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Sybil P Seitzinger - One of the best experts on this subject based on the ideXlab platform.
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New approaches to modeling Denitrification
Biogeochemistry, 2009Co-Authors: Peter M Groffman, Eric A. Davidson, Sybil P SeitzingerAbstract:Within the past few decades, humans have dramatically altered the earth’s nitrogen (N) cycle. Introduction of reactive nitrogen (N) into the biosphere by humans now exceeds the rate of biological N2-fixation in native terrestrial ecosystems (Galloway et al. 2004). This increased reactive N is due primarily to N fertilizer production and fossil fuel combustion used to support the food and energy demands of a rapidly expanding human population. The negative human and environment health effects of this increased N are many (Galloway et al. 2008; Howarth et al. 2005; UNEP and WHRC 2007). Denitrification is the main process that permanently removes fixed N from the environment. Denitrification, the microbial production of N2 from nitrate and nitrite, is a facultative anaerobic process (‘‘classical Denitrification’’); therefore, partially to fully saturated soils and aquatic sediments, and low oxygen waters are ideal sites for Denitrification. We now know that Denitrification occurs in almost all terrestrial, freshwater, coastal and (some) oceanic ecosystems, as well as human engineered systems (Seitzinger et al. 2006). Despite the large number of Denitrification studies there are still only a few locations with measurements adequate to quantify Denitrification rates, or to understand factors controlling Denitrification, at the ecosystem scale. This also has severely limited development and incorporation of Denitrification into models which are necessary to scale-up measurements to local ecosystem, regional or global scales. A Denitrification Research Coordination Network (Denitrification RCN) was established in 2005, with the overall goal to develop a coordinated network of Denitrification scientists from a wide array of disciplines, from molecular biology to ecosystem science, and from soil science to oceanography. The efforts of the Denitrification RCN are intended to advance quantification of Denitrification rates, development of process-based relationships between rates of Denitrification and controlling factors, and production of spatially explicit, process-based models that can be used to scale-up site specific measurements to ecosystem, regional and global scales. Specific objectives include facilitating the sharing of recent methodological advances in Denitrification measurement and models, stimulating additional methodological P. M. Groffman (&) Cary Institute of Ecosystem Studies, Box AB, Millbrook, NY 12545, USA e-mail: groffmanp@ecostudies.org
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Denitrification across landscapes and waterscapes a synthesis
Ecological Applications, 2006Co-Authors: Sybil P Seitzinger, Richard Lowrance, John A Harrison, J K Bohlke, A F Bouwman, Bruce J Peterson, Craig R Tobias, G Van DrechtAbstract:Denitrification is a critical process regulating the removal of bioavailable nitrogen (N) from natural and human-altered systems. While it has been extensively studied in terrestrial, freshwater, and marine systems, there has been limited communication among Denitrification scientists working in these individual systems. Here, we compare rates of Denitrification and controlling factors across a range of ecosystem types. We suggest that terrestrial, freshwater, and marine systems in which Denitrification occurs can be organized along a continuum ranging from (1) those in which nitrification and Denitrification are tightly coupled in space and time to (2) those in which nitrate production and Denitrification are relatively decoupled. In aquatic ecosystems, N inputs influence Denitrification rates whereas hydrology and geomorphology influence the proportion of N inputs that are denitrified. Relationships between Denitrification and water residence time and N load are remarkably similar across lakes, river reaches, estuaries, and continental shelves. Spatially distributed global models of Denitrification suggest that continental shelf sediments account for the largest portion (44%) of total global Denitrification, followed by terrestrial soils (22%) and oceanic oxygen minimum zones (OMZs; 14%). Freshwater systems (groundwater, lakes, rivers) account for about 20% and estuaries 1% of total global Denitrification. Denitrification of land-based N sources is distributed somewhat differently. Within watersheds, the amount of land-based N denitrified is generally highest in terrestrial soils, with progressively smaller amounts denitrified in groundwater, rivers, lakes and reservoirs, and estuaries. A number of regional exceptions to this general trend of decreasing Denitrification in a downstream direction exist, including significant Denitrification in continental shelves of N from terrestrial sources. Though terrestrial soils and groundwater are responsible for much Denitrification at the watershed scale, per-area Denitrification rates in soils and groundwater (kg Nkm � 2 � yr � 1 ) are, on average, approximately one-tenth the per-area rates of Denitrification in lakes, rivers, estuaries, continental shelves, or OMZs. A number of potential approaches to increase Denitrification on the landscape, and thus decrease N export to sensitive coastal systems exist. However, these have not generally been widely tested for their effectiveness at scales required to significantly reduce N export at the whole watershed scale.
