40 CFR Table 3 to Subpart Ooo of... - Batch Process Vent Monitoring Requirements

Code of Federal Regulations, 2014 CFR

2014-07-01

...) temperature Continuous records as specified in § 63.1416(d). a Carbon adsorber a Total regeneration steam flow or nitrogen flow, or pressure (gauge or absolute) during carbon bed regeneration cycle(s), and Record the total regeneration steam flow or nitrogen flow, or pressure for each carbon bed regeneration cycle...

Dynamic Kinetics of Nitrogen Cycle in Groundwater-Surface Water Interaction Zone at Hanford Site

NASA Astrophysics Data System (ADS)

Liu, Y.; Liu, C.; Liu, Y.; Xu, F.; Yan, A.; Shi, L.; Zachara, J. M.; Gao, Y.; Qian, W.; Nelson, W.; Fredrickson, J.; Zhong, L.; Thompson, C.

2015-12-01

Nitrogen cycle carried out by microbes is an important geobiological process that has global implications for carbon and nitrogen cycling and climate change. This presentation describes a study of nitrogen cycle in groundwater-surface water interaction zone (GSIZ) at the US Department of Energy's Hanford Site. Groundwater at Hanford sites has long been documented with nitrate contamination. Nearby Columbia River stage changes of up to 3 m every day because of daily discharge fluctuation from upstream Priest Rapids Dam; resulting an exchange of groundwater and surface water in a short time period. Yet, nitrogen cycle in the GSIZ at Hanford Site remains unclear. Column studies have been used to identify nitrogen metabolism pathways and investigate kinetics of nitrogen cycle in groundwater saturated zone, surface water saturated zone, and GSIZ. Functional gene and protein abundances were determined by qPCR and PRISM-SRM (high-pressure, high-resolution separations coupled with intelligent selection and multiplexing for sensitive selected reaction monitoring) to identify key enzymatic reactions and metabolic pathways of nitrogen cycle. The results showed that dissimilatory nitrate reduction to ammonium (DNRA) competed with denitrification under anaerobic conditions, reducing 30% of NO3- to NH4+, a cation strongly retained on the sediments. As dissolved oxygen intruded the anaerobic zone with river water, NH4+ was oxidized to NO3-, increasing the mobility of NO3-. Multiplicative Monod models were established to describe nitrogen cycle in columns fed with O2 depleted synthetic groundwater and O2 saturated synthetic river water, respectively. The two models were then coupled to predict the dynamic kinetics of nitrogen cycle in GSIZ.

Episodic inputs of atmospheric nitrogen to the Sargasso Sea: Contributions to new production and phytoplankton blooms

DOE Office of Scientific and Technical Information (OSTI.GOV)

Michaels, A.F.; Johnson, R.J.; Siegel, D.A.

1993-06-01

This paper compares a recent atmospheric wet deposition record (including all measurable daily rainfall events between October 1988 and June 1991) with concurrent measurements of nitrogen cycling and biomass at the U.S. Joint Global Ocean Flux Study Bermuda Atlantic Time Series Study station. The two data sets, among the most complete synoptic records of atmospheric nitrogen deposition and ocean nitrogen cycling, provide an opportunity to directly assess the importance of nitrogen deposition in the ocean. The results indicate that individual nitrogen wet deposition events are usually small compared to the ambient nitrogen cycle and that only under sustained calm conditionsmore » following large deposition events will nitrogen deposition processes be an important signal for the understanding of ocean biochemistry. 46 refs., 7 figs.« less

Combined Brayton-JT cycles with refrigerants for natural gas liquefaction

NASA Astrophysics Data System (ADS)

Chang, Ho-Myung; Park, Jae Hoon; Lee, Sanggyu; Choe, Kun Hyung

2012-06-01

Thermodynamic cycles for natural gas liquefaction with single-component refrigerants are investigated under a governmental project in Korea, aiming at new processes to meet the requirements on high efficiency, large capacity, and simple equipment. Based upon the optimization theory recently published by the present authors, it is proposed to replace the methane-JT cycle in conventional cascade process with a nitrogen-Brayton cycle. A variety of systems to combine nitrogen-Brayton, ethane-JT and propane-JT cycles are simulated with Aspen HYSYS and quantitatively compared in terms of thermodynamic efficiency, flow rate of refrigerants, and estimated size of heat exchangers. A specific Brayton-JT cycle is suggested with detailed thermodynamic data for further process development. The suggested cycle is expected to be more efficient and simpler than the existing cascade process, while still taking advantage of easy and robust operation with single-component refrigerants.

Nitrogen deposition and cycling across an elevation and vegetation gradient in southern Appalachian forests

Treesearch

Jennifer D. Knoepp; James M. Vose; Wayne T. Swank

2008-01-01

We studied nitrogen (N) cycling pools and processes across vegetation and elevation gradients in. the southern Appalachian Mountains in SE USA. Measurements included bulk deposition input, watershed export, throughfall fluxes, litterfall, soil N pools and processes, and soil solution N. N deposition increased with elevation and ranged from 9.5 to 12.4 kg ha-...

40 CFR Table 3 to Subpart Ooo of... - Batch Process Vent Monitoring Requirements

Code of Federal Regulations, 2012 CFR

2012-07-01

... specified in § 63.1416(d). a Carbon adsorber a Total regeneration steam flow or nitrogen flow, or pressure (gauge or absolute) during carbon bed regeneration cycle(s), and Record the total regeneration steam flow or nitrogen flow, or pressure for each carbon bed regeneration cycle. Temperature of the carbon bed...

40 CFR Table 3 to Subpart Ooo of... - Batch Process Vent Monitoring Requirements

Code of Federal Regulations, 2010 CFR

2010-07-01

... specified in § 63.1416(d). a Carbon adsorber a Total regeneration steam flow or nitrogen flow, or pressure (gauge or absolute) during carbon bed regeneration cycle(s), and Record the total regeneration steam flow or nitrogen flow, or pressure for each carbon bed regeneration cycle. Temperature of the carbon bed...

40 CFR Table 3 to Subpart Ooo of... - Batch Process Vent Monitoring Requirements

Code of Federal Regulations, 2011 CFR

2011-07-01

... specified in § 63.1416(d). a Carbon adsorber a Total regeneration steam flow or nitrogen flow, or pressure (gauge or absolute) during carbon bed regeneration cycle(s), and Record the total regeneration steam flow or nitrogen flow, or pressure for each carbon bed regeneration cycle. Temperature of the carbon bed...

Development of soil properties and nitrogen cycling in created wetlands

USGS Publications Warehouse

Wolf, K.L.; Ahn, C.; Noe, G.B.

2011-01-01

Mitigation wetlands are expected to compensate for the loss of structure and function of natural wetlands within 5–10 years of creation; however, the age-based trajectory of development in wetlands is unclear. This study investigates the development of coupled structural (soil properties) and functional (nitrogen cycling) attributes of created non-tidal freshwater wetlands of varying ages and natural reference wetlands to determine if created wetlands attain the water quality ecosystem service of nitrogen (N) cycling over time. Soil condition component and its constituents, gravimetric soil moisture, total organic carbon, and total N, generally increased and bulk density decreased with age of the created wetland. Nitrogen flux rates demonstrated age-related patterns, with younger created wetlands having lower rates of ammonification, nitrification, nitrogen mineralization, and denitrification potential than older created wetlands and natural reference wetlands. Results show a clear age-related trajectory in coupled soil condition and N cycle development, which is essential for water quality improvement. These findings can be used to enhance N processing in created wetlands and inform the regulatory evaluation of mitigation wetlands by identifying structural indicators of N processing performance.

The microbial nitrogen-cycling network.

PubMed

Kuypers, Marcel M M; Marchant, Hannah K; Kartal, Boran

2018-05-01

Nitrogen is an essential component of all living organisms and the main nutrient limiting life on our planet. By far, the largest inventory of freely accessible nitrogen is atmospheric dinitrogen, but most organisms rely on more bioavailable forms of nitrogen, such as ammonium and nitrate, for growth. The availability of these substrates depends on diverse nitrogen-transforming reactions that are carried out by complex networks of metabolically versatile microorganisms. In this Review, we summarize our current understanding of the microbial nitrogen-cycling network, including novel processes, their underlying biochemical pathways, the involved microorganisms, their environmental importance and industrial applications.

Quantifying the Global Nitrous Oxide Emissions Using a Trait-based Biogeochemistry Model

NASA Astrophysics Data System (ADS)

Zhuang, Q.; Yu, T.

2017-12-01

Nitrogen is an essential element for the global biogeochemical cycle. It is a key nutrient for organisms and N compounds including nitrous oxide significantly influence the global climate. The activities of bacteria and archaea are responsible for the nitrification and denitrification in a wide variety of environments, so microbes play an important role in the nitrogen cycle in soils. To date, most existing process-based models treated nitrification and denitrification as chemical reactions driven by soil physical variables including soil temperature and moisture. In general, the effect of microbes on N cycling has not been modeled in sufficient details. Soil organic carbon also affects the N cycle because it supplies energy to microbes. In my study, a trait-based biogeochemistry model quantifying N2O emissions from the terrestrial ecosystems is developed based on an extant process-based model TEM (Terrestrial Ecosystem Model). Specifically, the improvement to TEM includes: 1) Incorporating the N fixation process to account for the inflow of N from the atmosphere to biosphere; 2) Implementing the effects of microbial dynamics on nitrification process; 3) fully considering the effects of carbon cycling on N nitrogen cycling following the principles of stoichiometry of carbon and nitrogen in soils, plants, and microbes. The difference between simulations with and without the consideration of bacterial activity lies between 5% 25% based on climate conditions and vegetation types. The trait based module allows a more detailed estimation of global N2O emissions.

Effects of model structural uncertainty on carbon cycle projections: biological nitrogen fixation as a case study

NASA Astrophysics Data System (ADS)

Wieder, William R.; Cleveland, Cory C.; Lawrence, David M.; Bonan, Gordon B.

2015-04-01

Uncertainties in terrestrial carbon (C) cycle projections increase uncertainty of potential climate feedbacks. Efforts to improve model performance often include increased representation of biogeochemical processes, such as coupled carbon-nitrogen (N) cycles. In doing so, models are becoming more complex, generating structural uncertainties in model form that reflect incomplete knowledge of how to represent underlying processes. Here, we explore structural uncertainties associated with biological nitrogen fixation (BNF) and quantify their effects on C cycle projections. We find that alternative plausible structures to represent BNF result in nearly equivalent terrestrial C fluxes and pools through the twentieth century, but the strength of the terrestrial C sink varies by nearly a third (50 Pg C) by the end of the twenty-first century under a business-as-usual climate change scenario representative concentration pathway 8.5. These results indicate that actual uncertainty in future C cycle projections may be larger than previously estimated, and this uncertainty will limit C cycle projections until model structures can be evaluated and refined.

Microbial mediation of biogeochemical cycles revealed by simulation of global changes with soil transplant and cropping

PubMed Central

Zhao, Mengxin; Xue, Kai; Wang, Feng; Liu, Shanshan; Bai, Shijie; Sun, Bo; Zhou, Jizhong; Yang, Yunfeng

2014-01-01

Despite microbes' key roles in driving biogeochemical cycles, the mechanism of microbe-mediated feedbacks to global changes remains elusive. Recently, soil transplant has been successfully established as a proxy to simulate climate changes, as the current trend of global warming coherently causes range shifts toward higher latitudes. Four years after southward soil transplant over large transects in China, we found that microbial functional diversity was increased, in addition to concurrent changes in microbial biomass, soil nutrient content and functional processes involved in the nitrogen cycle. However, soil transplant effects could be overridden by maize cropping, which was attributed to a negative interaction. Strikingly, abundances of nitrogen and carbon cycle genes were increased by these field experiments simulating global change, coinciding with higher soil nitrification potential and carbon dioxide (CO2) efflux. Further investigation revealed strong correlations between carbon cycle genes and CO2 efflux in bare soil but not cropped soil, and between nitrogen cycle genes and nitrification. These findings suggest that changes of soil carbon and nitrogen cycles by soil transplant and cropping were predictable by measuring microbial functional potentials, contributing to a better mechanistic understanding of these soil functional processes and suggesting a potential to incorporate microbial communities in greenhouse gas emission modeling. PMID:24694714

Influence of Dynamic Hydraulic Conditions on Nitrogen Cycling in Column Experiments

NASA Astrophysics Data System (ADS)

Gassen, Niklas; von Netzer, Frederick; Ryabenko, Evgenia; Lüders, Tillmann; Stumpp, Christine

2015-04-01

In order to improve management strategies of agricultural nitrogen input, it is of major importance to further understand which factors influence turnover processes within the nitrogen cycle. Many studies have focused on the fate of nitrate in hydrological systems, but up to date only little is known about the influence of dynamic hydraulic conditions on the fate of nitrate at the soil-groundwater interface. We conducted column experiments with natural sediment and compared a system with a fluctuating water table to systems with different water content and static conditions under the constant input of ammonia into the system. We used hydrochemical methods in order to trace nitrogen species, 15N isotope methods to get information about dominating turnover processes and microbial community analysis in order to connect hydrochemical and microbial information. We found that added ammonia was removed more effectively under dynamic hydraulic conditions than under static conditions. Furthermore, denitrification is the dominant process under saturated, static conditions, while nitrification is more important under unsaturated, static conditions. We conclude that a fluctuating water table creates hot spots where both nitrification and denitrification processes can occur spatially close to each other and therefore remove nitrogen more effectively from the system. Furthermore, the fluctuating water table enhances the exchange of solutes and triggers hot moments of solute turnover. Therefore we conclude that a fluctuating water table can amplify hot spots and trigger hot moments of nitrogen cycling.

Thinking outside the channel: modeling nitrogen cycling in networked river ecosystems

Treesearch

Ashley M. Helton; Geoffrey C. Poole; Judy L. Meyer; Wilfred M. Wollheim; Bruce J. Peterson; Patrick J. Mulholland; Emily S. Bernhardt; Jack A. Stanford; Clay Arango; Linda R. Ashkenas; Lee W. Cooper; Walter K. Dodds; Stanley V. Gregory; Robert O. Hall; Stephen K. Hamilton; Sherri L. Johnson; William H. McDowell; Jody D. Potter; Jennifer L. Tank; Suzanne M. Thomas; H. Maurice Valett; Jackson R. Webster; Lydia Zeglin

2011-01-01

Agricultural and urban development alters nitrogen and other biogeochemical cycles in rivers worldwide. Because such biogeochemical processes cannot be measured empirically across whole river networks, simulation models are critical tools for understanding river-network biogeochemistry. However, limitations inherent in current models restrict our ability to simulate...

40 CFR Table 7 to Subpart Jjj of... - Group 1 Batch Process Vents and Aggregate Batch Vent Streams-Monitoring, Recordkeeping, and...

Code of Federal Regulations, 2012 CFR

2012-07-01

... collected—PR. d,e Carbon Adsorber f a. Total regeneration steam flow or nitrogen flow, or pressure (gauge or absolute) during carbon bed regeneration cycle(s), and 1. Record the total regeneration steam flow or nitrogen flow, or pressure for each carbon bed regeneration cycle.2. Record and report the total...

40 CFR Table 6 to Subpart U of... - Group 1 Batch Front-End Process Vents and Aggregate Batch Vent Streams-Monitoring, Recordkeeping...

Code of Federal Regulations, 2012 CFR

2012-07-01

... collected—PR. d,e Carbon adsorber f a. Total regeneration steam flow or nitrogen flow, or pressure gauge or absolute) during carbon bed regeneration cycle(s), and 1. Record of total regeneration steam flow or nitrogen flow, or pressure for each carbon bed regeneration cycle. 2. Record and report the total...

40 CFR Table 6 to Subpart U of... - Group 1 Batch Front-End Process Vents and Aggregate Batch Vent Streams-Monitoring, Recordkeeping...

Code of Federal Regulations, 2011 CFR

2011-07-01

... collected—PR. d,e Carbon adsorber f a. Total regeneration steam flow or nitrogen flow, or pressure gauge or absolute) during carbon bed regeneration cycle(s), and 1. Record of total regeneration steam flow or nitrogen flow, or pressure for each carbon bed regeneration cycle. 2. Record and report the total...

40 CFR Table 7 to Subpart Jjj of... - Group 1 Batch Process Vents and Aggregate Batch Vent Streams-Monitoring, Recordkeeping, and...

Code of Federal Regulations, 2010 CFR

2010-07-01

... collected—PR. d,e Carbon Adsorber f a. Total regeneration steam flow or nitrogen flow, or pressure (gauge or absolute) during carbon bed regeneration cycle(s), and 1. Record the total regeneration steam flow or nitrogen flow, or pressure for each carbon bed regeneration cycle.2. Record and report the total...

40 CFR Table 6 to Subpart U of... - Group 1 Batch Front-End Process Vents and Aggregate Batch Vent Streams-Monitoring, Recordkeeping...

Code of Federal Regulations, 2013 CFR

2013-07-01

... collected—PR. d,e Carbon adsorber f a. Total regeneration steam flow or nitrogen flow, or pressure gauge or absolute) during carbon bed regeneration cycle(s), and 1. Record of total regeneration steam flow or nitrogen flow, or pressure for each carbon bed regeneration cycle. 2. Record and report the total...

40 CFR Table 6 to Subpart U of... - Group 1 Batch Front-End Process Vents and Aggregate Batch Vent Streams-Monitoring, Recordkeeping...

Code of Federal Regulations, 2010 CFR

2010-07-01

... collected—PR. d,e Carbon adsorber f a. Total regeneration steam flow or nitrogen flow, or pressure gauge or absolute) during carbon bed regeneration cycle(s), and 1. Record of total regeneration steam flow or nitrogen flow, or pressure for each carbon bed regeneration cycle. 2. Record and report the total...

40 CFR Table 7 to Subpart Jjj of... - Group 1 Batch Process Vents and Aggregate Batch Vent Streams-Monitoring, Recordkeeping, and...

Code of Federal Regulations, 2013 CFR

2013-07-01

... collected—PR. d,e Carbon Adsorber f a. Total regeneration steam flow or nitrogen flow, or pressure (gauge or absolute) during carbon bed regeneration cycle(s), and 1. Record the total regeneration steam flow or nitrogen flow, or pressure for each carbon bed regeneration cycle.2. Record and report the total...

40 CFR Table 7 to Subpart Jjj of... - Group 1 Batch Process Vents and Aggregate Batch Vent Streams-Monitoring, Recordkeeping, and...

Code of Federal Regulations, 2011 CFR

2011-07-01

... collected—PR. d,e Carbon Adsorber f a. Total regeneration steam flow or nitrogen flow, or pressure (gauge or absolute) during carbon bed regeneration cycle(s), and 1. Record the total regeneration steam flow or nitrogen flow, or pressure for each carbon bed regeneration cycle.2. Record and report the total...

40 CFR Table 6 to Subpart U of... - Group 1 Batch Front-End Process Vents and Aggregate Batch Vent Streams-Monitoring, Recordkeeping...

Code of Federal Regulations, 2014 CFR

2014-07-01

... collected—PR. d e Carbon adsorber f a. Total regeneration steam flow or nitrogen flow, or pressure gauge or absolute) during carbon bed regeneration cycle(s), and 1. Record of total regeneration steam flow or nitrogen flow, or pressure for each carbon bed regeneration cycle. 2. Record and report the total...

40 CFR Table 7 to Subpart Jjj of... - Group 1 Batch Process Vents and Aggregate Batch Vent Streams-Monitoring, Recordkeeping, and...

Code of Federal Regulations, 2014 CFR

2014-07-01

... collected—PR. d e Carbon Adsorber f a. Total regeneration steam flow or nitrogen flow, or pressure (gauge or absolute) during carbon bed regeneration cycle(s), and 1. Record the total regeneration steam flow or nitrogen flow, or pressure for each carbon bed regeneration cycle.2. Record and report the total...

Influence of moisture regime and tree species composition on nitrogen cycling dynamics in hardwood forests of Mammoth Cave National Park, Kentucky, USA

Treesearch

Eric S. Fabio; Mary A. Arthur; Charles C. Rhoades

2009-01-01

Understanding how natural factors interact across the landscape to influence nitrogen (N) cycling is an important focus in temperate forests because of the great inherent variability in these forests. Site-specific attributes, including local topography, soils, and vegetation, can exert important controls on N processes and retention. Seasonal monitoring of N cycling...

Simulation and statistical analysis for the optimization of nitrogen liquefaction plant with cryogenic Claude cycle using process modeling tool: ASPEN HYSYS

NASA Astrophysics Data System (ADS)

Joshi, D. M.

2017-09-01

Cryogenic technology is used for liquefaction of many gases and it has several applications in food process engineering. Temperatures below 123 K are considered to be in the field of cryogenics. Extreme low temperatures are a basic need for many industrial processes and have several applications, such as superconductivity of magnets, space, medicine and gas industries. Several methods can be used to obtain the low temperatures required for liquefaction of gases. The process of cooling or refrigerating a gas to a temperature below its critical temperature so that liquid can be formed at some suitable pressure, which is below the critical pressure, is the basic liquefaction process. Different cryogenic cycle configurations are designed for getting the liquefied form of gases at different temperatures. Each of the cryogenic cycles like Linde cycle, Claude cycle, Kapitza cycle or modified Claude cycle has its own advantages and disadvantages. The placement of heat exchangers, Joule-Thompson valve and turboexpander decides the configuration of a cryogenic cycle. Each configuration has its own efficiency according to the application. Here, a nitrogen liquefaction plant is used for the analysis purpose. The process modeling tool ASPEN HYSYS can provide a software simulation approach before the actual implementation of the plant in the field. This paper presents the simulation and statistical analysis of the Claude cycle with the process modeling tool ASPEN HYSYS. It covers the technique used to optimize the liquefaction of the plant. The simulation results so obtained can be used as a reference for the design and optimization of the nitrogen liquefaction plant. Efficient liquefaction will give the best performance and productivity to the plant.

The Effect of Temperature on Key Aspects of the Nitrogen Cycle: Comparisons Across Systems

NASA Astrophysics Data System (ADS)

Warren, V.

2016-02-01

The nitrogen cycle sustains life by converting inert di-nitrogen gas (N2) into fixed bio-available forms (e.g. ammonium, nitrate), as well as returning it via gases such as N2 and nitrous oxide (N2O) back into the atmosphere. Recently, the effects of long term warming on key components of the carbon cycle, which is tightly coupled to the nitrogen cycle, have been highlighted but how global warming might systematically affect the balance of the nitrogen cycle is still largely unknown. The effect of long term warming on denitrification and nitrification were investigated using long-term, experimental mesocosm (2006 to present), allowing us to study the effect of warming on natural communities of bacteria involved in these processes. Denitrification activity responded to warming in the short-term in a predictable way, however, long-term moderate warming of 3-5oC (the predicted global increase by the end of the century) increased the specific activity of the sediment and had a pronounced effect on the ratio of N2O to N2. The latter suggesting that with sustained warming, denitrifying bacteria become more efficient at complete denitrification. Molecular analysis of denitrifying communities in our long-term mesocosm experiment also suggested a profound alteration of the communities underlying these differences in process. Similar short-term experiments were carried out on sediments and the water column of the North Eastern Tropical Pacific Oxygen minimum zone (NETP OMZ) including its effect on N2 fixation and here we contrast the findings from those markedly different settings. This research has indicated that we may see similar effects on the nitrogen cycle as we have previously determined in the carbon cycle, with the balance of N-species consumed and created becoming out of balance.

Beyond fossil fuel–driven nitrogen transformations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, Jingguang G.; Crooks, Richard M.; Seefeldt, Lance C.

Nitrogen is fundamental to all of life and many industrial processes. The interchange of nitrogen oxidation states in the industrial production of ammonia, nitric acid, and other commodity chemicals is largely powered by fossil fuels. Here, a key goal of contemporary research in the field of nitrogen chemistry is to minimize the use of fossil fuels by developing more efficient heterogeneous, homogeneous, photo-, and electrocatalytic processes or by adapting the enzymatic processes underlying the natural nitrogen cycle. These approaches, as well as the challenges involved, are discussed in this Review.

Beyond fossil fuel–driven nitrogen transformations

DOE PAGES

Chen, Jingguang G.; Crooks, Richard M.; Seefeldt, Lance C.; ...

2018-05-25

Nitrogen is fundamental to all of life and many industrial processes. The interchange of nitrogen oxidation states in the industrial production of ammonia, nitric acid, and other commodity chemicals is largely powered by fossil fuels. Here, a key goal of contemporary research in the field of nitrogen chemistry is to minimize the use of fossil fuels by developing more efficient heterogeneous, homogeneous, photo-, and electrocatalytic processes or by adapting the enzymatic processes underlying the natural nitrogen cycle. These approaches, as well as the challenges involved, are discussed in this Review.

POPULATION DYNAMICS OF SMALL MAMMALS ACROSS A NITROGEN AMENDED LANDSCAPE

EPA Science Inventory

Biogeochemical alterations of the nitrogen cycle from anthropogenic activities could have significant effects on ecological processes at the population, community and ecosystem levels. Nitrogen additions in grasslands have produced qualitative and quantitative changes in vegetat...

Assessment of watershed scale nitrogen cycling and dynamics by hydrochemical modeling

NASA Astrophysics Data System (ADS)

Onishi, T.; Hiramatsu, K.; Somura, H.

2017-12-01

Nitrogen cycling in terrestrial areas is affecting water quality and ecosystem of aquatic area such as lakes and oceans through rivers. Owing to the intensive researches on nitrogen cycling in each different type of ecosystem, we acquired rich knowledge on nitrogen cycling of each ecosystem. On the other hand, since watershed are composed of many different kinds of ecosystems, nitrogen cycling in a watershed as a complex of these ecosystems is not well quantified. Thus, comprehensive understanding of nitrogen cycling of watersheds by modelling efforts are required. In this study, we attempted to construct hydrochemical model of the Ise Bay watershed to reproduce discharge, TN, and NO3 concentration. The model is based on SWAT (Soil and Water Assessment Tools) model. As anthropogenic impacts related to both hydrological cycling and nitrogen cycling, agricultural water intake/drainage, and domestic water intake/drainage were considered. In addition, fertilizer input to agricultural lands were also considered. Calibration period and validation period are 2004-2006, and 2007-2009, respectively. As a result of calibration using 2000 times LCS (Latin Cubic Sampling) method, discharge of rivers were reproduced fairly well with NS of 0.6-0.8. In contrast, the calibration result of TN and NO3 concentration tended to show overestimate values in spite of considering parameter uncertainties. This implies that unimplemented denitrification processes in the model. Through exploring the results, it is indicated that riparian areas, and agricultural drainages might be important spots for denitrification. Based on the result, we also attempted to evaluate the impact of climate change on nitrogen cycling. Though it is fully explored, this result will also be reported.

Nitrogen cycling models and their application to forest harvesting

DOE Office of Scientific and Technical Information (OSTI.GOV)

Johnson, D.W.; Dale, V.H.

1986-01-01

The characterization of forest nitrogen- (N-) cycling processes by several N-cycling models (FORCYTE, NITCOMP, FORTNITE, and LINKAGES) is briefly reviewed and evaluated against current knowledge of N cycling in forests. Some important processes (e.g., translocation within trees, N dynamics in decaying leaf litter) appear to be well characterized, whereas others (e.g., N mineralization from soil organic matter, N fixation, N dynamics in decaying wood, nitrification, and nitrate leaching) are poorly characterized, primarily because of a lack of knowledge rather than an oversight by model developers. It is remarkable how well the forest models do work in the absence of datamore » on some key processes. For those systems in which the poorly understood processes could cause major changes in N availability or productivity, the accuracy of model predictions should be examined. However, the development of N-cycling models represents a major step beyond the much simpler, classic conceptual models of forest nutrient cycling developed by early investigators. The new generation of computer models will surely improve as research reveals how key nutrient-cycling processes operate.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

King, Paul W; Chen, Jingguang G.; Crooks, Richard M.

Nitrogen is fundamental to all of life and many industrial processes. The interchange of nitrogen oxidation states in the industrial production of ammonia, nitric acid, and other commodity chemicals is largely powered by fossil fuels. A key goal of contemporary research in the field of nitrogen chemistry is to minimize the use of fossil fuels by developing more efficient heterogeneous, homogeneous, photo-, and electrocatalytic processes or by adapting the enzymatic processes underlying the natural nitrogen cycle. These approaches, as well as the challenges involved, are discussed in this Review.

Thermodynamic Modeling and Mechanical Design of a Liquid Nitrogen Vaporization and Pressure Building Device

NASA Astrophysics Data System (ADS)

Leege, Brian J.

The design of a liquid nitrogen vaporization and pressure building device that has zero product waste while recovering some of its stored energy is of interest for the cost reduction of nitrogen for use in industrial processes. Current devices may waste up to 30% of the gaseous nitrogen product by venting it to atmosphere. Furthermore, no attempt is made to recover the thermal energy available in the coldness of the cryogen. A seven step cycle with changing volumes and ambient heat addition is proposed, eliminating all product waste and providing the means of energy recovery from the nitrogen. This thesis discusses the new thermodynamic cycle and modeling as well as the mechanical design and testing of a prototype device. The prototype was able to achieve liquid nitrogen vaporization and pressurization up to 1000 psi, while full cycle validation is ongoing with promising initial results.

Isotopic inferences of ancient biochemistries - Carbon, sulfur, hydrogen, and nitrogen

NASA Technical Reports Server (NTRS)

Schidlowski, M.; Hayes, J. M.; Kaplan, I. R.

1983-01-01

In processes of biological incorporation and subsequent biochemical processing sizable isotope effects occur as a result of both thermodynamic and kinetic fractionations which take place during metabolic and biosynthetic reactions. In this chapter a review is provided of earlier work and recent studies on isotope fractionations in the biogeochemical cycles of carbon, sulfur, hydrogen, and nitrogen. Attention is given to the biochemistry of carbon isotope fractionation, carbon isotope fractionation in extant plants and microorganisms, isotope fractionation in the terrestrial carbon cycle, the effects of diagenesis and metamorphism on the isotopic composition of sedimentary carbon, the isotopic composition of sedimentary carbon through time, implications of the sedimentary carbon isotope record, the biochemistry of sulfur isotope fractionation, pathways of the biogeochemical cycle of nitrogen, and the D/H ratio in naturally occurring materials.

A reappraisal of the terrestrial nitrogen cycle: what can we learn by extracting concepts from Gaia theory?

PubMed

Cresser, Malcolm S; Aitkenhead, Matthew J; Mian, Ishaq A

2008-08-01

Although soil scientists and most environmental scientists are acutely aware of the interactions between the cycling of carbon and nitrogen, for conceptual convenience when portraying the nitrogen cycle in text books the N cycle tends to be considered in isolation from its interactions with the cycling of other elements and water, usually as a snap shot at the current time; the origins of dinitrogen are rarely considered, for example. The authors suggest that Lovelock's Gaia hypothesis provides a useful and stimulating framework for consideration of the terrestrial nitrogen cycle. If it is used, it suggests that urbanization and management of sewage, and intensive animal rearing are probably bigger global issues than nitrogen deposition from fossil fuel combustion, and that plant evolution may be driven by the requirement of locally sustainable and near optimal soil mineral N supply dynamics. This may, in turn, be partially regulating global carbon and oxygen cycles. It is suggested that pollutant N deposition may disrupt this essential natural plant and terrestrial ecosystem evolutionary process, causing biodiversity change. Interactions between the Earth and other bodies in the solar system, and possibly beyond, also need to be considered in the context of the global N cycle over geological time scales. This is because of direct potential impacts on the nitrogen content of the atmosphere, potential long-term impacts of past boloid collisions on plate tectonics and thus on global N cycling via subduction and volcanic emissions, and indirect effects upon C, O and water cycling that all may impact upon the N cycle in the long term.

Atmosphere-Forest Exchange: Important Questions Regarding the Atmosphere's Role in the Delivery of Nutrient Nitrogen and Impacts on Nitrogen and Carbon Cycling

NASA Astrophysics Data System (ADS)

Carroll, M.; Shepson, P. B.; Bertman, S. B.; Sparks, J. P.; Holland, E. A.

2002-12-01

Atmosphere-Forest Exchange: Important Questions Regarding the Atmosphere's Role in the Delivery of Nutrient Nitrogen and Impacts on Nitrogen and Carbon Cycling Atmospheric composition and chemistry directly affect ecosystem nitrogen cycling and indirectly affect ecosystem carbon cycling and storage. Current understanding of atmosphere-forest nitrogen exchange and subsequent impacts is based almost exclusively on nitrogen deposition data obtained from networks using buckets placed in open areas, studies involving inorganic nitrogen, frequently with enhanced N deposition inputs applied only to soils, and that ignore multiple stresses (e.g., the combined effects of aerosols, ozone exposure, elevated CO2, and drought). Current models of nitrogen cycling treat deposited nitrogen (e.g., HNO3 and NO3-) as a permanent sink whereas data appear to indicate that photolytic and heterogeneous chemical processes occurring on surfaces and in dew can result in the re-evolution of gaseous species such as NO and HONO. Similarly, the direct uptake of gaseous nitrogen compounds by foliage has been neglected, compromising conclusions drawn from deposition experiments and ignoring a mechanism that may significantly affect nitrogen cycling and carbon storage, one that may become more significant with future atmospheric and climate change. We hypothesize that the atmosphere plays a significant role in the delivery of nutrient nitrogen to the N-limited mixed hardwood forest at the PROPHET research site at the University of Michigan Biological Station. We assert that a complete understanding of atmosphere- biosphere interactions and feedbacks is required to develop a predictive capability regarding forest response to increasing atmospheric CO2, reactive nitrogen, oxidants, and aerosols, increasing nitrogen and acidic deposition, and anticipated climate change. We further assert that conclusions drawn from studies that are limited to inorganic nitrogen, fertilization of soils, and/or that neglect the role of the canopy (in N uptake and/or remobilization) may not produce a complete understanding of N and C cycling in terrestrial ecosystems, including atmosphere-biosphere interactions and feedbacks. Here, as part of a new PROPHET focus on Biosphere Exchange of Atmospheric Carbon and Odd Nitrogen (BEACON), we identify a number of issues associated with nitrogen limited forest ecosystems and nitrogen saturation and important science questions that require collaborative studies involving the atmospheric and biospheric science communities.

Key ecological responses to nitrogen are altered by climate change

USGS Publications Warehouse

Greaver, T.L.; Clark, C.M.; Compton, J.E.; Vallano, D.; Talhelm, A. F.; Weaver, C.P.; Band, L.E.; Baron, Jill S.; Davidson, E.A.; Tague, C.L.; Felker-Quinn, E.; Lynch, J.A.; Herrick, J.D.; Liu, L.; Goodale, C.L.; Novak, K. J.; Haeuber, R. A.

2016-01-01

Climate change and anthropogenic nitrogen deposition are both important ecological threats. Evaluating their cumulative effects provides a more holistic view of ecosystem vulnerability to human activities, which would better inform policy decisions aimed to protect the sustainability of ecosystems. Our knowledge of the cumulative effects of these stressors is growing, but we lack an integrated understanding. In this Review, we describe how climate change alters key processes in terrestrial and freshwater ecosystems related to nitrogen cycling and availability, and the response of ecosystems to nitrogen addition in terms of carbon cycling, acidification and biodiversity.

Key ecological responses to nitrogen are altered by climate change

NASA Astrophysics Data System (ADS)

Greaver, T. L.; Clark, C. M.; Compton, J. E.; Vallano, D.; Talhelm, A. F.; Weaver, C. P.; Band, L. E.; Baron, J. S.; Davidson, E. A.; Tague, C. L.; Felker-Quinn, E.; Lynch, J. A.; Herrick, J. D.; Liu, L.; Goodale, C. L.; Novak, K. J.; Haeuber, R. A.

2016-09-01

Climate change and anthropogenic nitrogen deposition are both important ecological threats. Evaluating their cumulative effects provides a more holistic view of ecosystem vulnerability to human activities, which would better inform policy decisions aimed to protect the sustainability of ecosystems. Our knowledge of the cumulative effects of these stressors is growing, but we lack an integrated understanding. In this Review, we describe how climate change alters key processes in terrestrial and freshwater ecosystems related to nitrogen cycling and availability, and the response of ecosystems to nitrogen addition in terms of carbon cycling, acidification and biodiversity.

Nitrogen cycle in microbial mats: completely unknown?

NASA Astrophysics Data System (ADS)

Coban, O.; Bebout, B.

2015-12-01

Microbial mats are thought to have originated around 3.7 billion years ago, most likely in the areas around submarine hydrothermal vents, which supplied a source of energy in the form of reduced chemical species from the Earth's interior. Active hydrothermal vents are also believed to exist on Jupiter's moon Europa, Saturn's moon Enceladus, and on Mars, earlier in that planet's history. Microbial mats have been an important force in the maintenance of Earth's ecosystems and the first photosynthesis was also originated there. Microbial mats are believed to exhibit most, if not all, biogeochemical processes that exist in aquatic ecosystems, due to the presence of different physiological groups of microorganisms therein. While most microbially mediated biogeochemical transformations have been shown to occur within microbial mats, the nitrogen cycle in the microbial mats has received very little study in spite of the fact that nitrogen usually limits growth in marine environments. We will present the first results in the determination of a complete nitrogen budget for a photosynthetic microbial mat. Both in situ sources and sinks of nitrogen in photosynthetic microbial mats are being measured using stable isotope techniques. Our work has a particular focus on recently described, but poorly understood, processes, e.g., anammox and dissimilatory nitrate reduction, and an emphasis on understanding the role that nitrogen cycling may play in generating biogenic nitrogen isotopic signatures and biomarker molecules. Measurements of environmental controls on nitrogen cycling should offer insight into the nature of co-evolution of these microbial communities and their planets of origin. Identifying the spatial (microscale) as well as temporal (diel and seasonal) distribution of nitrogen transformations, e.g., rates of nitrification and denitrification, within mats, particularly with respect to the distribution of photosynthetically-produced oxygen, is anticipated. The results of this research, the first results of which will be presented here, will help us to improve our understanding of the cycle of the element most responsible for limiting the production of biomass on Earth and improved an ability to use stable isotopes of nitrogen, and nitrogen containing compounds, in our search for life elsewhere.

[Ammonia-oxidizing archaea and their important roles in nitrogen biogeochemical cycling: a review].

PubMed

Liu, Jing-Jing; Wu, Wei-Xiang; Ding, Ying; Shi, De-Zhi; Chen, Ying-Xu

2010-08-01

As the first step of nitrification, ammonia oxidation is the key process in global nitrogen biogeochemical cycling. So far, the autotrophic ammonia-oxidizing bacteria (AOB) in the beta- and gamma-subgroups of proteobacteria have been considered as the most important contributors to ammonia oxidation, but the recent researches indicated that ammonia-oxidizing archaea (AOA) are widely distributed in various kinds of ecosystems and quantitatively predominant, playing important roles in the global nitrogen biogeochemical cycling. This paper reviewed the morphological, physiological, and ecological characteristics and the molecular phylogenies of AOA, and compared and analyzed the differences and similarities of the ammonia monooxygenase (AMO) and its encoding genes between AOA and AOB. In addition, the potential significant roles of AOA in nitrogen biogeochemical cycling in aquatic and terrestrial ecosystems were summarized, and the future research directions of AOA in applied ecology and environmental protection were put forward.

Consistent differences between tropical forest and savanna nitrogen cycling characteristics as inferred by leaf and soil 15N/14N ratios across three continents

NASA Astrophysics Data System (ADS)

Schrodt, Franziska

2017-04-01

The ratio of 15N:14N can act as important indicator of ecosystem Nitrogen cycling and thus essential key ecosystem processes. Although evidence for general patterns accumulates across the globe, such as foliar δ15N decreasing with increasing mean annual precipitation and decreasing mean annual temperature, as well as forests generally having a more open Nitrogen cycle, a comprehensive understanding of the Nitrogen cycle in tropical ecosystems is still lacking. We present data on foliar and soil δ15N from 62 permanent sampling plots in tropical zones of transition - area where forest and savanna coexists under similar macro climatic conditions - across South America, Africa and Australia. After controlling for phylogeny and location, we show that δ15N relationships in tropical forests and Savannah are consistent irrespective of precipitation.

Integration of a Physically based Distributed Hydrological Model with a Model of Carbon and Nitrogen Cycling: A Case Study at the Luquillo Critical Zone Observatory, Puerto Rico

NASA Astrophysics Data System (ADS)

Bastola, S.; Dialynas, Y. G.; Bras, R. L.; Arnone, E.; Noto, L. V.

2015-12-01

The dynamics of carbon and nitrogen cycles, increasingly influenced by human activities, are the key to the functioning of ecosystems. These cycles are influenced by the composition of the substrate, availability of nitrogen, the population of microorganisms, and by environmental factors. Therefore, land management and use, climate change, and nitrogen deposition patterns influence the dynamics of these macronutrients at the landscape scale. In this work a physically based distributed hydrological model, the tRIBS model, is coupled with a process-based multi-compartment model of the biogeochemical cycle to simulate the dynamics of carbon and nitrogen (CN) in the Mameyes River basin, Puerto Rico. The model includes a wide range of processes that influence the movement, production, alteration of nutrients in the landscape and factors that affect the CN cycling. The tRIBS integrates geomorphological and climatic factors that influence the cycling of CN in soil. Implementing the decomposition module into tRIBS makes the model a powerful complement to a biogeochemical observation system and a forecast tool able to analyze the influences of future changes on ecosystem services. The soil hydrologic parameters of the model were obtained using ranges of published parameters and observed streamflow data at the outlet. The parameters of the decomposition module are based on previously published data from studies conducted in the Luquillio CZO (budgets of soil organic matter and CN ratio for each of the dominant vegetation types across the landscape). Hydrological fluxes, wet depositon of nitrogen, litter fall and its corresponding CN ratio drive the decomposition model. The simulation results demonstrate a strong influence of soil moisture dynamics on the spatiotemporal distribution of nutrients at the landscape level. The carbon in the litter pool and the nitrate and ammonia pool respond quickly to soil moisture content. Moreover, the CN ratios of the plant litter have significant influence in the dynamics of CN cycling.

The Nitrogen Cycle Before the Rise of Oxygen

NASA Astrophysics Data System (ADS)

Ward, L. M.; Hemp, J.; Fischer, W. W.

2016-12-01

The nitrogen cycle on Earth today is driven by a complex network of microbially-mediated transformations. Atmospheric N2 is fixed into biologically available forms that can either be incorporated into biomass or utilized for bioenergetic redox reactions. The cycle is kept in balance by the return of fixed nitrogen to the atmospheric N2 pool by anammox and denitrification. The early evolution and history of the nitrogen cycle is not well resolved, particularly before the evolution of oxygenic photosynthesis and rise of atmospheric oxygen ca. 2.3 Gya. Ammonia oxidation is a biochemically difficult reaction requiring activation of ammonia using O2 or oxidized nitrogen species that are produced using O2. Before the rise of oxygen, when O2 was largely unavailable, nitrification could not proceed, trapping fixed nitrogen in reduced forms such as ammonia and biomass. Without production of nitrite and nitrate, anammox and denitrification could not occur, preventing return of fixed nitrogen to the N2 pool and leaving the nitrogen cycle unclosed. While it has been hypothesized that ammonia oxidation could be driven anaerobically by processes such as phototrophy or iron reduction, these metabolisms have not been recovered in extant microorganisms, and would require complex unknown biochemical mechanisms. Furthermore, phylogenetic data for the key organisms and biochemical pathways involved in denitrification and anammox suggest that these metabolisms postdate the rise of oxygen. This is particularly clear for steps utilizing enzymes in the Heme-Copper Oxidoreductase superfamily, which appear to have originally evolved for O2 reduction at non-negligible substrate concentrations. Together, this suggests that the Archean nitrogen cycle was not closed, and that nitrogen fixed to reduced forms—either through biological nitrogen fixation or abiotic processes—was not easily returned to the atmospheric N2 pool. In principle, this could have stripped the atmosphere of N2 over timescales of hundreds of Myr, which is consistent with recent paleopressure estimates that suggest < 0.5 bar by late Archean time. The modern, N2-rich atmosphere and (largely) closed biological nitrogen cycle may therefore not have evolved until Proterozoic time, after the rise of oxygen.

