nitrification and denitrification in marine sediments

Processes involved in the C, N, S, and O cycles in a marine sediment were stimulated for a situation where most organic degradation occured in the top 2 mm and NO3− was not present in the overlying water. The effect of increasing organic loading was examined (degradation of C ? 7 to 107 mmol m−2 d−1). Increasing organic loading had the following results: (1) ? 50% of the dissolved organic nitrogen was lost by diffusion in all treatments; (2) the proportion of NH4++; flux increased, the proportion of nitrification increased slightly and then decreased; and (3) the proportion of NO3− of NO3− efflux.

Model of nitrification and denitrification in marine sediments

Model of nitrification and denitrification in marine sediments

Effects of oxygen on denitrification in marine sediments

Experiments were carried out to determine the effect of oxygen on denitrification, simultaneously in sediment and in a bacterial strain isolated from this sediment. Descriptions of the apparatus used are given. In sediment, denitrification was found to occur when the oxygen concentration increased to 5 mg l−1, but the activity was only 10% of that obtained under anaerobic conditions. The two first steps of denitrification measured in the sediment were less sensitive to oxygen. When the sediment was incubated in presence of 1,1 mg l−1 O2, the denitrification rate was never fully restored by returning it to anaerobic conditions.

Nitrous oxide production from nitrification and denitrification in marine sediment at low oxygen concentrations

Measurements of N2O production (release of free N2O), nitrification, and denitrification were made simultaneously in NH4Cl- and KNO3-amended suspensions of marine sediment. An open flow system was designed for the application of low partial pressures of O2 (0–10 kPa) to the sediment. The overall rate of N2O production increased dramatically at the lowest O2 tensions (0–0.2 kPa) and had a maximum at complete anoxia. The specific rates of N2O production from nitrification (N2On) and from denitrification (N2Od) were determined after separation of the processes with inhibitors. Within the range of 0–0.2 kPa O2, the rate of N2On production showed an apparent maximum of 0.1 kPa O2 where the production accounted for 25% of the total activity of nitrification ([Formula: see text] oxidation). The rate of N2Od production, however, continued to increase as the O2 fell to zero. The proportion of N2Od to the total N2Od plus N2 produced from denitrification increased at the higher O2 tensions and reached the maximum of about 50% at 5 kPa O2. Except for a narrow range between 0.1 and 0.2 kPa O2, denitrification was the main source of N2O at 0–10 kPa O2.

Denitrification in Marine Sediment: Measurement of Capacity and Estimate of In Situ Rate

The acetylene block technique was used to assay denitrification in undisturbed sediment cores of an intertidal mud flat. Nitrogen loss due to this process was estimated at 1 to 41 kg of N/hectare (ha) per year. Anaerobic nitrate-saturated slurry of the same sediment had a denitrification capacity of 1,026 kg of N/ha per year. The acetylene block technique failed at low nitrate concentrations, so that denitrification at average in situ nitrate concentrations could not be determined. Denitrification followed zero-order kinetics at nitrate concentrations high enough to allow successful blockage of N(2)O reduction. Thus, an estimate of in situ rates based on kinetic parameters and in situ nitrate concentrations was impossible. No denitrification was observed in a slurry of the top 1.5 cm under aerated conditions and nitrate saturation. In undisturbed sediment, significant denitrification occurred in few discrete sites within a matrix of undetectable or low activity. Despite numerous errors contributing to the uncertainty of the estimate of in situ rates, the result obtained by this method was considered more valuable than the determination of denitrification capacities. Methods which include severe changes of physical and chemical parameters may frequently lead to overestimates of denitrification rates.

Capacity for Denitrification and Reduction of Nitrate to Ammonia in a Coastal Marine Sediment

The capacity for dissimilatory reduction of NO(3) to N(2) (N(2)O) and NH(4) was measured in NO(3)-amended marine sediment. Incubation with acetylene (7 x 10 atmospheres [normal]) caused accumulation of N(2)O in the sediment. The rate of N(2)O production equaled the rate of N(2) production in samples without acetylene. Complete inhibition of the reduction of N(2)O to N(2) suggests that the "acetylene blockage technique" is applicable to assays for denitrification in marine sediments. The capacity for reduction of NO(3) by denitrification decreased rapidly with depth in the sediment, whereas the capacity for reduction of NO(3) to NH(4) was significant also in deeper layers. The data suggested that the latter process may be equally as significant as denitrification in the turnover of NO(3) in marine sediments.

Nitrification and denitrification in marine sediments from Puget Sound1

The anomalous interstitial water chemistry in Puget Sound sediments (200‐m water depth) indicates an intermediate zone at 20‐ to 30‐cm depths which consists of a mixture of 90% interstitial water and 10% bottom water. Irrigation by burrowing benthic organisms is believed responsible. The vertical distribution of interstitial ammonia, nitrate, and nitrite indicates that nitrification is occurring in this intermediate sedimentary zone, with oxygen being supplied by the irrigation process. Above and below this zone denitrification predominates.