Ecosystems Center
Permanent URI for this collection
The Ecosystems Center carries out research in ecosystems that range from the Arctic to the Antarctic, from Brazil to Martha’s Vineyard. In the Alaskan Arctic, scientists study the effect of warmer temperatures on tundra, stream and lake ecosystems. On the Arctic rivers of Eurasia, they measure how freshwater discharge is changing as the climate warms. On the western Antarctic peninsula, research focuses on the responses of the marine coastal ecosystem to rapid climate warming. In the western Amazon in Brazil, researchers assess how much the clearing of tropical forests will change the amount of greenhouse gas released into the atmosphere, while on the island of Martha’s Vineyard, scientists used controlled burns to restore coastal ecosystems. In central Massachusetts and in Abisko, Sweden, soil warming experiments are conducted to assess the forest’s response to climate warming. In northeastern Massachusetts, scientists study how changes in rural land use and urban development affect the flow of nutrients and organic matter into New England estuaries. In Boston Harbor, they measure the transfer of nitrogen from sediments to the water column as the harbor recovers from decades of sewage addition.
Browse
Browsing Ecosystems Center by Subject "Denitrification"
Results Per Page
Sort Options
-
ArticleDenitrification across landscapes and waterscapes : a synthesis(Ecological Society of America, 2006-12) Seitzinger, Sybil P. ; Harrison, John A. ; Bohlke, John K. ; Bouwman, A. F. ; Lowrance, R. Richard ; Peterson, Bruce J. ; Tobias, Craig R. ; Van Drecht, G.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 N·km−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.
-
ArticleDenitrification and total nitrate uptake in streams of a tropical landscape(Ecological Society of America, 2010-12) Potter, Jody D. ; McDowell, William H. ; Merriam, J. L. ; Peterson, Bruce J. ; Thomas, Suzanne M.Rapid increases in nitrogen (N) loading are occurring in many tropical watersheds, but the fate of N in tropical streams is not well documented. Rates of nitrate uptake and denitrification were measured in nine tropical low-order streams with contrasting land use as part of the Lotic Intersite Nitrogen eXperiment II (LINX II) in Puerto Rico using short term (24-hour) additions of K15NO3 and NaBr. Background nitrate concentrations ranged from 105 to 997 μg N/L, and stream nitrate uptake lengths were long, varying from 315 to 8480 m (median of 1200 m). Other indices of nitrate uptake (mass transfer coefficient, Vf [cm/s], and whole-stream nitrate uptake rate, U [μg N·m−2·s−1]) were low in comparison to other regions and were related to chemical, biological, and physical parameters. Denitrification rates were highly variable (0–133 μg N·m−2·min−1; median = 15 μg N·m−2·min−1), were dominated by the end product N2 (rather than N2O), and were best predicted by whole-stream respiration rates and stream NO3 concentration. Denitrification accounted for 1–97% of nitrate uptake with five of nine streams having 35% or more of nitrate uptake via denitrification, showing that denitrification is a substantial sink for nitrate in tropical streams. Whole-stream nitrate uptake and denitrification in our study streams closely followed first-order uptake kinetics, indicating that NO3 uptake is limited by delivery of substrate (NO3) to the organisms involved in uptake or denitrification. In the context of whole-catchment nitrogen budgets, our finding that in-stream denitrification results in lower proportional production of N2O than terrestrial denitrification suggests that small streams can be viewed as the preferred site of denitrification in a watershed in order to minimize greenhouse gas N2O emissions. Conservation of small streams is thus critical in tropical ecosystem management.