Operation and model description of a sequencing batch reactor treating reject water for biological nitrogen removal via nitrite.

PubMed

Dosta, J; Galí, A; Benabdallah El-Hadj, T; Macé, S; Mata-Alvarez, J

2007-08-01

The aim of this study was the operation and model description of a sequencing batch reactor (SBR) for biological nitrogen removal (BNR) from a reject water (800-900 mg NH(4)(+)-NL(-1)) from a municipal wastewater treatment plant (WWTP). The SBR was operated with three cycles per day, temperature 30 degrees C, SRT 11 days and HRT 1 day. During the operational cycle, three alternating oxic/anoxic periods were performed to avoid alkalinity restrictions. Oxygen supply and working pH range were controlled to achieve the BNR via nitrite, which makes the process more economical. Under steady state conditions, a total nitrogen removal of 0.87 kg N (m(3)day)(-1) was reached. A four-step nitrogen removal model was developed to describe the process. This model enlarges the IWA activated sludge models for a more detailed description of the nitrogen elimination processes and their inhibitions. A closed intermittent-flow respirometer was set up for the estimation of the most relevant model parameters. Once calibrated, model predictions reproduced experimental data accurately.

Nitrogen Cycling throughout Secondary Succession following Agricultural Disturbance in North-Central Virginia

NASA Astrophysics Data System (ADS)

Parisien, A.; Epstein, H. E.

2017-12-01

While much is known about the carbon cycle during succession that follows agricultural disturbance, less understood are the dynamics of the nitrogen cycle throughout secondary succession, and how plant-available nitrogen may or may not limit vegetation transitions and net primary productivity over time. Two chronosequences at the Blandy Experimental Farm in Boyce, north-central Virginia were examined to elucidate the complexities of the nitrogen cycle over a temporal successional gradient. Each chronosequence consists of one early, one mid, and one late secondary successional field ( 15 years, 30 years, and 100 years post agricultural abandonment, respectively). Five 10x10 m plots were established in each of the 6 fields for a total of 30 plots. Total soil nitrogen (and carbon) data were collected from soils to 30 cm depth at 10-cm intervals, and net nitrogen mineralization and nitrification were estimated using an in situ soil core with anion-cation exchange resin bag technique. Previous studies of carbon cycling at this location have indicated relatively constant soil CO2 efflux of approximately 1100 g C/m2, as well as increasing net primary production and therefore net ecosystem production, with time since abandonment. In addition, soil C and N, and the soil C:N ratio have been shown to increase from the early to late successional plots. Our current study marks the first comprehensive examination of soil nitrogen dynamics including mineralization and nitrification over a successional gradient at Blandy Farm. A thorough understanding of nitrogen dynamics during secondary succession is especially important in the southeastern United States, where a large portion of previously cultivated land has been abandoned over the past century, due to advances in farming efficiency and the move westward to more fertile soils. Much of the southeastern U.S. is now undergoing secondary succession, and quality data on the dynamics of nitrogen cycling during this procession can help guide future land management decisions and carbon cycling predictions.

Improved system integration for integrated gasification combined cycle (IGCC) systems.

PubMed

Frey, H Christopher; Zhu, Yunhua

2006-03-01

Integrated gasification combined cycle (IGCC) systems are a promising technology for power generation. They include an air separation unit (ASU), a gasification system, and a gas turbine combined cycle power block, and feature competitive efficiency and lower emissions compared to conventional power generation technology. IGCC systems are not yet in widespread commercial use and opportunities remain to improve system feasibility via improved process integration. A process simulation model was developed for IGCC systems with alternative types of ASU and gas turbine integration. The model is applied to evaluate integration schemes involving nitrogen injection, air extraction, and combinations of both, as well as different ASU pressure levels. The optimal nitrogen injection only case in combination with an elevated pressure ASU had the highest efficiency and power output and approximately the lowest emissions per unit output of all cases considered, and thus is a recommended design option. The optimal combination of air extraction coupled with nitrogen injection had slightly worse efficiency, power output, and emissions than the optimal nitrogen injection only case. Air extraction alone typically produced lower efficiency, lower power output, and higher emissions than all other cases. The recommended nitrogen injection only case is estimated to provide annualized cost savings compared to a nonintegrated design. Process simulation modeling is shown to be a useful tool for evaluation and screening of technology options.

Fate and Transport of Nitrogen and Carbon with Decomposition of Organic Matter in a Reduced Paddy Field Based on a Coupled Nitrogen-Carbon Cycling Model Using the HP1 Code

NASA Astrophysics Data System (ADS)

Toride, N.; Matsuoka, K.

2017-12-01

In order to predict the fate and transport of nitrogen in a reduced paddy field as a result of decomposition of organic matter, we implemented within the PHREEQC program a modified coupled carbon and nitrogen cycling model based on the LEACHM code. SOM decay processes from organic carbon (Org-C) to biomass carbon (Bio-C), humus carbon (Hum-C), and carbon dioxide (CO2) were described using first-order kinetics. Bio-C was recycled into the organic pool. When oxygen was available in an aerobic condition, O2 was used to produce CO2 as an electron accepter. When O2 availability is low, other electron acceptors such as NO3-, Mn4+, Fe3+, SO42-, were used depending on the redox potential. Decomposition of Org-N was related to the carbon cycle using the C/N ratio. Mineralization and immobilization were determined based on available NH4-N and the nitrogen demand for the formation of biomass and humus. Although nitrification was independently described with the first-order decay process, denitrification was linked with the SOM decay since NO3- was an electron accepter for the CO2 production. Proton reactions were coupled with the nitrification from NH4+ to NO3-, and the ammonium generation from NH3 to NH4+. Furthermore, cation and anion exchange reactions were included with the permanent negative charges and the pH dependent variable charges. The carbon and nitrogen cycling model described with PHREEQC was linked with HYDRUS-1D using the HP1 code. Various nitrogen and carbon transport scenarios were demonstrated for the application of organic matter to a saturated paddy soil.

Beyond fossil fuel-driven nitrogen transformations.

PubMed

Chen, Jingguang G; Crooks, Richard M; Seefeldt, Lance C; Bren, Kara L; Bullock, R Morris; Darensbourg, Marcetta Y; Holland, Patrick L; Hoffman, Brian; Janik, Michael J; Jones, Anne K; Kanatzidis, Mercouri G; King, Paul; Lancaster, Kyle M; Lymar, Sergei V; Pfromm, Peter; Schneider, William F; Schrock, Richard R

2018-05-25

Nitrogen is fundamental to all of life and many industrial processes. The interchange of nitrogen oxidation states in the industrial production of ammonia, nitric acid, and other commodity chemicals is largely powered by fossil fuels. A key goal of contemporary research in the field of nitrogen chemistry is to minimize the use of fossil fuels by developing more efficient heterogeneous, homogeneous, photo-, and electrocatalytic processes or by adapting the enzymatic processes underlying the natural nitrogen cycle. These approaches, as well as the challenges involved, are discussed in this Review. Copyright © 2018 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works.

Metagenomic analysis of nitrogen and methane cycling in the Arabian Sea oxygen minimum zone.

PubMed

Lüke, Claudia; Speth, Daan R; Kox, Martine A R; Villanueva, Laura; Jetten, Mike S M

2016-01-01

Oxygen minimum zones (OMZ) are areas in the global ocean where oxygen concentrations drop to below one percent. Low oxygen concentrations allow alternative respiration with nitrate and nitrite as electron acceptor to become prevalent in these areas, making them main contributors to oceanic nitrogen loss. The contribution of anammox and denitrification to nitrogen loss seems to vary in different OMZs. In the Arabian Sea, both processes were reported. Here, we performed a metagenomics study of the upper and core zone of the Arabian Sea OMZ, to provide a comprehensive overview of the genetic potential for nitrogen and methane cycling. We propose that aerobic ammonium oxidation is carried out by a diverse community of Thaumarchaeota in the upper zone of the OMZ, whereas a low diversity of Scalindua-like anammox bacteria contribute significantly to nitrogen loss in the core zone. Aerobic nitrite oxidation in the OMZ seems to be performed by Nitrospina spp. and a novel lineage of nitrite oxidizing organisms that is present in roughly equal abundance as Nitrospina. Dissimilatory nitrate reduction to ammonia (DNRA) can be carried out by yet unknown microorganisms harbouring a divergent nrfA gene. The metagenomes do not provide conclusive evidence for active methane cycling; however, a low abundance of novel alkane monooxygenase diversity was detected. Taken together, our approach confirmed the genomic potential for an active nitrogen cycle in the Arabian Sea and allowed detection of hitherto overlooked lineages of carbon and nitrogen cycle bacteria.

Metagenomic analysis of nitrogen and methane cycling in the Arabian Sea oxygen minimum zone

PubMed Central

Kox, Martine A.R.; Villanueva, Laura; Jetten, Mike S.M.

2016-01-01

Oxygen minimum zones (OMZ) are areas in the global ocean where oxygen concentrations drop to below one percent. Low oxygen concentrations allow alternative respiration with nitrate and nitrite as electron acceptor to become prevalent in these areas, making them main contributors to oceanic nitrogen loss. The contribution of anammox and denitrification to nitrogen loss seems to vary in different OMZs. In the Arabian Sea, both processes were reported. Here, we performed a metagenomics study of the upper and core zone of the Arabian Sea OMZ, to provide a comprehensive overview of the genetic potential for nitrogen and methane cycling. We propose that aerobic ammonium oxidation is carried out by a diverse community of Thaumarchaeota in the upper zone of the OMZ, whereas a low diversity of Scalindua-like anammox bacteria contribute significantly to nitrogen loss in the core zone. Aerobic nitrite oxidation in the OMZ seems to be performed by Nitrospina spp. and a novel lineage of nitrite oxidizing organisms that is present in roughly equal abundance as Nitrospina. Dissimilatory nitrate reduction to ammonia (DNRA) can be carried out by yet unknown microorganisms harbouring a divergent nrfA gene. The metagenomes do not provide conclusive evidence for active methane cycling; however, a low abundance of novel alkane monooxygenase diversity was detected. Taken together, our approach confirmed the genomic potential for an active nitrogen cycle in the Arabian Sea and allowed detection of hitherto overlooked lineages of carbon and nitrogen cycle bacteria. PMID:27077014

PEATBOG: a biogeochemical model for analyzing coupled carbon and nitrogen dynamics in northern peatlands

NASA Astrophysics Data System (ADS)

Wu, Y.; Blodau, C.

2013-08-01

Elevated nitrogen deposition and climate change alter the vegetation communities and carbon (C) and nitrogen (N) cycling in peatlands. To address this issue we developed a new process-oriented biogeochemical model (PEATBOG) for analyzing coupled carbon and nitrogen dynamics in northern peatlands. The model consists of four submodels, which simulate: (1) daily water table depth and depth profiles of soil moisture, temperature and oxygen levels; (2) competition among three plants functional types (PFTs), production and litter production of plants; (3) decomposition of peat; and (4) production, consumption, diffusion and export of dissolved C and N species in soil water. The model is novel in the integration of the C and N cycles, the explicit spatial resolution belowground, the consistent conceptualization of movement of water and solutes, the incorporation of stoichiometric controls on elemental fluxes and a consistent conceptualization of C and N reactivity in vegetation and soil organic matter. The model was evaluated for the Mer Bleue Bog, near Ottawa, Ontario, with regards to simulation of soil moisture and temperature and the most important processes in the C and N cycles. Model sensitivity was tested for nitrogen input, precipitation, and temperature, and the choices of the most uncertain parameters were justified. A simulation of nitrogen deposition over 40 yr demonstrates the advantages of the PEATBOG model in tracking biogeochemical effects and vegetation change in the ecosystem.

PEATBOG: a biogeochemical model for analyzing coupled carbon and nitrogen dynamics in northern peatlands

NASA Astrophysics Data System (ADS)

Wu, Y.; Blodau, C.

2013-03-01

Elevated nitrogen deposition and climate change alter the vegetation communities and carbon (C) and nitrogen (N) cycling in peatlands. To address this issue we developed a new process-oriented biogeochemical model (PEATBOG) for analyzing coupled carbon and nitrogen dynamics in northern peatlands. The model consists of four submodels, which simulate: (1) daily water table depth and depth profiles of soil moisture, temperature and oxygen levels; (2) competition among three plants functional types (PFTs), production and litter production of plants; (3) decomposition of peat; and (4) production, consumption, diffusion and export of dissolved C and N species in soil water. The model is novel in the integration of the C and N cycles, the explicit spatial resolution belowground, the consistent conceptualization of movement of water and solutes, the incorporation of stoichiometric controls on elemental fluxes and a consistent conceptualization of C and N reactivity in vegetation and soil organic matter. The model was evaluated for the Mer Bleue Bog, near Ottawa, Ontario, with regards to simulation of soil moisture and temperature and the most important processes in the C and N cycles. Model sensitivity was tested for nitrogen input, precipitation, and temperature, and the choices of the most uncertain parameters were justified. A simulation of nitrogen deposition over 40 yr demonstrates the advantages of the PEATBOG model in tracking biogeochemical effects and vegetation change in the ecosystem.

Mechanisms for retention of bioavailable nitrogen in volcanic rainforest soils

NASA Astrophysics Data System (ADS)

Huygens, Dries; Boeckx, Pascal; Templer, Pamela; Paulino, Leandro; van Cleemput, Oswald; Oyarzún, Carlos; Müller, Christoph; Godoy, Roberto

2008-08-01

Nitrogen cycling is an important aspect of forest ecosystem functioning. Pristine temperate rainforests have been shown to produce large amounts of bioavailable nitrogen, but despite high nitrogen turnover rates, loss of bioavailable nitrogen is minimal in these ecosystems. This tight nitrogen coupling is achieved through fierce competition for bioavailable nitrogen by abiotic processes, soil microbes and plant roots, all of which transfer bioavailable nitrogen to stable nitrogen sinks, such as soil organic matter and above-ground forest vegetation. Here, we use a combination of in situ 15N isotope dilution and 15N tracer techniques in volcanic soils of a temperate evergreen rainforest in southern Chile to further unravel retention mechanisms for bioavailable nitrogen. We find three processes that contribute significantly to nitrogen bioavailability in rainforest soils: heterotrophic nitrate production, nitrate turnover into ammonium and into a pool of dissolved organic nitrogen that is not prone to leaching loss, and finally, the decoupling of dissolved inorganic nitrogen turnover and leaching losses of dissolved organic nitrogen. Identification of these biogeochemical processes helps explain the retention of bioavailable nitrogen in pristine temperate rainforests.

Carbon amendment stimulates benthic nitrogen cycling during the bioremediation of particulate aquaculture waste

NASA Astrophysics Data System (ADS)

Robinson, Georgina; MacTavish, Thomas; Savage, Candida; Caldwell, Gary S.; Jones, Clifford L. W.; Probyn, Trevor; Eyre, Bradley D.; Stead, Selina M.

2018-03-01

The treatment of organic wastes remains one of the key sustainability challenges facing the growing global aquaculture industry. Bioremediation systems based on coupled bioturbation-microbial processing offer a promising route for waste management. We present, for the first time, a combined biogeochemical-molecular analysis of the short-term performance of one such system that is designed to receive nitrogen-rich particulate aquaculture wastes. Using sea cucumbers (Holothuria scabra) as a model bioturbator we provide evidence that adjusting the waste C : N from 5 : 1 to 20 : 1 promoted a shift in nitrogen cycling pathways towards the dissimilatory nitrate reduction to ammonium (DNRA), resulting in net NH4+ efflux from the sediment. The carbon amended treatment exhibited an overall net N2 uptake, whereas the control receiving only aquaculture waste exhibited net N2 production, suggesting that carbon supplementation enhanced nitrogen fixation. The higher NH4+ efflux and N2 uptake was further supported by meta-genome predictions that indicate that organic-carbon addition stimulated DNRA over denitrification. These findings indicate that carbon addition may potentially result in greater retention of nitrogen within the system; however, longer-term trials are necessary to determine whether this nitrogen retention is translated into improved sea cucumber biomass yields. Whether this truly constitutes a remediation process is open for debate as there remains the risk that any increased nitrogen retention may be temporary, with any subsequent release potentially raising the eutrophication risk. Longer and larger-scale trials are required before this approach may be validated with the complexities of the in-system nitrogen cycle being fully understood.

Nitrogen metabolism in haloarchaea

PubMed Central

Bonete, María José; Martínez-Espinosa, Rosa María; Pire, Carmen; Zafrilla, Basilio; Richardson, David J

2008-01-01

The nitrogen cycle (N-cycle), principally supported by prokaryotes, involves different redox reactions mainly focused on assimilatory purposes or respiratory processes for energy conservation. As the N-cycle has important environmental implications, this biogeochemical cycle has become a major research topic during the last few years. However, although N-cycle metabolic pathways have been studied extensively in Bacteria or Eukarya, relatively little is known in the Archaea. Halophilic Archaea are the predominant microorganisms in hot and hypersaline environments such as salted lakes, hot springs or salted ponds. Consequently, the denitrifying haloarchaea that sustain the nitrogen cycle under these conditions have emerged as an important target for research aimed at understanding microbial life in these extreme environments. The haloarchaeon Haloferax mediterranei was isolated 20 years ago from Santa Pola salted ponds (Alicante, Spain). It was described as a denitrifier and it is also able to grow using NO3-, NO2- or NH4+ as inorganic nitrogen sources. This review summarizes the advances that have been made in understanding the N-cycle in halophilic archaea using Hfx mediterranei as a haloarchaeal model. The results obtained show that this microorganism could be very attractive for bioremediation applications in those areas where high salt, nitrate and nitrite concentrations are found in ground waters and soils. PMID:18593475

Stoichiometric evaluation of partial nitritation, anammox and denitrification processes in a sequencing batch reactor and interpretation of online monitoring parameters.

PubMed

Langone, Michela; Ferrentino, Roberta; Cadonna, Maria; Andreottola, Gianni

2016-12-01

A laboratory-scale sequencing batch reactor (SBR) performing partial nitritation - anammox and denitrification was used to treat anaerobic digester effluents. The SBR cycle consisted of a short mixing filling phase followed by oxic and anoxic reaction phases. Working at 25 °C, an ammonium conversion efficiency of 96.5%, a total nitrogen removal efficiency of 88.6%, and an organic carbon removal efficiency of 63.5% were obtained at a nitrogen loading rate of 0.15 kg N m -3 d -1 , and a biodegradable organic carbon to nitrogen ratio of 0.37. The potential contribution of each biological process was evaluated by using a stoichiometric model. The nitritation contribution decreased as the temperature decreased, while the contribution from anammox depended on the wastewater type and soluble carbon to nitrogen ratio. Denitrification improved the total nitrogen removal efficiency, and it was influenced by the biodegradable organic carbon to nitrogen ratio. The characteristic patterns of conductivity, oxidation-reduction potential (ORP) and pH in the SBR cycle were well related to biological processes. Conductivity profiles were found to be directly related to the decreasing profiles of ammonium. Positive ORP values at the end of the anoxic phases were detected for total nitrogen removal efficiency of lower than 85%, and the occurrence of bending points on the ORP curves during the anoxic phases was associated with nitrite depletion by the anammox process. Copyright © 2016 Elsevier Ltd. All rights reserved.

The nitrogen cycle in anaerobic methanotrophic mats of the Black Sea is linked to sulfate reduction and biomass decomposition.

PubMed

Siegert, Michael; Taubert, Martin; Seifert, Jana; von Bergen-Tomm, Martin; Basen, Mirko; Bastida, Felipe; Gehre, Matthias; Richnow, Hans-Hermann; Krüger, Martin

2013-11-01

Anaerobic methanotrophic (ANME) mats host methane-oxidizing archaea and sulfate-reducing prokaryotes. Little is known about the nitrogen cycle in these communities. Here, we link the anaerobic oxidation of methane (AOM) to the nitrogen cycle in microbial mats of the Black Sea by using stable isotope probing. We used four different (15)N-labeled sources of nitrogen: dinitrogen, nitrate, nitrite and ammonium. We estimated the nitrogen incorporation rates into the total biomass and the methyl coenzyme M reductase (MCR). Dinitrogen played an insignificant role as nitrogen source. Assimilatory and dissimilatory nitrate reduction occurred. High rates of nitrate reduction to dinitrogen were stimulated by methane and sulfate, suggesting that oxidation of reduced sulfur compounds such as sulfides was necessary for AOM with nitrate as electron acceptor. Nitrate reduction to dinitrogen occurred also in the absence of methane as electron donor but at six times slower rates. Dissimilatory nitrate reduction to ammonium was independent of AOM. Ammonium was used for biomass synthesis under all conditions. The pivotal enzyme in AOM coupled to sulfate reduction, MCR, was synthesized from nitrate and ammonium. Results show that AOM coupled to sulfate reduction along with biomass decomposition drive the nitrogen cycle in the ANME mats of the Black Sea and that MCR enzymes are involved in this process. © 2013 Federation of European Microbiological Societies. Published by John Wiley & Sons Ltd. All rights reserved.

Genetics Home Reference: carbamoyl phosphate synthetase I deficiency

MedlinePlus

... synthetase I. This enzyme participates in the urea cycle, which is a sequence of biochemical reactions that occurs in liver cells. The urea cycle processes excess nitrogen, generated when protein is broken ...

Terrestrial nitrogen cycling in Earth system models revisited

USGS Publications Warehouse

Stocker, Benjamin D; Prentice, I. Colin; Cornell, Sarah; Davies-Barnard, T; Finzi, Adrien; Franklin, Oskar; Janssens, Ivan; Larmola, Tuula; Manzoni, Stefano; Näsholm, Torgny; Raven, John; Rebel, Karin; Reed, Sasha C.; Vicca, Sara; Wiltshire, Andy; Zaehle, Sönke

2016-01-01

Understanding the degree to which nitrogen (N) availability limits land carbon (C) uptake under global environmental change represents an unresolved challenge. First-generation ‘C-only’vegetation models, lacking explicit representations of N cycling,projected a substantial and increasing land C sink under rising atmospheric CO2 concentrations. This prediction was questioned for not taking into account the potentially limiting effect of N availability, which is necessary for plant growth (Hungate et al.,2003). More recent global models include coupled C and N cycles in land ecosystems (C–N models) and are widely assumed to be more realistic. However, inclusion of more processes has not consistently improved their performance in capturing observed responses of the global C cycle (e.g. Wenzel et al., 2014). With the advent of a new generation of global models, including coupled C, N, and phosphorus (P) cycling, model complexity is sure to increase; but model reliability may not, unless greater attention is paid to the correspondence of model process representations ande mpirical evidence. It was in this context that the ‘Nitrogen Cycle Workshop’ at Dartington Hall, Devon, UK was held on 1–5 February 2016. Organized by I. Colin Prentice and Benjamin D. Stocker (Imperial College London, UK), the workshop was funded by the European Research Council,project ‘Earth system Model Bias Reduction and assessing Abrupt Climate change’ (EMBRACE). We gathered empirical ecologists and ecosystem modellers to identify key uncertainties in terrestrial C–N cycling, and to discuss processes that are missing or poorly represented in current models.

Microbial ecology and biogeochemistry of continental Antarctic soils.

PubMed

Cowan, Don A; Makhalanyane, Thulani P; Dennis, Paul G; Hopkins, David W

2014-01-01

The Antarctica Dry Valleys are regarded as the coldest hyperarid desert system on Earth. While a wide variety of environmental stressors including very low minimum temperatures, frequent freeze-thaw cycles and low water availability impose severe limitations to life, suitable niches for abundant microbial colonization exist. Antarctic desert soils contain much higher levels of microbial diversity than previously thought. Edaphic niches, including cryptic and refuge habitats, microbial mats and permafrost soils all harbor microbial communities which drive key biogeochemical cycling processes. For example, lithobionts (hypoliths and endoliths) possess a genetic capacity for nitrogen and carbon cycling, polymer degradation, and other system processes. Nitrogen fixation rates of hypoliths, as assessed through acetylene reduction assays, suggest that these communities are a significant input source for nitrogen into these oligotrophic soils. Here we review aspects of microbial diversity in Antarctic soils with an emphasis on functionality and capacity. We assess current knowledge regarding adaptations to Antarctic soil environments and highlight the current threats to Antarctic desert soil communities.

Thinking outside the channel: Modeling nitrogen cycling in networked river ecosystems

DOE Office of Scientific and Technical Information (OSTI.GOV)

Helton, Ashley; Poole, Geoffrey C.; Meyer, Judy

2011-01-01

Agricultural and urban development alters nitrogen and other biogeochemical cycles in rivers worldwide. Because such biogeochemical processes cannot be measured empirically across whole river networks, simulation models are critical tools for understanding river-network biogeochemistry. However, limitations inherent in current models restrict our ability to simulate biogeochemical dynamics among diverse river networks. We illustrate these limitations using a river-network model to scale up in situ measures of nitrogen cycling in eight catchments spanning various geophysical and land-use conditions. Our model results provide evidence that catchment characteristics typically excluded from models may control river-network biogeochemistry. Based on our findings, we identify importantmore » components of a revised strategy for simulating biogeochemical dynamics in river networks, including approaches to modeling terrestrial-aquatic linkages, hydrologic exchanges between the channel, floodplain/riparian complex, and subsurface waters, and interactions between coupled biogeochemical cycles.« less

Restoring the Nitrogen Cycle in the Boreal Forest - a Case Study from Northern Alberta

NASA Astrophysics Data System (ADS)

Masse, Jacynthe; Grayston, Sue; Prescott, Cindy; Quideau, Sylvie

2014-05-01

The Athabasca oil sands deposit, located in the boreal forests of Northern Alberta, is one of the largest single oil deposits in the world. This deposit rests underneath 40,200 square kilometres of land. To date, an area of about 715 square kilometres has been disturbed by oil sands mining activity (Government of Alberta, 2013). Following surface mining, companies have the legal obligation to restore soil-like profiles that can support the previous land capabilities (Powter et al., 2012). Because of its importance for site productivity, re-establishment of the nitrogen cycle between these reconstructed soils and plants is one of the most critical factors required to insure long term sustainability of reclaimed boreal landscape. High nitrogen deposition recorded in the oil sands area combined with the high level of nitrate found in reclaimed soils raised concerns about the possibility of these reclaimed soils being in early stages of N saturation (Laxton et al 2010; Hemsley, 2012), although little evidence of net nitrification in these reclaimed soils suggests the contrary (Laxton et al. 2012). To date, results on the behaviour of the nitrogen cycle in the reclaimed sites are contradictory. A systematic study of the nitrogen cycle, and especially rates of gross mineralization, nitrification and denitrification, is needed. Our research aimed at 1) measuring the gross rates of nitrogen transformations under different vegetation treatments in both reclaimed and naturally-disturbed (fire) sites and 2) characterizing the microbial communities participating in the nitrogen cycle within the same soils. A series of 20 soils, covering different vegetation treatments (plots planted with aspen (Populus tremuloides), spruce (Picea glauca) and grassland) were investigated. Gross nitrogen transformation rates were measured using 15N pool-dilution (Müller et al. 2007). Microbial communities participating in the N-cycle were characterized using qPCR and pyrosequencing. Differences between nitrogen cycling processes in the different vegetation treatments and in the naturally disturbed sites were found. The reasons for these variances will be discussed. The oil sands will be Canada's environmental legacy for the next several hundred years and recreating functional soils is fundamental to our ability to restore boreal ecosystems after disturbance.

A Systems Approach to Nitrogen Delivery

DOE Office of Scientific and Technical Information (OSTI.GOV)

Goins, Bobby

A systems based approach will be used to evaluate the nitrogen delivery process. This approach involves principles found in Lean, Reliability, Systems Thinking, and Requirements. This unique combination of principles and thought process yields a very in depth look into the system to which it is applied. By applying a systems based approach to the nitrogen delivery process there should be improvements in cycle time, efficiency, and a reduction in the required number of personnel needed to sustain the delivery process. This will in turn reduce the amount of demurrage charges that the site incurs. In addition there should bemore » less frustration associated with the delivery process.« less

Measuring Nitrification: A Laboratory Approach to Nutrient Cycling.

ERIC Educational Resources Information Center

Hicks, David J.

1990-01-01

Presented is an approach to the study of nutrient cycling in the school laboratory. Discussed are obtaining, processing, and incubating samples; extraction of ions from soil; procedures for nitrate and ammonium analysis; data analysis; an example of results; and other aspects of the nitrogen cycle. (CW)

Fresh insight to functioning of selected enzymes of the nitrogen cycle.

PubMed

Eady, Robert R; Antonyuk, Svetlana V; Hasnain, S Samar

2016-04-01

The global nitrogen cycle is the process in which different forms of environmental N are interconverted by microorganisms either for assimilation into biomass or in respiratory energy-generating pathways. This short review highlights developments over the last 5 years in our understanding of functionality of nitrogenase, Cu-nitrite reductase, NO reductase and N2O reductase, complex metalloenzymes that catalyze electron/proton-coupled substrate reduction reactions. Copyright © 2016 Elsevier Ltd. All rights reserved.

Photoperiod length paces the temporal orchestration of cell cycle and carbon-nitrogen metabolism in Crocosphaera watsonii.

PubMed

Dron, Anthony; Rabouille, Sophie; Claquin, Pascal; Talec, Amélie; Raimbault, Virginie; Sciandra, Antoine

2013-12-01

We analysed the effect of photoperiod length (PPL) (16:8 and 8:16 h of light-dark regime, named long and short PPL, respectively) on the temporal orchestration of the two antagonistic, carbon and nitrogen acquisitions in the unicellular, diazotrophic cyanobacterium Crocosphaera watsonii strain WH8501 growing diazotrophically. Carbon and nitrogen metabolism were monitored at high frequency, and their patterns were compared with the cell cycle progression. The oxygen-sensitive N2 fixation process occurred mainly during the dark period, where photosynthesis cannot take place, inducing a light-dark cycle of cellular C : N ratio. Examination of circadian patterns in the cell cycle revealed that cell division occurred during the midlight period, (8 h and 4 h into the light in the long and short PPL conditions, respectively), thus timely separated from the energy-intensive diazotrophic process. Results consistently show a nearly 5 h time lag between the end of cell division and the onset of N2 fixation. Shorter PPLs affected DNA compaction of C. watsonii cells and also led to a decrease in the cell division rate. Therefore, PPL paces the growth of C. watsonii: a long PPL enhances cell division while a short PPL favours somatic growth (biomass production) with higher carbon and nitrogen cell contents. © 2013 Society for Applied Microbiology and John Wiley & Sons Ltd.

Food supply and size class depending variations in phytodetritus intake in the benthic foraminifer Ammonia tepida.

PubMed

Wukovits, Julia; Bukenberger, Patrick; Enge, Annekatrin Julie; Gerg, Maximillian; Wanek, Wolfgang; Watzka, Margarete; Heinz, Petra

2018-04-13

Ammonia tepida is a common and abundant benthic foraminifer in intertidal mudflats. Benthic foraminifera are primary consumers and detritivores and act as key players in sediment nutrient fluxes. In this study, laboratory feeding experiments using isotope-labeled phytodetritus were carried out with A. tepida collected at the German Wadden Sea, to investigate the response of A. tepida to varying food supply. Feeding mode (single pulse, constant feeding; different incubation temperatures) caused strong variations in cytoplasmic carbon and nitrogen cycling, suggesting generalistic adaptations to variations in food availability. To study the influence of intraspecific size to foraminiferal carbon and nitrogen cycling, three size fractions (125-250 µm, 250-355 µm, >355 µm) of A. tepida specimens were separated. Small individuals showed higher weight specific intake for phytodetritus, especially for phytodetrital nitrogen, highlighting that size distribution within foraminiferal populations is relevant to interpret foraminiferal carbon and nitrogen cycling. These results were used to extrapolate the data to natural populations of living A. tepida in sediment cores, demonstrating the impact of high abundances of small individuals on phytodetritus processing and nutrient cycling. It is estimated that at high abundances of individuals in the 125-250 µm size fraction, Ammonia populations can account for more than 11% of phytodetritus processing in intertidal benthic communities. © 2018. Published by The Company of Biologists Ltd.

Assessing heterogeneity in soil nitrogen cycling: a plot-scale approach

Treesearch

Peter Baas; Jacqueline E. Mohan; David Markewitz; Jennifer D. Knoepp

2014-01-01

The high level of spatial and temporal heterogeneity in soil N cycling processes hinders our ability to develop an ecosystem-wide understanding of this cycle. This study examined how incorporating an intensive assessment of spatial variability for soil moisture, C, nutrients, and soil texture can better explain ecosystem N cycling at the plot scale. Five sites...

The Interaction of Global Biochemical Cycles

NASA Technical Reports Server (NTRS)

Moore, B., III; Dastoor, M. N.

1984-01-01

The global biosphere in an exceedingly complex system. To gain an understanding of its structure and dynamic features, it is necessary not only to increase the knowledge about the detailed processes but also to develop models of how global interactions take place. Attempts to analyze the detailed physical, chemical and biological processes in this context need to be guided by an advancement of understanding of the latter. It is necessary to develop a strategy of data gathering that severs both these purposes simultaneously. The following papers deal with critical aspects in the global cycles of carbon, nitrogen, phosphorus and sulfur in details as well as the cycle of water and the flow of energy in the Earth's environment. The objective is to set partly the foundation for the development of mathematical models that allow exploration of the coupled dynamics of the global cycles of carbon, nitrogen, phosphorus, sulfur, as well as energy and water flux.

The natural and perturbed troposphere

NASA Technical Reports Server (NTRS)

Stewart, R. W.; Hameed, S.; Pinto, J.

1978-01-01

A quantitative assessment of the chemical and climatic effects of industrial emissions into the atmosphere requires an understanding of the complex interactions of species within the atmosphere and of the atmosphere with other physical systems such as the oceans, lithosphere, and biosphere. The concentration of a particular species is determined by competition between various production and loss processes. The abundances of tropospheric gases are examined. The reactions of the members of the oxygen group are considered along with the models which have been developed to describe the involved relationships. Attention is also given to the natural carbon cycle, perturbations to the carbon cycle, the natural nitrogen cycle, perturbations to the nitrogen cycle, the hydrogen group, the sulfur group, and the halogen group.

Nitrogen removal and its relationship with the nitrogen-cycle genes and microorganisms in the horizontal subsurface flow constructed wetlands with different design parameters.

PubMed

Chen, Jun; Ying, Guang-Guo; Liu, You-Sheng; Wei, Xiao-Dong; Liu, Shuang-Shuang; He, Liang-Ying; Yang, Yong-Qiang; Chen, Fan-Rong

2017-07-03

This study aims to investigate nitrogen removal and its relationship with the nitrogen-cycle genes and microorganisms in the horizontal subsurface flow constructed wetlands (CWs) with different design parameters. Twelve mesocosm-scale CWs with four substrates and three hydraulic loading rates were set up in the outdoor. The result showed the CWs with zeolite as substrate and HLR of 20 cm/d were selected as the best choice for the TN and NH 3 -N removal. It was found that the single-stage mesocosm-scale CWs were incapable to achieve high removals of TN and NH 3 -N due to inefficient nitrification process in the systems. This was demonstrated by the lower abundance of the nitrification genes (AOA and AOB) than the denitrification genes (nirK and nirS), and the less diverse nitrification microorganisms than the denitrification microorganisms in the CWs. The results also show that microorganism community structure including nitrogen-cycle microorganisms in the constructed wetland systems was affected by the design parameters especially the substrate type. These findings show that nitrification is a limiting factor for the nitrogen removal by CWs.

Parameterization of Nitrogen Limitation for a Dynamic Ecohydrological Model: a Case Study from the Luquillo Critical Zone Observatory

NASA Astrophysics Data System (ADS)

Bastola, S.; Bras, R. L.

2017-12-01

Feedbacks between vegetation and the soil nutrient cycle are important in ecosystems where nitrogen limits plant growth, and consequently influences the carbon balance in the plant-soil system. However, many biosphere models do not include such feedbacks, because interactions between carbon and the nitrogen cycle can be complex, and remain poorly understood. In this study we coupled a nitrogen cycle model with an eco-hydrological model by using the concept of carbon cost economics. This concept accounts for different "costs" to the plant of acquiring nitrogen via different pathways. This study builds on tRIBS-VEGGIE, a spatially explicit hydrological model coupled with a model of photosynthesis, stomatal resistance, and energy balance, by combining it with a model of nitrogen recycling. Driven by climate and spatially explicit data of soils, vegetation and topography, the model (referred to as tRIBS-VEGGIE-CN) simulates the dynamics of carbon and nitrogen in the soil-plant system; the dynamics of vegetation; and different components of the hydrological cycle. The tRIBS-VEGGIE-CN is applied in a humid tropical watershed at the Luquillo Critical Zone Observatory (LCZO). The region is characterized by high availability and cycling of nitrogen, high soil respiration rates, and large carbon stocks.We drive the model under contemporary CO2 and hydro-climatic forcing and compare results to a simulation under doubling CO2 and a range of future climate scenarios. The results with parameterization of nitrogen limitation based on carbon cost economics show that the carbon cost of the acquisition of nitrogen is 14% of the net primary productivity (NPP) and the N uptake cost for different pathways vary over a large range depending on leaf nitrogen content, turnover rates of carbon in soil and nitrogen cycling processes. Moreover, the N fertilization simulation experiment shows that the application of N fertilizer does not significantly change the simulated NPP. Furthermore, an experiment with doubling of the CO2 concentration level shows a significant increase of the NPP and turnover of plant tissues. The simulation with future climate scenarios shows consistent decrease in NPP but the uncertainties in projected NPP arising from selection of climate model and scenario is large.

Modeling the nitrogen cycle one gene at a time

NASA Astrophysics Data System (ADS)

Coles, V.; Stukel, M. R.; Hood, R. R.; Moran, M. A.; Paul, J. H.; Satinsky, B.; Zielinski, B.; Yager, P. L.

2016-02-01

Marine ecosystem models are lagging the revolution in microbial oceanography. As a result, modeling of the nitrogen cycle has largely failed to leverage new genomic information on nitrogen cycling pathways and the organisms that mediate them. We developed a nitrogen based ecosystem model whose community is determined by randomly assigning functional genes to build each organism's "DNA". Microbes are assigned a size that sets their baseline environmental responses using allometric response curves. These responses are modified by the costs and benefits conferred by each gene in an organism's genome. The microbes are embedded in a general circulation model where environmental conditions shape the emergent population. This model is used to explore whether organisms constructed from randomized combinations of metabolic capability alone can self-organize to create realistic oceanic biogeochemical gradients. Community size spectra and chlorophyll-a concentrations emerge in the model with reasonable fidelity to observations. The model is run repeatedly with randomly-generated microbial communities and each time realistic gradients in community size spectra, chlorophyll-a, and forms of nitrogen develop. This supports the hypothesis that the metabolic potential of a community rather than the realized species composition is the primary factor setting vertical and horizontal environmental gradients. Vertical distributions of nitrogen and transcripts for genes involved in nitrification are broadly consistent with observations. Modeled gene and transcript abundance for nitrogen cycling and processing of land-derived organic material match observations along the extreme gradients in the Amazon River plume, and they help to explain the factors controlling observed variability.

Nitrogen cycling in Bioregenerative Life Support Systems: Challenges for waste refinery and food production processes

NASA Astrophysics Data System (ADS)

Clauwaert, Peter; Muys, Maarten; Alloul, Abbas; De Paepe, Jolien; Luther, Amanda; Sun, Xiaoyan; Ilgrande, Chiara; Christiaens, Marlies E. R.; Hu, Xiaona; Zhang, Dongdong; Lindeboom, Ralph E. F.; Sas, Benedikt; Rabaey, Korneel; Boon, Nico; Ronsse, Frederik; Geelen, Danny; Vlaeminck, Siegfried E.

2017-05-01

In order to sustain human life in an isolated environment, an efficient conversion of wasted nutrients to food might become mandatory. This is particularly the case for space missions where resupply from earth or in-situ resource utilization is not possible or desirable. A combination of different technologies is needed to allow full recycling of e.g. nitrogenous compounds in space. In this review, an overview is given of the different essential processes and technologies that enable closure of the nitrogen cycle in Bioregenerative Life Support Systems (BLSS). Firstly, a set of biological and physicochemical refinery stages ensures efficient conversion of waste products into the building blocks, followed by the production of food with a range of biological methods. For each technology, bottlenecks are identified. Furthermore, challenges and outlooks are presented at the integrated system level. Space adaptation and integration deserve key attention to enable the recovery of nitrogen for the production of nutritional food in space, but also in closed loop systems on earth.

Matrix approaches to assess terrestrial nitrogen scheme in CLM4.5

NASA Astrophysics Data System (ADS)

Du, Z.

2017-12-01

Terrestrial carbon (C) and nitrogen (N) cycles have been commonly represented by a series of balance equations to track their influxes into and effluxes out of individual pools in earth system models (ESMs). This representation matches our understanding of C and N cycle processes well but makes it difficult to track model behaviors. To overcome these challenges, we developed a matrix approach, which reorganizes the series of terrestrial C and N balance equations in the CLM4.5 into two matrix equations based on original representation of C and N cycle processes and mechanisms. The matrix approach would consequently help improve the comparability of models and data, evaluate impacts of additional model components, facilitate benchmark analyses, model intercomparisons, and data-model fusion, and improve model predictive power.

Light-dark (12:12) cycle of carbon and nitrogen metabolism in Crocosphaera watsonii WH8501: relation to the cell cycle.

PubMed

Dron, Anthony; Rabouille, Sophie; Claquin, Pascal; Le Roy, Bertrand; Talec, Amélie; Sciandra, Antoine

2012-04-01

This study provides with original data sets on the physiology of the unicellular diazotrophic cyanobacterium Crocosphaera watsonii WH8501, maintained in continuous culture in conditions of obligate diazotrophy. Cultures were exposed to a 12:12 light-dark regime, representative of what they experience in nature and where growth is expected to be balanced. Nitrogen and carbon metabolism were monitored at high frequency and their dynamics was compared with the cell cycle. Results reveal a daily cycle in the physiological and biochemical parameters, tightly constrained by the timely decoupled processes of N(2) fixation and carbon acquisition. The cell division rate increased concomitantly to carbon accumulation and peaked 6 h into the light. The carbon content reached a maximum at the end of the light phase. N(2) fixation occurred mostly during the dark period and peaked between 9 and 10 h into the night, while DNA synthesis, reflected by DNA fluorescence, increased until the end of the night. Consequently, cells in G1- and S-phases present a marked decrease in their C:N ratio. Nitrogen acquisition through N(2) fixation exceeded 1.3- to 3-fold the nitrogen requirements for growth, suggesting that important amounts of nitrogen are excreted even under conditions supposed to favour balanced, carbon and nitrogen acquisitions. © 2011 Society for Applied Microbiology and Blackwell Publishing Ltd.

Comparison between reverse Brayton and Kapitza based LNG boil-off gas reliquefaction system using exergy analysis

NASA Astrophysics Data System (ADS)

Kochunni, Sarun Kumar; Chowdhury, Kanchan

2017-02-01

LNG boil-off gas (BOG) reliquefaction systems in LNG carrier ships uses refrigeration devices which are based on reverse Brayton, Claude, Kapitza (modified Claude) or Cascade cycles. Some of these refrigeration devices use nitrogen as the refrigerants and hence nitrogen storage vessels or nitrogen generators needs to be installed in LNG carrier ships which consume space and add weight to the carrier. In the present work, a new configuration based on Kapitza liquefaction cycle which uses BOG itself as working fluid is proposed and has been compared with Reverse Brayton Cycle (RBC) on sizes of heat exchangers and compressor operating parameters. Exergy analysis is done after simulating at steady state with Aspen Hysys 8.6® and the comparison between RBC and Kapitza may help designers to choose reliquefaction system with appropriate process parameters and sizes of equipment. With comparable exergetic efficiency as that of an RBC, a Kaptiza system needs only BOG compressor without any need of nitrogen gas.