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The enigma of progress in Denitrification research.
Ecological Applications, 2006Co-Authors: Eric A. Davidson, Sybil P SeitzingerAbstract:Humans have dramatically increased the amount of reactive nitrogen (primarily ammonium, nitrogen oxides, and organically bound N) circulating in the biosphere and atmosphere, creating a wide array of desirable products (e.g., food production) and undesirable consequences (e.g., eutrophication of aquatic ecosystems and air pollution). Only when this reactive N is converted back to the chemically unreactive dinitrogen (N2) form, do these cascading effects of elevated reactive N cease to be of concern. Among the quantitatively most important processes for converting reactive N to N2 gas is the biological process of classical Denitrification, in which oxides of nitrogen are used as terminal electron acceptors in anaerobic respiration. This Invited Feature on Denitrification includes a series of papers that integrate our current state of knowledge across terrestrial, freshwater, and marine systems on Denitrification rates, controlling factors, and methodologies for measuring and modeling Denitrification. In this paper, we present an overview of the role of Denitrification within the broader N cycle, the environmental and health concerns that have resulted from human alteration of the N cycle, and a brief historical perspective on why Denitrification has been so difficult to study. Despite over a century of research on Denitrification and numerous recent technological advances, we still lack a comprehensive, quantitative understanding of Denitrification rates and controlling factors across ecosystems. Inherent problems of measuring spatially and temporally heterogeneous N2 production under an N2-rich atmosphere account for much of this slow progress, but lack of interdisciplinary communication of research results and methodological developments has also impeded Denitrification research. An integrated multidisciplinary approach to Denitrification research, from upland terrestrial ecosystems, to small streams, river systems, estuaries, and continental shelf ecosystems, and to the open ocean, may yield new insights into Denitrification across landscapes and waterscapes.
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Estimating Denitrification in North Atlantic continental shelf sediments
Biogeochemistry, 1996Co-Authors: Sybil P Seitzinger, Anne E. GiblinAbstract:A model of coupled nitrification/Denitrification was developed for continental shelf sediments to estimate the spatial distribution of Denitrification throughout shelf regions in the North Atlantic basin. Using data from a wide range of continental shelf regions, we found a linear relationship between Denitrification and sediment oxygen uptake. This relationship was applied to specific continental shelf regions by combining it with a second regression relating sediment oxygen uptake to primary production in the overlying water. The combined equation was: Denitrification (mmol N m^−2 d^−1)=0.019^* phytoplankton production (mmol C m^−2 d^−1). This relationship suggests that approximately 13% of the N incorporated into phytoplankton in shelf waters is eventually denitrified in the sediments via coupled nitrification/Denitrification, assuming a C:N ratio of 6.625:1 for phytoplankton. The model calculated Denitrification rates compare favorably with rates reported for several shelf regions in the North Atlantic. The model-predicted average Denitrification rate for continental shelf sediments in the North Atlantic Basin is 0.69 mmol N m^− 2 d^−1. Denitrification rates (per unit area) predicted by the model are highest for the continental shelf region in the western North Atlantic between Cape Hatteras and South Florida and lowest for Hudson Bay, the Baffin Island region, and Greenland. Within latitudinal belts, average Denitrification rates were lowest in the high latitudes, intermediate in the tropics and highest in the mid-latitudes. Although Denitrification rates per unit area are lowest in the high latitudes, the total N removal by Denitrification (53 × 10^10 mol N y^−1) is similar to