-
PreprintEffects of experimental warming and carbon addition on nitrate reduction and respiration in coastal sediments( 2015-04) Brin, Lindsay D. ; Giblin, Anne E. ; Rich, Jeremy J.Climate change may have differing effects on microbial processes that control coastal N availability. We conducted a microcosm experiment to explore effects of warming and carbon availability on nitrate reduction pathways in marine sediments. Sieved continental shelf sediments were incubated for 12 weeks under aerated seawater amended with nitrate (~50 μM), at winter (4°C) or summer (17°C) temperatures, with or without biweekly particulate organic C additions. Treatments increased diffusive oxygen consumption as expected, with somewhat higher effects of C addition compared to warming. Combined warming and C addition had the strongest effect on nitrate flux across the sediment water interface, with a complete switch early in the experiment from influx to sustained efflux. Supporting this result, vial incubations with added 15N-nitrate indicated that C addition stimulated potential rates of dissimilatory nitrate reduction to ammonium (DNRA), but not denitrification. Overall capacity for both denitrification and DNRA was reduced in warmed treatments, possibly reflecting C losses due to increased respiration with warming. Anammox potential rates were much lower than DNRA or denitrification, and were slightly negatively affected by warming or C addition. Overall, results indicate that warming and C addition increased ammonium production through remineralization and possibly DNRA. This stimulated nitrate production through nitrification, but without a comparable increase in nitrate consumption through denitrification. The response to C of potential DNRA rates over denitrification, along with a switch to nitrate efflux, raises the possibility that DNRA is an important and previously overlooked source of internal N cycling in shelf sediments.
-
ArticleEmerging wetlands from river diversions can sustain high denitrification rates in a Coastal Delta(American Geophysical Union, 2021-03-31) Upreti, Kiran ; Rivera-Monroy, Victor H. ; Maiti, Kanchan ; Giblin, Anne E. ; Geaghan, James P.It is assumed that to treat excess NO3− high soil organic matter content (%OM) is required to maintain high denitrification rates in natural or restored wetlands. However, this excess also represents a risk by increasing soil decomposition rates triggering peat collapse and wetland fragmentation. Here, we evaluated the role of %OM and temperature interactions controlling denitrification rates in eroding (Barataria Bay-BLC) and emerging (Wax Lake Delta-WLD) deltaic regions in coastal Louisiana using the isotope pairing (IPT) and N2:Ar techniques. We also assessed differences between total (direct denitrification + coupled nitrification-denitrification) and net (total denitrification minus nitrogen fixation) denitrification rates in benthic and wetland habitats with contrasting %OM and bulk density (BD). Sediment (benthic) and soil (wetland) cores were collected during summer, spring, and winter (2015–2016) and incubated at close to in-situ temperatures (30°C, 20°C, and 10°C, respectively). Denitrification rates were linearly correlated with temperature; maximum mean rates ranged from 40.1–124.1 μmol m−2 h−1 in the summer with lower rates (<26.2 ± 5.3 μmol m−2 h−1) in the winter seasons. Direct denitrification was higher than coupled denitrification in all seasons. Denitrification rates were higher in WLD despite lower %OM, lower total N concentration, and higher BD in wetland soils. Therefore, in environments with low carbon availability, high denitrification rates can be sustained as long as NO3− concentrations are high (>30 μM) and water temperature is >10°C. In coastal Louisiana, substrates under these regimes are represented by emergent supra-tidal flats or land created by sediment diversions under oligohaline conditions (<1 ppt).
-
PreprintMethods for measuring denitrification : diverse approaches to a difficult problem( 2005-07-15) Groffman, Peter M. ; Altabet, Mark A. ; Bohlke, John K. ; Butterbach-Bahl, Klaus ; David, Mark B. ; Firestone, Mary K. ; Giblin, Anne E. ; Kana, Todd M. ; Nielsen, Lars Peter ; Voytek, Mary A.Denitrification, the reduction of the nitrogen (N) oxides, nitrate (NO3-) and nitrite (NO2-), to the gases nitric oxide (NO), nitrous oxide (N2O) and dinitrogen (N2), is important to primary production, water quality and the chemistry and physics of the atmosphere at ecosystem, landscape, regional and global scales. Unfortunately, this process is very difficult to measure, and existing methods are problematic for different reasons in different places at different times. In this paper, we review the major approaches that have been taken to measure denitrification in terrestrial and aquatic environments and discuss the strengths, weaknesses and future prospects for the different methods. Methodological approaches covered include; 1) acetylene-based methods, 2) 15N tracers, 3) direct N2 quantification, 4) N2/Ar ratio quantification, 5) mass balance approaches, 6) stoichiometric approaches, 7) methods based on stable isotopes, 8) in situ gradients with atmospheric environmental tracers and 9) molecular approaches. Our review makes it clear that the prospects for improved quantification of denitrification vary greatly in different environments and at different scales. While current methodology allows for the production of accurate estimates of denitrification at scales relevant to water and air quality and ecosystem fertility questions in some systems (e.g., aquatic sediments, well defined aquifers), methodology for other systems, especially upland terrestrial areas, still needs development. Comparison of mass balance and stoichiometric approaches that constrain estimates of denitrification at large scales with point measurements (made using multiple methods), in multiple systems, is likely to propel more improvement in denitrification methods over the next few years.