Potential roles of anaerobic ammonium and methane oxidation in the nitrogen cycle of wetland ecosystems.

PubMed

Zhu, Guibing; Jetten, Mike S M; Kuschk, Peter; Ettwig, Katharina F; Yin, Chengqing

2010-04-01

Anaerobic ammonium oxidation (anammox) and anaerobic methane oxidation (ANME coupled to denitrification) with nitrite as electron acceptor are two of the most recent discoveries in the microbial nitrogen cycle. Currently the anammox process has been relatively well investigated in a number of natural and man-made ecosystems, while ANME coupled to denitrification has only been observed in a limited number of freshwater ecosystems. The ubiquitous presence of anammox bacteria in marine ecosystems has changed our knowledge of the global nitrogen cycle. Up to 50% of N(2) production in marine sediments and oxygen-depleted zones may be attributed to anammox bacteria. However, there are only few indications of anammox in natural and constructed freshwater wetlands. In this paper, the potential role of anammox and denitrifying methanotrophic bacteria in natural and artificial wetlands is discussed in relation to global warming. The focus of the review is to explore and analyze if suitable environmental conditions exist for anammox and denitrifying methanotrophic bacteria in nitrogen-rich freshwater wetlands.

Community Composition of Nitrous Oxide-Related Genes in Salt Marsh Sediments Exposed to Nitrogen Enrichment.

PubMed

Angell, John H; Peng, Xuefeng; Ji, Qixing; Craick, Ian; Jayakumar, Amal; Kearns, Patrick J; Ward, Bess B; Bowen, Jennifer L

2018-01-01

Salt marshes provide many key ecosystem services that have tremendous ecological and economic value. One critical service is the removal of fixed nitrogen from coastal waters, which limits the negative effects of eutrophication resulting from increased nutrient supply. Nutrient enrichment of salt marsh sediments results in higher rates of nitrogen cycling and, commonly, a concurrent increase in the flux of nitrous oxide, an important greenhouse gas. Little is known, however, regarding controls on the microbial communities that contribute to nitrous oxide fluxes in marsh sediments. To address this disconnect, we generated profiles of microbial communities and communities of micro-organisms containing specific nitrogen cycling genes that encode several enzymes ( amoA, norB, nosZ) related to nitrous oxide flux from salt marsh sediments. We hypothesized that communities of microbes responsible for nitrogen transformations will be structured by nitrogen availability. Taxa that respond positively to high nitrogen inputs may be responsible for the elevated rates of nitrogen cycling processes measured in fertilized sediments. Our data show that, with the exception of ammonia-oxidizing archaea, the community composition of organisms involved in the production and consumption of nitrous oxide was altered under nutrient enrichment. These results suggest that previously measured rates of nitrous oxide production and consumption are likely the result of changes in community structure, not simply changes in microbial activity.

Cycling the Hot CNO: A Teaching Methodology

ERIC Educational Resources Information Center

Frost-Schenk, J. W.; Diget, C. Aa.; Bentley, M. A.; Tuff, A.

2018-01-01

An interactive activity to teach the hot Carbon, Nitrogen and Oxygen (HCNO) cycle is proposed. Justification for why the HCNO cycle is important is included via an example of x-ray bursts. The activity allows teaching and demonstration of half-life, nuclear isotopes, nuclear reactions, protons and a-particles, and catalytic processes. Whilst the…

Frequent fire alters nitrogen transformations in ponderosa pine stands of the inland Northwest

Treesearch

Thomas H. DeLuca; Sala Anna

2006-01-01

Recurrent, low-severity fire in ponderosa pine (Pinus ponderosa)/interior Douglas-fir (Pseudotsuga menziesii var. glauca) forests is thought to have directly influenced nitrogen (N) cycling and availability. However, no studies to date have investigated the influence of natural fire intervals on soil processes in undisturbed...

Molybdenum Trafficking for Nitrogen Fixation†

PubMed Central

Hernandez, Jose A.; George, Simon J.; Rubio, Luis M.

2009-01-01

The molybdenum nitrogenase is responsible for most biological nitrogen fixation, a prokaryotic metabolic process that determines the global biogeochemical cycles of nitrogen and carbon. Here we describe the trafficking of molybdenum for nitrogen fixation in the model diazotrophic bacterium Azotobacter vinelandii. The genes and proteins involved in molybdenum uptake, homeostasis, storage, regulation, and nitrogenase cofactor biosynthesis are reviewed. Molybdenum biochemistry in A. vinelandii reveals unexpected mechanisms and a new role for iron-sulfur clusters in the sequestration and delivery of molybdenum. PMID:19772354

Long-term records reveal decoupling of nitrogen and phosphorus cycles in a large, urban lake in response to an extreme rainfall event

NASA Astrophysics Data System (ADS)

Corman, J. R.; Loken, L. C.; Oliver, S. K.; Collins, S.; Butitta, V.; Stanley, E. H.

2017-12-01

Extreme events can play powerful roles in shifting ecosystem processes. In lakes, heavy rainfall can transport large amounts of particulates and dissolved nutrients into the water column and, potentially, alter biogeochemical cycling. However, the impacts of extreme rainfall events are often difficult to study due to a lack of long-term records. In this paper, we combine daily discharge records with long-term lake water quality information collected by the North Temperate Lakes Long-Term Ecological Research (NTL LTER) site to investigate the impacts of extreme events on nutrient cycling in lakes. We focus on Lake Mendota, an urban lake within the Yahara River Watershed in Madison, Wisconsin, USA, where nutrient data are available at least seasonally from 1995 - present. In June 2008, precipitation amounts in the Yahara watershed were 400% above normal values, triggering the largest discharge event on record for the 40 years of monitoring at the streamgage station; hence, we are able to compare water quality records before and after this event as a case study of how extreme rain events couple or decouple lake nutrient cycling. Following the extreme event, the lake-wide mass of nitrogen and phosphorus increased in the summer of 2008 by 35% and 21%, respectively, shifting lake stoichiometry by increasing N:P ratios (Figure 1). Nitrogen concentrations remained elevated longer than phosphorus, suggesting (1) that nitrogen inputs into the lake were sustained longer than phosphorus (i.e., a "smear" versus "pulse" loading of nitrogen versus phosphorus, respectively, in response to the extreme event) and/or (2) that in-lake biogeochemical processing was more efficient at removing phosphorus compared to nitrogen. While groundwater loading data are currently unavailable to test the former hypothesis, preliminary data from surficial nitrogen and phosphorus loading to Lake Mendota (available for 2011 - 2013) suggest that nitrogen removal efficiency is less than phosphorus, supporting the latter hypothesis. As climate change is expected to increase the frequency of extreme events, continued monitoring of lakes is needed to understand biogeochemical responses and when and how water quality threats may occur.

Integrated design of cryogenic refrigerator and liquid-nitrogen circulation loop for HTS cable

NASA Astrophysics Data System (ADS)

Chang, Ho-Myung; Ryu, Ki Nam; Yang, Hyung Suk

2016-12-01

A new concept of cryogenic cooling system is proposed and investigated for application to long-length HTS cables. One of major obstacles to the cable length of 1 km or longer is the difficulty in circulating liquid nitrogen (LN) along the cables, since the temperature rise and pressure drop of LN flow could be excessively large. This study attempts a breakthrough by integrating the refrigerator with the LN circulation loop in order to eliminate the cryogenic LN pumps, and generate a large LN flow with the power of compressors at ambient temperature. A variety of thermodynamic structures are investigated on standard and modified Claude cycles, where nitrogen is used as refrigerant and the LN circulation loop is included as part of the closed cycle. Four proposed cycles are fully analyzed and optimized with a process simulator (Aspen HYSYS) to evaluate the FOM (figure of merit) and examine the feasibility. The modified dual-pressure cycle cooled with expander stream is recommended for long HTS cables.

Fasting or fear: disentangling the roles of predation risk and food deprivation in the nitrogen metabolism of consumers.

PubMed

Dalton, Christopher M; Tracy, Karen E; Hairston, Nelson G; Flecker, Alexander S

2018-03-01

Predators can alter nutrient cycles simply by inducing stress in prey. This stress accelerates prey's protein catabolism, nitrogen waste production, and nitrogen cycling. Yet predators also reduce the feeding rates of their prey, inducing food deprivation that is expected to slow protein catabolism and nitrogen cycling. The physiology of prey under predation risk thus balances the influences of predation risk and food deprivation, and this balance is central to understanding the role of predators in nutrient cycles. We explored the separate and combined effects of predation risk and food deprivation on prey physiology and nutrient cycling by exposing guppies (Poecilia reticulata) to predation risk and food deprivation in a 2 × 2 design. We simulated predation risk using chemical cues from a natural predator of guppies, and we created food deprivation by rationing food availability. We measured guppy response as food consumption, growth, tissue energy density, tissue carbon:nitrogen, and nitrogen (N) excretion and assimilation. We found that N-linked physiological processes (N consumption, assimilation, excretion) were strongly affected by predation risk, independent of food consumption. Guppies excreted substantially less under predation risk than they did under food deprivation or control conditions. These results suggest that predation risk, per se, triggers physiological changes in guppies that increase N retention and decrease N excretion. We suggest that slower N metabolism under predation risk is an adaptive response that minimizes protein loss in the face of predictable, predator-induced food restriction. Notably, N metabolism shares common hormonal control with food seeking behavior, and we speculate that increased N retention is a direct and immediate result of reduced food seeking under predation risk. Contrary to predation-stress-based hypotheses for how predators affect nutrient cycling by prey, our result indicates that even short-term exposure to predators may decelerate, rather than accelerate, the speed of N cycling by suppressing N turnover by prey. © 2018 by the Ecological Society of America.

Disturbance decouples biogeochemical cycles across forests of the southeastern US

Treesearch

Ashley D. Keiser; Jennifer D. Knoepp; Mark A. Bradford

2016-01-01

Biogeochemical cycles are inherently linked through the stoichiometric demands of the organisms that cycle the elements. Landscape disturbance can alter element availability and thus the rates of biogeochemical cycling. Nitrification is a fundamental biogeochemical process positively related to plant productivity and nitrogen loss from soils to aquatic systems, and the...

Organization of biogeochemical nitrogen pathways with switch-like adjustment in fluctuating soil redox conditions

PubMed Central

Lamba, Sanjay; Bera, Soumen; Rashid, Mubasher; Medvinsky, Alexander B.; Acquisti, Claudia; Li, Bai-Lian

2017-01-01

Nitrogen is cycled throughout ecosystems by a suite of biogeochemical processes. The high complexity of the nitrogen cycle resides in an intricate interplay between reversible biochemical pathways alternatively and specifically activated in response to diverse environmental cues. Despite aggressive research, how the fundamental nitrogen biochemical processes are assembled and maintained in fluctuating soil redox conditions remains elusive. Here, we address this question using a kinetic modelling approach coupled with dynamical systems theory and microbial genomics. We show that alternative biochemical pathways play a key role in keeping nitrogen conversion and conservation properties invariant in fluctuating environments. Our results indicate that the biochemical network holds inherent adaptive capacity to stabilize ammonium and nitrate availability, and that the bistability in the formation of ammonium is linked to the transient upregulation of the amo-hao mediated nitrification pathway. The bistability is maintained by a pair of complementary subsystems acting as either source or sink type systems in response to soil redox fluctuations. It is further shown how elevated anthropogenic pressure has the potential to break down the stability of the system, altering substantially ammonium and nitrate availability in the soil, with dramatic effects on biodiversity. PMID:28280580

Accounting for the biogeochemical cycle of nitrogen in input-output life cycle assessment.

PubMed

Singh, Shweta; Bakshi, Bhavik R

2013-08-20

Nitrogen is indispensable for sustaining human activities through its role in the production of food, animal feed, and synthetic chemicals. This has encouraged significant anthropogenic mobilization of reactive nitrogen and its emissions into the environment resulting in severe disruption of the nitrogen cycle. This paper incorporates the biogeochemical cycle of nitrogen into the 2002 input-output model of the U.S. economy. Due to the complexity of this cycle, this work proposes a unique classification of nitrogen flows to facilitate understanding of the interaction between economic activities and various flows in the nitrogen cycle. The classification scheme distinguishes between the mobilization of inert nitrogen into its reactive form, use of nitrogen in various products, and nitrogen losses to the environment. The resulting inventory and model of the US economy can help quantify the direct and indirect impacts or dependence of economic sectors on the nitrogen cycle. This paper emphasizes the need for methods to manage the N cycle that focus not just on N losses, which has been the norm until now, but also include other N flows for a more comprehensive view and balanced decisions. Insight into the N profile of various sectors of the 2002 U.S. economy is presented, and the inventory can also be used for LCA or Hybrid LCA of various products. The resulting model is incorporated in the approach of Ecologically-Based LCA and available online.

Enzymology under global change: organic nitrogen turnover in alpine and sub-Arctic soils.

PubMed

Weedon, James T; Aerts, Rien; Kowalchuk, George A; van Bodegom, Peter M

2011-01-01

Understanding global change impacts on the globally important carbon storage in alpine, Arctic and sub-Arctic soils requires knowledge of the mechanisms underlying the balance between plant primary productivity and decomposition. Given that nitrogen availability limits both processes, understanding the response of the soil nitrogen cycle to shifts in temperature and other global change factors is crucial for predicting the fate of cold biome carbon stores. Measurements of soil enzyme activities at different positions of the nitrogen cycling network are an important tool for this purpose. We review a selection of studies that provide data on potential enzyme activities across natural, seasonal and experimental gradients in cold biomes. Responses of enzyme activities to increased nitrogen availability and temperature are diverse and seasonal dynamics are often larger than differences due to experimental treatments, suggesting that enzyme expression is regulated by a combination of interacting factors reflecting both nutrient supply and demand. The extrapolation from potential enzyme activities to prediction of elemental nitrogen fluxes under field conditions remains challenging. Progress in molecular '-omics' approaches may eventually facilitate deeper understanding of the links between soil microbial community structure and biogeochemical fluxes. In the meantime, accounting for effects of the soil spatial structure and in situ variations in pH and temperature, better mapping of the network of enzymatic processes and the identification of rate-limiting steps under different conditions should advance our ability to predict nitrogen fluxes.

The microbial nitrogen cycling potential is impacted by polyaromatic hydrocarbon pollution of marine sediments

DOE PAGES

Scott, Nicole M.; Hess, Matthias; Bouskill, Nick J.; ...

2014-03-25

During hydrocarbon exposure, the composition and functional dynamics of marine microbial communities are altered, favoring bacteria that can utilize this rich carbon source. Initial exposure of high levels of hydrocarbons in aerobic surface sediments can enrich growth of heterotrophic microorganisms having hydrocarbon degradation capacity. As a result, there can be a localized reduction in oxygen potential within the surface layer of marine sediments causing anaerobic zones. We hypothesized that increasing exposure to elevated hydrocarbon concentrations would positively correlate with an increase in denitrification processes and the net accumulation of dinitrogen. This hypothesis was tested by comparing the relative abundance ofmore » genes associated with nitrogen metabolism and nitrogen cycling identified in 6 metagenomes from sediments contaminated by polyaromatic hydrocarbons from the Deepwater Horizon (DWH) oil spill in the Gulf of Mexico, and 3 metagenomes from sediments associated with natural oil seeps in the Santa Barbara Channel. An additional 8 metagenomes from uncontaminated sediments from the Gulf of Mexico were analyzed for comparison. We predicted relative changes in metabolite turnover as a function of the differential microbial gene abundances, which showed predicted accumulation of metabolites associated with denitrification processes, including anammox, in the contaminated samples compared to uncontaminated sediments, with the magnitude of this change being positively correlated to the hydrocarbon concentration and exposure duration. Furthermore, these data highlight the potential impact of hydrocarbon inputs on N cycling processes in marine sediments and provide information relevant for system scale models of nitrogen metabolism in affected ecosystems.« less

The microbial nitrogen cycling potential is impacted by polyaromatic hydrocarbon pollution of marine sediments

DOE Office of Scientific and Technical Information (OSTI.GOV)

Scott, Nicole M.; Hess, Matthias; Bouskill, Nick J.

2014-03-25

During hydrocarbon exposure, the composition and functional dynamics of marine microbial communities are altered, favoring bacteria that can utilize this rich carbon source. Initial exposure of high levels of hydrocarbons in aerobic surface sediments can enrich growth of heterotrophic microorganisms having hydrocarbon degradation capacity. As a result, there can be a localized reduction in oxygen potential within the surface layer of marine sediments causing anaerobic zones. We hypothesized that increasing exposure to elevated hydrocarbon concentrations would positively correlate with an increase in denitrification processes and the net accumulation of dinitrogen. This hypothesis was tested by comparing the relative abundance ofmore » genes associated with nitrogen metabolism and nitrogen cycling identified in 6 metagenomes from sediments contaminated by polyaromatic hydrocarbons from the Deepwater Horizon (DWH) oil spill in the Gulf of Mexico, and 3 metagenomes from sediments associated with natural oil seeps in the Santa Barbara Channel. An additional 8 metagenomes from uncontaminated sediments from the Gulf of Mexico were analyzed for comparison. We predicted relative changes in metabolite turnover as a function of the differential microbial gene abundances, which showed predicted accumulation of metabolites associated with denitrification processes, including anammox, in the contaminated samples compared to uncontaminated sediments, with the magnitude of this change being positively correlated to the hydrocarbon concentration and exposure duration. These data highlight the potential impact of hydrocarbon inputs on N cycling processes in marine sediments and provide information relevant for system scale models of nitrogen metabolism in affected ecosystems« less

Increased nitrogen availability counteracts climatic change feedback from increased temperature on boreal forest soil organic matter degradation

NASA Astrophysics Data System (ADS)

Erhagen, Bjorn; Nilsson, Mats; Oquist, Mats; Ilstedt, Ulrik; Sparrman, Tobias; Schleucher, Jurgen

2014-05-01

Over the last century, the greenhouse gas concentrations in the atmosphere have increased dramatically, greatly exceeding pre-industrial levels that had prevailed for the preceding 420 000 years. At the same time the annual anthropogenic contribution to the global terrestrial nitrogen cycle has increased and currently exceeds natural inputs. Both temperature and nitrogen levels have profound effects on the global carbon cycle including the rate of organic matter decomposition, which is the most important biogeochemical process that returns CO2 to the atmosphere. Here we show for the first time that increasing the availability of nitrogen not only directly affects the rate of organic matter decomposition but also significantly affects its temperature dependence. We incubated litter and soil organic matter from a long-term (40 years) nitrogen fertilization experiment in a boreal Scots pine (Pinus silvestris L.) forest at different temperatures and determined the temperature dependence of the decomposition of the sample's organic matter in each case. Nitrogen fertilization did not affect the temperature sensitivity (Q10) of the decomposition of fresh plant litter but strongly reduced that for humus soil organic matter. The Q10 response of the 0-3 cm soil layer decreased from 2.5±0.35 to an average of 1.9±0.21 over all nitrogen treatments, and from 2.2±0.19 to 1.6±0.16 in response to the most intense nitrogen fertilization treatment in the 4-7 cm soil layer. Long-term nitrogen additions also significantly affected the organic chemical composition (as determined by 13C CP-MAS NMR spectroscopy) of the soil organic matter. These changes in chemical composition contributed significantly (p<0.05) to the reduced Q10 response. These new insights into the relationship between nitrogen availability and the temperature sensitivity of organic matter decomposition will be important for understanding and predicting how increases in global temperature and rising anthropogenic nitrogen inputs will affect the global carbon cycle and the associated climatic feedback processes.

When high waters recede and the floodplain reemerges: Evaluating the lingering effects of extreme flooding on stream nitrogen cycling.

NASA Astrophysics Data System (ADS)

Neville, J.; Emanuel, R. E.

2017-12-01

In 2016 Hurricane Matthew brought immense flooding and devastation to the Lumbee (aka Lumber) River basin. Some impacts are obvious, such as deserted homes and businesses, but other impacts, including long-term environmental, are uncertain. Extreme flooding throughout the basin established temporary hydrologic connectivity between aquatic environments and upland sources of nutrients and other pollutants. Though 27% of the basin is covered by wetlands, hurricane-induced flooding was so intense that wetlands may have had no opportunity to mitigate delivery of nutrients into surface waters. As a result, how Hurricane Matthew impacted nitrate retention and uptake in the Lumbee River remains uncertain. The unknown magnitude of nitrate transported into the Lumbee River from surrounding sources may have lingering impacts on nitrogen cycling in this stream. With these potential impacts in mind, we conducted a Lagrangian water quality sampling campaign to assess the ability of the Lumbee River to retain and process nitrogen following Hurricane Matthew. We collected samples before and after flooding and compare first order nitrogen uptake kinetics of both periods. The analysis and comparisons allow us to evaluate the long-term impacts of Hurricane Matthew on nitrogen cycling after floodwaters recede.

An investigation of the solar cycle response of odd-nitrogen in the thermosphere

NASA Technical Reports Server (NTRS)

Rusch, David W.; Solomon, Stanley C.

1992-01-01

This annual report covers the first year of funding for the study of the solar cycle variations of odd-nitrogen (N((sup 2)D), N((sup 4)S), NO) in the Earth's thermosphere. The study uses the extensive data base generated by the Atmosphere Explorer (AE) satellites, and the Solar Mesosphere Explorer Satellite. The AE data are being used, for the first time, to define the solar variability effect on the odd-nitrogen species through analysis of the emissions at 520 nano-m from N((sup 2)D) and the emission from O(+)((sup 2)P). Additional AE neutral and ion density data are used to help define and quantify the physical processes controlling the variations. The results from the airglow study will be used in the next two years of this study to explain the solar cycle changes in NO measured by the Solar Mesosphere Explorer.

Ecological issues related to N deposition to natural ecosystems: research needs.

PubMed

Adams, Mary Beth

2003-06-01

There has and continues to be concern about the effects of elevated nitrogen (N) deposition on natural ecosystems. In this paper, research on natural ecosystems, including wetlands, heathlands, grasslands, steppe, naturally regenerated forests and deserts, is evaluated to determine what is known about nitrogen cycling in these ecosystems, the effects of elevated nitrogen on them and to identify research gaps. Aquatic ecosystems are not included in this review, except as they are part of the larger ecosystem. Research needs fall into several categories: (1) improved understanding and quantification of the N cycle, particularly relatively unstudied processes such as dry deposition, N fixation and decomposition/mineralization; (2) carbon cycling as affected by increased N deposition; (3) effects on arid ecosystems and other "neglected" ecosystems; (4) effects on complex ecosystems and interactions with other pollutants; (5) indicators and assessment tools for natural ecosystems.

Evaluating alternative approaches to modeling terrestrial C and N interactions using observations of ecosystem response to nitrogen deposition and experimental fertilization

NASA Astrophysics Data System (ADS)

Thomas, R. Q.; Bonan, G. B.; Goodale, C. L.

2012-12-01

In many forest ecosystems, nitrogen deposition is increasing carbon storage and reducing climate warming from fossil fuel emissions. Accurately modeling the forest carbon sequestration response to elevated nitrogen deposition using global biogeochemical models coupled to climate models is therefore important. Here, we use observations of the forest carbon response to both nitrogen fertilization experiments and nitrogen deposition gradients to test and improve a global biogeochemical model (CLM-CN 4.0). We introduce a series of model modifications to the CLM-CN that 1) creates a more closed nitrogen cycle with reduced nitrogen fixation and N gas loss and 2) includes buffering of plant nitrogen uptake and buffering of soil nitrogen available for plants and microbial processes. Overall, the modifications improved the comparison of the model predictions to the observational data by increasing the carbon storage response to historical nitrogen deposition (1850-2004) in temperate forest ecosystems by 144% and reducing the response to nitrogen fertilization. The increased sensitivity to nitrogen deposition was primarily attributable to greater retention of nitrogen deposition in the ecosystem and a greater role of synergy between nitrogen deposition and rising atmospheric CO2. Based on our results, we suggest that nitrogen retention should be an important attribute investigated in model inter-comparisons. To understand the specific ecosystem processes that contribute to the sensitivity of carbon storage to nitrogen deposition, we examined sensitivity to nitrogen deposition in a set of intermediary models that isolate the key differences in model structure between the CLM-CN 4.0 and the modified version. We demonstrate that the nitrogen deposition response was most sensitive to the implementation of a more closed nitrogen cycle and buffered plant uptake of soil mineral nitrogen, and less sensitive to modifications of the canopy scaling of photosynthesis, soil buffering of available nitrogen, and plant buffering of labile nitrogen. By comparing carbon storage sensitivity to observational data from both nitrogen deposition gradients and nitrogen fertilization experiments, we show different observed estimates of sensitivity between these two approaches could be explained by differences in the magnitude and time-scale of nitrogen additions.

Thermodynamic design of natural gas liquefaction cycles for offshore application

NASA Astrophysics Data System (ADS)

Chang, Ho-Myung; Lim, Hye Su; Choe, Kun Hyung

2014-09-01

A thermodynamic study is carried out for natural gas liquefaction cycles applicable to offshore floating plants, as partial efforts of an ongoing governmental project in Korea. For offshore liquefaction, the most suitable cycle may be different from the on-land LNG processes under operation, because compactness and simple operation are important as well as thermodynamic efficiency. As a turbine-based cycle, closed Claude cycle is proposed to use NG (natural gas) itself as refrigerant. The optimal condition for NG Claude cycle is determined with a process simulator (Aspen HYSYS), and the results are compared with fully-developed C3-MR (propane pre-cooled mixed refrigerant) JT cycles and various N2 (nitrogen) Brayton cycles in terms of efficiency and compactness. The newly proposed NG Claude cycle could be a good candidate for offshore LNG processes.

Modeling greenhouse gas emissions (CO2, N2O, CH4) from managed arable soils with a fully coupled hydrology-biogeochemical modeling system simulating water and nutrient transport and associated carbon and nitrogen cycling at catchment scale

NASA Astrophysics Data System (ADS)

Klatt, Steffen; Haas, Edwin; Kraus, David; Kiese, Ralf; Butterbach-Bahl, Klaus; Kraft, Philipp; Plesca, Ina; Breuer, Lutz; Zhu, Bo; Zhou, Minghua; Zhang, Wei; Zheng, Xunhua; Wlotzka, Martin; Heuveline, Vincent

2014-05-01

The use of mineral nitrogen fertilizer sustains the global food production and therefore the livelihood of human kind. The rise in world population will put pressure on the global agricultural system to increase its productivity leading most likely to an intensification of mineral nitrogen fertilizer use. The fate of excess nitrogen and its distribution within landscapes is manifold. Process knowledge on the site scale has rapidly grown in recent years and models have been developed to simulate carbon and nitrogen cycling in managed ecosystems on the site scale. Despite first regional studies, the carbon and nitrogen cycling on the landscape or catchment scale is not fully understood. In this study we present a newly developed modelling approach by coupling the fully distributed hydrology model CMF (catchment modelling framework) to the process based regional ecosystem model LandscapeDNDC for the investigation of hydrological processes and carbon and nitrogen transport and cycling, with a focus on nutrient displacement and resulting greenhouse gas emissions in a small catchment at the Yanting Agro-ecological Experimental Station of Purple Soil, Sichuan province, China. The catchment hosts cypress forests on the outer regions, arable fields on the sloping croplands cultivated with wheat-maize rotations and paddy rice fields in the lowland. The catchment consists of 300 polygons vertically stratified into 10 soil layers. Ecosystem states (soil water content and nutrients) and fluxes (evapotranspiration) are exchanged between the models at high temporal scales (hourly to daily) forming a 3-dimensional model application. The water flux and nutrients transport in the soil is modelled using a 3D Richards/Darcy approach for subsurface fluxes with a kinematic wave approach for surface water runoff and the evapotranspiration is based on Penman-Monteith. Biogeochemical processes are modelled by LandscapeDNDC, including soil microclimate, plant growth and biomass allocation, organic matter mineralisation, nitrification, denitrification, chemodenitrification and methanogenesis producing and consuming soil based greenhouse gases. The model application will present first validation results of the coupled model to simulate soil based greenhouse gas emissions as well as nitrate discharge from the Yanting catchment. The model application will also present the effects of different management practices (fertilization rates and timings, tilling, residues management) on the redistribution of N surplus within the catchment causing biomass productivity gradients and different levels of indirect N2O emissions along topographical gradients.

Improved Environmental Life Cycle Assessment of Crop Production at the Catchment Scale via a Process-Based Nitrogen Simulation Model.

PubMed

Liao, Wenjie; van der Werf, Hayo M G; Salmon-Monviola, Jordy

2015-09-15

One of the major challenges in environmental life cycle assessment (LCA) of crop production is the nonlinearity between nitrogen (N) fertilizer inputs and on-site N emissions resulting from complex biogeochemical processes. A few studies have addressed this nonlinearity by combining process-based N simulation models with LCA, but none accounted for nitrate (NO3(-)) flows across fields. In this study, we present a new method, TNT2-LCA, that couples the topography-based simulation of nitrogen transfer and transformation (TNT2) model with LCA, and compare the new method with a current LCA method based on a French life cycle inventory database. Application of the two methods to a case study of crop production in a catchment in France showed that, compared to the current method, TNT2-LCA allows delineation of more appropriate temporal limits when developing data for on-site N emissions associated with specific crops in this catchment. It also improves estimates of NO3(-) emissions by better consideration of agricultural practices, soil-climatic conditions, and spatial interactions of NO3(-) flows across fields, and by providing predicted crop yield. The new method presented in this study provides improved LCA of crop production at the catchment scale.

Modeling reactive nitrogen in North America: recent ...

EPA Pesticide Factsheets

Nitrogen is an essential building block of all proteins and thus an essential nutrient for all life. The bulk of nitrogen in the environment is tightly bound as non-reactive N2. Reactive nitrogen, which is naturally produced via enzymatic reactions, forest fires and lightning, is continually recycled and cascades through air, water, and soil media (Galloway et al., 2003). Human activity has perturbed this cycle through the combustion of fossil fuels and synthesis of fertilizers. The anthropogenic contribution to this cycle is now larger than natural sources in the United States and globally (Galloway et al., 2004). Reactive nitrogen enters the biosphere primarily from emissions of oxidized nitrogen to the atmosphere from combustion sources, as inorganic fertilizer applied to crops as reduced nitrogen fixed from atmospheric N2 through the Haber-Bosch process, as organic fertilizers such as manure, and through the cultivation of nitrogen fixing crops (Canfield et al., 2010). Both the United States (US) Clean Air Act and the Canadian Environmental Protection Act (CEPA) have substantially reduced the emissions of oxidized nitrogen in North America through NOx controls on smokestacks and exhaust pipes (Sickles and Shadwick, 2015; AQA, 2015). However, reduced nitrogen emissions have remained constant during the last few decades of emission reductions. The National Exposure Research Laboratory’s Atmospheric Modeling Division (AMAD) c

Nitrogen processing by grazers in a headwater stream: riparian connections

DOE PAGES

Hill, Walter R.; Griffiths, Natalie A.

2016-10-19

Primary consumers play important roles in the cycling of nutrients in headwater streams, storing assimilated nutrients in growing tissue and recycling them through excretion. Though environmental conditions in most headwater streams and their surrounding terrestrial ecosystems vary considerably over the course of a year, relatively little is known about the effects of seasonality on consumer nutrient recycling these streams. Here, we measured nitrogen accumulated through growth and excreted by the grazing snail Elimia clavaeformis (Pleuroceridae) over the course of 12 months in Walker Branch, identifying close connections between in-stream nitrogen processing and seasonal changes in the surrounding forest.

The Evolution of Massive Close Binaries: Anomalous Relationship between Nitrogen Abundances and Rotational Velocities

NASA Astrophysics Data System (ADS)

Song, Hanfeng; Wang, Jiangtao; Song, Fen; Zhang, Ruiyu; Li, Zhi; Peng, Weiguo; Zhan, Qiong; Jing, Jianghong

2018-05-01

The combined effects of rotation and mass accretion on the evolution of binary systems are investigated in this work. Rotational binaries provide us with a promising channel that could explain the abnormal phenomenon of the nitrogen abundances in Groups 1 and 2 of the Galactic Hunter diagram. Group 1 contains fast-rotating but nitrogen-unenriched stars, whereas Group 2 includes apparently slowly rotating but nitrogen-enhanced stars. The donor star suffers from heavy mass loss that progressively exposes deep layers of nitrogen and corresponding angular momentum loss that can efficiently spin the star down. Rapid-rotation stars without nitrogen enrichment may be related to mass gainers that had accreted little matter from a close companion and then been spun up to rapid rotation. Nitrogen enrichment of mass gainers can be greatly suppressed by low accreting efficiency, which is induced by critical rotation, thermohaline mixing, and the gradient of mean molecular weight. Nitrogen enrichment due to mass accretion appears to be more efficient than that due to rotational mixing, because there exist thermohaline instabilities during Roche lobe overflow. The mixing in the enlarged convective core reduces carbon and nitrogen abundances but increases oxygen abundances in mass gainers. This process significantly triggers CNO cycling but does not support CN cycling. The orbital separation can be widened because of the nonconservative mass transfer, and this process gives rise to weak tidal torques. Therefore, invoking binaries has the potential to simultaneously explain the observed stars in Groups 1 and 2 of the Galactic Hunter diagram.

SOLAR ULTRAVIOLET RADIATION AND AQUATIC CARBON, NITROGEN, SULFUR AND METALS CYCLES

EPA Science Inventory

Solar ultraviolet radiation (290-400 nm) has a wide-ranging impact on biological and chemical processes that affect the cycling of elements in aquatic environments. This chapter uses recent field and laboratory observations along with models to assess these impacts on carbon, nit...

Nitrogen dynamics in an Alaskan salt marsh following spring use by geese

USGS Publications Warehouse

Zacheis, Amy B.; Ruess, Roger W.; Hupp, Jerry W.

2002-01-01

Lesser snow geese (Anser caerulescens caerulescens) and Canada geese (Branta canadensis) use several salt marshes in Cook Inlet, Alaska, as stopover areas for brief periods during spring migration. We investigated the effects of geese on nitrogen cycling processes in Susitna Flats, one of the marshes. We compared net nitrogen mineralization, organic nitrogen pools and production in buried bags, nitrogen fixation by cyanobacteria, and soil and litter characteristics on grazed plots versus paired plots that had been exclosed from grazing for 3 years. Grazed areas had higher rates of net nitrogen mineralization in the spring and there was no effect of grazing on organic nitrogen availability. The increased mineralization rates in grazed plots could not be accounted for by alteration of litter quality, litter quantity, microclimate, or root biomass, which were not different between grazed and exclosed plots. In addition, fecal input was very slight in the year that we studied nitrogen cycling. We propose that trampling had two effects that could account for greater nitrogen availability in grazed areas: litter incorporation into soil, resulting in increased rates of decomposition and mineralization of litter material, and greater rates of nitrogen fixation by cyanobacteria on bare, trampled soils. A path analysis indicated that litter incorporation by trampling played a primary role in the nitrogen dynamics of the system, with nitrogen fixation secondary, and that fecal input was of little importance.

Nitrogen cycling processes and microbial community composition in bed sediments in the Yukon River at Pilot Station

USGS Publications Warehouse

Repert, Deborah A.; Underwood, Jennifer C.; Smith, Richard L.; Song, Bongkeun

2014-01-01

Information on the contribution of nitrogen (N)-cycling processes in bed sediments to river nutrient fluxes in large northern latitude river systems is limited. This study examined the relationship between N-cycling processes in bed sediments and N speciation and loading in the Yukon River near its mouth at the Bering Sea. We conducted laboratory bioassays to measure N-cycling processes in sediment samples collected over distinct water cycle seasons. In conjunction, the microbial community composition in the bed sediments using genes involved in N-cycling (narG, napA, nosZ, and amoA) and 16S rRNA gene pyrosequences was examined. Temporal variation was observed in net N mineralization, nitrate uptake, and denitrification rate potentials and correlated strongly with sediment carbon (C) and extractable N content and microbial community composition rather than with river water nutrient concentrations. The C content of the bed sediment was notably impacted by the spring flood, ranging from 1.1% in the midst of an ice-jam to 0.1% immediately after ice-out, suggesting a buildup of organic material (OM) prior to scouring of the bed sediments during ice break up. The dominant members of the microbial community that explained differences in N-processing rates belonged to the genera Crenothrix,Flavobacterium, and the family of Comamonadaceae. Our results suggest that biogeochemical processing rates in the bed sediments appear to be more coupled to hydrology, nutrient availability in the sediments, and microbial community composition rather than river nutrient concentrations at Pilot Station.

Variation in nitrogen use efficiencies on Dutch dairy farms.

PubMed

Daatselaar, Co Hg; Reijs, Joan R; Oenema, Jouke; Doornewaard, Gerben J; Aarts, H Frans M

2015-12-01

On dairy farms, the input of nutrients including nitrogen is higher than the output in products such as milk and meat. This causes losses of nitrogen to the environment. One of the indicators for the losses of nitrogen is the nitrogen use efficiency. In the Dutch Minerals Policy Monitoring Program (LMM), many data on nutrients of a few hundred farms are collected which can be processed by the instrument Annual Nutrient Cycle Assessment (ANCA, in Dutch: Kringloopwijzer) in order to provide nitrogen use efficiencies. After dividing the dairy farms (available in the LMM program) according to soil type and in different classes for milk production ha(-1) , it is shown that considerable differences in nitrogen use efficiency exist between farms on the same soil type and with the same level of milk production ha(-1) . This offers opportunities for improvement of the nitrogen use efficiency on many dairy farms. Benchmarking will be a useful first step in this process. © 2015 Society of Chemical Industry.

Retrofitting activated sludge systems to intermittent aeration for nitrogen removal.

PubMed

Hanhan, O; Artan, N; Orhon, D

2002-01-01

The paper provides the basis and the conceptual approach of applying process kinetics and modelling to the design of alternating activated sludge systems for retrofitting existing activated sludge plants to intermittent aeration for nitrogen removal. It shows the significant role of the two specific parameters, namely, the aerated fraction and the cycle time ratio on process performance through model simulations and proposes a way to incorporate them into a design procedure using process stoichiometry and mass balance. It illustrates the effect of these parameters, together with the sludge age, in establishing the balance between the denitrification potential and the available nitrogen created in the anoxic/aerobic sequences of system operation.

Air. Ag Ed Environmental Education Series.

ERIC Educational Resources Information Center

Tulloch, Rodney W.

The document is a student resource unit to be used in teaching high school vocational agriculture students about air. The following natural processes are described: carbon dioxide cycle, nitrogen cycle, gravity and atmosphere, energy of the sun, greenhouse effect, atmospheric circulation, and precipitation. Sources of air pollution are discussed.…

Foliar nitrogen characteristics of four tree species planted in New York City forest restoration sites

Treesearch

Nancy Falxa-Raymond; Matthew I. Palmer; Timon McPhearson; Kevin L. Griffin

2014-01-01

Urban forests provide important environmental benefits, leading many municipal governments to initiate citywide tree plantings. However, nutrient cycling in urban ecosystems is difficult to predict, and nitrogen (N) use in urban trees may be quite different from use in rural forests. To gain insight into these biogeochemical and physiological processes, we compared...

Elucidation of major contributors involved in nitrogen removal and transcription level of nitrogen-cycling genes in activated sludge from WWTPs

NASA Astrophysics Data System (ADS)

Che, You; Liang, Peixin; Gong, Ting; Cao, Xiangyu; Zhao, Ying; Yang, Chao; Song, Cunjiang

2017-03-01

We investigated nitrogen-cycle bacterial communities in activated sludge from 8 municipal wastewater treatment plants (WWTPs). Redundancy analyses (RDA) showed that temperature was the most significant driving force in shaping microbial community structure, followed by influent NH4+ and total nitrogen (TN). The diversity of ammonia oxidizing and nitrite reducing bacteria were investigated by the construction of amoA, nirS and nirK gene clone libraries. Phylogenetic analysis indicated that Thauera and Mesorhizobium were the predominant nitrite reducing bacteria, and Nitrosomonas was the only detected ammonia oxidizing bacteria in all samples. Quantification of transcription level of nirS and nirK genes indicated that nirS-type nitrite reducing bacteria played the dominant roles in nitrite reduction process. Transcription level of nirS gene positively correlated with influent NH4+ and TN significantly, whereas inversely linked with hydraulic retention time. Temperature had a strong positive correlation to transcription level of amoA gene. Overall, this study deepened our understanding of the major types of ammonia oxidizing and nitrite reducing bacteria in activated sludge of municipal WWTPs. The relationship between transcription level of nitrogen-cycle genes and operational or environmental variables of WWTPs revealed in this work could provide guidance for optimization of operating parameters and improving the performance of nitrogen removal.

Decoupling of microbial carbon, nitrogen, and phosphorus cycling in response to extreme temperature events

PubMed Central

Mooshammer, Maria; Hofhansl, Florian; Frank, Alexander H.; Wanek, Wolfgang; Hämmerle, Ieda; Leitner, Sonja; Schnecker, Jörg; Wild, Birgit; Watzka, Margarete; Keiblinger, Katharina M.; Zechmeister-Boltenstern, Sophie; Richter, Andreas

2017-01-01

Predicted changes in the intensity and frequency of climate extremes urge a better mechanistic understanding of the stress response of microbially mediated carbon (C) and nutrient cycling processes. We analyzed the resistance and resilience of microbial C, nitrogen (N), and phosphorus (P) cycling processes and microbial community composition in decomposing plant litter to transient, but severe, temperature disturbances, namely, freeze-thaw and heat. Disturbances led temporarily to a more rapid cycling of C and N but caused a down-regulation of P cycling. In contrast to the fast recovery of the initially stimulated C and N processes, we found a slow recovery of P mineralization rates, which was not accompanied by significant changes in community composition. The functional and structural responses to the two distinct temperature disturbances were markedly similar, suggesting that direct negative physical effects and costs associated with the stress response were comparable. Moreover, the stress response of extracellular enzyme activities, but not that of intracellular microbial processes (for example, respiration or N mineralization), was dependent on the nutrient content of the resource through its effect on microbial physiology and community composition. Our laboratory study provides novel insights into the mechanisms of microbial functional stress responses that can serve as a basis for field studies and, in particular, illustrates the need for a closer integration of microbial C-N-P interactions into climate extremes research. PMID:28508070

Insights on the marine microbial nitrogen cycle from isotopic approaches to nitrification

PubMed Central

Casciotti, Karen L.; Buchwald, Carolyn

2012-01-01

The microbial nitrogen (N) cycle involves a variety of redox processes that control the availability and speciation of N in the environment and that are involved with the production of nitrous oxide (N2O), a climatically important greenhouse gas. Isotopic measurements of ammonium (NH+4), nitrite (NO−2), nitrate (NO−3), and N2O can now be used to track the cycling of these compounds and to infer their sources and sinks, which has lead to new and exciting discoveries. For example, dual isotope measurements of NO−3 and NO−2 have shown that there is NO−3 regeneration in the ocean's euphotic zone, as well as in and around oxygen deficient zones (ODZs), indicating that nitrification may play more roles in the ocean's N cycle than generally thought. Likewise, the inverse isotope effect associated with NO−2 oxidation yields unique information about the role of this process in NO−2 cycling in the primary and secondary NO−2 maxima. Finally, isotopic measurements of N2O in the ocean are indicative of an important role for nitrification in its production. These interpretations rely on knowledge of the isotope effects for the underlying microbial processes, in particular ammonia oxidation and nitrite oxidation. Here we review the isotope effects involved with the nitrification process and the insights provided by this information, then provide a prospectus for future work in this area. PMID:23091468

Insights on the marine microbial nitrogen cycle from isotopic approaches to nitrification.