that in the mid-latitudes (60 × 10^10 mol N y^−1) due to the large area of continental shelf in the high latitudes. The Gulf of St. Lawrence/Grand Banks area and the North Sea are responsible for seventy-five percent of the Denitrification in the high latitude region. N removal by Denitrification in the western North Atlantic (96 × 10^10 mol N y^−1) is two times greater than in the eastern North Atlantic (47 × 10^10 mol N y^−1). This is primarily due to differences in the area of continental shelf in the two regions, as the average Denitrification rate per unit area is similar in the western and eastern North Atlantic. We calculate that a total of 143 × 10^10 mol N y^−1 is removed via coupled nitrification/Denitrification on the North Atlantic continental shelf. This estimate is expected to underestimate total sediment Denitrification because it does not include direct Denitrification of nitrate from the overlying water. The rate of coupled nitrification/Denitrification calculated is greater than the nitrogen inputs from atmospheric deposition and river sources combined, and suggests that onwelling of nutrient rich slope water is a major source of N for Denitrification in shelf regions. For the two regions where N inputs to a shelf region from onwelling have been measured, onwelling appears to be able to balance the Denitrification loss.
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Linkages between organic matter mineralization and Denitrification in eight riparian wetlands
Biogeochemistry, 1994Co-Authors: Sybil P SeitzingerAbstract:Denitrification (N_2 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 ( r ^2 = 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 core^15N techniques that quantify coupled nitrification/Denitrification, and were higher than rates reported from aerobic (non-saturated) wetland sediments using acetylene block methods.
Scott F Korom - One of the best experts on this subject based on the ideXlab platform.
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natural Denitrification in the saturated zone a review
Water Resources Research, 1992Co-Authors: Scott F KoromAbstract:Denitrification is increasingly recognized for its ability to eliminate or reduce nitrate concentrations in groundwater. With this awareness comes a desire to predict the rate and extent of Denitrification in aquifers. The limiting factor in making predictive models, however, is our limited knowledge of the physical characteristics of this process. This review synthesizes the published literature on natural aquifer Denitrification. A background section discusses Denitrification requirements and dissimilatory nitrate reduction to ammonium, which occurs in environments similar to those where Denitrification occurs, and gives a historical perspective on Denitrification. Other sections discuss Denitrification with organic carbon serving as the electron donor (heterotrophic Denitrification) and with reduced inorganic compounds serving as the electron donor (autotrophic Denitrification). The section on heterotrophic Denitrification is structured around two tables that summarize natural aquifer Denitrification rates reported by laboratory studies and natural aquifer Denitrification rates reported by field studies. The section on autotrophic Denitrification discusses Denitrification with reduced iron and reduced sulfur. Thus far, most studies only consider a single electron donor or donor type, whether heterotrophic or autotrophic. This review demonstrates, however, that multiple electron donors may be present in a given aquifer. Future research efforts are recommended to determine the factors affecting the availability of electron donors and their Denitrification rates. Additional research is also suggested on how dissolved oxygen affects Denitrification rates and on the factors influencing the partitioning of nitrate reduction products to nitrous oxide, a potential contributor to the destruction of the ozone layer, and to ammonium.
Peter M Groffman - One of the best experts on this subject based on the ideXlab platform.
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Denitrification in a semi-arid grazing ecosystem.