-
PreprintModeling denitrification in aquatic sediments( 2008-10-10) Fennel, Katja ; Brady, Damian C. ; DiToro, Dominic ; Fulweiler, Robinson W. ; Gardner, Wayne S. ; Giblin, Anne E. ; McCarthy, Mark J. ; Rao, Alexandra ; Seitzinger, Sybil P. ; Thouvenot-Korppoo, Marie ; Tobias, Craig R.Sediment denitrification is a major pathway of fixed nitrogen loss from aquatic systems. Due to technical difficulties in measuring this process and its spatial and temporal variability, estimates of local, regional and global denitrification have to rely on a combination of measurements and models. Here we review approaches to describing denitrification in aquatic sediments, ranging from mechanistic diagenetic models to empirical parameterizations of nitrogen fluxes across the sediment-water interface. We also present a compilation of denitrification measurements and ancillary data for different aquatic systems, ranging from freshwater to marine. Based on this data compilation we reevaluate published parameterizations of denitrification. We recommend that future models of denitrification use (1) a combination of mechanistic diagenetic models and measurements where bottom waters are temporally hypoxic or anoxic, and (2) the much simpler correlations between denitrification and sediment oxygen consumption for oxic bottom waters. For our data set, inclusion of bottom water oxygen and nitrate concentrations in a multivariate regression did not improve the statistical fit.
-
ArticleNitrous oxide nitrification and denitrification 15N enrichment factors from Amazon forest soils(Ecological Society of America, 2006-12) Perez, Tibisay ; Garcia-Montiel, Diana ; Trumbore, Susan E. ; Tyler, Stanley ; de Camargo, Plinio ; Moreira, Marcelo ; Piccolo, Marisa C. ; Cerri, Carlos C.The isotopic signatures of 15N and 18O in N2O emitted from tropical soils vary both spatially and temporally, leading to large uncertainty in the overall tropical source signature and thereby limiting the utility of isotopes in constraining the global N2O budget. Determining the reasons for spatial and temporal variations in isotope signatures requires that we know the isotope enrichment factors for nitrification and denitrification, the two processes that produce N2O in soils. We have devised a method for measuring these enrichment factors using soil incubation experiments and report results from this method for three rain forest soils collected in the Brazilian Amazon: soil with differing sand and clay content from the Tapajos National Forest (TNF) near Santarém, Pará, and Nova Vida Farm, Rondônia. The 15N enrichment factors for nitrification and denitrification differ with soil texture and site: −111‰ ± 12‰ and −31‰ ± 11‰ for a clay-rich Oxisol (TNF), −102‰ ± 5‰ and −45‰ ± 5‰ for a sandier Ultisol (TNF), and −10.4‰ ± 3.5‰ (enrichment factor for denitrification) for another Ultisol (Nova Vida) soil, respectively. We also show that the isotopomer site preference (δ15Nα − δ15Nβ, where α indicates the central nitrogen atom and β the terminal nitrogen atom in N2O) may allow differentiation between processes of production and consumption of N2O and can potentially be used to determine the contributions of nitrification and denitrification. The site preferences for nitrification and denitrification from the TNF-Ultisol incubated soils are: 4.2‰ ± 8.4‰ and 31.6‰ ± 8.1‰, respectively. Thus, nitrifying and denitrifying bacteria populations under the conditions of our study exhibit significantly different 15N site preference fingerprints. Our data set strongly suggests that N2O isotopomers can be used in concert with traditional N2O stable isotope measurements as constraints to differentiate microbial N2O processes in soil and will contribute to interpretations of the isotopic site preference N2O values found in the free troposphere.