PubMed

Casciotti, Karen L; Buchwald, Carolyn

2012-01-01

The microbial nitrogen (N) cycle involves a variety of redox processes that control the availability and speciation of N in the environment and that are involved with the production of nitrous oxide (N(2)O), a climatically important greenhouse gas. Isotopic measurements of ammonium (NH(+) (4)), nitrite (NO(-) (2)), nitrate (NO(-) (3)), and N(2)O can now be used to track the cycling of these compounds and to infer their sources and sinks, which has lead to new and exciting discoveries. For example, dual isotope measurements of NO(-) (3) and NO(-) (2) have shown that there is NO(-) (3) regeneration in the ocean's euphotic zone, as well as in and around oxygen deficient zones (ODZs), indicating that nitrification may play more roles in the ocean's N cycle than generally thought. Likewise, the inverse isotope effect associated with NO(-) (2) oxidation yields unique information about the role of this process in NO(-) (2) cycling in the primary and secondary NO(-) (2) maxima. Finally, isotopic measurements of N(2)O in the ocean are indicative of an important role for nitrification in its production. These interpretations rely on knowledge of the isotope effects for the underlying microbial processes, in particular ammonia oxidation and nitrite oxidation. Here we review the isotope effects involved with the nitrification process and the insights provided by this information, then provide a prospectus for future work in this area.

Cycling the hot CNO: a teaching methodology

NASA Astrophysics Data System (ADS)

Frost-Schenk, J. W.; Diget, C. Aa; Bentley, M. A.; Tuff, A.

2018-03-01

An interactive activity to teach the hot Carbon, Nitrogen and Oxygen (HCNO) cycle is proposed. Justification for why the HCNO cycle is important is included via an example of x-ray bursts. The activity allows teaching and demonstration of half-life, nuclear isotopes, nuclear reactions, protons and α-particles, and catalytic processes. Whilst the process example is specific to astrophysics it may be used to teach more broadly about catalytic processes. This practical is designed for use with 10-20 participants, with the intention that the exercise will convey nuclear physics principles in a fun and interactive manner.

Regenerating temperate forest mesocosms in elevated CO2: belowground growth and nitrogen cycling.

PubMed

Berntson, G M; Bazzaz, F A

1997-12-01

The response of temperate forest ecosystems to elevated atmospheric CO 2 concentrations is important because these ecosystems represent a significant component of the global carbon cycle. Two important but not well understood processes which elevated CO 2 may substantially alter in these systems are regeneration and nitrogen cycling. If elevated CO 2 leads to changes in species composition in regenerating forest communities then the structure and function of these ecosystems may be affected. In most temperate forests, nitrogen appears to be a limiting nutrient. If elevated CO 2 leads to reductions in nitrogen cycling through increased sequestration of nitrogen in plant biomass or reductions in mineralization rates, long-term forest productivity may be constrained. To study these processes, we established mesocosms of regenerating forest communities in controlled environments maintained at either ambient (375 ppm) or elevated (700 ppm) CO 2 concentrations. Mesocosms were constructed from intact monoliths of organic forest soil. We maintained these mesocosms for 2 years without any external inputs of nitrogen and allowed the plants naturally present as seeds and rhizomes to regenerate. We used 15 N pool dilution techniques to quantify nitrogen fluxes within the mesocosms at the end of the 2 years. Elevated atmospheric CO 2 concentration significantly affected a number of plant and soil processes in the experimental regenerating forest mesocosms. These changes included increases in total plant biomass production, plant C/N ratios, ectomycorrhizal colonization of tree fine roots, changes in tree fine root architecture, and decreases in plant NH 4 + uptake rates, gross NH 4 + mineralization rates, and gross NH 4 + consumption rates. In addition, there was a shift in the relative biomass contribution of the two dominant regenerating tree species; the proportion of total biomass contributed by white birch (Betula papyrifera) decreased and the proportion of total biomass contributed by yellow birch (B. alleghaniensis) increased. However, elevated CO 2 had no significant effect on the total amount of nitrogen in plant and soil microbial biomass. In this study we observed a suite of effects due to elevated CO 2 , some of which could lead to increases in potential long term growth responses to elevated CO 2 , other to decreases. The reduced plant NH 4 + uptake rates we observed are consistent with reduced NH 4 + availability due to reduced gross mineralization rates. Reduced NH 4 + mineralization rates are consistent with the increases in C/N ratios we observed for leaf and fine root material. Together, these data suggest the positive increases in plant root architectural parameters and mycorrhizal colonization may not be as important as the potential negative effects of reduced nitrogen availability through decreased decomposition rates in a future atmosphere with elevated CO 2 .

Ecological Energetic Perspectives on Responses of Nitrogen-Transforming Chemolithoautotrophic Microbiota to Changes in the Marine Environment

PubMed Central

Dang, Hongyue; Chen, Chen-Tung A.

2017-01-01

Transformation and mobilization of bioessential elements in the biosphere, lithosphere, atmosphere, and hydrosphere constitute the Earth’s biogeochemical cycles, which are driven mainly by microorganisms through their energy and material metabolic processes. Without microbial energy harvesting from sources of light and inorganic chemical bonds for autotrophic fixation of inorganic carbon, there would not be sustainable ecosystems in the vast ocean. Although ecological energetics (eco-energetics) has been emphasized as a core aspect of ecosystem analyses and microorganisms largely control the flow of matter and energy in marine ecosystems, marine microbial communities are rarely studied from the eco-energetic perspective. The diverse bioenergetic pathways and eco-energetic strategies of the microorganisms are essentially the outcome of biosphere-geosphere interactions over evolutionary times. The biogeochemical cycles are intimately interconnected with energy fluxes across the biosphere and the capacity of the ocean to fix inorganic carbon is generally constrained by the availability of nutrients and energy. The understanding of how microbial eco-energetic processes influence the structure and function of marine ecosystems and how they interact with the changing environment is thus fundamental to a mechanistic and predictive understanding of the marine carbon and nitrogen cycles and the trends in global change. By using major groups of chemolithoautotrophic microorganisms that participate in the marine nitrogen cycle as examples, this article examines their eco-energetic strategies, contributions to carbon cycling, and putative responses to and impacts on the various global change processes associated with global warming, ocean acidification, eutrophication, deoxygenation, and pollution. We conclude that knowledge gaps remain despite decades of tremendous research efforts. The advent of new techniques may bring the dawn to scientific breakthroughs that necessitate the multidisciplinary combination of eco-energetic, biogeochemical and “omics” studies in this field. PMID:28769878

Global Coupled Carbon and Nitrogen Models: Successes, Failures and What next?

NASA Astrophysics Data System (ADS)

Holland, E. A.

2011-12-01

Over the last few years, there has been a great deal of progress in modeling coupled terrestrial global carbon and nitrogen cycles and their roles in Earth System models. The collection of recent models provides some surprising results and insights. A critical question for Earth system models is: How do the coupled C/N model results impact atmospheric carbon dioxide concentrations compared to carbon only models? Some coupled models predict increased atmospheric carbon dioxide concentrations, the result expected from nitrogen-limited photosynthesis uptake of carbon dioxide, while others predict little change or decreased carbon dioxide uptake with a coupled carbon and nitrogen cycle. With this range of impacts for climate critical atmospheric carbon dioxide concentrations, there is clearly a need for additional comparison of measurements and models. Randerson et al.'s CLAMP study provided important constraints and comparison for primarily for aboveground carbon uptake. However, nitrogen supply is largely determined decomposition and soil processes. I will present comparisons of NCAR's CESM results with soil and litter carbon and nitrogen fluxes and standing stocks. These belowground data sets of both carbon and nitrogen provide important benchmarks for coupled C/N models.

Life cycle energy and greenhouse gas profile of a process for the production of ammonium sulfate from nitrogen-fixing photosynthetic cyanobacteria.

PubMed

Razon, Luis F

2012-03-01

In this paper, an alternative means for nitrogen fixation that may consume less energy and release less greenhouse gases than the Haber-Bosch process is explored. A life-cycle assessment was conducted on a process to: culture the cyanobacterium, Anabaena sp. ATCC 33047, in open ponds; harvest the biomass and exopolysaccharides and convert these to biogas; strip and convert the ammonia from the biogas residue to ammonium sulfate; dry the ammonium sulfate solution to ammonium sulfate crystals and transport the finished product. The results suggest that substantial reductions in non-renewable energy use and greenhouse gas emissions may be realized. The study opens the possibility that Haber-Bosch ammonia may be replaced with ammonia from a biomass process which simultaneously generates renewable energy. The process is intrinsically safer than the Haber-Bosch process. However, there are trade-offs in terms of land use and possibly, water. Copyright © 2011 Elsevier Ltd. All rights reserved.

The environmental controls that govern the end product of bacterial nitrate respiration

DOE PAGES

Kraft, Beate; Tegetmeyer, Halina E.; Sharma, Ritin; ...

2014-08-08

In the biogeochemical nitrogen cycle, microbial respiration processes compete for nitrate as an electron acceptor. Denitrification converts nitrate into nitrogenous gas and thus removes fixed nitrogen from the biosphere, whereas ammonification converts nitrate into ammonium, which is directly reusable by primary producers. In this paper, we combined multiple parallel long-term incubations of marine microbial nitrate-respiring communities with isotope labeling and metagenomics to unravel how specific environmental conditions select for either process. Microbial generation time, supply of nitrite relative to nitrate, and the carbon/nitrogen ratio were identified as key environmental controls that determine whether nitrite will be reduced to nitrogenous gasmore » or ammonium. Finally, our results define the microbial ecophysiology of a biogeochemical feedback loop that is key to global change, eutrophication, and wastewater treatment.« less

Genetics Home Reference: lysinuric protein intolerance

MedlinePlus

... abnormally large amount of these amino acids in urine. A shortage of lysine, arginine, and ornithine disrupts many vital functions. Arginine and ornithine are involved in a cellular process called the urea cycle, which processes excess nitrogen (in the form ...

The Impact of Extreme Flooding on Mussel and Microbial Nutrient Dynamics at the Water-Sediment Interface

NASA Astrophysics Data System (ADS)

Bril, J.; Just, C. L.; Newton, T.; Young, N.; Parkin, G.

2009-12-01

Labeled by the National Academy of Engineering as one of fourteen grand challenges for engineering, the management of the nitrogen cycle has become an increasingly difficult obstacle for sustainable development. In an effort to improve nitrogen cycle management practices, we are attempting to expand on the limited scientific knowledge of how aquatic environments are affected by increasing human- and climate-induced changes. To accomplish this, we are using freshwater mussels as a sentinel species to indicate how natural processes within large river systems may be altered by human activity. Freshwater mussels have been referred to as ‘ecosystem engineers’ because they exert control over food resources and alter habitats for other organisms. Also, mussels and bacteria play a major role in nutrient cycling in large river systems by cycling nutrients taken up by phytoplankton and zooplankton. Under ‘normal’ environmental conditions, mussels appear to process nitrogen more rapidly than denitrifying bacteria. However, substantial deposition of carbon-rich sediment resulting from extreme flooding may increase bacterial nitrogen cycling rates and subsequently alter overall denitrification rates. We hypothesize that intense depositions of particulate matter from recent extreme floods in the Upper Mississippi River Basin (UMRB) have altered the freshwater mussel and microbial food webs through physical and chemical means. This work will be done in a 1200-m reach of the UMRB near Buffalo, Iowa. The reach contains a healthy and diverse assemblage of freshwater mussels. A historic flood event during May-July 2008 coincided with intense spring cultivation and nutrient application activities in the heavily farmed landscape of the Upper Midwest and resulted in a significant pulse of agricultural contaminants to the UMRB. This led scientists to predict an almost unprecedented delivery of sediment and nutrients to the mussel bed, the broader Mississippi River, and ultimately to the Gulf of Mexico. We will correlate the rate of nitrogen removal by mussels to the concentrations of organic carbon that may have been deposited during the flood. Initial studies suggest that the highest amount of total organic carbon exists in areas of fine sediments within the mussel bed. Additionally, bacterial nitrate reduction studies indicate that significantly higher rates of denitrification occur in areas of high organic content. Increased availability of organic carbon may affect the rate that mussels process nitrogen. In field studies, mussel densities are generally greater in areas of coarser sediments (thus, less carbon and less bacterial nutrient processing). We are currently working to determine the role of organic carbon availability on denitrification in a laboratory system containing mussels and bacteria. We also hope to couple sediment grain size with organic carbon to compare organic carbon content pre- and post-flood.

Isotopic Biomarkers of Nitrogenase Metalloenzymes: Forging Links Between the Cycles of Nitrogen and Trace Metals

NASA Astrophysics Data System (ADS)

Zhang, X.; McRose, D. L.; Darnajoux, R.; Bellenger, J. P.; Kraepiel, A. M. L.

2015-12-01

Biological N2 fixation, catalyzed by the metalloenzyme nitrogenase, is a critical process that makes life possible on Earth. Environmental N2 fixation has been automatically attributed to canonical Mo-based nitrogenases despite over two decades of knowledge that two other metalloenzyme forms of nitrogenase exist: those containing catalytic V or Fe-only. A key area of missing information is the contribution of the "alternative" V and Fe-only nitrogenases, as the interpretation of field data to construct budgets and assess N availability depends on the type of nitrogenase metalloenzyme used to fix N2. Additionally, substantial changes in metal speciation over geological time may have favored the use of different metalloenzymes, with implications for evolution of the biosphere. Despite the potential importance of alternative nitrogenases in modern and ancient N cycling, few methods can determine their contributions to environmental N2 fixation. Here, we present new isotopic methods to distinguish between the activities of Mo, V, and Fe-only nitrogenases. We show evidence for alternative N2 fixation in diverse environments (cyanolichens, microbial mats, sediments, leaf litter), thereby linking a key process in the nitrogen cycle to specific metalloenzyme forms of nitrogenase. The results invite a reexamination of the conditions under which the different nitrogenase metalloenzymes are active and may lead to new insights into the coupling of the cycles of nitrogen and trace metals.

Nitrogen attenuation of terrestrial carbon cycle response to global environmental factors

Treesearch

Atul Jain; Xiaojuan Yang; Haroon Kheshgi; A. David McGuire; Wilfred Post; David Kicklighter

2009-01-01

Nitrogen cycle dynamics have the capacity to attenuate the magnitude of global terrestrial carbon sinks and sources driven by CO2 fertilization and changes in climate. In this study, two versions of the terrestrial carbon and nitrogen cycle components of the Integrated Science Assessment Model (ISAM) are used to evaluate how variation in nitrogen...

Identification of anthropogenic impact on nitrogen cycling using stable isotopes and distibuted hydrologic modeling

NASA Astrophysics Data System (ADS)

Macko, S. A.; O'Connell, M. T.; Fu, Y.

2016-12-01

The Najinhe watershed is a topographically diverse, heavily agricultural watershed in northeastern China that provides opportunities for identification of the impact of land use on nitrogen cycling. Land use, both historic and current, influences the biological processing of nitrogen in a particular area. Soil conditions, including moisture, texture, and organic content, control the capacity of a parcel for processing reactive nitrogen. Compounds derived from natural and anthropogenic sources exhibit characteristic ratios of stable isotopes of nitrogen and oxygen that serve as tracers of origin as well as integrators of biological processes. A distributed hydrologic model coupled with one focusing on reactive transport is able to help determine locations with the highest impact on the dissolved N in this system. Gaussian Markov Random Fields were used to determine the biogeochemical influence of model locations whereas δ15N measurements from NO3- and NH4+ in soil extracts were used to calibrate and validate model predictions based on measured precipitation and streamflow values. Sources were integrated using a Bayesian mixing model to determine likely fate and transport parameters for various N inputs to the watershed. The application of the coupled hydrologic and transport models to a village scale catchment suggests integration and expansion to larger watersheds on the basin scale. Identification of sensitive parcels on multiple spatial scales can direct targeted land management efforts to mitigate ecological and health effects of reactive N in surface waters.

Review of nitrogen fate models applicable to forest landscapes in the Southern U.S.

Treesearch

D. M. Amatya; C. G. Rossi; A. Saleh; Z. Dai; M. A. Youssef; R. G. Williams; D. D. Bosch; G. M. Chescheir; G. Sun; R. W. Skaggs; C. C. Trettin; E. D. Vance; J. E. Nettles; S. Tian

2013-01-01

Assessing the environmental impacts of fertilizer nitrogen (N) used to increase productivity in managed forests is complex due to a wide range of abiotic and biotic factors affecting its forms and movement. Models developed to predict fertilizer N fate (e.g., cycling processes) and water quality impacts vary widely in their design, scope, and potential application. We...

Richness, biomass, and nutrient content of a wetland macrophyte community affect soil nitrogen cycling in a diversity-ecosystem functioning experiment

USGS Publications Warehouse

Korol, Alicia R.; Ahn, Changwoo; Noe, Gregory

2016-01-01

The development of soil nitrogen (N) cycling in created wetlands promotes the maturation of multiple biogeochemical cycles necessary for ecosystem functioning. This development proceeds from gradual changes in soil physicochemical properties and influential characteristics of the plant community, such as competitive behavior, phenology, productivity, and nutrient composition. In the context of a 2-year diversity experiment in freshwater mesocosms (0, 1, 2, 3, or 4 richness levels), we assessed the direct and indirect impacts of three plant community characteristics – species richness, total biomass, and tissue N concentration – on three processes in the soil N cycle – soil net ammonification, net nitrification, and denitrification potentials. Species richness had a positive effect on net ammonification potential (NAP) through higher redox potentials and likely faster microbial respiration. All NAP rates were negative, however, due to immobilization and high rates of ammonium removal. Net nitrification was inhibited at higher species richness without mediation from the measured soil properties. Higher species richness also inhibited denitrification potential through increased redox potential and decreased nitrification. Both lower biomass and/or higher tissue ratios of carbon to nitrogen, characteristics indicative of the two annual plants, were shown to have stimulatory effects on all three soil N processes. The two mediating physicochemical links between the young macrophyte community and microbial N processes were soil redox potential and temperature. Our results suggest that early-successional annual plant communities play an important role in the development of ecosystem N multifunctionality in newly created wetland soils.

Representing leaf and root physiological traits in CLM improves global carbon and nitrogen cycling predictions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ghimire, Bardan; Riley, William J.; Koven, Charles D.

In many ecosystems, nitrogen is the most limiting nutrient for plant growth and productivity. However, current Earth System Models (ESMs) do not mechanistically represent functional nitrogen allocation for photosynthesis or the linkage between nitrogen uptake and root traits. The current version of CLM (4.5) links nitrogen availability and plant productivity via (1) an instantaneous downregulation of potential photosynthesis rates based on soil mineral nitrogen availability, and (2) apportionment of soil nitrogen between plants and competing nitrogen consumers assumed to be proportional to their relative N demands. However, plants do not photosynthesize at potential rates and then downregulate; instead photosynthesis ratesmore » are governed by nitrogen that has been allocated to the physiological processes underpinning photosynthesis. Furthermore, the role of plant roots in nutrient acquisition has also been largely ignored in ESMs. We therefore present a new plant nitrogen model for CLM4.5 with (1) improved representations of linkages between leaf nitrogen and plant productivity based on observed relationships in a global plant trait database and (2) plant nitrogen uptake based on root-scale Michaelis-Menten uptake kinetics. Our model improvements led to a global bias reduction in GPP, LAI, and biomass of 70%, 11%, and 49%, respectively. Furthermore, water use efficiency predictions were improved conceptually, qualitatively, and in magnitude. The new model's GPP responses to nitrogen deposition, CO 2 fertilization, and climate also differed from the baseline model. The mechanistic representation of leaf-level nitrogen allocation and a theoretically consistent treatment of competition with belowground consumers led to overall improvements in global carbon cycling predictions.« less

Representing leaf and root physiological traits in CLM improves global carbon and nitrogen cycling predictions

DOE PAGES

Ghimire, Bardan; Riley, William J.; Koven, Charles D.; ...

2016-05-01

In many ecosystems, nitrogen is the most limiting nutrient for plant growth and productivity. However, current Earth System Models (ESMs) do not mechanistically represent functional nitrogen allocation for photosynthesis or the linkage between nitrogen uptake and root traits. The current version of CLM (4.5) links nitrogen availability and plant productivity via (1) an instantaneous downregulation of potential photosynthesis rates based on soil mineral nitrogen availability, and (2) apportionment of soil nitrogen between plants and competing nitrogen consumers assumed to be proportional to their relative N demands. However, plants do not photosynthesize at potential rates and then downregulate; instead photosynthesis ratesmore » are governed by nitrogen that has been allocated to the physiological processes underpinning photosynthesis. Furthermore, the role of plant roots in nutrient acquisition has also been largely ignored in ESMs. We therefore present a new plant nitrogen model for CLM4.5 with (1) improved representations of linkages between leaf nitrogen and plant productivity based on observed relationships in a global plant trait database and (2) plant nitrogen uptake based on root-scale Michaelis-Menten uptake kinetics. Our model improvements led to a global bias reduction in GPP, LAI, and biomass of 70%, 11%, and 49%, respectively. Furthermore, water use efficiency predictions were improved conceptually, qualitatively, and in magnitude. The new model's GPP responses to nitrogen deposition, CO 2 fertilization, and climate also differed from the baseline model. The mechanistic representation of leaf-level nitrogen allocation and a theoretically consistent treatment of competition with belowground consumers led to overall improvements in global carbon cycling predictions.« less

Representing leaf and root physiological traits in CLM improves global carbon and nitrogen cycling predictions

NASA Astrophysics Data System (ADS)

Ghimire, Bardan; Riley, William J.; Koven, Charles D.; Mu, Mingquan; Randerson, James T.

2016-06-01

In many ecosystems, nitrogen is the most limiting nutrient for plant growth and productivity. However, current Earth System Models (ESMs) do not mechanistically represent functional nitrogen allocation for photosynthesis or the linkage between nitrogen uptake and root traits. The current version of CLM (4.5) links nitrogen availability and plant productivity via (1) an instantaneous downregulation of potential photosynthesis rates based on soil mineral nitrogen availability, and (2) apportionment of soil nitrogen between plants and competing nitrogen consumers assumed to be proportional to their relative N demands. However, plants do not photosynthesize at potential rates and then downregulate; instead photosynthesis rates are governed by nitrogen that has been allocated to the physiological processes underpinning photosynthesis. Furthermore, the role of plant roots in nutrient acquisition has also been largely ignored in ESMs. We therefore present a new plant nitrogen model for CLM4.5 with (1) improved representations of linkages between leaf nitrogen and plant productivity based on observed relationships in a global plant trait database and (2) plant nitrogen uptake based on root-scale Michaelis-Menten uptake kinetics. Our model improvements led to a global bias reduction in GPP, LAI, and biomass of 70%, 11%, and 49%, respectively. Furthermore, water use efficiency predictions were improved conceptually, qualitatively, and in magnitude. The new model's GPP responses to nitrogen deposition, CO2 fertilization, and climate also differed from the baseline model. The mechanistic representation of leaf-level nitrogen allocation and a theoretically consistent treatment of competition with belowground consumers led to overall improvements in global carbon cycling predictions.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Goins, Bobby

A systems based approach will be used to evaluate the nitrogen delivery process. This approach involves principles found in Lean, Reliability, Systems Thinking, and Requirements. This unique combination of principles and thought process yields a very in depth look into the system to which it is applied. By applying a systems based approach to the nitrogen delivery process there should be improvements in cycle time, efficiency, and a reduction in the required number of personnel needed to sustain the delivery process. This will in turn reduce the amount of demurrage charges that the site incurs. In addition there should bemore » less frustration associated with the delivery process.« less

NITROGEN OUTPUTS FROM FECAL AND URINE DEPOSITION OF SMALL MAMMALS: IMPLICATIONS FOR NITROGEN CYCLING

EPA Science Inventory

The contribution of small mammals to nitrogen cycling is poorly understood, but it could have reverberations back to the producer community by maintaining or perhaps magnifying nitrogen availability. Our objective was to model nitrogen outputs (deposition of feces and urine) of ...

NITROGEN OUTPUTS OF SMALL MAMMALS FROM FECAL AND URINE DEPOSITION: IMPLICATIONS FOR NITROGEN CYCLING

EPA Science Inventory

The contribution of small mammals in nitrogen cycling is poorly understood and could have reverberations back to the producer community by maintaining or even magnifying increased nitrogen availability. Our objective was to model nitrogen outputs (deposition of feces and urine) ...

New, national bottom-up estimate for tree-based biological nitrogen fixation in the US

EPA Science Inventory

Nitrogen is a limiting nutrient in many ecosystems, but is also a chief pollutant from human activity. Quantifying human impacts on the nitrogen cycle and investigating natural ecosystem nitrogen cycling both require an understanding of the magnitude of nitrogen inputs from biolo...

Linking N2O emissions from biochar-amended soil to the structure and function of the N-cycling microbial community

PubMed Central

Harter, Johannes; Krause, Hans-Martin; Schuettler, Stefanie; Ruser, Reiner; Fromme, Markus; Scholten, Thomas; Kappler, Andreas; Behrens, Sebastian

2014-01-01

Nitrous oxide (N2O) contributes 8% to global greenhouse gas emissions. Agricultural sources represent about 60% of anthropogenic N2O emissions. Most agricultural N2O emissions are due to increased fertilizer application. A considerable fraction of nitrogen fertilizers are converted to N2O by microbiological processes (that is, nitrification and denitrification). Soil amended with biochar (charcoal created by pyrolysis of biomass) has been demonstrated to increase crop yield, improve soil quality and affect greenhouse gas emissions, for example, reduce N2O emissions. Despite several studies on variations in the general microbial community structure due to soil biochar amendment, hitherto the specific role of the nitrogen cycling microbial community in mitigating soil N2O emissions has not been subject of systematic investigation. We performed a microcosm study with a water-saturated soil amended with different amounts (0%, 2% and 10% (w/w)) of high-temperature biochar. By quantifying the abundance and activity of functional marker genes of microbial nitrogen fixation (nifH), nitrification (amoA) and denitrification (nirK, nirS and nosZ) using quantitative PCR we found that biochar addition enhanced microbial nitrous oxide reduction and increased the abundance of microorganisms capable of N2-fixation. Soil biochar amendment increased the relative gene and transcript copy numbers of the nosZ-encoded bacterial N2O reductase, suggesting a mechanistic link to the observed reduction in N2O emissions. Our findings contribute to a better understanding of the impact of biochar on the nitrogen cycling microbial community and the consequences of soil biochar amendment for microbial nitrogen transformation processes and N2O emissions from soil. PMID:24067258

Global terrestrial carbon and nitrogen cycling insensitive to estimates of biological N fixation

NASA Astrophysics Data System (ADS)

Steinkamp, J.; Weber, B.; Werner, C.; Hickler, T.

2015-12-01

Dinitrogen (N2) is the most abundant molecule in the atmosphere and incorporated in other molecules an essential nutrient for life on earth. However, only few natural processes can initiate a reaction of N2. These natural processes are fire, lightning and biological nitrogen fixation (BNF) with BNF being the largest source. In the course of the last century humans have outperformed the natural processes of nitrogen fixation by the production of fertilizer. Industrial and other human emission of reactive nitrogen, as well as fire and lightning lead to a deposition of 63 Tg (N) per year. This is twice the amount of BNF estimated by the default setup of the dynamic global vegetation model LPJ-GUESS (30 Tg), which is a conservative approach. We use different methods and parameterizations for BNF in LPJ-GUESS: 1.) varying total annual amount; 2.) annual evenly distributed and daily calculated fixation rates; 3.) an improved dataset of BNF by cryptogamic covers (free-living N-fixers). With this setup BNF is ranging from 30 Tg to 60 Tg. We assess the impact of BNF on carbon storage and grand primary production (GPP) of the natural vegetation. These results are compared to and evaluated against available independent datasets. We do not see major differences in the productivity and carbon stocks with these BNF estimates, suggesting that natural vegetation is insensitive to BNF on a global scale and the vegetation can compensate for the different nitrogen availabilities. Current deposition of nitrogen compounds and internal cycling through mineralization and uptake is sufficient for natural vegetation productivity. However, due to the coarse model grid and spatial heterogeneity in the real world this conclusion does not exclude the existence of habitats constrained by BNF.

Quantitative Relationships between Photosynthetic, Nitrogen Fixing, and Fermentative H2 Metabolism in a Photosynthetic Microbial Mat

NASA Technical Reports Server (NTRS)

Hoehler, Tori M.; Albert, Daniel B.; Bebout, Brad M.; Turk, Kendra A.; DesMarais, David J.

2004-01-01

The ultimate potential of any microbial ecosystem to contribute chemically to its environment - and therefore, to impact planetary biogeochemistry or to generate recognizable biosignatures - depends not only on the individual metabolic capabilities of constituent organisms, but also on how those capabilities are expressed through interactions with neighboring organisms. This is particularly important for microbial mats, which compress an extremely broad range of metabolic potential into a small and dynamic system. H2 participates in many of these metabolic processes, including the major elemental cycling processes of photosynthesis, nitrogen fixation, sulfate reduction, and fermentation, and may therefore serve as a mediator of microbial interactions within the mat system. Collectively, the requirements of energy, electron transfer, and biomass element stoichiometry suggest quantitative relationships among the major element cycling processes, as regards H2 metabolism We determined experimentally the major contributions to 32 cycling in hypersaline microbial mats from Baja California, Mexico, and compared them to predicted relationships. Fermentation under dark, anoxic conditions is quantitatively the most important mechanism of H2 production, consistent with expectations for non-heterocystous mats such as those under study. Up to 16% of reducing equivalents fixed by photosynthesis during the day may be released by this mechanism. The direct contribution of nitrogen fixation to H2 production is small in comparison, but this process may indirectly stimulate substantial H2 generation, by requiring higher rates of fermentation. Sulfate reduction, aerobic consumption, diffusive and ebulitive loss, and possibly H2-based photoreduction of CO2 serve as the principal H2 sinks. Collectively, these processes interact to create an orders-of-magnitude daily variation in H2 concentrations and fluxes, and thereby in the oxidation-reduction potential that is imposed on microbial processes occuring within the mat matrix.

Global biogeography of microbial nitrogen-cycling traits in soil

NASA Astrophysics Data System (ADS)

Nelson, M.; Martiny, A.; Martiny, J. B. H.

2016-12-01

Microorganisms drive much of the Earth's nitrogen (N) cycle. However, despite their importance, many ecosystem models do not explicitly consider microbial communities and their functions. One obstacle in doing this is that we lack a complete understanding of the role that microbes play in biogeochemical processes. To address this challenge we used metagenomics to assess various N cycling traits of soil microorganisms in samples from around the globe. As measurable characteristics of an organism, traits can be used to quantify the role of microbes in ecosystem processes. Using 365 publically available soil metagenomes, we characterized the biogeography of microbial N cycling traits, defined as the abundance and composition of eight N pathways. We found strong biogeographic patterns in the frequency of N pathway traits; however, our models explained much less variation in taxonomic composition across sites. Focusing on individual N pathways, we identified the prominent taxa harboring these pathways. In addition, we found an unexpectedly high frequency of Bacteria encoding the dissimilatory nitrate reduction to ammonium (DNRA) pathway, a little studied N cycle process in soils. Finally, across all N pathways, phylogenetic analysis revealed that some phyla seem to be N cycle generalists (i.e delta-Proteobacteria), with the potential to carry out many N transformations, whereas others seem to be specialists (i.e. Cyanobacteria). As the most comprehensive map to date of the global distribution of microbial N traits, this study provides a springboard for further investigation of the prominent players in N cycling in soils. Overall, biogeographic patterns of traits can provide a foundation for understanding how microbial diversity impacts ecosystem processes and ultimately predicting how this diversity may shift in the face of global change.

Highly crystalline lithium titanium oxide sheets coated with nitrogen-doped carbon enable high-rate lithium-ion batteries.

PubMed

Han, Cuiping; He, Yan-Bing; Li, Baohua; Li, Hongfei; Ma, Jun; Du, Hongda; Qin, Xianying; Yang, Quan-Hong; Kang, Feiyu

2014-09-01

Sheets of Li4Ti5O12 with high crystallinity are coated with nitrogen-doped carbon (NC-LTO) using a controlled process, comprising hydrothermal reaction followed by chemical vapor deposition (CVD). Acetonitrile (CH3 CN) vapor is used as carbon and nitrogen source to obtain a thin coating layer of nitrogen-doped carbon. The layer enables the NC-LTO material to maintain its sheet structure during the high-temperature CVD process and to achieve high crystallinity. Doping with nitrogen introduces defects into the carbon coating layer, and this increased degree of disorder allows fast transportation of lithium ions in the layer. An electrode of NC-LTO synthesized at 700 °C exhibits greatly improved rate and cycling performance due to a markedly decreased total cell resistance and enhanced Li-ion diffusion coefficient (D(Li)). Specific capacities of 159.2 and 145.8 mA h g(-1) are obtained using the NC-LTO sheets, at charge/discharge rates of 1 and 10 C, respectively. These values are much higher than values for LTO particles did not undergo the acetonitrile CVD treatment. A capacity retention value as high as 94.7% is achieved for the NC-LTO sheets after 400 cycles in a half-cell at 5 C discharge rate. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Inhibition of nitrogenase by oxygen in marine cyanobacteria controls the global nitrogen and oxygen cycles

NASA Astrophysics Data System (ADS)

Berman-Frank, I.; Chen, Y.-B.; Gerchman, Y.; Dismukes, G. C.; Falkowski, P. G.

2005-03-01

Cyanobacterial N2-fixation supplies the vast majority of biologically accessible inorganic nitrogen to nutrient-poor aquatic ecosystems. The process, catalyzed by the heterodimeric protein complex, nitrogenase, is thought to predate that of oxygenic photosynthesis. Remarkably, while the enzyme plays such a critical role in Earth's biogeochemical cycles, the activity of nitrogenase in cyanobacteria is markedly inhibited in vivo at a post-translational level by the concentration of O2 in the contemporary atmosphere leading to metabolic and biogeochemical inefficiency in N2 fixation. We illustrate this crippling effect with data from Trichodesmium spp. an important contributor of "new nitrogen" to the world's subtropical and tropical oceans. The enzymatic inefficiency of nitrogenase imposes a major elemental taxation on diazotrophic cyanobacteria both in the costs of protein synthesis and for scarce trace elements, such as iron. This restriction has, in turn, led to a global limitation of fixed nitrogen in the contemporary oceans and provides a strong biological control on the upper bound of oxygen concentration in Earth's atmosphere.

Tillage and cropping sequence impacts on nitrogen cycling in dryland farming in eastern Montana, USA

USDA-ARS?s Scientific Manuscript database

Information on N cycling in dryland crops and soils as influenced by long-term tillage and cropping sequence is needed to quantify soil N sequestration, mineralization, and N balance to reduce N fertilization rate and N losses through soil processes. We evaluated the 21-yr effects of combinations of...

Invasive species' leaf traits and dissimilarity from natives shape their impact on nitrogen cycling: a meta-analysis.

PubMed

Lee, Marissa R; Bernhardt, Emily S; van Bodegom, Peter M; Cornelissen, J Hans C; Kattge, Jens; Laughlin, Daniel C; Niinemets, Ülo; Peñuelas, Josep; Reich, Peter B; Yguel, Benjamin; Wright, Justin P

2017-01-01

Many exotic species have little apparent impact on ecosystem processes, whereas others have dramatic consequences for human and ecosystem health. There is growing evidence that invasions foster eutrophication. We need to identify species that are harmful and systems that are vulnerable to anticipate these consequences. Species' traits may provide the necessary insights. We conducted a global meta-analysis to determine whether plant leaf and litter functional traits, and particularly leaf and litter nitrogen (N) content and carbon: nitrogen (C : N) ratio, explain variation in invasive species' impacts on soil N cycling. Dissimilarity in leaf and litter traits among invaded and noninvaded plant communities control the magnitude and direction of invasion impacts on N cycling. Invasions that caused the greatest increases in soil inorganic N and mineralization rates had a much greater litter N content and lower litter C : N in the invaded than the reference community. Trait dissimilarities were better predictors than the trait values of invasive species alone. Quantifying baseline community tissue traits, in addition to those of the invasive species, is critical to understanding the impacts of invasion on soil N cycling. © 2016 The Authors. New Phytologist © 2016 New Phytologist Trust.

Microbially mediated transformations of phosphorus in the sea: new views of an old cycle.

PubMed

Karl, David M

2014-01-01

Phosphorus (P) is a required element for life. Its various chemical forms are found throughout the lithosphere and hydrosphere, where they are acted on by numerous abiotic and biotic processes collectively referred to as the P cycle. In the sea, microorganisms are primarily responsible for P assimilation and remineralization, including recently discovered P reduction-oxidation bioenergetic processes that add new complexity to the marine microbial P cycle. Human-induced enhancement of the global P cycle via mining of phosphate-bearing rock will likely influence the pace of P-cycle dynamics, especially in coastal marine habitats. The inextricable link between the P cycle and cycles of other bioelements predicts future impacts on, for example, nitrogen fixation and carbon dioxide sequestration. Additional laboratory and field research is required to build a comprehensive understanding of the marine microbial P cycle.

Nitrogen in rock: Occurrences and biogeochemical implications

USGS Publications Warehouse

Holloway, J.M.; Dahlgren, R.A.

2002-01-01

There is a growing interest in the role of bedrock in global nitrogen cycling and potential for increased ecosystem sensitivity to human impacts in terrains with elevated background nitrogen concentrations. Nitrogen-bearing rocks are globally distributed and comprise a potentially large pool of nitrogen in nutrient cycling that is frequently neglected because of a lack of routine analytical methods for quantification. Nitrogen in rock originates as organically bound nitrogen associated with sediment, or in thermal waters representing a mixture of sedimentary, mantle, and meteoric sources of nitrogen. Rock nitrogen concentrations range from trace levels (>200 mg N kg -1) in granites to ecologically significant concentrations exceeding 1000 mg N kg -1 in some sedimentary and metasedimentary rocks. Nitrate deposits accumulated in arid and semi-arid regions are also a large potential pool. Nitrogen in rock has a potentially significant impact on localized nitrogen cycles. Elevated nitrogen concentrations in water and soil have been attributed to weathering of bedrock nitrogen. In some environments, nitrogen released from bedrock may contribute to nitrogen saturation of terrestrial ecosystems (more nitrogen available than required by biota). Nitrogen saturation results in leaching of nitrate to surface and groundwaters, and, where soils are formed from ammonium-rich bedrock, the oxidation of ammonium to nitrate may result in soil acidification, inhibiting revegetation in certain ecosystems. Collectively, studies presented in this article reveal that geologic nitrogen may be a large and reactive pool with potential for amplification of human impacts on nitrogen cycling in terrestrial and aquatic ecosystems.

Electrons, life and the evolution of Earth's oxygen cycle.

PubMed

Falkowski, Paul G; Godfrey, Linda V

2008-08-27

The biogeochemical cycles of H, C, N, O and S are coupled via biologically catalysed electron transfer (redox) reactions. The metabolic processes responsible for maintaining these cycles evolved over the first ca 2.3 Ga of Earth's history in prokaryotes and, through a sequence of events, led to the production of oxygen via the photobiologically catalysed oxidation of water. However, geochemical evidence suggests that there was a delay of several hundred million years before oxygen accumulated in Earth's atmosphere related to changes in the burial efficiency of organic matter and fundamental alterations in the nitrogen cycle. In the latter case, the presence of free molecular oxygen allowed ammonium to be oxidized to nitrate and subsequently denitrified. The interaction between the oxygen and nitrogen cycles in particular led to a negative feedback, in which increased production of oxygen led to decreased fixed inorganic nitrogen in the oceans. This feedback, which is supported by isotopic analyses of fixed nitrogen in sedimentary rocks from the Late Archaean, continues to the present. However, once sufficient oxygen accumulated in Earth's atmosphere to allow nitrification to out-compete denitrification, a new stable electron 'market' emerged in which oxygenic photosynthesis and aerobic respiration ultimately spread via endosymbiotic events and massive lateral gene transfer to eukaryotic host cells, allowing the evolution of complex (i.e. animal) life forms. The resulting network of electron transfers led a gas composition of Earth's atmosphere that is far from thermodynamic equilibrium (i.e. it is an emergent property), yet is relatively stable on geological time scales. The early coevolution of the C, N and O cycles, and the resulting non-equilibrium gaseous by-products can be used as a guide to search for the presence of life on terrestrial planets outside of our Solar System.

Metagenomic assessment of the potential microbial nitrogen pathways in the rhizosphere of a mediterranean forest after a wildfire.

PubMed

Cobo-Díaz, José F; Fernández-González, Antonio J; Villadas, Pablo J; Robles, Ana B; Toro, Nicolás; Fernández-López, Manuel

2015-05-01

Wildfires are frequent in the forests of the Mediterranean Basin and have greatly influenced this ecosystem. Changes to the physical and chemical properties of the soil, due to fire and post-fire conditions, result in alterations of both the bacterial communities and the nitrogen cycle. We explored the effects of a holm oak forest wildfire on the rhizospheric bacterial communities involved in the nitrogen cycle. Metagenomic data of the genes involved in the nitrogen cycle showed that both the undisturbed and burned rhizospheres had a conservative nitrogen cycle with a larger number of sequences related to the nitrogen incorporation pathways and a lower number for nitrogen output. However, the burned rhizosphere showed a statistically significant increase in the number of sequences for nitrogen incorporation (allantoin utilization and nitrogen fixation) and a significantly lower number of sequences for denitrification and dissimilatory nitrite reductase subsystems, possibly in order to compensate for nitrogen loss from the soil after burning. The genetic potential for nitrogen incorporation into the ecosystem was assessed through the diversity of the nitrogenase reductase enzyme, which is encoded by the nifH gene. We found that nifH gene diversity and richness were lower in burned than in undisturbed rhizospheric soils. The structure of the bacterial communities involved in the nitrogen cycle showed a statistically significant increase of Actinobacteria and Firmicutes phyla after the wildfire. Both approaches showed the important role of gram-positive bacteria in the ecosystem after a wildfire.

Biological cycling of atmospheric trace gases

NASA Technical Reports Server (NTRS)

Hitchcock, D. R.; Wechsler, A. E.

1972-01-01

A detailed critical review was conducted of present knowledge of the influence of biological processes on the cycling of selected atmospheric gas constituents--methane, carbon monoxide, and gaseous compounds of nitrogen (nitrous oxide, ammonia, nitric oxide, and nitrogen dioxide) and sulfur (hydrogen sulfide and sulfur dioxide). The identification was included of biological and other sources of each gas, a survey of abundance measurements reported in the literature, and a review of the atmospheric fate of each contituent. Information is provided on which to base conclusions regarding the importance of biological processes on the atmospheric distribution and surface-atmosphere exchange of each constituent, and a basis for estimating the adequacy of present knowledge of these factors. A preliminary analysis was conducted of the feasibility of monitoring the biologically influenced temporal and spatial variations in abundance of these gases in the atmosphere from satellites.

Experimental investigation of anaerobic nitrogen fixation rates with varying pressure, temperature and metal concentration with application to the atmospheric evolution of early Earth and Mars.