Oecologia, 2015Co-Authors: Douglas A. Frank, Peter M GroffmanAbstract:The effect of large herbivores on gaseous N loss from grasslands, particularly via Denitrification, is poorly understood. In this study, we examined the influence of native migratory ungulates on Denitrification in grasslands of Yellowstone National Park in two ways, by (1) examining the effect of artificial urine application on Denitrification, and (2) comparing rates inside and outside long-term exclosures at topographically diverse locations. Artificial urine did not influence Denitrification 3 and 12 days after application at hilltop, mid-slope, and slope-bottom sites. Likewise, grazers had no effect on community-level Denitrification at dry exclosure sites, where rates were low. At mesic sites, however, ungulates enhanced Denitrification by as much as 4 kg N ha−1 year−1, which was double atmospheric N inputs to this ecosystem. Denitrification enzyme activity (DEA, a measure of Denitrification potential) was positively associated with soil moisture at exclosure sites, and herbivores stimulated DEA when accounting for the soil moisture effect. Glucose additons to soils increased Denitrification and nitrate additions had no influence, suggesting that Denitrification was limited by the amount of labile soil carbon, which previously has been shown to be enhanced by ungulates in Yellowstone. These results indicate that Denitrification can be an ecologically important flux in portions of semi-arid landscapes, and that there is a previously unsuspected regulation of this process by herbivores.
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using a soil topographic index to distribute Denitrification fluxes across a northeastern headwater catchment
Journal of Hydrology, 2015Co-Authors: Todd R Anderson, Peter M Groffman, Todd M WalterAbstract:Summary Riparian zones are considered potential hotspots of Denitrification because they allow for the confluence of necessary electron acceptors (nitrate) and donors (carbon) via hydrologic flowpaths in low oxygen (reducing) conditions. While riparian areas have received considerable research attention, other soils prone to saturation have similar physicochemical characteristics but are less frequently studied. We quantified in situ Denitrification rates in the shallow saturated zone, a dynamic portion of the landscape, across a range of hydroperiodicities, i.e., frequencies and durations of saturated conditions, as characterized by a topographic index in a small mixed land-use headwater catchment in central New York State. We found a strong positive relationship between topographic index and Denitrification, indicating that the highest rates of Denitrification occur in the relatively small portion of the landscape prone to saturation. We used the resulting relationship to distribute Denitrification rates across the catchment and estimate Denitrification fluxes from the shallow saturated zone. While the highest rates of Denitrification were observed in wetter portions of the landscape, including riparian zones, we found that the shallow saturated zone beneath drier upland soils contributed to a larger portion of whole-catchment Denitrification due to a larger areal extent. A topographic index-Denitrification model is a promising and simple tool that allows for scaling of in situ Denitrification rates across the landscape and provides insight into the spatial organization of Denitrification at the catchment scale.
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New approaches to modeling Denitrification
Biogeochemistry, 2009Co-Authors: Peter M Groffman, Eric A. Davidson, Sybil P SeitzingerAbstract:Within the past few decades, humans have dramatically altered the earth’s nitrogen (N) cycle. Introduction of reactive nitrogen (N) into the biosphere by humans now exceeds the rate of biological N2-fixation in native terrestrial ecosystems (Galloway et al. 2004). This increased reactive N is due primarily to N fertilizer production and fossil fuel combustion used to support the food and energy demands of a rapidly expanding human population. The negative human and environment health effects of this increased N are many (Galloway et al. 2008; Howarth et al. 2005; UNEP and WHRC 2007). Denitrification is the main process that permanently removes fixed N from the environment. Denitrification, the microbial production of N2 from nitrate and nitrite, is a facultative anaerobic process (‘‘classical Denitrification’’); therefore, partially to fully saturated soils and aquatic sediments, and low oxygen waters are ideal sites for Denitrification. We now know that Denitrification occurs in almost all terrestrial, freshwater, coastal and (some) oceanic ecosystems, as well as human engineered systems (Seitzinger et al. 2006). Despite the large number of Denitrification studies there are still only a few locations with measurements adequate to quantify Denitrification rates, or to understand factors controlling Denitrification, at the ecosystem scale. This also has severely limited development and incorporation of Denitrification into models which are necessary to scale-up measurements to local ecosystem, regional or global scales. A Denitrification Research Coordination Network (Denitrification RCN) was established in 2005, with the overall goal to develop a coordinated network of Denitrification scientists from a wide array of disciplines, from molecular biology to ecosystem science, and from soil science to oceanography. The efforts of the Denitrification RCN are intended to advance quantification of Denitrification rates, development of process-based relationships between rates of Denitrification and controlling factors, and production of spatially explicit, process-based models that can be used to scale-up site specific measurements to ecosystem, regional and global scales. Specific objectives include facilitating the sharing of recent methodological advances in Denitrification measurement and models, stimulating additional methodological P. M. Groffman (&) Cary Institute of Ecosystem Studies, Box AB, Millbrook, NY 12545, USA e-mail: groffmanp@ecostudies.org