-
ArticleNutrient gradients in Panamanian estuaries : effects of watershed deforestation, rainfall, upwelling, and within-estuary transformations(Inter-Research, 2013-05-22) Valiela, Ivan ; Giblin, Anne E. ; Barth-Jensen, Coralie ; Harris, Carolynn ; Stone, Thomas A. ; Fox, Sophia E. ; Crusius, JohnTo test whether deforestation of tropical forests alters coupling of watersheds, estuaries, and coastal waters, we measured nutrients in 8 watershed-estuarine systems on the Pacific coast of Panama where watershed forest cover ranged from 23 to 92%. Watersheds with greater forest cover discharged larger dissolved inorganic nitrogen concentrations and higher N/P into estuary headwaters. As freshwater mixed with seawater down-estuary, within-estuary biogeochemical processes erased the imprint of watershed deforestation, increased ammonium, lowered nitrate concentrations, and otherwise altered down-estuary water column composition. As estuarine water left mangrove estuaries, ammonium, nitrate, and phosphate, but not dissolved organic nitrogen, were exported to receiving near-shore waters. Mangrove estuaries in this region thus provide important ecological services, by uncoupling coastal waters from changes in terrestrial land covers, as well as by subsidizing adjoined receiving coastal waters by providing nutrients. The pattern of land-sea coupling and exports was disrupted during La Niña-influenced conditions. In one instance when La Niña conditions led to upwelling of deeper layers, high concentrations of marine-derived ammonium were inserted into estuaries. In another instance, La Niña-associated high rainfall diluted nutrient concentrations within estuaries and lowered salinity regionally, and the fresher upper layer impaired coastal upwelling. Regional rainfall has increased during the last decade. If La Niña rainfall continues to increase, disruptions of current land-estuary-sea couplings may become more frequent, with potentially significant changes in nutrient cycles and ecological services in these coupled ecosystems.
-
ArticlePredicting microbial nitrate reduction pathways in coastal sediments(Inter-Research, 2014-01-23) Algar, Christopher K. ; Vallino, Joseph J.We present an ecosystem model that describes the biogeochemistry of a sediment nitrate reducing microbial community. In the model, the microbial community is represented as a distributed metabolic network. Biogeochemical pathways are controlled through the synthesis and allocation of biological structure that serves to catalyze each process. Allocation is determined by way of a thermodynamically constrained optimization according to the principle of maximum entropy production (MEP). According to the MEP principle, ecosystems will organize so as to maximize the dissipation of free energy based upon the available resources (nutrients and electron donors and acceptors). In the model, 3 nitrate reduction pathways, viz. heterotrophic denitrification, anammox, and dissimilatory nitrate reduction to ammonium, compete for electron acceptors (nitrate and nitrite). The model predicts switches in the dominant nitrate cycling pathways based upon the ratio of carbon to nitrate supply. An advantage of this approach over a traditional organism-centric kinetic approach is that the Monod growth parameters, maximum uptake rate (νmax), and half saturation (kM) constants are determined during the optimization procedure as opposed to parameters specified a priori. Such a model is therefore useful for applications where these kinetic parameters are unknown and difficult to measure, such as the marine subsurface, or when ecosystems undergo large-scale environmental perturbations resulting in shifts in the dominant organisms.
-
ArticleResponse of benthic metabolism and nutrient cycling to reductions in wastewater loading to Boston Harbor, USA(Elsevier, 2014-10-02) Tucker, Jane ; Giblin, Anne E. ; Hopkinson, Charles S. ; Kelsey, Samuel W. ; Howes, Brian L.We describe the long-term response of benthic metabolism in depositional sediments of Boston Harbor, MA, to large reductions in organic matter and nutrient loading. Although Boston Harbor received very high loadings of nutrients and solids it differs from many eutrophic estuaries in that severe hypoxia was prevented by strong tidal flushing. Our study was conducted for 9 years during which a series of improvements to sewage treatment were implemented, followed by 10 years after the culminating step in the clean-up, which was to divert all wastewater effluent offshore. Counter to expectations, sediment oxygen demand and nutrient effluxes initially increased at some stations, reaching some of the highest rates recorded in the literature, and were spatially and temporally quite variable. Early increases were attributed to macrofaunal effects, as sediments at some sites were rapidly colonized by tube-building amphipods, Ampelisca spp., which dominated a dense macrofaunal mat community. As reductions in loading progressed, however, mean rates in oxygen uptake and release of ammonium, nitrate, and phosphate all decreased. At the point of outfall diversion, rates and variability had already decreased substantially. By the end of the study, average oxygen uptake had decreased from 74 to 41 mmol m−2 d−1 and spatial and temporal variability had decreased. Similarly, nutrient fluxes were less than half the rates measured at the start of the project and also less variable. Other evidence of improved conditions included a decrease in the carbon content of sediments at most stations and higher Eh values at all stations, illustrating less reducing conditions. Denitrification also showed an overall decrease from the beginning to the end of the 19-year study, but was highest during the intermediate phases of the cleanup, reaching 9 mmol N m−2 d−1. At the end of the study denitrification averaged for all sites was 2.2 mmol N m−2 d−1, but when compared to current loadings, had become a more important overall sink for N within the harbor. Few long-term examinations of the responses of sediment biogeochemistry to reductions in nutrient and organic matter loading have been reported. Our findings demonstrate that benthic fluxes may respond to reductions in loading in complex ways, and sediments need not represent a long-term legacy that would impede ecosystems recovery.