NASA Astrophysics Data System (ADS)

Gupta, Prateek

2012-07-01

The atmosphere of the early Earth is thought to have been significantly different than the modern composition of 21% O2 and 78% N2, yet the planet has been clearly established as hosting microbial life as far back as 3.8 billion years ago. As such, constraining the atmospheric composition of the early Earth is fundamental to establishing a database of habitable atmospheric compositions. A similar argument can be made for the planet Mars, where nitrates have been hypothesized to exist in the subsurface. During the early period on Mars when liquid water was likely more abundant, life may have developed to take advantage of available nitrates and a biologically-driven Martian nitrogen cycle could have evolved. Early Earth atmospheric composition has been investigated numerically, but only recently has the common assumption of a pN2 different than modern been investigated. Nonetheless, these latest attempts fail to take into account a key atmospheric parameter: life. On modern Earth, nitrogen is cycled vigorously by biology. The nitrogen cycle likely operated on the early Earth, but probably differed in the metabolic processes responsible, dominantly due to the lack of abundant oxygen which stabilizes oxidized forms of N that drive de-nitrification today. Recent advances in evolutionary genomics suggest that microbial pathways that are relatively uncommon today (i.e. vanadium and iron-based nitrogen fixation) probably played important roles in the early N cycle. We quantitatively investigate in the laboratory the effects of variable pressure, temperature and metal concentration on the rates of anoxic nitrogen fixation, as possible inputs for future models investigating atmospheric evolution, and better understand the evolution of the nitrogen cycle on Earth. A common anaerobic methanogenic archaeal species with i) a fully sequenced genome, ii) all three nitrogenases (molybdenum, vanadium and iron-based) and iii) the ability to be genetically manipulated will be used as a model species. This species will be genetically modified to create knock-out mutants lacking one or more nitrogenase genes. These mutants will be used in variable pressure, temperature and metal-concentration experiments. Nitrogen fixation rate and nitrogenase gene expression will be measured using isotope dilution and quantitative polymerase chain reaction, respectively.

Bayesian integration of flux tower data into a process-based simulator for quantifying uncertainty in simulated output

NASA Astrophysics Data System (ADS)

Raj, Rahul; van der Tol, Christiaan; Hamm, Nicholas Alexander Samuel; Stein, Alfred

2018-01-01

Parameters of a process-based forest growth simulator are difficult or impossible to obtain from field observations. Reliable estimates can be obtained using calibration against observations of output and state variables. In this study, we present a Bayesian framework to calibrate the widely used process-based simulator Biome-BGC against estimates of gross primary production (GPP) data. We used GPP partitioned from flux tower measurements of a net ecosystem exchange over a 55-year-old Douglas fir stand as an example. The uncertainties of both the Biome-BGC parameters and the simulated GPP values were estimated. The calibrated parameters leaf and fine root turnover (LFRT), ratio of fine root carbon to leaf carbon (FRC : LC), ratio of carbon to nitrogen in leaf (C : Nleaf), canopy water interception coefficient (Wint), fraction of leaf nitrogen in RuBisCO (FLNR), and effective soil rooting depth (SD) characterize the photosynthesis and carbon and nitrogen allocation in the forest. The calibration improved the root mean square error and enhanced Nash-Sutcliffe efficiency between simulated and flux tower daily GPP compared to the uncalibrated Biome-BGC. Nevertheless, the seasonal cycle for flux tower GPP was not reproduced exactly and some overestimation in spring and underestimation in summer remained after calibration. We hypothesized that the phenology exhibited a seasonal cycle that was not accurately reproduced by the simulator. We investigated this by calibrating the Biome-BGC to each month's flux tower GPP separately. As expected, the simulated GPP improved, but the calibrated parameter values suggested that the seasonal cycle of state variables in the simulator could be improved. It was concluded that the Bayesian framework for calibration can reveal features of the modelled physical processes and identify aspects of the process simulator that are too rigid.

Nitrogen Cycling in Seagrass Beds Dominated by Thalassia testudinum and Halodule wrightii: the Role of Nitrogen Fixation and Ammonium Oxidation in Regulating Ammonium Availability

NASA Astrophysics Data System (ADS)

Capps, R.; Caffrey, J. M.; Hester, C.

2016-02-01

Seagrass meadows provide key ecosystem services including nursery and foraging grounds, storm and erosion buffers, biodiversity enhancers and global carbon and nutrient cycling. Nitrogen concentrations are often very low in coastal waters and sediments, which may limit primary productivity. Biological nitrogen fixation is a microbial process that converts dinitrogen to ammonium, which is readily taken up by seagrasses. In the oxygenated rhizospheres, diazotrophs provide the plant with ammonium and use root exudates as an energy source. Nitrogen fixation rates and nutrient concentrations differ between seagrass species and substrate types. Thalassia testudinum has a higher biomass and is a climax species than Halodule wrightii, which is a pioneer species. Nitrogen fixation rates are relatively consistent in Thalassia testudinum dominated sediments. However, it is relatively variable in sediments occupied by Halodule wrightii. Nitrogen fixation rates are higher in bare substrate compared to areas with Thalassia testudinum, which may be due to T. testudinum's greater efficiency in nutrient retention because it is a climax species. We hypothesize that seasonal shifts in nitrogen fixation will coincide with seasonal shifts in seagrass biomass due to higher nutrient requirements during peak growth and lower requirements during senescence and dormancy. The ratio of porewater ammonium to phosphate suggests that seagrass growth may be nitrogen limited as does nitrogen demand, estimated from gross primary productivity. Significant rates of ammonium oxidation in both surface and rhizosphere sediments contribute to this imbalance. Thus, nitrogen fixation may be critical in supporting plant growth.

Are phenolic compounds released from the Mediterranean shrub Cistus albidus responsible for changes in N cycling in siliceous and calcareous soils?

Treesearch

Eva Castells; Josep Peñuelas; David W. Valentine

2004-01-01

We studied the effects of Cistus albidus leaf leachates on nitrogen-cycling processes in two siliceous soils (granite and schist) and one calcareous soil. We compared those effects with gross N-transformation rates in soils sampled underneath Cistus. Our results show that although phenolic compounds leached from green foliage...

Changes in Microbial Nitrogen Across a 100-Year Chronosequence of Upland Hardwood Forests

Treesearch

Travis W. Idol; Phillip E. Pope; Felix, Jr. Ponder

2002-01-01

Soil microorganisms mediate many of the major processes involved in soil N cycling. Also, they are strong competitors with plants for available soil N. Thus, changes in microbial N because of forest harvesting may have significant impacts on N availability and overall forest N cycling. A chronosequence of upland hardwood forest stands in southern Indiana, USA, ranging...

Temporal variations and scaling of streamflow and baseflow and their nitrate-nitrogen concentrations and loads

USGS Publications Warehouse

Zhang, Y.-K.; Schilling, K.

2005-01-01

The patterns of temporal variations of precipitation (P), streamflow (SF) and baseflow (BF) as well as their nitrate-nitrogen (nitrate) concentrations (C) and loads (L) from a long-term record (28 years) in the Raccoon River, Iowa, were analyzed using variogram and spectral analyses. The daily P is random but scaling may exist in the daily SF and BF with a possible break point in the scaling at about 18 days and 45 days, respectively. The nitrate concentrations and loads are shown to have a half-year cycle while daily P, SF, and BF have a one-year cycle. Furthermore, there may be a low-frequency cycle of 6-8 years in C. The power spectra of C and L in both SF and BF exhibit fractal 1/f scaling with two characteristic frequencies of half-year and one-year, and are fitted well with the spectrum of the gamma distribution. The nitrate input to SF and BF at the Raccoon watershed seems likely to be a white noise process superimposed on another process with a half-year and one-year cycle. ?? 2005 Elsevier Ltd. All rights reserved.

Leaky nitrogen cycle in pristine African montane rainforest soil

NASA Astrophysics Data System (ADS)

Rütting, Tobias; Cizungu Ntaboba, Landry; Roobroeck, Dries; Bauters, Marijn; Huygens, Dries; Boeckx, Pascal

2015-10-01

Many pristine humid tropical forests show simultaneously high nitrogen (N) richness and sustained loss of bioavailable N forms. To better understand this apparent upregulation of the N cycle in tropical forests, process-based understanding of soil N transformations, in geographically diverse locations, remains paramount. Field-based evidence is limited and entirely lacking for humid tropical forests on the African continent. This study aimed at filling both knowledge gaps by monitoring N losses and by conducting an in situ 15N labeling experiment in the Nyungwe tropical montane forest in Rwanda. Here we show that this tropical forest shows high nitrate (NO3-) leaching losses, confirming findings from other parts of the world. Gross N transformation rates point to an open soil N cycle with mineralized N nitrified rather than retained via immobilization; gross immobilization of NH4+ and NO3- combined accounted for 37% of gross mineralization, and plant N uptake is dominated by ammonium (NH4+). This study provided new process understanding of soil N cycling in humid tropical forests and added geographically independent evidence that humid tropical forests are characterized by soil N dynamics and N inputs sustaining bioavailable N loss.

Quantifying manganese and nitrogen cycle coupling in manganese-rich, organic carbon-starved marine sediments: Examples from the Clarion-Clipperton fracture zone

NASA Astrophysics Data System (ADS)

Mogollón, José M.; Mewes, Konstantin; Kasten, Sabine

2016-07-01

Extensive deep-sea sedimentary areas are characterized by low organic carbon contents and thus harbor suboxic sedimentary environments where secondary (autotrophic) redox cycling becomes important for microbial metabolic processes. Simulation results for three stations in the Eastern Equatorial Pacific with low organic carbon content (<0.5 dry wt %) and low sedimentation rates (10-1-100 mm ky-1) show that ammonium generated during organic matter degradation may act as a reducing agent for manganese oxides below the oxic zone. Likewise, at these sedimentary depths, dissolved reduced manganese may act as a reducing agent for oxidized nitrogen species. These manganese-coupled transformations provide a suboxic conversion pathway of ammonium and nitrate to dinitrogen. These manganese-nitrogen interactions further explain the presence and production of dissolved reduced manganese (up to tens of μM concentration) in sediments with high nitrate (>20 μM) concentrations.

Physicochemical processes in embryonic plant tissue during the transition to the state of cold anabiosis and storage at liquid nitrogen temperature

NASA Astrophysics Data System (ADS)

Khodko, A. T.; Lysak, Yu. S.

2017-10-01

Critical opalescence phenomenon was observed in the cytoplasm of garlic embryonic tissue—meristem—upon cooling in liquid nitrogen vapor, indicating liquid-liquid phase transition in the system. It was established that cells of the meristem tissue survive the cooling-thawing cycle. We suggest that the transition of meristem tissue to the state of anabiosis is mainly due to a drastic slowing of the diffusion in the cytoplasm caused by the passage of the solution through the critical point, followed by the formation of a dispersed system—a highly concentrated emulsion—as a result of a liquid-liquid phase transition. This macrophase separation is characteristic of polymer-solvent systems. We established the regime of cooling down to liquid nitrogen temperature and subsequent thawing in the cryopreservation cycle for the biological object under study, which ensures the preservation of tissue viability.

Reversible control of biofilm formation by Cellulomonas spp. in response to nitrogen availability.

PubMed

Young, Jenna M; Leschine, Susan B; Reguera, Gemma

2012-03-01

The microbial degradation of cellulose contributes greatly to the cycling of carbon in terrestrial environments and feedbacks to the atmosphere, a process that is highly responsive to nitrogen inputs. Yet how key groups of cellulolytic microorganisms adaptively respond to the global conditions of nitrogen limitation and/or anthropogenic or climate nitrogen inputs is poorly understood. The actinobacterial genus Cellulomonas is of special interest because it incorporates the only species known to degrade cellulose aerobically and anaerobically. Furthermore, despite their inability to fix nitrogen, they are active decomposers in nitrogen-limited environments. Here we show that nitrogen limitation induced biofilm formation in Cellulomonas spp., a process that was coupled to carbon sequestration and storage in a curdlan-type biofilm matrix. The response was reversible and the curdlan matrix was solubilized and used as a carbon and energy source for biofilm dispersal once nitrogen sources became available. The biofilms attached strongly to cellulosic surfaces and, despite the growth limitation, produced cellulases and degraded cellulose more efficiently. The results show that biofilm formation is a competitive strategy for carbon and nitrogen acquisition and provide valuable insights linking nitrogen inputs to carbon sequestration and remobilization in terrestrial environments. © 2011 Society for Applied Microbiology and Blackwell Publishing Ltd.

Key ecological responses to nitrogen are altered by climate change

EPA Science Inventory

Here we review the effects of nitrogen and climate (e.g. temperature and precipitation) on four aspects of ecosystem structure and function including hydrologic-coupled nitrogen cycling, carbon cycling, acidification and biodiversity.

TRANSLOCATION OF NUTRIENTS BY FRESHWATER MUSSELS – ALTERATION OF ECOSYSTEM AND COMMUNITY PROCESSES

EPA Science Inventory

Nutrient demand and availability is a major driver of ecosystem processes. We examined the impact of freshwater mussels, a highly imperiled faunal group, on nitrogen (N) and phosphorus (P) cycling and storage in three Oklahoma streams. We found that filter-feeding by freshwater m...

Altered nutrition during hot droughts will impair forest functions in the future

NASA Astrophysics Data System (ADS)

Grossiord, C.; Gessler, A.; Reed, S.; Dickman, L. T.; Collins, A.; Schönbeck, L.; Sevanto, S.; Vilagrosa, A.; McDowell, N. G.

2017-12-01

Rising greenhouse gas emissions will increase atmospheric temperature globally and alter hydrological cycles resulting in more extreme and recurrent droughts in the coming century. Nutrition is a key component affecting the vulnerability of forests to extreme climate. Models typically assume that global warming will enhance nitrogen cycling in terrestrial ecosystems and lead to improved plant functions. Drought on the other hand is expected to weaken the same processes, leading to a clear conflict and inability to predict how nutrition and plant functions will be impacted by a simultaneously warming and drying climate. We used a unique setup consisting of long-term manipulation of climate on mature trees to examine how individual vs. combined warming and drought would alter soil N cycling and tree functions. The site consists of the longest record of tree responses to experimental warming and precipitation reduction in natural conditions.Changes in soil nitrogen cycling (e.g. microbial activity, nitrification and ammonification rates, N concentration) occurred in response to the treatments. In addition, temperature rise and precipitation reduction altered the ability of trees to take up nitrogen and modified nitrogen allocation patterns between aboveground and belowground compartments. Although no additive effect of warming and drying were found for the two studied species, contrasting responses to warming and droughts were observed between the two functional types. Overall, our results show that higher temperature and reduced precipitation will alter the nutrition of forest ecosystems in the future with potentially large consequences for forest functions, structure and biodiversity.

Nitrogen isotope and mass balance approach in the Elbe Estuary

NASA Astrophysics Data System (ADS)

Sanders, Tina; Wankel, Scott D.; Dähnke, Kirstin

2017-04-01

The supply of bioavailable nitrogen is crucial to primary production in the world's oceans. Especially in estuaries, which act as a nutrient filter for coastal waters, microbial nitrogen turnover and removal has a particular significance. Nitrification as well as other nitrogen-based processes changes the natural abundance of the stable isotope, which can be used as proxies for sources and sinks as well as for process identification. The eutrophic Elbe estuary in northern Germany is loaded with fertilizer-derived nitrogen, but management efforts have started to reduce this load effectively. However, an internal nitrate source in turn gained in importance and the estuary changed from a sink to a source of dissolved inorganic nitrogen: Nitrification is responsible for significant estuarine nutrient regeneration, especially in the Hamburg Port. In our study, we aimed to quantify sources and sinks of nitrogen based on a mass and stable isotope budget in the Elbe estuary. A model was developed reproduce internal N-cycling and associated isotope changes. For that approach we measured dissolved inorganic nitrogen (DIN), particulate nitrogen and their stable isotopes in a case study in July 2013. We found an almost closed mass balance of nitrogen, with only low lost or gains which we attribute to sediment resuspension. The isotope values of different DIN components and the model approach both support a high fractionation of up to -25‰ during nitrification. However, the nitrogen balance and nitrogen stable isotopes suggest that most important processes are remineralization of organic matter to ammonium and further on the oxidation to nitrate. Denitrification and nitrate assimilation play a subordinate role in the Elbe Estuary.

Controlled electrochemical doping of graphene-based 3D nanoarchitecture electrodes for supercapacitors and capacitive deionisation.

PubMed

Abdelkader, A M; Fray, D J

2017-10-05

Chemically-doped graphenes are promising electrode materials for energy storage and electrosorption applications. Here, an affordable electrochemical green process is introduced to dope graphene with nitrogen. The process is based on reversing the polarity of two identical graphene oxide (GO) electrodes in molten KCl-LiCl-Li 3 N. During the cathodic step, the oxygen functional groups on the GO surface are removed through direct electro-deoxidation reactions or a reaction with the deposited lithium. In the anodic step, nitrogen is adsorbed onto the surface of graphene and subsequently reacts to form nitrogen-doped graphene. The doping process is controllable, and graphene with up to 7.4 at% nitrogen can be produced. The electrochemically treated electrodes show a specific capacitance of 320 F g -1 in an aqueous KOH electrolyte and maintain 96% of this value after 10 000 cycles. The electrodes also display excellent electrosorption performance in capacitive deionisation devices with the salt removal efficiency reaching up to 18.6 mg g -1 .

Life-cycle evaluation of nitrogen-use in rice-farming systems: implications for economically-optimal nitrogen rates

NASA Astrophysics Data System (ADS)

Xia, Y.; Yan, X.

2011-11-01

Nitrogen (N) fertilizer plays an important role in agricultural systems in terms of food yield. However, N application rates (NARs) are often overestimated over the rice (Oryza sativa L.) growing season in the Taihu Lake region of China. This is largely because negative externalities are not entirely included when evaluating economically-optimal nitrogen rate (EONR), such as only individual N losses are taken into account, or the inventory flows of reactive N have been limited solely to the farming process when evaluating environmental and economic effects of N fertilizer. This study integrates important material and energy flows resulting from N use into a rice agricultural inventory that constitutes the hub of the life-cycle assessment (LCA) method. An economic evaluation is used to determine an environmental and economic NAR for the Taihu Lake region. The analysis reveals that production and exploitation processes consume the largest proportion of resources, accounting for 77.2 % and 22.3 % of total resources, respectively. Regarding environmental impact, global warming creates the highest cost with contributions stemming mostly from fertilizer production and farming processes. Farming process incurs the biggest environmental impact of the three environmental impact categories considered, whereas transportation has a much smaller effect. When taking account of resource consumption and environmental cost, the marginal benefit of 1 kg rice would decrease from 2.4 to only 1.05 yuan. Accordingly, our current EONR has been evaluated at 187 kg N ha-1 for a single rice-growing season. This could enhance profitability, as well as reduce the N losses associated with rice growing.

Improving representation of nitrogen uptake, allocation, and carbon assimilation in the Community Land Model

NASA Astrophysics Data System (ADS)

Ghimire, B.; Riley, W. J.; Koven, C.

2013-12-01

Nitrogen is the most important nutrient limiting plant carbon assimilation and growth, and is required for production of photosynthetic enzymes, growth and maintenance respiration, and maintaining cell structure. The forecasted rise in plant available nitrogen through atmospheric nitrogen deposition and the release of locked soil nitrogen by permafrost thaw in high latitude ecosystems is likely to result in an increase in plant productivity. However a mechanistic representation of plant nitrogen dynamics is lacking in earth system models. Most earth system models ignore the dynamic nature of plant nutrient uptake and allocation, and further lack tight coupling of below- and above-ground processes. In these models, the increase in nitrogen uptake does not translate to a corresponding increase in photosynthesis parameters, such as maximum Rubisco capacity and electron transfer rate. We present an improved modeling framework implemented in the Community Land Model version 4.5 (CLM4.5) for dynamic plant nutrient uptake, and allocation to different plant parts, including leaf enzymes. This modeling framework relies on imposing a more realistic flexible carbon to nitrogen stoichiometric ratio for different plant parts. The model mechanistically responds to plant nitrogen uptake and leaf allocation though changes in photosynthesis parameters. We produce global simulations, and examine the impacts of the improved nitrogen cycling. The improved model is evaluated against multiple observations including TRY database of global plant traits, nitrogen fertilization observations and 15N tracer studies. Global simulations with this new version of CLM4.5 showed better agreement with the observations than the default CLM4.5-CN model, and captured the underlying mechanisms associated with plant nitrogen cycle.

Modeling forest carbon cycle using long-term carbon stock field measurement in the Delaware River Basin

Treesearch

Bing Xu; Yude Pan; Alain F. Plante; Kevin McCullough; Richard Birdsey

2017-01-01

Process-based models are a powerful approach to test our understanding of biogeochemical processes, to extrapolate ground survey data from limited plots to the landscape scale, and to simulate the effects of climate change, nitrogen deposition, elevated atmospheric CO2, increasing natural disturbances, and land-use change on ecological processes...

Modelling Nitrogen Cycling in a Mariculture Ecosystem as a Tool to Evaluate its Outflow

NASA Astrophysics Data System (ADS)

Lefebvre, S.; Bacher, C.; Meuret, A.; Hussenot, J.

2001-03-01

A model was constructed to describe an intensive mariculture ecosystem growing sea bass ( Dicentrarchus labrax), located in the salt marshes of the Fiers d'Ars Bay on the French Atlantic coast, in order to assess nitrogen cycling within the system and nitrogen outflow from the system. The land-based system was separated into three main compartments: a seawater reservoir, fish ponds and a lagoon (sedimentation pond). Three submodels were built for simulation purposes: (1) a hydrological submodel which simulated water exchange; (2) a fish growth and excretion bioenergetic submodel; and (3) a nitrogen compound transformation and loss submodel (i.e. ammonification, nitrification and assimilation processes). A two-year sampling period of nitrogen water quality concentrations and fish growth was used to validate the model. The model fitted the observations of dissolved nitrogen components, fish growth and water fluxes on a daily basis in all the compartments. The dissolved inorganic nitrogen ranged widely and over time from 0·5 to 9 g N m -3within the system, depending on seawater supply and water temperature, without affecting fish growth. Fish feed was the most important input of nitrogen into the system. The mean average input of nitrogen in the feed was 205 kg N day -1, of which 19% was retained by fish, 4% accumulated in the sediment and 61% flowed from the system as dissolved components. The farm represented about 25% of the total dissolved nitrogen export from the bay, although the farm surface area was 100 times smaller than that of the bay.

Soil Microbial Communities and Gas Dynamics Contribute to Arbuscular Mycorrhizal Nitrogen Uptake and Transfer to Plants

NASA Astrophysics Data System (ADS)

Hestrin, R.; Harrison, M. J.; Lehmann, J.

2016-12-01

Arbuscular mycorrhizal fungi (AMF) associate with most terrestrial plants and influence ecosystem ecology and biogeochemistry. There is evidence that AMF play a role in soil nitrogen cycling, in part by taking up nitrogen and transferring it to plants. However, many aspects of this process are poorly understood, including the factors that control fungal access to nitrogen stored in soil organic matter. In this study, we used stable isotopes and root exclusion to track nitrogen movement from organic matter into AMF and host plants. AMF significantly increased total plant biomass and nitrogen content, but both AMF and other soil microbes seemed to compete with plants for nitrogen. Surprisingly, gaseous nitrogen species also contributed significantly to plant nitrogen content under alkaline soil conditions. Our current experiments investigate whether free-living microbial communities that have evolved under a soil nitrogen gradient influence AMF access to soil organic nitrogen and subsequent nitrogen transfer to plants. This research links interactions between plants, mycorrhizal symbionts, and free-living microbes with terrestrial carbon and nitrogen dynamics.

Effects of timber harvesting on the genetic potential for carbon and nitrogen cycling in five North American forest ecozones.

PubMed

Cardenas, Erick; Orellana, Luis H; Konstantinidis, Konstantinos T; Mohn, William W

2018-02-16

Forest ecosystems are critical to global biogeochemical cycles but under pressure from harvesting and climate change. We investigated the effects of organic matter (OM) removal during forest harvesting on the genetic potential of soil communities for biomass decomposition and nitrogen cycling in five ecozones across North America. We analyzed 107 samples, representing four treatments with varied levels of OM removal, at Long-Term Soil Productivity Study sites. Samples were collected more than ten years after harvesting and replanting and were analyzed via shotgun metagenomics. High-quality short reads totaling 1.2 Tbp were compared to the Carbohydrate Active Enzyme (CAZy) database and a custom database of nitrogen cycle genes. Gene profile variation was mostly explained by ecozone and soil layer. Eleven CAZy and nine nitrogen cycle gene families were associated with particular soil layers across all ecozones. Treatment effects on gene profiles were mainly due to harvesting, and only rarely to the extent of OM removal. Harvesting generally decreased the relative abundance of CAZy genes while increasing that of nitrogen cycle genes, although these effects varied among ecozones. Our results suggest that ecozone-specific nutrient availability modulates the sensitivity of the carbon and nitrogen cycles to harvesting with possible consequences for long-term forest sustainability.

Modelling the pelagic nitrogen cycle and vertical particle flux in the Norwegian sea

NASA Astrophysics Data System (ADS)

Haupt, Olaf J.; Wolf, Uli; v. Bodungen, Bodo

1999-02-01

A 1D Eulerian ecosystem model (BIological Ocean Model) for the Norwegian Sea was developed to investigate the dynamics of pelagic ecosystems. The BIOM combines six biochemical compartments and simulates the annual nitrogen cycle with specific focus on production, modification and sedimentation of particles in the water column. The external forcing and physical framework is based on a simulated annual cycle of global radiation and an annual mixed-layer cycle derived from field data. The vertical resolution of the model is given by an exponential grid with 200 depth layers, allowing specific parameterization of various sinking velocities, breakdown of particles and the remineralization processes. The aim of the numerical experiments is the simulation of ecosystem dynamics considering the specific biogeochemical properties of the Norwegian Sea, for example the life cycle of the dominant copepod Calanus finmarchicus. The results of the simulations were validated with field data. Model results are in good agreement with field data for the lower trophic levels of the food web. With increasing complexity of the organisms the differences increase between simulated processes and field data. Results of the numerical simulations suggest that BIOM is well adapted to investigate a physically controlled ecosystem. The simulation of grazing controlled pelagic ecosystems, like the Norwegian Sea, requires adaptations of parameterization to the specific ecosystem features. By using seasonally adaptation of the most sensible processes like utilization of light by phytoplankton and grazing by zooplankton results were greatly improved.

Determining the N and O isotope effects of microbial nitrite reduction: the global N cycle implications of an enzyme-dependent isotope effect

NASA Astrophysics Data System (ADS)

Martin, T. S.; Casciotti, K. L.

2014-12-01

The marine nitrogen (N) cycle is a dynamic system of critical importance, since nitrogen is the limiting nutrient in over half of the world's oceans. Denitrification and anammox, the main N loss processes from the ocean, have different effects on carbon cycling and greenhouse gas emission. Understanding the balance between the two processes is vital to understanding the role of the N cycle in global climate change. One approach for investigating these processes is by using stable isotope analysis to estimate the relative magnitudes of N fluxes, particularly for biologically mediated processes. In order to make the most of the currently available isotope analysis techniques, it is necessary to know the isotope effects for each processes occurring in the environment. Nitrite reduction is an important step in denitrification. Previous work had begun to explore the N isotope effects for nitrite reduction, but no oxygen (O) isotope effect has been measured. Additionally, no consideration has been given to the type of nitrite reductase carrying out the reaction. There are two main types of respiratory nitrite reductase, one that is Cu-based and another that is Fe-based. We performed batch culture experiments with denitrifier strains possessing either a Cu-type or Fe-type nitrite reductase. Both N and O isotope effects for nitrite reduction were determined for each of these experiments by measuring the NO2- concentration, as well as the N and O isotopes of nitrite and applying a Rayleigh fractionation model. Both the N and O isotope effects were found to be significantly different between the two types of enzymes. This enzyme-linked difference in isotope effects emphasizes the importance of microbial community composition within the global N cycle.

Indigenous Fixed Nitrogen on Mars: Implications for Habitability

NASA Astrophysics Data System (ADS)

Stern, J. C.; Sutter, B.; Navarro-Gonzalez, R.; McKay, C. P.; Freissinet, C.; Archer, D., Jr.; Eigenbrode, J. L.; Mahaffy, P. R.; Conrad, P. G.

2015-12-01

Nitrate has been detected in Mars surface sediments and aeolian deposits by the Sample Analysis at Mars (SAM) instrument on the Mars Science Laboratory Curiosity rover (Stern et al., 2015). This detection is significant because fixed nitrogen is necessary for life, a requirement that drove the evolution of N-fixing metabolism in life on Earth. The question remains as to the extent to which a primitive N cycle ever developed on Mars, and whether N is currently being deposited on the martian surface at a non-negligible rate. It is also necessary to consider processes that could recycle oxidized N back into the atmosphere, and how these processes may have changed the soil inventory of N over time. The abundance of fixed nitrogen detected as NO from thermal decomposition of nitrate is consistent with both delivery of nitrate via impact generated thermal shock early in martian history and dry deposition from photochemistry of thermospheric NO, occurring in the present. Processes that could recycle N back into the atmosphere may include nitrate reduction by Fe(II) in aqueous environments on early Mars, impact decomposition, and/or UV photolysis. In order to better understand the history of nitrogen fixation on Mars, we look to cycling of N in Mars analog environments on Earth such as the Atacama Desert and the Dry Valleys of Antarctica. In particular, we examine the ratio of nitrate to perchlorate (NO3-/ClO4-) in these areas compared to those calculated from data acquired on Mars.

The microstructural evolution, crystallography, and thermal processing of ultrahigh carbon Fe-1.85 pct C melt-spun ribbon

NASA Technical Reports Server (NTRS)

Spanos, G.; Ayers, J. D.; Vold, C. L.; Locci, I. E.

1993-01-01

A study is presented to determine if fine microstructures could be achieved using rapid solidification to produce a fine-grained fully austenitic starting structure and then using thermal processing cycles to produce an even finer ferrite-cementite structure. The evolution, mechanisms of grain refinement, and crystallography of the resultant microstructures were examined by TEM. A thermal processing cycle consisted of quenching the ribbon in liquid nitrogen, tempering at 600 C for 10 sec, 'upquenching' to 750 C for 10 sec, and subsequently quenching again in liquid nitrogen. The heat-treatment resulted in martensite grains with sizes of about 1 micron or less in both length and thickness and cementite particles of 0.4 micron or less. It is concluded that these microstructures could be used for producing fine-grained ultrahigh carbon steels of very high strength without the brittleness associated with the formation of coarse carbide particles of the loss of strength due to graphite formation.

Dissimilatory nitrogen reduction in intertidal sediments of a temperate estuary: small scale heterogeneity and novel nitrate-to-ammonium reducers.

PubMed

Decleyre, Helen; Heylen, Kim; Van Colen, Carl; Willems, Anne

2015-01-01

The estuarine nitrogen cycle can be substantially altered due to anthropogenic activities resulting in increased amounts of inorganic nitrogen (mainly nitrate). In the past, denitrification was considered to be the main ecosystem process removing reactive nitrogen from the estuarine ecosystem. However, recent reports on the contribution of dissimilatory nitrate reduction to ammonium (DNRA) to nitrogen removal in these systems indicated a similar or higher importance, although the ratio between both processes remains ambiguous. Compared to denitrification, DNRA has been underexplored for the last decades and the key organisms carrying out the process in marine environments are largely unknown. Hence, as a first step to better understand the interplay between denitrification, DNRA and reduction of nitrate to nitrite in estuarine sediments, nitrogen reduction potentials were determined in sediments of the Paulina polder mudflat (Westerschelde estuary). We observed high variability in dominant nitrogen removing processes over a short distance (1.6 m), with nitrous oxide, ammonium and nitrite production rates differing significantly between all sampling sites. Denitrification occurred at all sites, DNRA was either the dominant process (two out of five sites) or absent, while nitrate reduction to nitrite was observed in most sites but never dominant. In addition, novel nitrate-to-ammonium reducers assigned to Thalassospira, Celeribacter, and Halomonas, for which DNRA was thus far unreported, were isolated, with DNRA phenotype reconfirmed through nrfA gene amplification. This study demonstrates high small scale heterogeneity among dissimilatory nitrate reduction processes in estuarine sediments and provides novel marine DNRA organisms that represent valuable alternatives to the current model organisms.

Dissimilatory nitrogen reduction in intertidal sediments of a temperate estuary: small scale heterogeneity and novel nitrate-to-ammonium reducers

PubMed Central

Decleyre, Helen; Heylen, Kim; Van Colen, Carl; Willems, Anne

2015-01-01

The estuarine nitrogen cycle can be substantially altered due to anthropogenic activities resulting in increased amounts of inorganic nitrogen (mainly nitrate). In the past, denitrification was considered to be the main ecosystem process removing reactive nitrogen from the estuarine ecosystem. However, recent reports on the contribution of dissimilatory nitrate reduction to ammonium (DNRA) to nitrogen removal in these systems indicated a similar or higher importance, although the ratio between both processes remains ambiguous. Compared to denitrification, DNRA has been underexplored for the last decades and the key organisms carrying out the process in marine environments are largely unknown. Hence, as a first step to better understand the interplay between denitrification, DNRA and reduction of nitrate to nitrite in estuarine sediments, nitrogen reduction potentials were determined in sediments of the Paulina polder mudflat (Westerschelde estuary). We observed high variability in dominant nitrogen removing processes over a short distance (1.6 m), with nitrous oxide, ammonium and nitrite production rates differing significantly between all sampling sites. Denitrification occurred at all sites, DNRA was either the dominant process (two out of five sites) or absent, while nitrate reduction to nitrite was observed in most sites but never dominant. In addition, novel nitrate-to-ammonium reducers assigned to Thalassospira, Celeribacter, and Halomonas, for which DNRA was thus far unreported, were isolated, with DNRA phenotype reconfirmed through nrfA gene amplification. This study demonstrates high small scale heterogeneity among dissimilatory nitrate reduction processes in estuarine sediments and provides novel marine DNRA organisms that represent valuable alternatives to the current model organisms. PMID:26528270

Relating soil biochemistry to sustainable crop production

USDA-ARS?s Scientific Manuscript database

Amino acids, amino sugars, carbohydrates, phenols, and fatty acids together comprise appreciable proportions of soil organic matter (SOM). Their cycling contribute to soil processes, including nitrogen availability, carbon sequestration and aggregation. For example, soil accumulation of phenols has ...

Pluronic F127 as auxiliary template for preparing nitrogen and oxygen dual doped mesoporous carbon cathode of lithium-oxygen batteries

NASA Astrophysics Data System (ADS)

Wu, Junwei; Liu, Yanchen; Cui, Yanhui; Ouyang, Jue; Baker, Andrew P.; Li, Zuohua; Zhang, Huayu

2018-02-01

Two mesoporous carbon foam (MCF) with nitrogen and oxygen dual doped are fabricated through facile templated hydrothermal process. One using fumed silica as single template is named S-MCF, and another using fumed silica and Pluronic F127 as double templates is named D-MCF. When using Pluronic F127 as an auxiliary template, the D-MCF shows different porous architecture and surface chemical nature from S-MCF, thus they behave differently as cathode materials in Li-O2 batteries. The D-MCF electrode exhibits a slight lower discharge capacity and an increased overpotential than that of S-SCF due to the decreased surface area and oxygen content. However, a better cycle stability was proved for the D-MCF electrode because of its higher nitrogen and lower oxygen content. When further composited with RuO2 nanoparticles, the RuO2/D-MCF cathode can operate 160 cycles with capacity cutoff of 500 mAh g-1, and this prolonged cycle life, compared to the 102 cycles of S-MCF cathode, verifies the superior electrochemical stability of D-MCF further and illuminates the crucial role of carbon substrate in the cathodes of Li-O2 batteries.

Comparative genomic analysis of carbon and nitrogen assimilation mechanisms in three indigenous bioleaching bacteria: predictions and validations

PubMed Central

Levicán, Gloria; Ugalde, Juan A; Ehrenfeld, Nicole; Maass, Alejandro; Parada, Pilar

2008-01-01

Background Carbon and nitrogen fixation are essential pathways for autotrophic bacteria living in extreme environments. These bacteria can use carbon dioxide directly from the air as their sole carbon source and can use different sources of nitrogen such as ammonia, nitrate, nitrite, or even nitrogen from the air. To have a better understanding of how these processes occur and to determine how we can make them more efficient, a comparative genomic analysis of three bioleaching bacteria isolated from mine sites in Chile was performed. This study demonstrated that there are important differences in the carbon dioxide and nitrogen fixation mechanisms among bioleaching bacteria that coexist in mining environments. Results In this study, we probed that both Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans incorporate CO2 via the Calvin-Benson-Bassham cycle; however, the former bacterium has two copies of the Rubisco type I gene whereas the latter has only one copy. In contrast, we demonstrated that Leptospirillum ferriphilum utilizes the reductive tricarboxylic acid cycle for carbon fixation. Although all the species analyzed in our study can incorporate ammonia by an ammonia transporter, we demonstrated that Acidithiobacillus thiooxidans could also assimilate nitrate and nitrite but only Acidithiobacillus ferrooxidans could fix nitrogen directly from the air. Conclusion The current study utilized genomic and molecular evidence to verify carbon and nitrogen fixation mechanisms for three bioleaching bacteria and provided an analysis of the potential regulatory pathways and functional networks that control carbon and nitrogen fixation in these microorganisms. PMID:19055775

Geochemical cycles of atmospheric gases

NASA Technical Reports Server (NTRS)

Walker, J. C. G.; Drever, J. I.

1988-01-01

The processes that control the atmosphere and atmospheric changes are reviewed. The geochemical cycles of water vapor, nitrogen, carbon dioxide, oxygen, and minor atmospheric constituents are examined. Changes in atmospheric chemistry with time are discussed using evidence from the rock record and analysis of the present atmosphere. The role of biological evolution in the history of the atmosphere and projected changes in the future atmosphere are considered.

Climate response of the soil nitrogen cycle in three forest types of a headwater Mediterranean catchment

NASA Astrophysics Data System (ADS)

Lupon, Anna; Gerber, Stefan; Sabater, Francesc; Bernal, Susana

2015-05-01

Future changes in climate may affect soil nitrogen (N) transformations, and consequently, plant nutrition and N losses from terrestrial to stream ecosystems. We investigated the response of soil N cycling to changes in soil moisture, soil temperature, and precipitation across three Mediterranean forest types (evergreen oak, beech, and riparian) by fusing a simple process-based model (which included climate modifiers for key soil N processes) with measurements of soil organic N content, mineralization, nitrification, and concentration of ammonium and nitrate. The model describes sources (atmospheric deposition and net N mineralization) and sinks (plant uptake and hydrological losses) of inorganic N from and to the 0-10 cm soil pool as well as net nitrification. For the three forest types, the model successfully recreated the magnitude and temporal pattern of soil N processes and N concentrations (Nash-Sutcliffe coefficient = 0.49-0.96). Changes in soil water availability drove net N mineralization and net nitrification at the oak and beech forests, while temperature and precipitation were the strongest climatic factors for riparian soil N processes. In most cases, net N mineralization and net nitrification showed a different sensitivity to climatic drivers (temperature, soil moisture, and precipitation). Our model suggests that future climate change may have a minimal effect on the soil N cycle of these forests (<10% change in mean annual rates) because positive warming and negative drying effects on the soil N cycle may counterbalance each other.

Climatic implications of Nitrogen constraints on terrestrial C sequestration estimates in CMIP5 model projection

NASA Astrophysics Data System (ADS)

Zaehle, S.; Jones, C.; Robertson, E.; Lamarque, J.; Houlton, B. Z.

2012-12-01

Nitrogen is an essential nutrient for living organisms and a key mediator of carbon cycle processes. An increasing number of global terrestrial ecosystem models has been recently developed. These models show that nitrogen dynamics strongly affect terrestrial carbon budget projections for the 21st century as they tend to significantly reduce the carbon sequestration capacity of the terrestrial biosphere in response to CO2 fertilization and to modify the climate sensitivity of the global carbon cycle. However, only one of these models (included into two Earth system models) has been used in the CMIP5 study. Therefore the effect of C:N interactions on the CMIP5 projections can only be estimated indirectly. Here, we analyze results of 13 Earth system models from four RCP scenarios (RCP 2.6, 4.5, 6.0, 8.5) with respect to the implied nitrogen requirement to afford the simulated terrestrial carbon sequestration. We compare this N demand to scenarios of changes in terrestrial N availability due to natural variability in the N cycle, as well as changes in biological nitrogen fixation, nitrogen deposition, and ecosystem stoichiometry. Unlike previous studies of a similar type, we base our analyses on a grid-cell basis and explicitly track changes in the carbon and nitrogen cycles over time, and analyze multiple scenarios with different rates of climatic and atmospheric CO2 abundance changes. Consistent with current understanding, the emerging geographic pattern shows N limitation that is stronger in temperate/boreal ecosystems than tropical ecosystems and in pristine areas than highly polluted areas. While the extent and distribution of implied N limitation varies widely between the models, all show some nitrogen limitation of the simulated C sequestration. The magnitude of the N limitation is clearly scenario-dependent, mostly due to the different rates of increased atmospheric CO2 abundance and therefore the extend of CO2 fertilization. Under the most extreme scenario (RCP8.5), an implied nitrogen deficit of 1.9-18.8 Pg N would reduce terrestrial C sequestration by 92-400 Pg C. Assuming the average airborne fraction of 0.6 in the RCP 8.5 scenarios (Jones et al. in review) would cause an increase in atmospheric CO2 abundance of 26-113 ppm by the year 2100, implying an added radiative forcing of 0.15-0.61 Wm-2.

15N indicates an active N-cycling microbial community in low carbon, freshwater sediments.

NASA Astrophysics Data System (ADS)

Sheik, C.

2017-12-01

Earth's large lakes are unique aquatic ecosystems, but we know little of the microbial life driving sedimentary biogeochemical cycles and ultimately the isotopic record. In several of these large lakes, water column productivity is constrained by element limitation, such as phosphorus and iron, creating oligotrophic water column conditions that drive low organic matter content in sediments. Yet, these sediments are biogeochemically active and have been shown to have oxygen consumption rates akin to pelagic ocean sediments and complex sulfur cycling dynamics. Thus, large oligotrophic lakes provide unique and interesting biogeochemical contrast to highly productive freshwater and coastal marine systems. Using Lake Superior as our study site, we found microbial community structure followed patterns in bulk sediment carbon and nitrogen concentrations. These observed patterns were loosely driven by land proximity, as some stations are more coastal and have higher rates of sedimentation, allochthonous carbon inputs and productivity than pelagic sites. Interestingly, upper sediment carbon and nitrogen stable isotopes were quite different from water column. Sediment carbon and nitrogen isotopes correlated significantly with microbial community structure. However, 15N showed much stronger correlation than 13C, and became heavier with core depth. Coinciding with the increase in 15N values, we see evidence of both denitrification and anammox processes in 16S rRNA gene libraries and metagenome assembled genomes. Given that microorganisms prefer light isotopes and that these N-cycling processes both contribute to N2 production and efflux from the sediment, the increase in 15N with sediment depth suggests microbial turnover. Abundance of these genomes also varies with depth suggesting these novel microorganisms are partitioning into specific sediment geochemical zones. Additionally, several of these genomes contain genes involved in sulphur cycling, suggesting a dual biogeochemical role and potential for a cryptic sulfur cycle. Together, Lake Superior sediments offer a glimpse into microbial metabolism in carbon limited environments. Further the pervasiveness of co-metabolic pathways suggests interpretation of isotopic records may be messier than previously thought.

Global sensitivity analysis of DRAINMOD-FOREST, an integrated forest ecosystem model

Treesearch

Shiying Tian; Mohamed A. Youssef; Devendra M. Amatya; Eric D. Vance

2014-01-01

Global sensitivity analysis is a useful tool to understand process-based ecosystem models by identifying key parameters and processes controlling model predictions. This study reported a comprehensive global sensitivity analysis for DRAINMOD-FOREST, an integrated model for simulating water, carbon (C), and nitrogen (N) cycles and plant growth in lowland forests. The...

The role of multiple partners in a digestive mutualism with a protocarnivorous plant.