S. K. Datta - One of the best experts on this subject based on the ideXlab platform.
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Denitrification losses from puddled rice soils in the tropics
Biology and Fertility of Soils, 1990Co-Authors: R. J. Buresh, S. K. DattaAbstract:Although Denitrification has long been considered a major loss mechanism for N fertilizer applied to lowland rice ( Oryza sativa L.) soils, direct field measurements of Denitrification losses from puddled rice soils in the tropics have only been made recently. This paper summarizes the results of direct measurement and indirect estimation of Denitrification losses from puddled rice fields and reviews the status of research methodology for measurement of Denitrification in rice fields. The direct recovery of (N_2+N_2O)-^15N from ^15N-enriched urea has recently been measured at sites in the Philippines, Thailand, and Indonesia. In all 12 studies, recoveries of (N_2+N_2O)-^15N ranged from less than 0.1 to 2.2% of the applied N. Total gaseous N losses, estimated by the ^15N-balance technique, were much greater, ranging from 10 to 56% of the applied urea-N. Denitrification was limited by the nitrate supply rather than by available C, as indicated by the values for water-soluble soil organic C, floodwater (nitrate+nitrite)-N, and evolved (N_2+N_2O)-^15N from added nitrate. In the absence of runoff and leaching losses, the amount of (N_2+N_2O)-^15N evolved from ^15N-labeled nitrate was consistently less than the unrecovered ^15N in ^15N balances with labeled nitrate, which presumably represented total Denitrification losses. This finding indicates that the measured recoveries of (N_2+N_2O)-^15N had underestimated the Denitrification losses from urea. Even with a probable two-or threefold underestimation, direct measurements of (N_2+N_2O)-^15N failed to confirm the appreciable Denitrification losses often estimated by the indirect difference method. This method, which determines Denitrification losses by the difference between total ^15N loss and determined ammonia loss, is prone to high variability. Measurements of nitrate disappearance and ^15N-balance studies suggest that nitrification-Denitrification occurs under alternate soil drying and wetting conditions both during the rice cropping period and between rice crops. Research is needed to determine the magnitude of Denitrification losses when soils are flooded and puddled for production of rice.
Mohamed Kheireddine Aroua - One of the best experts on this subject based on the ideXlab platform.
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bio electrochemical removal of nitrate from water and wastewater a review
Bioresource Technology, 2008Co-Authors: Shahin Ghafari, Masitah Hasan, Mohamed Kheireddine ArouaAbstract:Nitrates in different water and wastewater streams raised concerns due to severe impacts on human and animal health. Diverse methods are reported to remove nitrate from water streams which almost fail to entirely treat nitrate, except biological Denitrification which is capable of reducing inorganic nitrate compounds to harmless nitrogen gas. Review of numerous studies in biological Denitrification of nitrate containing water resources, aquaculture wastewaters and industrial wastewater confirmed the potential of this method and its flexibility towards the remediation of different concentrations of nitrate. The denitrifiers could be fed with organic and inorganic substrates which have different performances and subsequent advantages or disadvantages. Review of heterotrophic and autotrophic Denitrifications with different food and energy sources concluded that autotrophic denitrifiers are more effective in Denitrification. Autotrophs utilize carbon dioxide and hydrogen as the source of carbon substrate and electron donors, respectively. The application of this method in bio-electro reactors (BERs) has many advantages and is promising. However, this method is not so well established and documented. BERs provide proper environment for simultaneous hydrogen production on cathodes and appropriate consumption by immobilized autotrophs on these cathodes. This survey covers various designs and aspects of BERs and their performances.