-
ArticleSeparation of river network–scale nitrogen removal among the main channel and two transient storage compartments(American Geophysical Union, 2011-08-30) Stewart, Robert J. ; Wollheim, Wilfred M. ; Gooseff, Michael N. ; Briggs, Martin A. ; Jacobs, Jennifer M. ; Peterson, Bruce J. ; Hopkinson, Charles S.Transient storage (TS) zones are important areas of dissolved inorganic nitrogen (DIN) processing in rivers. We assessed sensitivities regarding the relative impact that the main channel (MC), surface TS (STS), and hyporheic TS (HTS) have on network denitrification using a model applied to the Ipswich River in Massachusetts, United States. STS and HTS connectivity and size were parameterized using the results of in situ solute tracer studies in first- through fifth-order reaches. DIN removal was simulated in all compartments for every river grid cell using reactivity derived from Lotic Intersite Nitrogen Experiment (LINX2) studies, hydraulic characteristics, and simulated discharge. Model results suggest that although MC-to-STS connectivity is greater than MC-to-HTS connectivity at the reach scale, at basin scales, there is a high probability of water entering the HTS at some point along its flow path through the river network. Assuming our best empirical estimates of hydraulic parameters and reactivity, the MC, HTS, and STS removed approximately 38%, 21%, and 14% of total DIN inputs during a typical base flow period, respectively. There is considerable uncertainty in many of the parameters, particularly the estimates of reaction rates in the different compartments. Using sensitivity analyses, we found that the size of TS is more important for DIN removal processes than its connectivity with the MC when reactivity is low to moderate, whereas TS connectivity is more important when reaction rates are rapid. Our work suggests a network perspective is needed to understand how connectivity, residence times, and reactivity interact to influence DIN processing in hierarchical river systems.
-
PreprintSimilar temperature responses suggest future climate warming will not alter partitioning between denitrification and anammox in temperate marine sediments( 2016-05-09) Brin, Lindsay D. ; Giblin, Anne E. ; Rich, Jeremy J.Removal of biologically available nitrogen (N) by the microbially mediated processes denitrification and anaerobic ammonium oxidation (anammox) affects ecosystem N availability. Although few studies have examined temperature responses of denitrification and anammox, previous work suggests that denitrification could become more important than anammox in response to climate warming. To test this hypothesis, we determined whether temperature responses of denitrification and anammox differed in shelf and estuarine sediments from coastal Rhode Island over a seasonal cycle. The influence of temperature and organic C availability was further assessed in a 12-week laboratory microcosm experiment. Temperature responses, as characterized by thermal optima (Topt) and apparent activation energy (Ea), were determined by measuring potential rates of denitrification and anammox at 31 discrete temperatures ranging from 3 to 59°C. With a few exceptions, Topt and Ea of denitrification and anammox did not differ in Rhode Island sediments over the seasonal cycle. In microcosm sediments, Ea was somewhat lower for anammox compared to denitrification across all treatments. However, Topt did not differ between processes, and neither Ea nor Topt changed with warming or carbon addition. Thus, the two processes behaved similarly in terms of temperature response, and this response was not influenced by warming. This led us to reject the hypothesis that anammox is more cold-adapted than denitrification in our study system. Overall, our study suggests that temperature responses of both processes can be accurately modeled for temperate regions in the future using a single set of parameters, which are likely not to change over the next century as a result of predicted climate warming. We further conclude that climate warming will not directly alter the partitioning of N flow through anammox and denitrification.