PubMed

Nishi, Aline Hiroko; Vasconcellos-Neto, João; Romero, Gustavo Quevedo

2013-01-01

The protocarnivorous plant Paepalanthus bromelioides (Eriocaulaceae) is similar to bromeliads in that this plant has a rosette-like structure that allows rainwater to accumulate in leaf axils (i.e. phytotelmata). Although the rosettes of P. bromelioides are commonly inhabited by predators (e.g. spiders), their roots are wrapped by a cylindrical termite mound that grows beneath the rosette. In this study it is predicted that these plants can derive nutrients from recycling processes carried out by termites and from predation events that take place inside the rosette. It is also predicted that bacteria living in phytotelmata can accelerate nutrient cycling derived from predators. The predictions were tested by surveying plants and animals, and also by performing field experiments in rocky fields from Serra do Cipó, Brazil, using natural abundance and enriched isotopes of (15)N. Laboratory bioassays were also conducted to test proteolytic activities of bacteria from P. bromelioides rosettes. Analyses of (15)N in natural nitrogen abundances showed that the isotopic signature of P. bromelioides is similar to that of carnivorous plants and higher than that of non-carnivorous plants in the study area. Linear mixing models showed that predatory activities on the rosettes (i.e. spider faeces and prey carcass) resulted in overall nitrogen contributions of 26·5 % (a top-down flux). Although nitrogen flux was not detected from termites to plants via decomposition of labelled cardboard, the data on (15)N in natural nitrogen abundance indicated that 67 % of nitrogen from P. bromelioides is derived from termites (a bottom-up flux). Bacteria did not affect nutrient cycling or nitrogen uptake from prey carcasses and spider faeces. The results suggest that P. bromelioides derive nitrogen from associated predators and termites, despite differences in nitrogen cycling velocities, which seem to have been higher in nitrogen derived from predators (leaves) than from termites (roots). This is the first study that demonstrates partitioning effects from multiple partners in a digestion-based mutualism. Despite most of the nitrogen being absorbed through their roots (via termites), P. bromelioides has all the attributes necessary to be considered as a carnivorous plant in the context of digestive mutualism.

EMERGY ANALYSIS OF THE PREHISTORIC NITROGEN CYCLE

EPA Science Inventory

Several relationships between the specific emergy or the emergy per unit mass and the mass concentration of nitrogen were shown to exist through an analysis of the global nitrogen cycle. These observed relationships were interpreted by examining the nature of the underlying ener...

The geobiological nitrogen cycle: From microbes to the mantle.

PubMed

Zerkle, A L; Mikhail, S

2017-05-01

Nitrogen forms an integral part of the main building blocks of life, including DNA, RNA, and proteins. N 2 is the dominant gas in Earth's atmosphere, and nitrogen is stored in all of Earth's geological reservoirs, including the crust, the mantle, and the core. As such, nitrogen geochemistry is fundamental to the evolution of planet Earth and the life it supports. Despite the importance of nitrogen in the Earth system, large gaps remain in our knowledge of how the surface and deep nitrogen cycles have evolved over geologic time. Here, we discuss the current understanding (or lack thereof) for how the unique interaction of biological innovation, geodynamics, and mantle petrology has acted to regulate Earth's nitrogen cycle over geologic timescales. In particular, we explore how temporal variations in the external (biosphere and atmosphere) and internal (crust and mantle) nitrogen cycles could have regulated atmospheric pN 2 . We consider three potential scenarios for the evolution of the geobiological nitrogen cycle over Earth's history: two in which atmospheric pN 2 has changed unidirectionally (increased or decreased) over geologic time and one in which pN 2 could have taken a dramatic deflection following the Great Oxidation Event. It is impossible to discriminate between these scenarios with the currently available models and datasets. However, we are optimistic that this problem can be solved, following a sustained, open-minded, and multidisciplinary effort between surface and deep Earth communities. © 2017 The Authors Geobiology Published by John Wiley & Sons Ltd.

Understanding spatial heterogeneity in soil carbon and nitrogen cycling in regenerating tropical dry forests

NASA Astrophysics Data System (ADS)

Waring, B. G.; Powers, J. S.; Branco, S.; Adams, R.; Schilling, E.

2015-12-01

Tropical dry forests (TDFs) currently store significant amounts of carbon in their biomass and soils, but these highly seasonal ecosystems may be uniquely sensitive to altered climates. The ability to quantitatively predict C cycling in TDFs under global change is constrained by tremendous spatial heterogeneity in soil parent material, land-use history, and plant community composition. To explore this variation, we examined soil carbon and nitrogen dynamics in 18 permanent plots spanning orthogonal gradients of stand age and soil fertility. Soil C and N pools, microbial biomass, and microbial extracellular enzyme activities were most variable at small (m2) spatial scales. However, the ratio of organic vs. inorganic N cycling was consistently higher in forest stands dominated by slow-growing, evergreen trees that associate with ectomycorrhizal fungi. Similarly, although bulk litter stocks and turnover rates varied greatly among plots, litter decomposition tended to be slower in ectomycorrhizae-dominated stands. Soil N cycling tended to be more conservative in older plots, although the relationship between stand age and element cycling was weak. Our results emphasize that microscale processes, particularly interactions between mycorrhizal fungi and free-living decomposers, are important controls on ecosystem-scale element cycling.

Use It or Lose It: Advances in Our Understanding of Terrestrial Nitrogen Retention and Loss (Invited)

NASA Astrophysics Data System (ADS)

Silver, W. L.; Yang, W. H.

2013-12-01

Understanding of the terrestrial nitrogen (N) cycle has grown over the last decade to include a variety of pathways that have the potential to either retain N in the ecosystem or result in losses to the atmosphere or groundwater. Early work has described the mechanics of these N transformations, but the relevance of these processes to ecosystem, regional, or global scale N cycling has not been well quantified. In this study, we review advances in our understanding of the terrestrial N cycle, and focus on three pathways with particular relevance to N retention and loss: dissimilatory nitrate and nitrite reduction to ammonium (DNRA), anaerobic ammonium oxidation (annamox), and anaerobic ammonium oxidation coupled to iron reduction (Feammox). We discuss the role of these processes in the microbial N economy (sensu Burgin et al. 2011) of the terrestrial N cycle, the environmental and ecological constraints, and relationships with other key biogeochemical cycles. We also discuss recent advances in analytical approaches that have improved our ability to detect these and related N fluxes in terrestrial ecosystems. Finally, we present a scaling exercise that identifies the potential importance of these pathways for N retention and loss across a range of spatial and temporal scales, and discuss their significance in terms of N limitation to net primary productivity, N leaching to groundwater, and the release of reactive N gases to the atmosphere.

Investigating the Trimethylaluminium/Water ALD Process on Mesoporous Silica by In Situ Gravimetric Monitoring.

PubMed

Strempel, Verena E; Knemeyer, Kristian; Naumann d'Alnoncourt, Raoul; Driess, Matthias; Rosowski, Frank

2018-05-24

A low amount of AlO x was successfully deposited on an unordered, mesoporous SiO₂ powder using 1⁻3 ALD (Atomic Layer Deposition) cycles of trimethylaluminium and water. The process was realized in a self-built ALD setup featuring a microbalanceand a fixed particle bed. The reactor temperature was varied between 75, 120, and 200 °C. The self-limiting nature of the deposition was verified by in situ gravimetric monitoring for all temperatures. The coated material was further analyzed by nitrogen sorption, inductively coupled plasma-optical emission spectroscopy, powder X-ray diffraction, high-resolution transmission electron microscopy, attenuated total reflection Fourier transformed infrared spectroscopy, and elemental analysis. The obtained mass gains correspond to average growth between 0.81⁻1.10 Å/cycle depending on substrate temperature. In addition, the different mass gains during the half-cycles in combination with the analyzed aluminum content after one, two, and three cycles indicate a change in the preferred surface reaction of the trimethylaluminium molecule from a predominately two-ligand exchange with hydroxyl groups to more single-ligand exchange with increasing cycle number. Nitrogen sorption isotherms demonstrate (1) homogeneously coated mesopores, (2) a decrease in surface area, and (3) a reduction of the pore size. The experiment is successfully repeated in a scale-up using a ten times higher substrate batch size.

Global patterns of foliar nitrogen isotopes and their relationships with climate, mycorrhizal fungi, foliar nutrient concentrations, and nitrogen availability

Treesearch

Joseph M. Craine; Andrew J. Elmore; Marcos P. M. Aidar; Mercedes Bustamante; Todd E. Dawson; Erik A. Hobbie; Ansgar Kahmen; Michelle C. Mack; Kendra K. McLauchlan; Anders Michelsen; Gabriela Nardoto; Linda H. Pardo; Josep Penuelas; Peter B. Reich; Edward A.G. Schuur; William D. Stock; Pamela H. Templer; Ross A. Virginia; Jeffrey M. Welker; Ian J. Wright

2009-01-01

Ratios of nitrogen (N) isotopes in leaves could elucidate underlying patterns of N cycling across ecological gradients. To better understand global-scale patterns of N cycling, we compiled data on foliar N isotope ratios, foliar N concentrations, mycorrhizal type and climate for over 11 000 plants worldwide. Global-scale comparisons of other components of the N cycle...

Proposal to support the 4th international conference on nitrification and related processes (ICoN4)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Klotz, Martin Gunter

The 4th International Conference on Nitrification and Related Processes (ICoN4) commencing between June 27 and July 1, 2015, at the University of Alberta in Edmonton, Alberta, Canada brings together an international collection of academic, government, and private sector researchers of the global biogeochemical nitrogen cycle to share their scientific discoveries, innovations and pertinent societal impacts. The classical understanding of “nitrification” describes the two-step transformation of ammonium to nitrite and nitrite to nitrate; however, we now know from the analysis genome sequences, the application of ‘omics technologies, microbial ecology, biogeochemistry, and microbial physiology that the transformation of ammonium is not performedmore » by a few particular groups of microorganisms nor is it confined to oxic environments. Past ICoN meetings have explored the interconnections between ammonium- and nitrite-consuming processes in all ecosystems, the emission of greenhouse gases by these processes and their control, and the intersection between intermediates of the nitrification process and other elemental cycles; this has generated tremendous progress in our understanding of the global nitrogen cycle and it has generated excitement in the next generation of N cycle researchers. Nitrification research has a long-standing connection to the Community Science Program of the DOE. Between 1999 and 2001, the JGI generated the first genome sequence of an ammonia-oxidizing bacterium, Nitrosomonas europaea ATCC 19718, and it has subsequently sequenced, or is in the process of sequencing over 50 additional genomes from ammonia-oxidizing bacteria, nitrite-oxidizing bacteria, and ammonia-oxidizing archaea. Autotrophic ammonia- and nitrite-transforming microorganisms play also a critical role in carbon cycling and sequestration in nearly all ecosystems. Not only do they control the concentration and speciation of biologically available N to plants and other microorganisms, nitrification is also the source of the various forms of nitrogen pollution. Nitrate pollution from over-fertilization of managed soils causes eutrophication and the reduction of nitrate and nitrate also results in emission of N2O, a denitrification process that leads to the accumulation of this major greenhouse gas in the atmosphere. Anaerobic ammonia oxidation (anammox) and nitrite-driven anaerobic methane oxidation (n-DAMO) are involved in the transformation of ammonium, nitrite, and nitrate to dinitrogen without N2O as an intermediate, acting as mitigating processes to nitrification. Along with the vast international participation in the ICoN conferences, encouragement and inclusion of early career investigators and graduate students is viewed as critical to the continued success of our discipline.« less

Modeling greenhouse gas emissions and nutrient transport in managed arable soils with a fully coupled hydrology-biogeochemical modeling system

NASA Astrophysics Data System (ADS)

Haas, Edwin; Klatt, Steffen; Kiese, Ralf; Butterbach-Bahl, Klaus; Kraft, Philipp; Breuer, Lutz

2015-04-01

The use of mineral nitrogen fertilizer sustains the global food production and therefore the livelihood of human kind. The rise in world population will put pressure on the global agricultural system to increase its productivity leading most likely to an intensification of mineral nitrogen fertilizer use. The fate of excess nitrogen and its distribution within landscapes is manifold. Process knowledge on the site scale has rapidly grown in recent years and models have been developed to simulate carbon and nitrogen cycling in managed ecosystems on the site scale. Despite first regional studies, the carbon and nitrogen cycling on the landscape or catchment scale is not fully understood. In this study we present a newly developed modelling approach by coupling the fully distributed hydrology model CMF (catchment modelling framework) to the process based regional ecosystem model LandscapeDNDC for the investigation of hydrological processes and carbon and nitrogen transport and cycling, with a focus on nutrient displacement and resulting greenhouse gas emissions in various virtual landscapes / catchment to demonstrate the capabilities of the modelling system. The modelling system was applied to simulate water and nutrient transport at the at the Yanting Agro-ecological Experimental Station of Purple Soil, Sichuan province, China. The catchment hosts cypress forests on the outer regions, arable fields on the sloping croplands cultivated with wheat-maize rotations and paddy rice fields in the lowland. The catchment consists of 300 polygons vertically stratified into 10 soil layers. Ecosystem states (soil water content and nutrients) and fluxes (evapotranspiration) are exchanged between the models at high temporal scales (hourly to daily) forming a 3-dimensional model application. The water flux and nutrients transport in the soil is modelled using a 3D Richards/Darcy approach for subsurface fluxes with a kinematic wave approach for surface water runoff and the evapotranspiration is based on Penman-Monteith. Biogeochemical processes are modelled by LandscapeDNDC, including soil microclimate, plant growth and biomass allocation, organic matter mineralisation, nitrification, denitrification, chemodenitrification and methanogenesis producing and consuming soil based greenhouse gases. The model application will present first results of the coupled model to simulate soil based greenhouse gas emissions as well as nitrate discharge from the Yanting catchment. The model application will also present the effects of different management practices (fertilization rates and timings, tilling, residues management) on the redistribution of N surplus within the catchment causing biomass productivity gradients and different levels of indirect N2O emissions along topographical gradients.

NITROGEN: DEFINING LIMITS TO ECOSYSTEM RESTORATION; THE INFLUENCE OF SUCCESSION AND TROPHIC INTERACTIONS

EPA Science Inventory

A goal of this research is to investigate the interacting characteristics of biota and abiotic conditions relative to nitrogen cycling in the ecosystem. The research will support development of nitrogen cycling models with an ultimate application directed towards identification ...

Assessment of global nitrogen pollution in rivers using an integrated biogeochemical modeling framework.

PubMed

He, Bin; Kanae, Shinjiro; Oki, Taikan; Hirabayashi, Yukiko; Yamashiki, Yosuke; Takara, Kaoru

2011-04-01

This study has analyzed the global nitrogen loading of rivers resulting from atmospheric deposition, direct discharge, and nitrogenous compounds generated by residential, industrial, and agricultural sources. Fertilizer use, population distribution, land cover, and social census data were used in this study. A terrestrial nitrogen cycle model with a 24-h time step and 0.5° spatial resolution was developed to estimate nitrogen leaching from soil layers in farmlands, grasslands, and natural lands. The N-cycle in this model includes the major processes of nitrogen fixation, nitrification, denitrification, immobilization, mineralization, leaching, and nitrogen absorption by vegetation. The previously developed Total Runoff Integrating Pathways network was used to analyze nitrogen transport from natural and anthropogenic sources through river channels, as well as the collecting and routing of nitrogen to river mouths by runoff. Model performance was evaluated through nutrient data measured at 61 locations in several major world river basins. The dissolved inorganic nitrogen concentrations calculated by the model agreed well with the observed data and demonstrate the reliability of the proposed model. The results indicate that nitrogen loading in most global rivers is proportional to the size of the river basin. Reduced nitrate leaching was predicted for basins with low population density, such as those at high latitudes or in arid regions. Nitrate concentration becomes especially high in tropical humid river basins, densely populated basins, and basins with extensive agricultural activity. On a global scale, agriculture has a significant impact on the distribution of nitrogenous compound pollution. The map of nitrate distribution indicates that serious nitrogen pollution (nitrate concentration: 10-50 mg N/L) has occurred in areas with significant agricultural activities and small precipitation surpluses. Analysis of the model uncertainty also suggests that the nitrate export in most rivers is sensitive to the amount of nitrogen leaching from agricultural lands. Copyright © 2011 Elsevier Ltd. All rights reserved.

Benchmarking carbon-nitrogen interactions in Earth System Models to observations: An inter-comparison of nitrogen limitation in global land surface models with carbon and nitrogen cycles (CLM-CN and O-CN)

NASA Astrophysics Data System (ADS)

Thomas, R. Q.; Zaehle, S.; Templer, P. H.; Goodale, C. L.

2011-12-01

Predictions of climate change depend on accurately modeling the feedbacks among the carbon cycle, nitrogen cycle, and climate system. Several global land surface models have shown that nitrogen limitation determines how land carbon fluxes respond to rising CO2, nitrogen deposition, and climate change, thereby influencing predictions of climate change. However, the magnitude of the carbon-nitrogen-climate feedbacks varies considerably by model, leading to critical and timely questions of why they differ and how they compare to field observations. To address these questions, we initiated a model inter-comparison of spatial patterns and drivers of nitrogen limitation. The experiment assessed the regional consequences of sustained nitrogen additions in a set of 25-year global nitrogen fertilization simulations. The model experiments were designed to cover effects from small changes in nitrogen inputs associated with plausible increases in nitrogen deposition to large changes associated with field-based nitrogen fertilization experiments. The analyses of model simulations included assessing the geographically varying degree of nitrogen limitation on plant and soil carbon cycling and the mechanisms underlying model differences. Here, we present results from two global land-surface models (CLM-CN and O-CN) with differing approaches to modeling carbon-nitrogen interactions. The predictions from each model were compared to a set of globally distributed observational data that includes nitrogen fertilization experiments, 15N tracer studies, small catchment nitrogen input-output studies, and syntheses across nitrogen deposition gradients. Together these datasets test many aspects of carbon-nitrogen coupling and are able to differentiate between the two models. Overall, this study is the first to explicitly benchmark carbon and nitrogen interactions in Earth System Models using a range of observations and is a foundation for future inter-comparisons.

The influence of leaf-atmosphere NH3(g ) exchange on the isotopic composition of nitrogen in plants and the atmosphere.

PubMed

Johnson, Jennifer E; Berry, Joseph A

2013-10-01

The distribution of nitrogen isotopes in the biosphere has the potential to offer insights into the past, present and future of the nitrogen cycle, but it is challenging to unravel the processes controlling patterns of mixing and fractionation. We present a mathematical model describing a previously overlooked process: nitrogen isotope fractionation during leaf-atmosphere NH3(g ) exchange. The model predicts that when leaf-atmosphere exchange of NH3(g ) occurs in a closed system, the atmospheric reservoir of NH3(g ) equilibrates at a concentration equal to the ammonia compensation point and an isotopic composition 8.1‰ lighter than nitrogen in protein. In an open system, when atmospheric concentrations of NH3(g ) fall below or rise above the compensation point, protein can be isotopically enriched by net efflux of NH3(g ) or depleted by net uptake. Comparison of model output with existing measurements in the literature suggests that this process contributes to variation in the isotopic composition of nitrogen in plants as well as NH3(g ) in the atmosphere, and should be considered in future analyses of nitrogen isotope circulation. The matrix-based modelling approach that is introduced may be useful for quantifying isotope dynamics in other complex systems that can be described by first-order kinetics. © 2013 John Wiley & Sons Ltd.

Organic and nitrogen removal from landfill leachate in aerobic granular sludge sequencing batch reactors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wei Yanjie; Key Laboratory of Environmental Protection in Water Transport Engineering Ministry of Communications, Tianjin Research Institute of Water Transport Engineering, Tianjin 300456; Ji Min, E-mail: jmtju@yahoo.cn

2012-03-15

Highlights: Black-Right-Pointing-Pointer Aerobic granular sludge SBR was used to treat real landfill leachate. Black-Right-Pointing-Pointer COD removal was analyzed kinetically using a modified model. Black-Right-Pointing-Pointer Characteristics of nitrogen removal at different ammonium inputs were explored. Black-Right-Pointing-Pointer DO variations were consistent with the GSBR performances at low ammonium inputs. - Abstract: Granule sequencing batch reactors (GSBR) were established for landfill leachate treatment, and the COD removal was analyzed kinetically using a modified model. Results showed that COD removal rate decreased as influent ammonium concentration increasing. Characteristics of nitrogen removal at different influent ammonium levels were also studied. When the ammonium concentration inmore » the landfill leachate was 366 mg L{sup -1}, the dominant nitrogen removal process in the GSBR was simultaneous nitrification and denitrification (SND). Under the ammonium concentration of 788 mg L{sup -1}, nitrite accumulation occurred and the accumulated nitrite was reduced to nitrogen gas by the shortcut denitrification process. When the influent ammonium increased to a higher level of 1105 mg L{sup -1}, accumulation of nitrite and nitrate lasted in the whole cycle, and the removal efficiencies of total nitrogen and ammonium decreased to only 35.0% and 39.3%, respectively. Results also showed that DO was a useful process controlling parameter for the organics and nitrogen removal at low ammonium input.« less

Differential sensitivity to climate change of C and N cycling processes across soil horizons in a northern hardwood forest

Treesearch

Jorge Durán; Jennifer L. Morse; Alexandra Rodríguez; John L. Campbell; Lynn M. Christenson; Charles T. Driscoll; Timothy J. Fahey; Melany C. Fisk; Myron J. Mitchell; Pamela H. Templer; Peter M. Groffman

2017-01-01

Climate of the northern hardwood forests of North America will become significantly warmer in the coming decades. Associated increases in soil temperature, decreases in water availability and changes in winter snow pack and soil frost are likely to affect soil carbon (C) and nitrogen (N) cycling. Most studies of the effects of climate change on soil function have...

Overview of the 1988 GCE/CASE/WATOX Studies of biogeochemical cycles in the North Atlantic region

NASA Astrophysics Data System (ADS)

Pszenny, Alexander A. P.; Galloway, James N.; Artz, Richard S.; Boatman, Joseph F.

1990-06-01

The 1988 Global Change Expedition/Coordinated Air-Sea Experiment/Western Atlantic Ocean Experiment (GCE/CASE/WATOX) was a multifaceted research program designed to study atmospheric and oceanic processes affecting the biogeochemical cycles of carbon, nitrogen, sulfur, and trace metals in the North Atlantic Ocean region. Field work included (1) a 49-day research cruise aboard NOAA ship Mt. Mitchell (Global Change Expedition) from Norfolk, Virginia, to Bermuda, Iceland, the Azores, and Barbados, (2) eight flights of the NOAA King Air research aircraft, four off the Virginia Capes and four near Bermuda (CASE/WATOX), and (3) a research cruise aboard the yacht Fleurtie near Bermuda (WATOX). Objectives of GCE/CASE/WATOX were (1) to examine processes controlling the mesoscale distributions of productivity, chlorophyll, and phytoplankton growth rates in Atlantic surface waters, (2) to identify factors controlling the distribution of ozone in the North Atlantic marine boundary layer, and (3) to estimate the contributions of sources on surrounding continents to the biogeochemical cycles of sulfur, nitrogen, and trace metals over the North Atlantic region during the boreal summer season. The individual papers in this and the next two issues of Global Biogeochemical Cycles provide details on the results and analyses of the individual measurement efforts. This paper provides a brief overview of GCE/CASE/WATOX.

TThe role of nitrogen availability in land-atmosphere interactions: a systematic evaluation of carbon-nitrogen coupling in a global land surface model using plot-level nitrogen fertilization experiments

NASA Astrophysics Data System (ADS)

Thomas, R. Q.; Goodale, C. L.; Bonan, G. B.; Mahowald, N. M.; Ricciuto, D. M.; Thornton, P. E.

2010-12-01

Recent research from global land surface models emphasizes the important role of nitrogen cycling on global climate, via its control on the terrestrial carbon balance. Despite the implications of nitrogen cycling on global climate predictions, the research community has not performed a systematic evaluation of nitrogen cycling in global models. Here, we present such an evaluation for one global land model, CLM-CN. In the evaluation we simulated 45 plot-scale nitrogen-fertilization experiments distributed across 33 temperate and boreal forest sites. Model predictions were evaluated against field observations by comparing the vegetation and soil carbon responses to the additional nitrogen. Aggregated across all experiments, the model predicted a larger vegetation carbon response and a smaller soil carbon response than observed; the responses partially offset each other, leading to a slightly larger total ecosystem carbon response than observed. However, the model-observation agreement improved for vegetation carbon when the sites with observed negative carbon responses to nitrogen were excluded, which may be because the model lacks mechanisms whereby nitrogen additions increase tree mortality. Among experiments, younger forests and boreal forests’ vegetation carbon responses were less than predicted and mature forests (> 40 years old) were greater than predicted. Specific to the CLM-CN, this study used a systematic evaluation to identify key areas to focus model development, especially soil carbon- nitrogen interactions and boreal forest nitrogen cycling. Applicable to the modeling community, this study demonstrates a standardized protocol for comparing carbon-nitrogen interactions among global land models.

A Natural Light/Dark Cycle Regulation of Carbon-Nitrogen Metabolism and Gene Expression in Rice Shoots.

PubMed

Li, Haixing; Liang, Zhijun; Ding, Guangda; Shi, Lei; Xu, Fangsen; Cai, Hongmei

2016-01-01

Light and temperature are two particularly important environmental cues for plant survival. Carbon and nitrogen are two essential macronutrients required for plant growth and development, and cellular carbon and nitrogen metabolism must be tightly coordinated. In order to understand how the natural light/dark cycle regulates carbon and nitrogen metabolism in rice plants, we analyzed the photosynthesis, key carbon-nitrogen metabolites, and enzyme activities, and differentially expressed genes and miRNAs involved in the carbon and nitrogen metabolic pathway in rice shoots at the following times: 2:00, 6:00, 10:00, 14:00, 18:00, and 22:00. Our results indicated that more CO2 was fixed into carbohydrates by a high net photosynthetic rate, respiratory rate, and stomatal conductance in the daytime. Although high levels of the nitrate reductase activity, free ammonium and carbohydrates were exhibited in the daytime, the protein synthesis was not significantly facilitated by the light and temperature. In mRNA sequencing, the carbon and nitrogen metabolism-related differentially expressed genes were obtained, which could be divided into eight groups: photosynthesis, TCA cycle, sugar transport, sugar metabolism, nitrogen transport, nitrogen reduction, amino acid metabolism, and nitrogen regulation. Additionally, a total of 78,306 alternative splicing events have been identified, which primarily belong to alternative 5' donor sites, alternative 3' acceptor sites, intron retention, and exon skipping. In sRNA sequencing, four carbon and nitrogen metabolism-related miRNAs (osa-miR1440b, osa-miR2876-5p, osa-miR1877 and osa-miR5799) were determined to be regulated by natural light/dark cycle. The expression level analysis showed that the four carbon and nitrogen metabolism-related miRNAs negatively regulated their target genes. These results may provide a good strategy to study how natural light/dark cycle regulates carbon and nitrogen metabolism to ensure plant growth and development.

Effect of mineral fertilizers on microbiological and biochemical characteristics of agrochernozem.

NASA Astrophysics Data System (ADS)

Tkhakakhova, Azida; Vasilenko, Elena; Kutovaya, Olga

2013-04-01

The problem of reproduction of soil fertility of chernozems are solved with integrated action, the ecological condition of the soil can be assessed by the activity of physiological groups of microorganisms. Microorganisms are the most important in the transformation of compounds of biogenic elements and therefore it is very interesting to study the nature of the relationship of some biochemical parameters with the development of microflora and micromycetes eco-trophic groups. Agrochemical researches have been conducted at agroecological station "Stone Steppe" in central Russia. Experiment variants: 1 - Control (without fertilizer); 2 - N10,5 P10,5 K10,5; 3 - N56,5 P56,5 K56,5; 4 - deposit soil. Mobile forms of humic substances (mobile carbon and carbon water extract) have changed during the cultivation of the chernozem soil. Amount of mobile humus has doubled in the variants with the use of mineral fertilizers. It's just mobile humus which determines the soil response to any impact, especially ecological. Water extract carbon - organic matter contained in the soil solution and the subject of assimilation of plants and microorganisms. It increased in agricultural soils. The total nitrogen and nitrate nitrogen amount in the variants of agricultural use is higher than in the deposit soil. This is probably because of the soil aeration, the release of nitrogen from the labile humus due to biological activity and nitrification. Amount of ammonia nitrogen has increased in the variant with the use of high doses of fertilizers. Deposit soil (40 years without agricultural use) has a lower, but more stable microbial activity. Process of anoxic decomposition of plant remains develops more active than others, due to the natural structure of the soil anaerobiosis in the spring time. Processes of nitrogen cycle (nitrogen accumulation - fixation of atmospheric nitrogen, nitrogen losses - denitrification) are progressing very intensively in agricultural soil with fertilizer. Content of humic substances in the soil affects all groups of microorganisms, except actinomycetes and cellulolytices. These microorganisms have an active system of hydrolytic enzymes that taking action on hard organic materials. Movable carbon largely affects the anaerobic microorganisms nitrogen cycle and inverse relationship takes place during with the developing of actinomycetes. Correlation between the aqueous extract carbon with cellulolitic bacteria, aerobic nitrogen-fixing bacteria and amylolytic microorganisms using mineral nitrogen is the highest. Organic material of the soil solution in the growing season associated with NO3-. The content of total nitrogen and nitrate associated with anaerobic denitrifying bacteria, nitrogen-fixing bacteria and amylolytic microorganisms. The content of ammonia nitrogen N-NH4+ renders very strong influence on soil microorganisms. A positive correlation is observed with ammonifiers, nitrogen-fixing bacteria, denitrifying bacteria. There is inverse relationship with actinomycetes (R = - 0,96) and anaerobic cellulolitic bacteria (R = - 0,80). Representatives of these microorganisms are active participants in the carbon cycle; their development in the presence of the ammonium form of nitrogen is possibly suspended. There is a complicated relationship of biochemical indicators of the development of soil microorganisms in the black earth. The problem preserving stable humus and physiologically active mobile forms that affect plant growth can only be achieved while maintaining the living organisms in it.

Bioproducts and environmental quality: Biofuels, greenhouse gases, and water quality

NASA Astrophysics Data System (ADS)

Ren, Xiaolin

Promoting bio-based products is one oft-proposed solution to reduce GHG emissions because the feedstocks capture carbon, offsetting at least partially the carbon discharges resulting from use of the products. However, several life cycle analyses point out that while biofuels may emit less life cycle net carbon emissions than fossil fuels, they may exacerbate other parts of biogeochemical cycles, notably nutrient loads in the aquatic environment. In three essays, this dissertation explores the tradeoff between GHG emissions and nitrogen leaching associated with biofuel production using general equilibrium models. The first essay develops a theoretical general equilibrium model to calculate the second-best GHG tax with the existence of a nitrogen leaching distortion. The results indicate that the second-best GHG tax could be higher or lower than the first-best tax rates depending largely on the elasticity of substitution between fossil fuel and biofuel. The second and third essays employ computable general equilibrium models to further explore the tradeoff between GHG emissions and nitrogen leaching. The computable general equilibrium models also incorporate multiple biofuel pathways, i.e., biofuels made from different feedstocks using different processes, to identify the cost-effective combinations of biofuel pathways under different policies, and the corresponding economic and environmental impacts.

Development and Implementation of an inquiry lesson for grades 6-12 explicitly teaching the Nature and Process of Science, from ship to shore, for core data of the Cretaceous-Paleogene (K-Pg)

NASA Astrophysics Data System (ADS)

Cohen, E.; Quan, T. M.

2012-12-01

The mass extinction event at the Cretaceous-Paleogene (K-Pg) boundary was the result of a bolide impact, and is popularly known for the extinction of the dinosaurs, but is also one of the largest Paleogene mass extinctions identified. In addition, it was followed by a period of drastic changes in ecological conditions, including a complete alteration of the global carbon cycle; the root cause of this change is still debated. Little information is known regarding changes in the nitrogen cycle during these periods of mass extinction and recovery. Given the importance of the nitrogen cycle to primary production and its relationship to the redox state of the local environment, determining changes in the nitrogen cycle will provide important information as to the processes of global mass extinction and the subsequent recovery. Three lessons for students' grade 6-12 were created to support the content surrounding: National Science Education Content Standards: Standard A: Science as Inquiry Standard D: Earth and Space Science Ocean Literacy Essential Principles: 3. The ocean is a major influence on weather and climate 7. The ocean is largely unexplored In the Nature of Science activity, students sequence a series of photographs to illustrate the scientific process of one scientist, Dr. Tracy Quan, of Oklahoma State University as she uses deep sea core data obtained by the JOIDES Resolution research vessel to investigate the climate during the mass extinction that took place ~ 65 million years ago. By reading the information contained on each card and studying the pictures, students learn that science is a dynamic, non-linear, and creative process. Students do not have to create the exact order Dr. Quan uses as her scientific process, but they need to justify their reasoning for placing the pictures in the order they did. The activity begins with a photo of the JOIDES Resolution and ends during a presentation at a scientific conference. There are 21 other photo cards showing the conduction of the science on the ship and shore.

Development of Advanced Eco-hydrologic and Biogeochemical Coupling Model to Constrain Missing Role of Inland Waters on Boundless Biogeochemical Cycle

NASA Astrophysics Data System (ADS)

Nakayama, T.; Maksyutov, S. S.

2016-12-01

Inland waters including rivers, lakes, and groundwater are suggested to act as a transport pathway for water and dissolved substances, and play some role in continental biogeochemical cycling (Cole et al., 2007; Battin et al., 2009). The authors have developed process-based National Integrated Catchment-based Eco-hydrology (NICE) model (Nakayama, 2014, 2015, etc.), which includes feedback between hydrologic-geomorphic-ecological processes. In this study, NICE was further developed to couple with various biogeochemical cycle models in biosphere, those for water quality in aquatic ecosystems, and those for carbon weathering, etc. (NICE-BGC) (Nakayama, accepted). The new model incorporates connectivity of the biogeochemical cycle accompanied by hydrologic cycle between surface water and groundwater, hillslopes and river networks, and other intermediate regions. The model also includes reaction between inorganic and organic carbons, and its relation to nitrogen and phosphorus in terrestrial-aquatic continuum. The model results of CO2 evasion to the atmosphere, sediment storage, and carbon transport to the ocean (DOC, POC, and DIC flux) were reasonably in good agreement with previous compiled data. The model also showed carbon budget in major river basins and in each continent in global scale. In order to decrease uncertainty about carbon cycle, it became clear the previous empirical estimation by compiled data should be extended to this process-oriented model and higher resolution data to further clarify mechanistic interplay between inorganic and organic carbon and its relationship to nitrogen and phosphorus in terrestrial-aquatic linkages. NICE-BGC would play important role to re-evaluate greenhouse gas budget of the biosphere, and to bridge gap between top-down and bottom-up approaches (Battin et al., 2009; Regnier et al., 2013).

Carbon capture by sorption-enhanced water-gas shift reaction process using hydrotalcite-based material

DOE Office of Scientific and Technical Information (OSTI.GOV)

van Selow, E.R.; Cobden, P.D.; Verbraeken, P.A.

2009-05-15

A novel route for precombustion decarbonization is the sorption-enhanced water-gas shift (SEWGS) process. In this process carbon dioxide is removed from a synthesis gas at elevated temperature by adsorption. Simultaneously, carbon monoxide is converted to carbon dioxide by the water-gas shift reaction. The periodic adsorption and desorption of carbon dioxide is induced by a pressure swing cycle, and the cyclic capacity can be amplified by purging with steam. From previous studies is it known that for SEWGS applications, hydrotalcite-based materials are particularly attractive as sorbent, and commercial high-temperature shift catalysts can be used for the conversion of carbon monoxide. Tabletsmore » of a potassium promoted hydrotalcite-based material are characterized in both breakthrough and cyclic experiments in a 2 m tall fixed-bed reactor. When exposed to a mixture of carbon dioxide, steam, and nitrogen at 400{sup o}C, the material shows a breakthrough capacity of 1.4 mmol/g. In subsequent experiments the material was mixed with tablets of promoted iron-chromium shift catalyst and exposed to a mixture of carbon dioxide, carbon monoxide, steam, hydrogen, and nitrogen. It is demonstrated that carbon monoxide conversion can be enhanced to 100% in the presence of a carbon dioxide sorbent. At breakthrough, carbon monoxide and carbon dioxide simultaneously appear at the end of the bed. During more than 300 cycles of adsorption/reaction and desorption, the capture rate, and carbon monoxide conversion are confirmed to be stable. Two different cycle types are investigated: one cycle with a CO{sub 2} rinse step and one cycle with a steam rinse step. The performance of both SEWGS cycles are discussed.« less

Nutrient Dynamics In Flooded Wetlands. I: Model Development

EPA Science Inventory

Wetlands are rich ecosystems recognized for ameliorating floods, improving water quality and providing other ecosystem benefits. In this part of a two-paper sequel, we present a relatively detailed process-based model for nitrogen and phosphorus retention, cycling and removal in...

A microbial biogeochemistry network for soil carbon and nitrogen cycling and methane flux: model structure and application to Asia

NASA Astrophysics Data System (ADS)

Xu, X.; Song, C.; Wang, Y.; Ricciuto, D. M.; Lipson, D.; Shi, X.; Zona, D.; Song, X.; Yuan, F.; Oechel, W. C.; Thornton, P. E.

2017-12-01

A microbial model is introduced for simulating microbial mechanisms controlling soil carbon and nitrogen biogeochemical cycling and methane fluxes. The model is built within the CN (carbon-nitrogen) framework of Community Land Model 4.5, named as CLM-Microbe to emphasize its explicit representation of microbial mechanisms to biogeochemistry. Based on the CLM4.5, three new pools were added: bacteria, fungi, and dissolved organic matter. It has 11 pools and 34 transitional processes, compared with 8 pools and 9 transitional flow in the CLM4.5. The dissolve organic carbon was linked with a new microbial functional group based methane module to explicitly simulate methane production, oxidation, transport and their microbial controls. Comparing with CLM4.5-CN, the CLM-Microbe model has a number of new features, (1) microbial control on carbon and nitrogen flows between soil carbon/nitrogen pools; (2) an implicit representation of microbial community structure as bacteria and fungi; (3) a microbial functional-group based methane module. The model sensitivity analysis suggests the importance of microbial carbon allocation parameters on soil biogeochemistry and microbial controls on methane dynamics. Preliminary simulations validate the model's capability for simulating carbon and nitrogen dynamics and methane at a number of sites across the globe. The regional application to Asia has verified the model in simulating microbial mechanisms in controlling methane dynamics at multiple scales.

Contrasting soil microbial community functional structures in two major landscapes of the Tibetan alpine meadow

DOE PAGES

Chu, Houjuan; Wang, Shiping; Yue, Haowei; ...

2014-07-07

The grassland and shrubland are two major landscapes of the Tibetan alpine meadow, a region very sensitive to the impact of global warming and anthropogenic perturbation. Herein, we report a study showing that a majority of differences in soil microbial community functional structures, measured by a functional gene array named GeoChip 4.0, in two adjacent shrubland and grassland areas, were explainable by environmental properties, suggesting that the harsh environments in the alpine grassland rendered niche adaptation important. Furthermore, genes involved in labile carbon degradation were more abundant in the shrubland than those of the grassland but genes involved in recalcitrantmore » carbon degradation were less abundant, which was conducive to long-term carbon storage and sequestration in the shrubland despite low soil organic carbon content. In addition, genes of anerobic nitrogen cycling processes such as denitrification and dissimilatory nitrogen reduction were more abundant, shifting soil nitrogen cycling toward ammonium biosynthesis and consequently leading to higher soil ammonium contents. In conclusion, we also noted higher abundances of stress genes responsive to nitrogen limitation and oxygen limitation, which might be attributed to low total nitrogen and higher water contents in the shrubland. Together, these results provide mechanistic knowledge about microbial linkages to soil carbon and nitrogen storage and potential consequences of vegetation shifts in the Tibetan alpine meadow.« less

Sedimentary denitrification: Isotope fractionation and its impact on water column nitrate isotopes

NASA Astrophysics Data System (ADS)

Dähnke, K.; Thamdrup, B.

2012-04-01

The global marine nitrogen cycle is constrained by one major source and two processes that act as nitrogen sinks: nitrogen fixation on the one side and denitrification or anammox on the other. These processes with their respective isotope effecst set the marine nitrate 15N-isotope value to a relatively constant average of 5 per mil. This value can be used to better assess the magnitude of these source and sink terms, but the underlying assumption at present is that sedimentary denitrification, a process responsible for approximately one third of global nitrogen removal, has little to no isotope effect on the water column. We tested this hypothesis in sediment incubations, measuring net denitrification and nitrogen and oxygen stable isotope fractionation in surface sediments from the coastal Baltic Sea (Boknis Eck, Northern Germany). We found tremendously high denitrification rates, and regardless of current paradigms assuming little fractionation during sediment denitrification, we measured fractionation factors of 19 per mil for nitrogen and 11 per mil for oxygen in nitrate. These results potentially challenge the current view of fractionation during sedimentary denitrification and imply that nitrogen budget calculation may need to consider this variability. Furthermore, the ratio of fractionation factors for nitrogen and oxygen is distinct from the 1 : 1 ratio otherwise found in marine systems, and suggests that isotope kinetics of sedimentary denitrification might be entirely different from water column denitrification. Acknowledgements: This work was funded by the German Research Foundation (DFG) and in parts by the Danish National Research Foundation.

Nitrogen attenuation of terrestrial carbon cycle response to global environmental factors

USGS Publications Warehouse

Jain, A.A.; Yang, Xiaojuan; Kheshgi, H.; McGuire, A. David; Post, W.; Kicklighter, David W.

2009-01-01

Nitrogen cycle dynamics have the capacity to attenuate the magnitude of global terrestrial carbon sinks and sources driven by CO2 fertilization and changes in climate. In this study, two versions of the terrestrial carbon and nitrogen cycle components of the Integrated Science Assessment Model (ISAM) are used to evaluate how variation in nitrogen availability influences terrestrial carbon sinks and sources in response to changes over the 20th century in global environmental factors including atmospheric CO2 concentration, nitrogen inputs, temperature, precipitation and land use. The two versions of ISAM vary in their treatment of nitrogen availability: ISAM-NC has a terrestrial carbon cycle model coupled to a fully dynamic nitrogen cycle while ISAM-C has an identical carbon cycle model but nitrogen availability is always in sufficient supply. Overall, the two versions of the model estimate approximately the same amount of global mean carbon uptake over the 20th century. However, comparisons of results of ISAM-NC relative to ISAM-C reveal that nitrogen dynamics: (1) reduced the 1990s carbon sink associated with increasing atmospheric CO2 by 0.53 PgC yr−1 (1 Pg = 1015g), (2) reduced the 1990s carbon source associated with changes in temperature and precipitation of 0.34 PgC yr−1 in the 1990s, (3) an enhanced sink associated with nitrogen inputs by 0.26 PgC yr−1, and (4) enhanced the 1990s carbon source associated with changes in land use by 0.08 PgC yr−1 in the 1990s. These effects of nitrogen limitation influenced the spatial distribution of the estimated exchange of CO2 with greater sink activity in high latitudes associated with climate effects and a smaller sink of CO2 in the southeastern United States caused by N limitation associated with both CO2 fertilization and forest regrowth. These results indicate that the dynamics of nitrogen availability are important to consider in assessing the spatial distribution and temporal dynamics of terrestrial carbon sources and sinks.

Nitrogen cycling process rates across urban ecosystems.

PubMed

Reisinger, Alexander J; Groffman, Peter M; Rosi-Marshall, Emma J

2016-09-21

Nitrogen (N) pollution of freshwater, estuarine, and marine ecosystems is widespread and has numerous environmental and economic impacts. A portion of this excess N comes from urban watersheds comprised of natural and engineered ecosystems which can alter downstream N export. Studies of urban N cycling have focused on either specific ecosystems or on watershed-scale mass balances. Comparisons of specific N transformations across ecosystems are required to contextualize rates from individual studies. Here we reviewed urban N cycling in terrestrial, aquatic, and engineered ecosystems, and compared N processing in these urban ecosystem types to native reference ecosystems. We found that net N mineralization and net nitrification rates were enhanced in urban forests and riparian zones relative to reference ecosystems. Denitrification was highly variable across urban ecosystem types, but no significant differences were found between urban and reference denitrification rates. When focusing on urban streams, ammonium uptake was more rapid than nitrate uptake in urban streams. Additionally, reduction of stormwater runoff coupled with potential decreases in N concentration suggests that green infrastructure may reduce downstream N export. Despite multiple environmental stressors in urban environments, ecosystems within urban watersheds can process and transform N at rates similar to or higher than reference ecosystems. © FEMS 2016. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.

A parsimonious modular approach to building a mechanistic belowground carbon and nitrogen model

NASA Astrophysics Data System (ADS)

Abramoff, Rose Z.; Davidson, Eric A.; Finzi, Adrien C.

2017-09-01

Soil decomposition models range from simple empirical functions to those that represent physical, chemical, and biological processes. Here we develop a parsimonious, modular C and N cycle model, the Dual Arrhenius Michaelis-Menten-Microbial Carbon and Nitrogen Phyisology (DAMM-MCNiP), that generates testable hypotheses regarding the effect of temperature, moisture, and substrate supply on C and N cycling. We compared this model to DAMM alone and an empirical model of heterotrophic respiration based on Harvard Forest data. We show that while different model structures explain similar amounts of variation in respiration, they differ in their ability to infer processes that affect C flux. We applied DAMM-MCNiP to explain an observed seasonal hysteresis in the relationship between respiration and temperature and show using an exudation simulation that the strength of the priming effect depended on the stoichiometry of the inputs. Low C:N inputs stimulated priming of soil organic matter decomposition, but high C:N inputs were preferentially utilized by microbes as a C source with limited priming. The simplicity of DAMM-MCNiP's simultaneous representations of temperature, moisture, substrate supply, enzyme activity, and microbial growth processes is unique among microbial physiology models and is sufficiently parsimonious that it could be incorporated into larger-scale models of C and N cycling.

Nitrogen Cycling Potential of a Grassland Litter Microbial Community

PubMed Central

Berlemont, Renaud; Martiny, Adam C.; Martiny, Jennifer B. H.

2015-01-01

Because microorganisms have different abilities to utilize nitrogen (N) through various assimilatory and dissimilatory pathways, microbial composition and diversity likely influence N cycling in an ecosystem. Terrestrial plant litter decomposition is often limited by N availability; however, little is known about the microorganisms involved in litter N cycling. In this study, we used metagenomics to characterize the potential N utilization of microbial communities in grassland plant litter. The frequencies of sequences associated with eight N cycling pathways differed by several orders of magnitude. Within a pathway, the distributions of these sequences among bacterial orders differed greatly. Many orders within the Actinobacteria and Proteobacteria appeared to be N cycling generalists, carrying genes from most (five or six) of the pathways. In contrast, orders from the Bacteroidetes were more specialized and carried genes for fewer (two or three) pathways. We also investigated how the abundance and composition of microbial N cycling genes differed over time and in response to two global change manipulations (drought and N addition). For many pathways, the abundance and composition of N cycling taxa differed over time, apparently reflecting precipitation patterns. In contrast to temporal variability, simulated global change had minor effects on N cycling potential. Overall, this study provides a blueprint for the genetic potential of N cycle processes in plant litter and a baseline for comparisons to other ecosystems. PMID:26231641

Unmasked adult-onset urea cycle disorders in the critical care setting.

PubMed

Summar, Marshall L; Barr, Frederick; Dawling, Sheila; Smith, Wendy; Lee, Brendan; Singh, Rani H; Rhead, William J; Sniderman King, Lisa; Christman, Brian W

2005-10-01

Most often, urea cycle disorders have been described as acute onset hyperammonemia in the newborn period; however, there is a growing awareness that urea cycle disorders can present at almost any age, frequently in the critical care setting. This article presents three cases of adult-onset hyperammonemia caused by inherited defects in nitrogen processing in the urea cycle, and reviews the diagnosis, management, and pathophysiology of adult-onset urea cycle disorders. Individuals who have milder molecular urea cycle defects can lead a relatively normal life until a severe environmental stress triggers a hyperammonemic crisis. Comorbid conditions such as physical trauma often delay the diagnosis of the urea cycle defect. Prompt recognition and treatment are essential in determining the outcome of these patients.

Microbial ecology of soda lakes: investigating sulfur and nitrogen cycling at Mono Lake, CA, USA

NASA Astrophysics Data System (ADS)

Fairbanks, D.; Phillips, A. A.; Wells, M.; Bao, R.; Fullerton, K. M.; Stamps, B. W.; Speth, D. R.; Johnson, H.; Sessions, A. L.

2017-12-01

Soda lakes represent unique ecosystems characterized by extremes of pH, salinity and distinct geochemical cycling. Despite these extreme conditions, soda lakes are important repositories of biological adaptation and have a highly functional microbial system. We investigated the biogeochemical cycling of sulfur and nitrogen compounds in Mono Lake, California, located east of the Sierra Nevada mountains. Mono lake is characterized by hyperalkaline, hypersaline and high sulfate concentrations and can enter prolonged periods of meromixis due to freshwater inflow. Typically, the microbial sulfur cycle is highly active in soda lakes with both oxidation and reduction of sulfur compounds. However, the biological sulfur cycle is connected to many other main elemental cycles such as carbon, nitrogen and metals. Here we investigated the interaction between sulfur and nitrogen cycling in Mono lake using a combination of molecular, isotopic, and geochemical observations to explore the links between microbial phylogenetic composition and functionality. Metagenomic and 16S rRNA gene amplicon sequencing were determined at two locations and five depths in May 2017. 16S rRNA gene amplicon sequencing analysis revealed organisms capable of both sulfur and nitrogen cycling. The relative abundance and distribution of functional genes (dsrA, soxAB, nifH, etc) were also determined. These genetic markers indicate the potential in situ relevance of specific carbon, nitrogen, and sulfur pathways in the water column prior to the transition to meromictic stratification. However, genes for sulfide oxidation, denitrification, and ammonification were present. Genome binning guided by the most abundant dsrA sequences, GC content, and abundance with depth identified a Thioalkalivibrio paradoxus bin containing genes capable of sulfur oxidation, denitrification, and nitrate reduction. The presence of a large number of sulfur and nitrogen cycling genes associated with Thioalkalivibrio paradoxus suggests thiosulfate oxidation may be coupled to nitrate reduction despite the extremely low level of nitrate in Mono Lake. Our results illustrate the centrality of living organisms in both shaping and responding to geochemical cycles, as well as future directions for exploring coupled biogeochemical cycles in Mono Lake.

The Importance of Uncertainty and Sensitivity Analysis in Process-based Models of Carbon and Nitrogen Cycling in Terrestrial Ecosystems with Particular Emphasis on Forest Ecosystems — Selected Papers from a Workshop Organized by the International Society for Ecological Modelling (ISEM) at the Third Biennal Meeting of the International Environmental Modelling and Software Society (IEMSS) in Burlington, Vermont, USA, August 9-13, 2006

USGS Publications Warehouse

Larocque, Guy R.; Bhatti, Jagtar S.; Liu, Jinxun; Ascough, James C.; Gordon, Andrew M.

2008-01-01

Many process-based models of carbon (C) and nitrogen (N) cycles have been developed for terrestrial ecosystems, including forest ecosystems. They address many basic issues of ecosystems structure and functioning, such as the role of internal feedback in ecosystem dynamics. The critical factor in these phenomena is scale, as these processes operate at scales from the minute (e.g. particulate pollution impacts on trees and other organisms) to the global (e.g. climate change). Research efforts remain important to improve the capability of such models to better represent the dynamics of terrestrial ecosystems, including the C, nutrient, (e.g. N) and water cycles. Existing models are sufficiently well advanced to help decision makers develop sustainable management policies and planning of terrestrial ecosystems, as they make realistic predictions when used appropriately. However, decision makers must be aware of their limitations by having the opportunity to evaluate the uncertainty associated with process-based models (Smith and Heath, 2001 and Allen et al., 2004). The variation in scale of issues currently being addressed by modelling efforts makes the evaluation of uncertainty a daunting task.

Processes regulating progressive nitrogen limitation under elevated carbon dioxide: a meta-analysis

NASA Astrophysics Data System (ADS)

Liang, J.; Qi, X.; Souza, L.; Luo, Y.

2015-10-01

Nitrogen (N) cycle has the potential to regulate climate change through its influence on carbon (C) sequestration. Although extensive researches have been done to explore whether or not progressive N limitation (PNL) occurs under CO2 enrichment, a comprehensive assessment of the processes that regulate PNL is still lacking. Here, we quantitatively synthesized the responses of all major processes and pools in terrestrial N cycle with meta-analysis of CO2 experimental data available in the literature. The results showed that CO2 enrichment significantly increased N sequestration in plant and litter pools but not in soil pool. Thus, the basis of PNL occurrence partially exists. However, CO2 enrichment also significantly increased the N influx via biological N fixation, but decreased the N efflux via leaching. In addition, no general diminished CO2 fertilization effect on plant growth over time was observed. Overall, our analyses suggest that the extra N supply by the increased biological N fixation and decreased leaching may potentially alleviate PNL under elevated CO2 conditions. Moreover, our synthesis showed that CO2 enrichment increased soil ammonium (NH4+) but decreased nitrate (NO3-). The different responses of NH4+ and NO3-, and the consequent biological processes, may result in changes in soil microenvironment, community structures and above-belowground interactions, which could potentially affect the terrestrial biogeochemical cycles and the feedback to climate change.

Impacts of prescribed fire on ecosystem C and N cycles at Fort Benning Installation, Georgia

NASA Astrophysics Data System (ADS)

Zhao, S.; Liu, S.; Tieszen, L.

2007-12-01

A critical challenge for the land managers at military installation is to maintain the ecological sustainability of natural resources while meeting the needs of military training. Prescribed ground fire as a land management practice has been used to remove the ground layer plants at Fort Benning for two purposes: to facilitate access for military training, and to maintain and restore fire-adapted longleaf pine communities that are critical habitat for the federally endangered red-cockaded woodpecker (Picoides borealis). Nevertheless, the impacts of prescribed fire on ecosystem processes and health are not well-understood and quantified at the plot to regional scales. Frequent fire may result in ecosystem nitrogen (N) deficiency due to repeated N loss through combustion, volatilization, and leaching, threatening ecosystem sustainability at Fort Benning. On the other hand, N loss may be offset by enhanced symbiotic N2 fixation since fire favors herbaceous legumes by scarifying legume seeds and stimulating germination. Quantifying the impacts of prescribed fire on ecosystem carbon (C) and N cycles is further complicated by interactions and feedbacks among burning, nitrogen inputs, other land use practices (e.g. tree thinning or clear-cutting), and soil properties. In this study, we used the Erosion-Deposition-Carbon Model (EDCM), a process-based biogeochemical model, to simulate C and N dynamic at Fort Benning under different combinations of fire frequency, fire intensity, nitrogen deposition, legume nitrogen input, forest harvesting, and soil sand content. Model simulations indicated that prescribed fire led to nitrogen losses from ecosystems at Fort Benning, especially with high intensity and high frequency fires. Forest harvesting further intensified ecosystem nitrogen limitation, leading to reduced biophysical potential of C sequestration. The adverse impacts of prescribed fire and forest harvesting on C and N cycles were much higher in more sandy soil than in less sandy soil. N inputs from nitrogen deposition and legume N fixation helped replenish N losses to some extent. However, N losses due to fire and harvesting were not balanced or exceeded under current atmospheric N deposition and legume N input rates, suggesting additional N input (e.g., fertilization) may be needed to maintain the sustainability of current ecosystem states and management practices at Fort Benning.

Metabolic peculiarities of the citric acid overproduction from glucose in yeasts Yarrowia lipolytica.

PubMed

Kamzolova, Svetlana V; Morgunov, Igor G

2017-11-01

Comparative study of 43 natural yeast strains belonging to 20 species for their capability for overproduction of citric acid (CA) from glucose under nitrogen limitation of cell growth was carried out. As a result, natural strain Yarrowia lipolytica VKM Y-2373 was selected. The effect of growth limitation by biogenic macroelements (nitrogen, phosphorus, or sulfur) on the CA production by the selected strain was studied. It was shown that yeasts Y. lipolytica grown under deficiency of nitrogen, phosphorus, or sulfur were able to excrete CA in industrially sufficient amounts (80-85g/L with the product yield (Y CA ) of 0.70-0.75g/g and the process selectivity of 92.5-95.3%). Based on the obtained data on activities of enzymes involved in the initial stages of glucose oxidation, the cycle of tricarboxylic acids, and the glyoxylate cycle, the conception of the mechanism responsible for the CA overproduction from glucose in Y. lipolytica was formulated. Copyright © 2017 Elsevier Ltd. All rights reserved.

Nitrogen-doped 3D flower-like carbon materials derived from polyimide as high-performance anode materials for lithium-ion batteries

NASA Astrophysics Data System (ADS)

Wu, Qiong; Liu, Jiaqi; Yuan, Chenpei; Li, Qiang; Wang, Heng-guo

2017-12-01

Nitrogen-doped 3D flower-like carbon materials (NFCs) have been fabricated using a simple and effective strategy, namely, the hierarchical assembly of polyimide (PI) and subsequent thermal treatment. The effect of pyrolysis temperature on the structural evolution process of PI is also investigated systematically. When evaluated as anode materials for lithium ion batteries (LIBs), the as-obtained NFCs, especially NFCs-550, exhibit good electrochemical performance, including a high reversible capacity (1488.1 mAh g-1 at 0.05 A g-1), excellent rate performance (287.6 mAh g-1 at 2 A g-1), and good cycling stability (645 mAh g-1 with 96% retention after 300 cycles at 0.1 A g-1). The good electrochemical performance is attributed to the synergistic effect between 3D flower-like nanostructure and high nitrogen content. This approach may provide some inspiration to construct a series of heteroatom doped and hierarchical structured carbon materials using polymers for LIBs.

Nitrogen and phosphorus in the Upper Mississippi River: Transport, processing, and effects on the river ecosystem

USGS Publications Warehouse

Houser, J.N.; Richardson, W.B.

2010-01-01

Existing research on nutrients (nitrogen and phosphorus) in the Upper Mississippi River (UMR) can be organized into the following categories: (1) Long-term changes in nutrient concentrations and export, and their causes; (2) Nutrient cycling within the river; (3) Spatial and temporal patterns of river nutrient concentrations; (4) Effects of elevated nutrient concentrations on the river; and (5) Actions to reduce river nutrient concentrations and flux. Nutrient concentration and flux in the Mississippi River have increased substantially over the last century because of changes in land use, climate, hydrology, and river management and engineering. As in other large floodplain rivers, rates of processes that cycle nitrogen and phosphorus in the UMR exhibit pronounced spatial and temporal heterogeneity because of the complex morphology of the river. This spatial variability in nutrient processing creates clear spatial patterns in nutrient concentrations. For example, nitrate concentrations generally are much lower in off-channel areas than in the main channel. The specifics of in-river nutrient cycling and the effects of high rates of nutrient input on UMR have been less studied than the factors affecting nutrient input to the river and transport to the Gulf of Mexico, and important questions concerning nutrient cycling in the UMR remain. Eutrophication and resulting changes in river productivity have only recently been investigated the UMR. These recent studies indicate that the high nutrient concentrations in the river may affect community composition of aquatic vegetation (e. g., the abundance of filamentous algae and duckweeds), dissolved oxygen concentrations in off-channel areas, and the abundance of cyanobacteria. Actions to reduce nutrient input to the river include changes in land-use practices, wetland restoration, and hydrological modifications to the river. Evidence suggests that most of the above methods can contribute to reducing nutrient concentration in, and transport by, the UMR, but the impacts of mitigation efforts will likely be only slowly realized. ?? USGS, US Government 2010.

Optimization of the nitrification process of wastewater resulting from cassava starch production.

PubMed

Fleck, Leandro; Ferreira Tavares, Maria Hermínia; Eyng, Eduardo; Orssatto, Fabio

2018-05-14

The present study has the objective of optimizing operational conditions of an aerated reactor applied to the removal of ammoniacal nitrogen from wastewater resulting from the production of cassava starch. An aerated reactor with a usable volume of 4 L and aeration control by rotameter was used. The airflow and cycle time parameters were controlled and their effects on the removal of ammoniacal nitrogen and the conversion to nitrate were evaluated. The highest ammoniacal nitrogen removal, of 96.62%, occurred under conditions of 24 h and 0.15 L min -1 L reactor -1 . The highest nitrate conversion, of 24.81%, occurred under conditions of 40.92 h and 0.15 L min -1  L reactor -1 . The remaining value of ammoniacal nitrogen was converted primarily into nitrite, energy, hydrogen and water. The optimal operational values of the aerated reactor are 29.25 h and 0.22 L min -1  L reactor -1 . The mathematical models representative of the process satisfactorily describe ammoniacal nitrogen removal efficiency and nitrate conversion, presenting errors of 2.87% and 3.70%, respectively.

Nitrate Leaching Management

USDA-ARS?s Scientific Manuscript database

Nitrate (NO3) leaching is a significant nitrogen (N) loss process for agriculture that must be managed to minimize NO3 enrichment of groundwater and surface waters. Managing NO3 leaching should involve the application of basic principles of understanding the site’s hydrologic cycle, avoiding excess ...

Transformation of the nitrogen cycle: recent trends, questions, and potential solutions.

PubMed

Galloway, James N; Townsend, Alan R; Erisman, Jan Willem; Bekunda, Mateete; Cai, Zucong; Freney, John R; Martinelli, Luiz A; Seitzinger, Sybil P; Sutton, Mark A

2008-05-16

Humans continue to transform the global nitrogen cycle at a record pace, reflecting an increased combustion of fossil fuels, growing demand for nitrogen in agriculture and industry, and pervasive inefficiencies in its use. Much anthropogenic nitrogen is lost to air, water, and land to cause a cascade of environmental and human health problems. Simultaneously, food production in some parts of the world is nitrogen-deficient, highlighting inequities in the distribution of nitrogen-containing fertilizers. Optimizing the need for a key human resource while minimizing its negative consequences requires an integrated interdisciplinary approach and the development of strategies to decrease nitrogen-containing waste.

Effect of clonal integration on nitrogen cycling in rhizosphere of rhizomatous clonal plant, Phyllostachys bissetii, under heterogeneous light.

PubMed

Li, Yang; Chen, Jing-Song; Xue, Ge; Peng, Yuanying; Song, Hui-Xing

2018-07-01

Clonal integration plays an important role in clonal plant adapting to heterogeneous habitats. It was postulated that clonal integration could exhibit positive effects on nitrogen cycling in the rhizosphere of clonal plant subjected to heterogeneous light conditions. An in-situ experiment was conducted using clonal fragments of Phyllostachys bissetii with two successive ramets. Shading treatments were applied to offspring or mother ramets, respectively, whereas counterparts were treated to full sunlight. Rhizomes between two successive ramets were either severed or connected. Extracellular enzyme activities and nitrogen turnover were measured, as well as soil properties. Abundance of functional genes (archaeal or bacterial amoA, nifH) in the rhizosphere of shaded, offspring or mother ramets were determined using quantitative polymerase chain reaction. Carbon or nitrogen availabilities were significantly influenced by clonal integration in the rhizosphere of shaded ramets. Clonal integration significantly increased extracellular enzyme activities and abundance of functional genes in the rhizosphere of shaded ramets. When rhizomes were connected, higher nitrogen turnover (nitrogen mineralization or nitrification rates) was exhibited in the rhizosphere of shaded offspring ramets. However, nitrogen turnover was significantly decreased by clonal integration in the rhizosphere of shaded mother ramets. Path analysis indicated that nitrogen turnover in the rhizosphere of shaded, offspring or mother ramets were primarily driven by the response of soil microorganisms to dissolved organic carbon or nitrogen. This unique in-situ experiment provided insights into the mechanism of nutrient recycling mediated by clonal integration. It was suggested that effects of clonal integration on the rhizosphere microbial processes were dependent on direction of photosynthates transport in clonal plant subjected to heterogeneous light conditions. Copyright © 2018 Elsevier B.V. All rights reserved.

Gram-scale production of B, N co-doped graphene-like carbon for high performance supercapacitor electrodes

NASA Astrophysics Data System (ADS)

Chen, Zhuo; Hou, Liqiang; Cao, Yan; Tang, Yushu; Li, Yongfeng

2018-03-01

Boron and nitrogen co-doped graphene-like carbon (BNC) with a gram scale was synthesized via a two-step method including a ball-milling process and a calcination process and used as electrode materials for supercapacitors. High surface area and abundant active sites of graphene-like carbon were created by the ball-milling process. Interestingly, the nitrogen atoms are doped in carbon matrix without any other N sources except for air. The textual and chemical properties can be easily tuned by changing the calcination temperature, and at 900 oC the BNC with a high surface area (802.35 m2/g), a high boron content (2.19 at%), a hierarchical pore size distribution and a relatively high graphitic degree was obtained. It shows an excellent performance of high specific capacitance retention about 78.2% at high current density (199 F/g at 100 A/g) of the initial capacitance (254 F/g at 0.25 A/g) and good cycling stability (90% capacitance retention over 1000 cycles at 100 A/g) measured in a three-electrode system. Furthermore, in a two-electrode system, a specific capacitance of 225 F/g at 0.25 A/g and a good cycling stability (93% capacitance retention over 20,000 cycles at 25 A/g) were achieved by using BNC as electrodes. The strategy of synthesis is facile and effective to fabricate multi-doped graphene-like carbon for promising candidates as electrode materials in supercapacitors.

Effect of Freeze-Thaw Cycles on Soil Nitrogen Reactive Transport in a Polygonal Arctic Tundra Ecosystem at Barrow AK Using 3-D Coupled ALM-PFLOTRAN

NASA Astrophysics Data System (ADS)

Yuan, F.; Wang, G.; Painter, S. L.; Tang, G.; Xu, X.; Kumar, J.; Bisht, G.; Hammond, G. E.; Mills, R. T.; Thornton, P. E.; Wullschleger, S. D.

2017-12-01

In Arctic tundra ecosystem soil freezing-thawing is one of dominant physical processes through which biogeochemical (e.g., carbon and nitrogen) cycles are tightly coupled. Besides hydraulic transport, freezing-thawing can cause pore water movement and aqueous species gradients, which are additional mechanisms for soil nitrogen (N) reactive-transport in Tundra ecosystem. In this study, we have fully coupled an in-development ESM(i.e., Advanced Climate Model for Energy, ACME)'s Land Model (ALM) aboveground processes with a state-of-the-art massively parallel 3-D subsurface thermal-hydrology and reactive transport code, PFLOTRAN. The resulting coupled ALM-PFLOTRAN model is a Land Surface Model (LSM) capable of resolving 3-D soil thermal-hydrological-biogeochemical cycles. This specific version of PFLOTRAN has incorporated CLM-CN Converging Trophic Cascade (CTC) model and a full and simple but robust soil N cycle. It includes absorption-desorption for soil NH4+ and gas dissolving-degasing process as well. It also implements thermal-hydrology mode codes with three newly-modified freezing-thawing algorithms which can greatly improve computing performance in regarding to numerical stiffness at freezing-point. Here we tested the model in fully 3-D coupled mode at the Next Generation Ecosystem Experiment-Arctic (NGEE-Arctic) field intensive study site at the Barrow Environmental Observatory (BEO), AK. The simulations show that: (1) synchronous coupling of soil thermal-hydrology and biogeochemistry in 3-D can greatly impact ecosystem dynamics across polygonal tundra landscape; and (2) freezing-thawing cycles can add more complexity to the system, resulting in greater mobility of soil N vertically and laterally, depending upon local micro-topography. As a preliminary experiment, the model is also implemented for Pan-Arctic region in 1-D column mode (i.e. no lateral connection), showing significant differences compared to stand-alone ALM. The developed ALM-PFLOTRAN coupling codes embeded within ESM will be used for Pan-Arctic regional evaluation of climate change-caused ecosystem responses and their feedbacks to climate system at various scales.

Abiotic controls on N2O emissions from soils and wetlands

NASA Astrophysics Data System (ADS)

Horwath, W. R.

2016-12-01

The increase in atmospheric nitrous oxide (N2O) is a critical climate change issue contributing to global warming. Most studies on N2O production attribute microbial processes and their associated enzymatic reactions to be the main driver affecting emissions. The role of redox capable iron, manganese and organic compounds that can react with intermediates in the nitrogen cycle has also been shown to produce N2O abiotically. The importance of the abiotic pathways, however, is highly debated. The abiotic production of N2O is related to biophysiochemical controls and unique isotopic signatures of nitrogen cycle intermediates (hydroxylamine, nitric oxide, and nitrite), redox-active metals (iron and manganese) and organic matter (humic and fulvic acids). In a range of soils, we find that the iron directly associated with organic compounds is the strongest variable relating to N2O emissions. In addition to these factors, management is also assumed to affect abiotic N2O production through its impact on nitrogen cycle intermediates, but the environmental and physiochemical conditions that are changed by management are rarely considered in the abiotic production of N2O. We find that the amount and quality of organic compounds in soils directly determines the fate of soil N2O production (i.e. be emitted or consumed). Water depth in rice paddies and wetlands also plays a significant role in partitioning production and consumption of N2O. What is evident from studies on N2O emission is that abiotic reactions are coupled to biotic processes and they cannot be easily separated. The biotic/abiotic interactions have important ecological outcomes that influence abiotic production mechanisms and should be recognized as important controllers of N2O production and consumption processes in soils and sediments.

Nitrogen and Phosphorus Pollutants in Cosmetics Wastewater and Its Treatment Process of a Certain Brand

NASA Astrophysics Data System (ADS)

Ma, Guosheng; Chen, Juan

2018-02-01

Cosmetics wastewater is one of the sources of nitrogen and phosphorus pollutants that cause eutrophication of water bodies. This paper is to test the cosmetics wastewater in the production process with American Hach method, and the pH and other indicators would be detected during a whole production cycle. The results show that the pH value in wastewater is 8.6~8.7 (average 8.67), SS 880~1090 mg. L-1 (average 968.57), TN 65.2~100.4 mg.m-3 (average 80.50), TP 6.6~11.4 mg.m-3 (average 9.84), NH3-N 44.2~77.0 mg.m-3 (average 55.61), COD 4650~5900 mg.m-3 (average 5490). After pollutant treatment, the nitrogen and phosphorus pollutants in wastewater can reach the standard discharge.

Parasite infection alters nitrogen cycling at the ecosystem scale.

PubMed

Mischler, John; Johnson, Pieter T J; McKenzie, Valerie J; Townsend, Alan R

2016-05-01

Despite growing evidence that parasites often alter nutrient flows through their hosts and can comprise a substantial amount of biomass in many systems, whether endemic parasites influence ecosystem nutrient cycling, and which nutrient pathways may be important, remains conjectural. A framework to evaluate how endemic parasites alter nutrient cycling across varied ecosystems requires an understanding of the following: (i) parasite effects on host nutrient excretion; (ii) ecosystem nutrient limitation; (iii) effects of parasite abundance, host density, host functional role and host excretion rate on nutrient flows; and (iv) how this infection-induced nutrient flux compares to other pools and fluxes. Pathogens that significantly increase the availability of a limiting nutrient within an ecosystem should produce a measurable ecosystem-scale response. Here, we combined field-derived estimates of trematode parasite infections in aquatic snails with measurements of snail excretion and tissue stoichiometry to show that parasites are capable of altering nutrient excretion in their intermediate host snails (dominant grazers). We integrated laboratory measurements of host nitrogen excretion with field-based estimates of infection in an ecosystem model and compared these fluxes to other pools and fluxes of nitrogen as measured in the field. Eighteen nitrogen-limited ponds were examined to determine whether infection had a measurable effect on ecosystem-scale nitrogen cycling. Because of their low nitrogen content and high demand for host carbon, parasites accelerated the rate at which infected hosts excreted nitrogen to the water column in a dose-response manner, thereby shifting nutrient stoichiometry and availability at the ecosystem scale. Infection-enhanced fluxes of dissolved inorganic nitrogen were similar to other commonly important environmental sources of bioavailable nitrogen to the system. Additional field measurements within nitrogen-limited ponds indicated that nitrogen flux rates from the periphyton to the water column in high-snail density/high-infection ponds were up to 50% higher than low-infection ponds. By altering host nutrient assimilation/excretion flexibility, parasites could play a widespread, but currently unrecognized, role in ecosystem nutrient cycling, especially when parasite and host abundances are high and hosts play a central role in ecosystem nutrient cycling. © 2016 The Authors. Journal of Animal Ecology © 2016 British Ecological Society.

Community size and composition of ammonia oxidizers and denitrifiers in an alluvial intertidal wetland ecosystem

PubMed Central

Hu, Ziye; Meng, Han; Shi, Jin-Huan; Bu, Nai-Shun; Fang, Chang-Ming; Quan, Zhe-Xue

2014-01-01

Global nitrogen cycling is mainly mediated by the activity of microorganisms. Nitrogen cycle processes are mediated by functional groups of microorganisms that are affected by constantly changing environmental conditions and substrate availability. In this study, we investigated the temporal and spatial patterns of nitrifier and denitrifier communities in an intertidal wetland. Soil samples were collected over four distinct seasons from three locations with different vegetative cover. Multiple environmental factors and process rates were measured and analyzed together with the community size and composition profiles. We observed that the community size and composition of the nitrifiers and denitrifiers are affected significantly by seasonal factors, while vegetative cover affected the community composition. The seasonal impacts on the community size of ammonia oxidizing archaea (AOA) are much higher than that of ammonia oxidizing bacteria (AOB). The seasonal change was a more important indicator for AOA community composition patterns, while vegetation was more important for the AOB community patterns. The microbial process rates were correlated with both the community size and composition. PMID:25101072

A meta-analysis of soil salinization effects on nitrogen pools, cycles and fluxes in coastal ecosystems.

PubMed

Zhou, Minghua; Butterbach-Bahl, Klaus; Vereecken, Harry; Brüggemann, Nicolas

2017-03-01

Salinity intrusion caused by land subsidence resulting from increasing groundwater abstraction, decreasing river sediment loads and increasing sea level because of climate change has caused widespread soil salinization in coastal ecosystems. Soil salinization may greatly alter nitrogen (N) cycling in coastal ecosystems. However, a comprehensive understanding of the effects of soil salinization on ecosystem N pools, cycling processes and fluxes is not available for coastal ecosystems. Therefore, we compiled data from 551 observations from 21 peer-reviewed papers and conducted a meta-analysis of experimental soil salinization effects on 19 variables related to N pools, cycling processes and fluxes in coastal ecosystems. Our results showed that the effects of soil salinization varied across different ecosystem types and salinity levels. Soil salinization increased plant N content (18%), soil NH 4 + (12%) and soil total N (210%), although it decreased soil NO 3 - (2%) and soil microbial biomass N (74%). Increasing soil salinity stimulated soil N 2 O fluxes as well as hydrological NH 4 + and NO 2 - fluxes more than threefold, although it decreased the hydrological dissolved organic nitrogen (DON) flux (59%). Soil salinization also increased the net N mineralization by 70%, although salinization effects were not observed on the net nitrification, denitrification and dissimilatory nitrate reduction to ammonium in this meta-analysis. Overall, this meta-analysis improves our understanding of the responses of ecosystem N cycling to soil salinization, identifies knowledge gaps and highlights the urgent need for studies on the effects of soil salinization on coastal agro-ecosystem and microbial N immobilization. Additional increases in knowledge are critical for designing sustainable adaptation measures to the predicted intrusion of salinity intrusion so that the productivity of coastal agro-ecosystems can be maintained or improved and the N losses and pollution of the natural environment can be minimized. © 2016 John Wiley & Sons Ltd.

The Effect of Surface Ice and Topography on the Atmospheric Circulation and Distribution of Nitrogen Ice on Pluto

NASA Astrophysics Data System (ADS)

Rafkin, Scot C. R.; Soto, Alejandro; Michaels, Timothy I.

2016-10-01

A newly developed general circulation model (GCM) for Pluto is used to investigate the impact of a heterogeneous distribution of nitrogen surface ice and large scale topography on Pluto's atmospheric circulation. The GCM is based on the GFDL Flexible Modeling System (FSM). Physics include a gray model radiative-conductive scheme, subsurface conduction, and a nitrogen volatile cycle. The radiative-conductive model takes into account the 2.3, 3.3 and 7.8 μm bands of CH4 and CO, including non-local thermodynamic equilibrium effects. including non-local thermodynamic equilibrium effects. The nitrogen volatile cycle is based on a vapor pressure equilibrium assumption between the atmosphere and surface. Prior to the arrival of the New Horizons spacecraft, the expectation was that the volatile ice distribution on the surface of Pluto would be strongly controlled by the latitudinal temperature gradient. If this were the case, then Pluto would have broad latitudinal bands of both ice covered surface and ice free surface, as dictated by the season. Further, the circulation, and the thus the transport of volatiles, was thought to be driven almost exclusively by sublimation and deposition flows associated with the volatile cycle. In contrast to expectations, images from New Horizon showed an extremely complex, heterogeneous distribution of surface ices draped over substantial and variable topography. To produce such an ice distribution, the atmospheric circulation and volatile transport must be more complex than previously envisioned. Simulations where topography, surface ice distributions, and volatile cycle physics are added individually and in various combinations are used to individually quantify the importance of the general circulation, topography, surface ice distributions, and condensation flows. It is shown that even regional patches of ice or large craters can have global impacts on the atmospheric circulation, the volatile cycle, and hence, the distribution of surface ices. The work demonstrates that explaining Pluto's volatile cycle and the expression of that cycle in the surface ice distributions requires consideration of atmospheric processes beyond simple vapor pressure equilibrium arguments.

Nutrient cycle benchmarks for earth system land model

NASA Astrophysics Data System (ADS)

Zhu, Q.; Riley, W. J.; Tang, J.; Zhao, L.

2017-12-01

Projecting future biosphere-climate feedbacks using Earth system models (ESMs) relies heavily on robust modeling of land surface carbon dynamics. More importantly, soil nutrient (particularly, nitrogen (N) and phosphorus (P)) dynamics strongly modulate carbon dynamics, such as plant sequestration of atmospheric CO2. Prevailing ESM land models all consider nitrogen as a potentially limiting nutrient, and several consider phosphorus. However, including nutrient cycle processes in ESM land models potentially introduces large uncertainties that could be identified and addressed by improved observational constraints. We describe the development of two nutrient cycle benchmarks for ESM land models: (1) nutrient partitioning between plants and soil microbes inferred from 15N and 33P tracers studies and (2) nutrient limitation effects on carbon cycle informed by long-term fertilization experiments. We used these benchmarks to evaluate critical hypotheses regarding nutrient cycling and their representation in ESMs. We found that a mechanistic representation of plant-microbe nutrient competition based on relevant functional traits best reproduced observed plant-microbe nutrient partitioning. We also found that for multiple-nutrient models (i.e., N and P), application of Liebig's law of the minimum is often inaccurate. Rather, the Multiple Nutrient Limitation (MNL) concept better reproduces observed carbon-nutrient interactions.

Terrestrial nitrogen-carbon cycle interactions at the global scale.

PubMed

Zaehle, S

2013-07-05

Interactions between the terrestrial nitrogen (N) and carbon (C) cycles shape the response of ecosystems to global change. However, the global distribution of nitrogen availability and its importance in global biogeochemistry and biogeochemical interactions with the climate system remain uncertain. Based on projections of a terrestrial biosphere model scaling ecological understanding of nitrogen-carbon cycle interactions to global scales, anthropogenic nitrogen additions since 1860 are estimated to have enriched the terrestrial biosphere by 1.3 Pg N, supporting the sequestration of 11.2 Pg C. Over the same time period, CO2 fertilization has increased terrestrial carbon storage by 134.0 Pg C, increasing the terrestrial nitrogen stock by 1.2 Pg N. In 2001-2010, terrestrial ecosystems sequestered an estimated total of 27 Tg N yr(-1) (1.9 Pg C yr(-1)), of which 10 Tg N yr(-1) (0.2 Pg C yr(-1)) are due to anthropogenic nitrogen deposition. Nitrogen availability already limits terrestrial carbon sequestration in the boreal and temperate zone, and will constrain future carbon sequestration in response to CO2 fertilization (regionally by up to 70% compared with an estimate without considering nitrogen-carbon interactions). This reduced terrestrial carbon uptake will probably dominate the role of the terrestrial nitrogen cycle in the climate system, as it accelerates the accumulation of anthropogenic CO2 in the atmosphere. However, increases of N2O emissions owing to anthropogenic nitrogen and climate change (at a rate of approx. 0.5 Tg N yr(-1) per 1°C degree climate warming) will add an important long-term climate forcing.

High-Precision Measurements of 15N15N, 14N15N, and 14N2 in N2 and Potential Applications to Oceanic Nitrogen Cycle Research

NASA Astrophysics Data System (ADS)

Li, S.; Yeung, L.; Young, E. D.; Ostrom, N. E.; Haslun, J. A.

2016-02-01

The balance of nitrogen fixation and nitrogen loss in the oceans is uncertain. For example, anaerobic ammonia oxidation could account for 50% or more of marine N2 production, although its global importance is still poorly known. Isotopic ratios in fixed nitrogen species (e.g., δ15N and δ18O values of NO2- and NO3-) are widely used to trace preservation and removal of N-bearing compounds and/or isotopic variations of their different sources. However, these approaches in general probe only one side of the nitrogen mass balance—the "fixed" nitrogen reservoir—so they offer few constraints on the ultimate loss of nitrogen from that pool as N2. The rare isotopologue ratio 15N15N/14N2 in N2may provide information about those nitrogen-loss processes directly. We will report the first measurements of Δ30 (the abundance of 15N15N relative to that predicted by chance alone), made on a unique high-resolution mass spectrometer (the Nu Instruments Panorama), and we will discuss the potential utility of Δ30 as an independent tracer of the nitrogen cycle. The parameter Δ30 is insensitive to the bulk 15N/14N isotopic ratio of the reservoir; instead, it reflects isotopic ordering in N2, which is altered when N-N bonds are made or broken. Our preliminary measurements of N2 from denitrifying soils and pure cultures of denitrifiers indicate large kinetic isotopic effects during N-N bond formation that favor 15N15N production during denitrification. We also observed a nonstochastic excess of 15N15N in tropospheric N2 [Δ30 = +19.05 ± 0.12‰ (1σ)]. This excess likely comes from fixed-nitrogen loss processes in the biosphere. Variations in Δ30 of N2 from pure culture experiments (+16.96 to +18.95‰) probably reflect the different isotopic signatures of the enzymes that catalyze denitrification. So, enzyme-specific Δ30 values of dissolved N2 should provide information about the importance of different biochemical pathways of fixed-nitrogen loss (e.g., denitrification vs. anammox) in the oceans.

On the linkages between the global carbon-nitrogen-phosphorus cycles

NASA Astrophysics Data System (ADS)

Tanaka, Katsumasa; Mackenzie, Fred; Bouchez, Julien; Knutti, Reto

2013-04-01

State-of-the-art earth system models used for long-term climate projections are becoming ever more complex in terms of not only spatial resolution but also the number of processes. Biogeochemical processes are beginning to be incorporated into these models. The motivation of this study is to quantify how climate projections are influenced by biogeochemical feedbacks. In the climate modeling community, it is virtually accepted that climate-Carbon (C) cycle feedbacks accelerate the future warming (Cox et al. 2000; Friedlingstein et al. 2006). It has been demonstrated that the Nitrogen (N) cycle suppresses climate-C cycle feedbacks (Thornton et al. 2009). On the contrary, biogeochemical studies show that the coupled C-N-Phosphorus (P) cycles are intimately interlinked via biosphere and the N-P cycles amplify C cycle feedbacks (Ver et al. 1999). The question as to whether the N-P cycles enhance or attenuate C cycle feedbacks is debated and has a significant implication for projections of future climate. We delve into this problem by using the Terrestrial-Ocean-aTmosphere Ecosystem Model 3 (TOTEM3), a globally-aggregated C-N-P cycle box model. TOTEM3 is a process-based model that describes the biogeochemical reactions and physical transports involving these elements in the four domains of the Earth system: land, atmosphere, coastal ocean, and open ocean. TOTEM3 is a successor of earlier TOTEM models (Ver et al. 1999; Mackenzie et al. 2011). In our presentation, we provide an overview of fundamental features and behaviors of TOTEM3 such as the mass balance at the steady state and the relaxation time scales to various types of perturbation. We also show preliminary results to investigate how the N-P cycles influence the behavior of the C cycle. References Cox PM, Betts RA, Jones CD, Spall SA, Totterdell IJ (2000) Acceleration of global warming due to carbon-cycle feedbacks in a coupled climate model. Nature, 408, 184-187. Friedlingstein P, Cox P, Betts R, Bopp L, von Bloh W, Brovkin V, Cadule P, Doney S, Eby M, Fung I, Bala G, John J, Jones C, Joos F, Kato T, Kawamiya M, Knorr W, Lindsay K, Matthews HD, Raddatz T, Rayner P, Reick C, Roeckner E, Schnitzler KG, Schnur R, Strassmann K, Weaver AJ, Yoshikawa C, Zeng N (2006) Climate-Carbon Cycle Feedback Analysis: Results from the C4MIP Model Intercomparison. Journal of Climate, 19, 3337-3353. Mackenzie FT, De Carlo EH, Lerman A (2011) Coupled C, N, P, and O biogeochemical cycling at the land-ocean interface. In: Wolanski E, McLusky DS (eds) Treatise on Estuarine and Coastal Science, vol 5. Academic Press, Waltham, pp 317-342. Thornton PE, Doney SC, Lindsay K, Moore JK, Mahowald N, Randerson JT, Fung I, Lamarque JF, Feddema JJ, Lee YH (2009) Carbon-nitrogen interactions regulate climate-carbon cycle feedbacks: results from an atmosphere-ocean general circulation model. Biogeosciences, 6, 2099-2120. Ver LMB, Mackenzie FT, Lerman A (1999) Biogeochemical responses of the carbon cycle to natural and human perturbations: Past, present, and future. American Journal of Science, 299, 762-801.

Emiliania huxleyi endures N-limitation with an efficient metabolic budgeting and effective ATP synthesis.

PubMed

Rokitta, Sebastian D; Von Dassow, Peter; Rost, Björn; John, Uwe

2014-12-02

Global change will affect patterns of nutrient upwelling in marine environments, potentially becoming even stricter regulators of phytoplankton primary productivity. To better understand phytoplankton nutrient utilization on the subcellular basis, we assessed the transcriptomic responses of the life-cycle stages of the biogeochemically important microalgae Emiliania huxleyi to nitrogen-limitation. Cells grown in batch cultures were harvested at 'early' and 'full' nitrogen-limitation and were compared with non-limited cells. We applied microarray-based transcriptome profilings, covering ~10.000 known E. huxleyi gene models, and screened for expression patterns that indicate the subcellular responses. The diploid life-cycle stage scavenges nitrogen from external organic sources and -like diatoms- uses the ornithine-urea cycle to rapidly turn over cellular nitrogen. The haploid stage reacts similarly, although nitrogen scavenging is less pronounced and lipid oxidation is more prominent. Generally, polyamines and proline appear to constitute major organic pools that back up cellular nitrogen. Both stages induce a malate:quinone-oxidoreductase that efficiently feeds electrons into the respiratory chain and drives ATP generation with reduced respiratory carbon throughput. The use of the ornithine-urea cycle to budget the cellular nitrogen in situations of limitation resembles the responses observed earlier in diatoms. This suggests that underlying biochemical mechanisms are conserved among distant clades of marine phototrophic protists. The ornithine-urea cycle and proline oxidation appear to constitute a sensory-regulatory system that monitors and controls cellular nitrogen budgets under limitation. The similarity between the responses of the life-cycle stages, despite the usage of different genes, also indicates a strong functional consistency in the responses to nitrogen-limitation that appears to be owed to biochemical requirements. The malate:quinone-oxidoreductase is a genomic feature that appears to be absent from diatom genomes, and it is likely to strongly contribute to the uniquely high endurance of E. huxleyi under nutrient limitation.

The Global Nitrogen Cycle

NASA Astrophysics Data System (ADS)

Galloway, J. N.

2003-12-01

Once upon a time nitrogen did not exist. Today it does. In the intervening time the universe was formed, nitrogen was created, the Earth came into existence, and its atmosphere and oceans were formed! In this analysis of the Earth's nitrogen cycle, I start with an overview of these important events relative to nitrogen and then move on to the more traditional analysis of the nitrogen cycle itself and the role of humans in its alteration.The universe is ˜15 Gyr old. Even after its formation, there was still a period when nitrogen did not exist. It took ˜300 thousand years after the big bang for the Universe to cool enough to create atoms; hydrogen and helium formed first. Nitrogen was formed in the stars through the process of nucleosynthesis. When a star's helium mass becomes great enough to reach the necessary pressure and temperature, helium begins to fuse into still heavier elements, including nitrogen.Approximately 10 Gyr elapsed before Earth was formed (˜4.5 Ga (billion years ago)) by the accumulation of pre-assembled materials in a multistage process. Assuming that N2 was the predominate nitrogen species in these materials and given that the temperature of space is -270 °C, N2 was probably a solid when the Earth was formed since its boiling point (b.p.) and melting point (m.p.) are -196 °C and -210 °C, respectively. Towards the end of the accumulation period, temperatures were probably high enough for significant melting of some of the accumulated material. The volcanic gases emitted by the resulting volcanism strongly influenced the surface environment. Nitrogen was converted from a solid to a gas and emitted as N2. Carbon and sulfur were probably emitted as CO and H2S (Holland, 1984). N2 is still the most common nitrogen volcanic gas emitted today at a rate of ˜2 TgN yr-1 (Jaffee, 1992).Once emitted, the gases either remained in the atmosphere or were deposited to the Earth's surface, thus continuing the process of biogeochemical cycling. The rate of transfer depended on the reactivity of the emitted material. At the lower extreme of reactivity are the noble gases, neon and argon. Most neon and argon emitted during the degassing of the newly formed Earth is still in the atmosphere, and essentially none has been transferred to the hydrosphere or crust. At the other extreme are carbon and sulfur. Over 99% of the carbon and sulfur emitted during degassing are no longer in the atmosphere, but reside in the hydrosphere or the crust. Nitrogen is intermediate. Of the ˜6×106 TgN in the atmosphere, hydrosphere, and crust, ˜2/3 is in the atmosphere as N2 with most of the remainder in the crust. The atmosphere is a large nitrogen reservoir primarily, because the triple bond of the N2 molecule requires a significant amount of energy to break. In the early atmosphere, the only sources of such energy were solar radiation and electrical discharges.At this point we had an earth with mostly N2 and devoid of life. How did we get to an earth with mostly N2 and teeming with life? First, N2 had to be converted into reactive N (Nr). (The term reactive nitrogen (Nr) includes all biologically active, photochemically reactive, and radiatively active nitrogen compounds in the atmosphere and biosphere of the Earth. Thus, Nr includes inorganic reduced forms of nitrogen (e.g., NH3 and NH4+), inorganic oxidized forms (e.g., NOx, HNO3, N2O, and NO3-), and organic compounds (e.g., urea, amines, and proteins).) The early atmosphere was reducing and had limited NH3. However, NH3 was a necessary ingredient in forming early organic matter. One possibility for NH3 generation was the cycling of seawater through volcanics (Holland, 1984). Under such a process, NH3 could then be released to the atmosphere where, when combined with CH4, H2, H2O, and electrical energy, organic molecules including amino acids could be formed (Miller, 1953). In essence, electrical discharges and UV radiation can convert mixtures of reduced gases into mixtures of organic molecules that can then be deposited to land surfaces and oceans ( Holland, 1984).To recap, Earth was formed at 4.5 Ga, water condensed at 4 Ga, and organic molecules were formed thereafter. By 3.5 Ga simple organisms (prokaryotes) were able to survive without O2 and produced NH3. At about the same time, the first organisms that could create O2 in photosynthesis (e.g., cyanobacteria) evolved. It was not until 1.5-2.0 Ga that O2 began to build up in the atmosphere. Up to this time, the O2 had been consumed by chemical reactions (e.g., iron oxidation). By 0.5 Ga the O2 concentration of the atmosphere reached the same value found today. As the concentration of O2 built up, so did the possibility that NO could be formed in the atmosphere during electrical discharges from the reaction of N2 and O2.Today we have an atmosphere with N2 and there is energy to produce some NO (reaction of N2 and O2). Precipitation can transfer Nr to the Earth's surface. Electrical discharges can create nitrogen-containing organic molecules. Simple cells evolved ˜3.5 Ga and, over the succeeding years, more complicated forms of life have evolved, including humans. Nature formed nitrogen and created life. By what route did that "life" discover nitrogen?To address this question, we now jump from 3.5 Ga to ˜2.3×10-7 Ga. In the 1770s, three scientists - Carl Wilhelm Scheele (Sweden), Daniel Rutherford (Scotland), and Antoine Lavosier (France) - independently discovered the existence of nitrogen. They performed experiments in which an unreactive gas was produced. In 1790, Jean Antoine Claude Chaptal formally named the gas nitrogène. This discovery marked the beginning of our understanding of nitrogen and its role in Earth systems.By the beginning of the second half of the nineteenth century, it was known that nitrogen is a common element in plant and animal tissues, that it is indispensable for plant growth, that there is constant cycling between organic and inorganic compounds, and that it is an effective fertilizer. However, the source of nitrogen was still uncertain. Lightning and atmospheric deposition were thought to be the most important sources. Although the existence of biological nitrogen fixation (BNF) was unknown at that time, in 1838 Boussingault demonstrated that legumes restore Nr to the soil and that somehow they create Nr directly. It took almost 50 more years to solve the puzzle. In 1888, Herman Hellriegel (1831-1895) and Hermann Wilfarth (1853-1904) published their work on microbial communities. They noted that microorganisms associated with legumes have the ability to assimilate atmospheric N2 (Smil, 2001). They also said that it was necessary for a symbiotic relationship to exist between legumes and microorganisms.Other important processes that drive the cycle were elucidated in the nineteenth century. In the late 1870s, Theophile Scholesing proved the bacterial origins of nitrification. About a decade later, Serfei Nikolaevich Winogradsky isolated the two nitrifers - Nitrosomonas and Nitrobacter - and showed that the species of the former genus oxidize ammonia to nitrite and that the species of the latter genus convert nitrite to nitrate. Then in 1885, Ulysse Gayon isolated cultures of two bacteria that convert nitrate to N2. Although there are only two bacterial genera that can convert N2 to Nr, several can convert Nr back to N2, most notably Pseudomonas, Bacillus, and Alcaligenes (Smil, 2001).By the end of the nineteenth century, humans had discovered nitrogen and the essential components of the nitrogen cycle. In other words, they then knew that some microorganisms convert N2 to NH4+, other microorganisms convert NH4+ to NO3-, and yet a third class of microorganisms convert NO3- back to N2, thus completing the cycle.The following sections of this chapter examine the biogeochemical reactions of Nr, the distribution of Nr in Earth's reservoirs, and the exchanges between the reservoirs. This chapter then discusses Nr creation by natural and anthropogenic processes and nitrogen budgets for the global land mass and for continents and oceans using Galloway and Cowling (2002) and material from Cory Cleveland (University of Colorado) and Douglas Capone (University of Southern California) from a paper in review in Biogeochemistry ( Galloway et al., 2003a). This chapter also presents an overview of the consequences of Nr accumulation in the environment (using Galloway et al. (2003b) as a primary reference) and then concludes with estimates of minima and maxima Nr creation rates in 2050.

Shifts in lake N: P stoichiometry and nutrient limitation driven by atmospheric nitrogen deposition

USGS Publications Warehouse

Elser, J.J.; Andersen, T.; Baron, Jill S.; Bergstrom, A.-K.; Jansson, M.; Kyle, M.; Nydick, K.R.; Steger, L.; Hessen, D.O.

2009-01-01

Human activities have more than doubled the amount of nitrogen (N) circulating in the biosphere. One major pathway of this anthropogenic N input into ecosystems has been increased regional deposition from the atmosphere. Here we show that atmospheric N deposition increased the stoichiometric ratio of N and phosphorus (P) in lakes in Norway, Sweden, and Colorado, United States, and, as a result, patterns of ecological nutrient limitation were shifted. Under low N deposition, phytoplankton growth is generally N-limited; however, in high-N deposition lakes, phytoplankton growth is consistently P-limited. Continued anthropogenic amplification of the global N cycle will further alter ecological processes, such as biogeochemical cycling, trophic dynamics, and biological diversity, in the world's lakes, even in lakes far from direct human disturbance.

The cyanobacterial ornithine-ammonia cycle involves an arginine dihydrolase.

PubMed

Zhang, Hao; Liu, Yujie; Nie, Xiaoqun; Liu, Lixia; Hua, Qiang; Zhao, Guo-Ping; Yang, Chen

2018-06-01

Living organisms have evolved mechanisms for adjusting their metabolism to adapt to environmental nutrient availability. Terrestrial animals utilize the ornithine-urea cycle to dispose of excess nitrogen derived from dietary protein. Here, we identified an active ornithine-ammonia cycle (OAC) in cyanobacteria through an approach combining dynamic 15 N and 13 C tracers, metabolomics, and mathematical modeling. The pathway starts with carbamoyl phosphate synthesis by the bacterial- and plant-type glutamine-dependent enzyme and ends with conversion of arginine to ornithine and ammonia by a novel arginine dihydrolase. An arginine dihydrolase-deficient mutant showed disruption of OAC and severely impaired cell growth when nitrogen availability oscillated. We demonstrated that the OAC allows for rapid remobilization of nitrogen reserves under starvation and a high rate of nitrogen assimilation and storage after the nutrient becomes available. Thus, the OAC serves as a conduit in the nitrogen storage-and-remobilization machinery in cyanobacteria and enables cellular adaptation to nitrogen fluctuations.

Nitrogen cycle and ecosystem services in the Brazilian La Plata Basin: anthropogenic influence and climate change.

PubMed

Watanabe, M; Ortega, E; Bergier, I; Silva, J S V

2012-08-01

The increasing human demand for food, raw material and energy has radically modified both the landscape and biogeochemical cycles in many river basins in the world. The interference of human activities on the Biosphere is so significant that it has doubled the amount of reactive nitrogen due to industrial fertiliser production (Haber-Bosch), fossil fuel burning and land-use change over the last century. In this context, the Brazilian La Plata Basin contributes to the alteration of the nitrogen cycle in South America because of its huge agricultural and grazing area that meets the demands of its large urban centres - Sao Paulo, for instance - and also external markets abroad. In this paper, we estimate the current inputs and outputs of anthropogenic nitrogen (in kg N.km(-2).yr(-1)) in the basin. In the results, we observe that soybean plays a very important role in the Brazilian La Plata, since it contributes with an annual entrance of about 1.8 TgN due to biological nitrogen fixation. Moreover, our estimate indicates that the export of soybean products accounts for roughly 1.0 TgN which is greater than the annual nitrogen riverine exports from Brazilian Parana, Paraguay and Uruguay rivers together. Complimentarily, we built future scenarios representing changes in the nitrogen cycle profile considering two scenarios of climate change for 2070-2100 (based on IPCC's A2 and B2) that will affect land-use, nitrogen inputs, and loss of such nutrients in the basin. Finally, we discuss how both scenarios will affect human well-being since there is a connection between nitrogen cycle and ecosystem services that affect local and global populations, such as food and fibre production and climate regulation.

Nitrogen/Sulfur-Codoped Carbon Materials from Chitosan for Supercapacitors

NASA Astrophysics Data System (ADS)

Li, Mei; Han, Xianlong; Chang, Xiaoqing; Yin, Wenchao; Ma, Jingyun

2016-08-01

d-Methionine and chitosan have been used for fabrication of nitrogen/sulfur-codoped carbon materials by a hydrothermal process followed by carbonization at 750°C for 3 h. The as-prepared carbon materials showed enhanced electrochemical performance, combining electrical double-layer capacitance with pseudocapacitance owing to the doping with sulfur and nitrogen. The specific capacitance of the obtained carbon material reached 135 F g-1 at current density of 1 A g-1, which is much higher than undoped chitosan (67 F g-1). The capacitance retention of the carbon material was almost 97.2% after 5000 cycles at current density of 1 A g-1. With such improved electrochemical performance, the nitrogen/sulfur-codoped carbon material may have promising potential for use in energy-storage electrodes of supercapacitors.

Novel metabolic attributes of the genus cyanothece, comprising a group of unicellular nitrogen-fixing Cyanothece.

PubMed

Bandyopadhyay, Anindita; Elvitigala, Thanura; Welsh, Eric; Stöckel, Jana; Liberton, Michelle; Min, Hongtao; Sherman, Louis A; Pakrasi, Himadri B

2011-01-01

The genus Cyanothece comprises unicellular cyanobacteria that are morphologically diverse and ecologically versatile. Studies over the last decade have established members of this genus to be important components of the marine ecosystem, contributing significantly to the nitrogen and carbon cycle. System-level studies of Cyanothece sp. ATCC 51142, a prototypic member of this group, revealed many interesting metabolic attributes. To identify the metabolic traits that define this class of cyanobacteria, five additional Cyanothece strains were sequenced to completion. The presence of a large, contiguous nitrogenase gene cluster and the ability to carry out aerobic nitrogen fixation distinguish Cyanothece as a genus of unicellular, aerobic nitrogen-fixing cyanobacteria. Cyanothece cells can create an anoxic intracellular environment at night, allowing oxygen-sensitive processes to take place in these oxygenic organisms. Large carbohydrate reserves accumulate in the cells during the day, ensuring sufficient energy for the processes that require the anoxic phase of the cells. Our study indicates that this genus maintains a plastic genome, incorporating new metabolic capabilities while simultaneously retaining archaic metabolic traits, a unique combination which provides the flexibility to adapt to various ecological and environmental conditions. Rearrangement of the nitrogenase cluster in Cyanothece sp. strain 7425 and the concomitant loss of its aerobic nitrogen-fixing ability suggest that a similar mechanism might have been at play in cyanobacterial strains that eventually lost their nitrogen-fixing ability. The unicellular cyanobacterial genus Cyanothece has significant roles in the nitrogen cycle in aquatic and terrestrial environments. Cyanothece sp. ATCC 51142 was extensively studied over the last decade and has emerged as an important model photosynthetic microbe for bioenergy production. To expand our understanding of the distinctive metabolic capabilities of this cyanobacterial group, we analyzed the genome sequences of five additional Cyanothece strains from different geographical habitats, exhibiting diverse morphological and physiological attributes. These strains exhibit high rates of N(2) fixation and H(2) production under aerobic conditions. They can generate copious amounts of carbohydrates that are stored in large starch-like granules and facilitate energy-intensive processes during the dark, anoxic phase of the cells. The genomes of some Cyanothece strains are quite unique in that there are linear elements in addition to a large circular chromosome. Our study provides novel insights into the metabolism of this class of unicellular nitrogen-fixing cyanobacteria.

An introduction to the nitrogen dynamics in controlled systems workshop. Life support and nitrogen: NASA's interest in nitrogen cycling

NASA Technical Reports Server (NTRS)

MacElroy, R. D.; Smernoff, D. T.

1996-01-01

A Workshop on "Nitrogen Dynamics in Controlled Systems" was held September 26-28, 1995 at the Lawrence Berkeley National Laboratory. The meetings were sponsored by the NASA Advanced Life Support program and the Lawrence Berkeley National Laboratory, and hosted by Prof. Lester Packer of the University of California at Berkeley, and of the Lawrence Berkeley National Laboratory. The Workshop participants were asked to: 1. summarize current knowledge on the cycling of nitrogen in closed systems; 2. identify the needs that closed systems may have for specific forms of nitrogen; 3. identify possible ways of generating and maintaining (or avoiding) specific forms and concentrations of nitrogen; 4. compare biological and physical/chemical methods of transforming nitrogen.

Recovery of Nitrogen Pools and Processes in Degraded Riparian Zones in the Southern Appalachians

Treesearch

John T. Walker; James M. Vose; Jennifer Knoepp; Christopher D. Geron

2009-01-01

Establishment of riparian buffers is an effective method for reducing nutrient input to streams. However, the underlying biogeochemical processes are not fully understood. The objective of this 4-yr study was to examine the effects of riparian zone restoration on soil N cycling mechanisms in a mountain pasture previously degraded by cattle. Soil inorganic N pools,...

Budgets of fixed nitrogen in the Orinoco Savannah Region: Role of pyrodenitrification

NASA Astrophysics Data System (ADS)

Sanhueza, Eugenio; Crutzen, Paul J.

1998-12-01

Human activities have strongly altered the amount of fixed nitrogen that cycles in many regions of the industrialized world, with serious environmental consequences. Past studies conducted at the Orinoco savannahs of Venezuela offer a unique possibility for reviewing the cycling of nitrogen species in a tropical environment. The available information for the Orinoco savannahs is critically reviewed, and, despite many uncertainties, we present a budget analysis of both the fixed N in the soil-vegetation system and atmospheric NOy. Analysis of the data indicates that nitrogen fixation, especially by legumes, and ammonia emission from vegetation and animal wastes needs considerable attention in future research efforts. In contrast with many regions of the world, in the studied region, nonindustrial sources, foremost biomass burning, dominate the soil-vegetation and atmospheric budgets of fixed N. In general, N cycling is mainly driven by biomass burning. The resulting pyrodenitrification in the soil-vegetation system is the largest single process that, during the following wet season, may promote biological fixation to compensate for the N losses from fires during the burning season. However, a gradual impoverishment of the N status of the savannah ecosystems cannot be excluded. During the dry season, biomass burning is also the main source of atmospheric NOy, which is largely exported, mainly in the direction of the Amazon forest. Together with other nutrients, a "fertilization" of the Amazon forest due to biomass burning in the savannah may be the result. These issues require further scientific analysis.

Effects of flood inundation and invasion by Phalaris arundinacea on nitrogen cycling in an Upper Mississippi River floodplain forest

USGS Publications Warehouse

Swanson, Whitney; DeJager, Nathan R.; Strauss, Eric A.; Thomsen, Meredith

2017-01-01

Although floodplains are thought to serve as important buffers against nitrogen (N) transport to aquatic systems, frequent flooding and high levels of nutrient availability also make these systems prone to invasion by exotic plant species. Invasive plants could modify the cycling and availability of nutrients within floodplains, with effects that could feedback to promote the persistence of the invasive species and impact N export to riverine and coastal areas. We examined the effect of flooding on soil properties and N cycling at a floodplain site in Pool 8 of the Upper Mississippi River with 2 plant communities: mature native forest (Acer saccharinum) and patches of an invasive grass (Phalaris arundinacea). Plots were established within each vegetation type along an elevation gradient and sampled throughout the summers of 2013 and 2014. Spatial trends in flooding resulted in higher soil organic matter, porosity, and total nitrogen and carbon in low elevations. Nutrient processes and NH4+ and NO3− availability, however, were best explained by vegetation type and time after flooding. Phalaris plots maintained higher rates of nitrification and higher concentrations of available NH4+ and NO3−. These results suggest that invasion by Phalarismay make nitrogen more readily available and could help to reinforce this species' persistence in floodplain wetlands. They also raise the possibility that Phalaris may decrease floodplain N storage capacity and influence downstream transport of N to coastal zones.

Biomass burning in the tropics: Impact on atmospheric chemistry and biogeochemical cycles

DOE Office of Scientific and Technical Information (OSTI.GOV)

Crutzen, P.J.; Andreae, M.O.

1990-12-21

Biomass burning is widespread, especially in the tropics. It serves to clear land for shifting cultivation, to convert forests to agricultural and pastoral lands, and to remove dry vegetation in order to promote agricultural productivity and the growth of higher yield grasses. Furthermore, much agricultural waste and fuel wood is being combusted, particularly in developing countries. Biomass containing 2 to 5 petagrams of carbon is burned annually (1 petagram = 10{sup 15} grams), producing large amounts of trace gases and aerosol particles that play important roles in atmospheric chemistry and climate. Emissions of carbon monoxide and methane by biomass burningmore » affect the oxidation efficiency of the atmosphere by reacting with hydroxyl radicals, and emissions of nitric oxide and hydrocarbons lead to high ozone concentrations in the tropics during the dry season. Large quantities of smoke particles are produced as well, and these can serve as cloud condensation nuclei. These particles may thus substantially influence cloud microphysical and optical properties, an effect that could have repercussions for the radiation budget and the hydrological cycle in the tropics. Widespread burning may also disturb biogeochemical cycles, especially that of nitrogen. About 50% of the nitrogen in the biomass fuel can be released as molecular nitrogen. This pyrodenitrification process causes a sizable loss of fixed nitrogen in tropical ecosystems, in the range of 10 to 20 teragrams per year (1 teragram = 10{sup 12} grams).« less

Restoration and Purification of Dissolved Organic Nitrogen by Bacteria and Phytoremediation in Shallow Eutrophic Lakes Sediments

NASA Astrophysics Data System (ADS)

Li, Xin; Yue, Yi

2018-06-01

Endogenous organic nitrogen loadings in lake sediments have increased with human activity in recent decades. A 6-month field study from two disparate shallow eutrophic lakes could partly reveal these issues by analysing seasonal variations of biodegradation and phytoremediation in the sediment. This paper describes the relationship between oxidation reduction potential, temperature, microbial activity and phytoremediation in nitrogen cycling by calculation degradative index of dissolved organic nitrogen and amino acid decomposition. The index was being positive in winter and negative in summer while closely positive correlated with biodegradation. Our analysis revealed that rather than anoxic condition, biomass is the primary factor to dissolved organic nitrogen distribution and decomposition. Some major amino acids statistics also confirm the above view. The comparisons of organic nitrogen and amino acid in abundance and seasons in situ provides that demonstrated plants cue important for nitrogen removal by their roots adsorption and immobilization. In conclusion, enhanced microbial activity and phytoremediation with the seasons will reduce the endogenous nitrogen loadings by the coupled mineralization and diagenetic process.

[Research advances in identifying nitrate pollution sources of water environment by using nitrogen and oxygen stable isotopes].

PubMed

Mao, Wei; Liang, Zhi-wei; Li, Wei; Zhu, Yao; Yanng, Mu-yi; Jia, Chao-jie

2013-04-01

Water body' s nitrate pollution has become a common and severe environmental problem. In order to ensure human health and water environment benign evolution, it is of great importance to effectively identify the nitrate pollution sources of water body. Because of the discrepant composition of nitrogen and oxygen stable isotopes in different sources of nitrate in water body, nitrogen and oxygen stable isotopes can be used to identify the nitrate pollution sources of water environment. This paper introduced the fractionation factors of nitrogen and oxygen stable isotopes in the main processes of nitrogen cycling and the composition of these stable isotopes in main nitrate sources, compared the advantages and disadvantages of five pre-treatment methods for analyzing the nitrogen and oxygen isotopes in nitrate, and summarized the research advances in this aspect into three stages, i. e. , using nitrogen stable isotope alone, using nitrogen and oxygen stable isotopes simultaneously, and combining with mathematical models. The future research directions regarding the nitrate pollution sources identification of water environment were also discussed.

Coupled cycling of dissolved organic nitrogen and carbon in a forest stream

Treesearch

E.N. Jack Brookshire; H. Maurice Valett; Steven A. Thomas; Jackson R. Webster

2005-01-01

Dissolved organic nitrogen (DON) is an abundant but poorly understood pool of N in many ecosystems. We assessed DON cycling in a N-limited headwater forest stream via whole-ecosystem additions of dissolved inorganic nitrogen (DIN) and labile dissolved organic matter (DOM), hydrologic transport and biogeochemical modeling, and laboratory experiments with native...

Carbon Accumulation and Nitrogen Pool Recovery during Transitions from Savanna to Forest in Central Brazil

NASA Astrophysics Data System (ADS)

Pellegrini, A.; Hoffmann, W. A.; Franco, A. C.

2014-12-01

The expansion of tropical forest into savanna may potentially be a large carbon sink, but little is known about the patterns of carbon sequestration during transitional forest formation. Moreover, it is unclear how nutrient limitation, due to extended exposure to firedriven nutrient losses, may constrain carbon accumulation. Here, we sampled plots that spanned a woody biomass gradient from savanna to transitional forest in response to differential fire protection in central Brazil. These plots were used to investigate how the process of transitional forest formation affects the size and distribution of carbon (C) and nitrogen (N) pools. This was paired with a detailed analysis of the nitrogen cycle to explore possible connections between carbon accumulation and nitrogen limitation. An analysis of carbon pools in the vegetation, upper soil, and litter shows that the transition from savanna to transitional forest can result in a fourfold increase in total carbon (from 43 to 179 Mg C/ha) with a doubling of carbon stocks in the litter and soil layers. Total nitrogen in the litter and soil layers increased with forest development in both the bulk (+68%) and plant-available (+150%) pools, with the most pronounced changes occurring in the upper layers. However, the analyses of nitrate concentrations, nitrate : ammonium ratios, plant stoichiometry of carbon and nitrogen, and soil and foliar nitrogen isotope ratios suggest that a conservative nitrogen cycle persists throughout forest development, indicating that nitrogen remains in low supply relative to demand. Furthermore, the lack of variation in underlying soil type (>20 cm depth) suggests that the biogeochemical trends across the gradient are driven by vegetation. Our results provide evidence for high carbon sequestration potential with forest encroachment on savanna, but nitrogen limitation may play a large and persistent role in governing carbon sequestration in savannas or other equally fire-disturbed tropical landscapes. In turn, the link between forest development and nitrogen pool recovery creates a framework for evaluating potential positive feedbacks on savanna-forest boundaries.

The role of multiple partners in a digestive mutualism with a protocarnivorous plant

PubMed Central

Nishi, Aline Hiroko; Vasconcellos-Neto, João; Romero, Gustavo Quevedo

2013-01-01

Background and aims The protocarnivorous plant Paepalanthus bromelioides (Eriocaulaceae) is similar to bromeliads in that this plant has a rosette-like structure that allows rainwater to accumulate in leaf axils (i.e. phytotelmata). Although the rosettes of P. bromelioides are commonly inhabited by predators (e.g. spiders), their roots are wrapped by a cylindrical termite mound that grows beneath the rosette. In this study it is predicted that these plants can derive nutrients from recycling processes carried out by termites and from predation events that take place inside the rosette. It is also predicted that bacteria living in phytotelmata can accelerate nutrient cycling derived from predators. Methods The predictions were tested by surveying plants and animals, and also by performing field experiments in rocky fields from Serra do Cipó, Brazil, using natural abundance and enriched isotopes of 15N. Laboratory bioassays were also conducted to test proteolytic activities of bacteria from P. bromelioides rosettes. Key Results Analyses of 15N in natural nitrogen abundances showed that the isotopic signature of P. bromelioides is similar to that of carnivorous plants and higher than that of non-carnivorous plants in the study area. Linear mixing models showed that predatory activities on the rosettes (i.e. spider faeces and prey carcass) resulted in overall nitrogen contributions of 26·5 % (a top-down flux). Although nitrogen flux was not detected from termites to plants via decomposition of labelled cardboard, the data on 15N in natural nitrogen abundance indicated that 67 % of nitrogen from P. bromelioides is derived from termites (a bottom-up flux). Bacteria did not affect nutrient cycling or nitrogen uptake from prey carcasses and spider faeces. Conclusions The results suggest that P. bromelioides derive nitrogen from associated predators and termites, despite differences in nitrogen cycling velocities, which seem to have been higher in nitrogen derived from predators (leaves) than from termites (roots). This is the first study that demonstrates partitioning effects from multiple partners in a digestion-based mutualism. Despite most of the nitrogen being absorbed through their roots (via termites), P. bromelioides has all the attributes necessary to be considered as a carnivorous plant in the context of digestive mutualism. PMID:23131297

Reducing equifinality using isotopes in a process-based stream nitrogen model highlights the flux of algal nitrogen from agricultural streams

NASA Astrophysics Data System (ADS)

Ford, William I.; Fox, James F.; Pollock, Erik

2017-08-01

The fate of bioavailable nitrogen species transported through agricultural landscapes remains highly uncertain given complexities of measuring fluxes impacting the fluvial N cycle. We present and test a new numerical model named Technology for Removable Annual Nitrogen in Streams For Ecosystem Restoration (TRANSFER), which aims to reduce model uncertainty due to erroneous parameterization, i.e., equifinality, in stream nitrogen cycle assessment and quantify the significance of transient and permanent removal pathways. TRANSFER couples nitrogen elemental and stable isotope mass-balance equations with existing hydrologic, hydraulic, sediment transport, algal biomass, and sediment organic matter mass-balance subroutines and a robust GLUE-like uncertainty analysis. We test the model in an agriculturally impacted, third-order stream reach located in the Bluegrass Region of Central Kentucky. Results of the multiobjective model evaluation for the model application highlight the ability of sediment nitrogen fingerprints including elemental concentrations and stable N isotope signatures to reduce equifinality of the stream N model. Advancements in the numerical simulations allow for illumination of the significance of algal sloughing fluxes for the first time in relation to denitrification. Broadly, model estimates suggest that denitrification is slightly greater than algal N sloughing (10.7% and 6.3% of dissolved N load on average), highlighting the potential for overestimation of denitrification by 37%. We highlight the significance of the transient N pool given the potential for the N store to be regenerated to the water column in downstream reaches, leading to harmful and nuisance algal bloom development.

Novel phased isolation ditch system for enhanced nutrient removal and its optimal operating strategy.

PubMed

Hong, K i-Ho; Chang, Duk; Hur, Joon-Moo; Han, Sang-Bae

2003-01-01

Phased isolation ditch system with intrachannel clarifier is a simplified novel oxidation ditch system enhancing simultaneous removal of biological nitrogen and phosphorus in municipal wastewater. The system employs two ditches with intra-clarifier, and eliminates external final clarifier, additional preanaerobic reactor, and recycle of sludge and nitrified effluent. Separation of anoxic, anaerobic, and aerobic phases can be accomplished by alternating flow and intermittent aeration. Its pilot-scale system operated at HRTs of 10-21 h, SRTs of 15-41 days, and a cycle times of 2-8 h showed removals of BOD, TN, and TP in the range of mixed liquor temperature above 10 degrees C as high as 88-97, 70-84, and 65-90%, respectively. As the SRTs became longer, the effluent TN decreased dramatically, whereas the effluent TP increased. Higher nitrogen removal was accomplished at shorter cycle times, while better phosphorus removal was achieved in longer cycle times. Optimal system operating strategies maximizing the performance and satisfying both the best nitrogen and phosphorus removals included HRTs ranged 10-14 h, SRTs ranged 25-30 days, and a cycle time of 4 h at the mixed liquor temperature above 10 degrees C. Thus, complete phase separation in a cycle maximizing phosphorus release and uptake as well as nitrification and denitrification was accomplished by scheduling of alternating flow and intermittent aeration in the simplified process scheme. Especially, temporal phase separation for phosphorus release without additional anaerobic reactor was successfully accomplished during anaerobic period without any nitrate interference and carbon-limiting.

Effect of exogenous carbon addition and the freeze-thaw cycle on soil microbes and mineral nitrogen pools1

NASA Astrophysics Data System (ADS)

Hu, Xia; Yin, Peng; Nong, Xiang; Liao, Jinhua

2018-01-01

To elucidate the alpine soil process in winter, the response mechanism of soil mineral nitrogen and soil microbes to exogenous carbon (0 mg C, 1 mg C, 2 mg C, 4 mg C and 8 mg C·g-1 dry soil) and the freeze-thaw cycle (-2 °C, -2 ∼ 2 °C, -20 ∼2°C) were studied by laboratory simulation. The freeze-thaw treatment had no significant effect on microbial biomass nitrogen and the number of bacteria. The soil mineral N pool, the number of fungi, and enzyme activities were obviously affected by the freeze-thaw cycle. A mild freeze-thaw cycle (-2∼2°C) significantly increased the number of fungi and catalase activity, while severe freeze-thaw cycle (-20∼2°C) obviously decreased invertase activity. The results suggested that both the freeze-thaw rate and freeze-thaw temperature amplitudes have a strong effect on soil microbial dynamics in the alpine zone in winter. The results showed that exogenous carbon addition significantly decreased soil NO3-N and NH4 +-N contents, increased soil microbial biomass, the number of microbes, and soil enzyme activities. The results showed that microbial growth in the eastern Tibetan Plateau was somewhat limited by available C. It may represent a larger potential pulse of soil nutrient for alpine plants in the next spring, and may be instrumental for plant community shifts under future climate change predictions due to the possible increased litter addition.

Nitric oxide cycle in mammals and the cyclicity principle.

PubMed

Reutov, V P

2002-03-01

This paper continues a series of reports considering nitric oxide (NO) and its cyclic conversions in mammals. Numerous facts are summarized with the goal of developing a general concept that would allow the statement of the multiple effects of NO on various systems of living organisms in the form of a short and comprehensive law. The current state of biological aspects of NO research is analyzed in term of elucidation of possible role of these studies in the system of biological sciences. The general concept is based on a notion on cyclic conversions of NO and its metabolites. NO cycles in living organisms and nitrogen turnover in the biosphere and also the Bethe nitrogen-carbon cycle in star matter are considered. A hypothesis that the cyclic organization of processes in living organisms and the biosphere reflects the evolution of life is proposed: the development of physiological functions and metabolism are suggested to be closely related to space and evolution of the Earth as a planet of the Solar System.

Carbon and nitrogen isotope variations in tree-rings as records of perturbations in regional carbon and nitrogen cycles.

PubMed

Bukata, Andrew R; Kyser, T Kurtis

2007-02-15

Increasing anthropogenic pollution from urban centers and fossil fuel combustion can impact the carbon and nitrogen cycles in forests. To assess the impact of twentieth century anthropogenic pollution on forested system carbon and nitrogen cycles, variations in the carbon and nitrogen isotopic compositions of tree-rings were measured. Individual annual growth rings in trees from six sites across Ontario and one in New Brunswick, Canada were used to develop site chronologies of tree-ring delta 15N and delta 13C values. Tree-ring 615N values were approximately 0.5% per hundred higher and correlated with contemporaneous foliar samples from the same tree, but not with delta 15N values of soil samples. Temporal trends in carbon and nitrogen isotopic compositions of these tree-rings are consistent with increasing anthropogenic influence on both the carbon and nitrogen cycles since 1945. Tree-ring delta 13C values and delta 15N values are correlated at both remote and urban-proximal sites, with delta 15N values decreasing since 1945 and converging on 1% per hundred at urban-proximal sites and decreasing but not converging on a single delta 15N value in remote sites. These results indicate that temporal trends in tree-ring nitrogen and carbon isotopic compositions record the regional extent of pollution.

Cost-Effectiveness of Nitrogen Mitigation by Alternative ...

EPA Pesticide Factsheets

Household wastewater, especially from conventional septic systems, is a major contributor to nitrogen pollution. Alternative household wastewater management technologies provide similar sewerage management services but their life cycle costs and nitrogen flow implications remain uncertain. We seek to address two key questions: (1) what are the total costs, nitrogen mitigation potential, and cost-effectiveness of a range of conventional and alternative municipal wastewater treatment technologies, and (2) what uncertainties influence these outcomes, and how can we improve our understanding of these technologies? We estimate a household nitrogen mass balance for various household wastewater treatment systems and combine this mass balance with life cycle cost assessment to calculate the cost-effectiveness of nitrogen mitigation, which we define as nitrogen removed from the local watershed. We apply our methods to Falmouth, MA, where failing septic systems have caused heightened eutrophication in local receiving water bodies. We find that flushing and dry (composting) urine-diversion toilets paired with conventional septic systems for greywater management demonstrate the lowest life cycle cost and highest cost-effectiveness (dollars per kilogram of nitrogen removed from the watershed). Composting toilets and neighborhood-scale blackwater digesters are also attractive options in some cases, particularly best-case nitrogen mitigation; innovative/advanced septic system

Coupled nutrient cycling determines tropical forest trajectory under elevated CO2.

NASA Astrophysics Data System (ADS)

Bouskill, N.; Zhu, Q.; Riley, W. J.

2017-12-01

Tropical forests have a disproportionate capacity to affect Earth's climate relative to their areal extent. Despite covering just 12 % of land surface, tropical forests account for 35 % of global net primary productivity and are among the most significant of terrestrial carbon stores. As atmospheric CO2 concentrations increase over the next century, the capacity of tropical forests to assimilate and sequester anthropogenic CO2 depends on limitation by multiple factors, including the availability of soil nutrients. Phosphorus availability has been considered to be the primary factor limiting metabolic processes within tropical forests. However, recent evidence points towards strong spatial and temporal co-limitation of tropical forests by both nitrogen and phosphorus. Here, we use the Accelerated Climate Modeling for Energy (ACME) Land Model (ALMv1-ECA-CNP) to examine how nutrient cycles interact and affect the trajectory of the tropical forest carbon sink under, (i) external nutrient input, (ii) climate (iii) elevated CO2, and (iv) a combination of 1-3. ALMv1 includes recent theoretical advances in representing belowground competition between roots, microbes and minerals for N and P uptake, explicit interactions between the nitrogen and phosphorus cycles (e.g., phosphatase production and nitrogen fixation), the dynamic internal allocation of plant N and P resources, and the integration of global datasets of plant physiological traits. We report nutrient fertilization (N, P, N+P) predictions for four sites in the tropics (El Verde, Puerto Rico, Barro Colorado Island, Panama, Manaus, Brazil and the Osa Peninsula, Coast Rica) to short-term nutrient fertilization (N, P, N+P), and benchmarking of the model against a meta-analysis of forest fertilization experiments. Subsequent simulations focus on the interaction of the carbon, nitrogen, and phosphorus cycles across the tropics with a focus on the implications of coupled nutrient cycling and the fate of the tropical forest carbon sink. Our results highlight the importance of transient CNP allocation, leaf-level stoichiometric controls on photosynthesis, and trade-offs between above and belowground plant investments.

Nitrogen fluxes in the forests of the Congo Basin

NASA Astrophysics Data System (ADS)

Bauters, Marijn; Verbeeck, Hans; Cizungu, Landry; Makelele, Isaac; Boeckx, Pascal

2017-04-01

The tropical forest of the Congo basin remains very poorly investigated and understood; mainly because of logistic, political and research capacity constraints. Nevertheless, characterization and monitoring of fundamental processes in this biome is vital to understand future responses and to correctly parameterize Earth system models. Nutrient fluxes are key in these processes for the functioning of tropical forests, since CO2 uptake by terrestrial ecosystems strongly depends on site fertility, i.e. nutrient availability. Accurate projections of future net forest growth and terrestrial CO2 uptake thus necessitate an improved understanding on nutrient cycles and how these are coupled to the carbon (C) cycle in forests. Research in the Congo Basin region should combine assessments of both carbon fluxes and the underlying nutrient cycles which directly impact the forest productivity. We set up a monitoring network for nitrogen fluxes in four different forest types in the Congo Basin, resulting in a unique and integrate dataset. The questions to be answered: How do the N-budgets of four different forest types in the Congo Basin compare? How do these fluxes compare to fluxes in the Amazon forest? What is the influence from the strong slash-and-burn regimes on the N-cycle in the natural forests? We answer these questions with our empirical dataset of one hydrological year, combined with satellite and modeling data.

Rapid cycling of reactive nitrogen in the marine boundary layer.

PubMed

Ye, Chunxiang; Zhou, Xianliang; Pu, Dennis; Stutz, Jochen; Festa, James; Spolaor, Max; Tsai, Catalina; Cantrell, Christopher; Mauldin, Roy L; Campos, Teresa; Weinheimer, Andrew; Hornbrook, Rebecca S; Apel, Eric C; Guenther, Alex; Kaser, Lisa; Yuan, Bin; Karl, Thomas; Haggerty, Julie; Hall, Samuel; Ullmann, Kirk; Smith, James N; Ortega, John; Knote, Christoph

2016-04-28

Nitrogen oxides are essential for the formation of secondary atmospheric aerosols and of atmospheric oxidants such as ozone and the hydroxyl radical, which controls the self-cleansing capacity of the atmosphere. Nitric acid, a major oxidation product of nitrogen oxides, has traditionally been considered to be a permanent sink of nitrogen oxides. However, model studies predict higher ratios of nitric acid to nitrogen oxides in the troposphere than are observed. A 'renoxification' process that recycles nitric acid into nitrogen oxides has been proposed to reconcile observations with model studies, but the mechanisms responsible for this process remain uncertain. Here we present data from an aircraft measurement campaign over the North Atlantic Ocean and find evidence for rapid recycling of nitric acid to nitrous acid and nitrogen oxides in the clean marine boundary layer via particulate nitrate photolysis. Laboratory experiments further demonstrate the photolysis of particulate nitrate collected on filters at a rate more than two orders of magnitude greater than that of gaseous nitric acid, with nitrous acid as the main product. Box model calculations based on the Master Chemical Mechanism suggest that particulate nitrate photolysis mainly sustains the observed levels of nitrous acid and nitrogen oxides at midday under typical marine boundary layer conditions. Given that oceans account for more than 70 per cent of Earth's surface, we propose that particulate nitrate photolysis could be a substantial tropospheric nitrogen oxide source. Recycling of nitrogen oxides in remote oceanic regions with minimal direct nitrogen oxide emissions could increase the formation of tropospheric oxidants and secondary atmospheric aerosols on a global scale.

Bacterial quorum sensing and nitrogen cycling in rhizosphere soil

DOE Office of Scientific and Technical Information (OSTI.GOV)

DeAngelis, K.M.; Lindow, S.E.; Firestone, M.K.

2008-10-01

Plant photosynthate fuels carbon-limited microbial growth and activity, resulting in increased rhizosphere nitrogen (N)-mineralization. Most soil organic N is macromolecular (chitin, protein, nucleotides); enzymatic depolymerization is likely rate-limiting for plant N accumulation. Analyzing Avena (wild oat) planted in microcosms containing sieved field soil, we observed increased rhizosphere chitinase and protease specific activities, bacterial cell densities, and dissolved organic nitrogen (DON) compared to bulk soil. Low-molecular weight DON (<3000 Da) was undetectable in bulk soil but comprised 15% of rhizosphere DON. Extracellular enzyme production in many bacteria requires quorum sensing (QS), cell-density dependent group behavior. Because proteobacteria are considered major rhizospheremore » colonizers, we assayed the proteobacterial QS signals acyl-homoserine lactones (AHLs), which were significantly increased in the rhizosphere. To investigate the linkage between soil signaling and N cycling, we characterized 533 bacterial isolates from Avena rhizosphere: 24% had chitinase or protease activity and AHL production; disruption of QS in 7 of 8 eight isolates disrupted enzyme activity. Many {alpha}-Proteobacteria were newly found with QS-controlled extracellular enzyme activity. Enhanced specific activities of N-cycling enzymes accompanied by bacterial density-dependent behaviors in rhizosphere soil gives rise to the hypothesis that QS could be a control point in the complex process of rhizosphere N-mineralization.« less

A nitrogen-doped 3D hierarchical carbon/sulfur composite for advanced lithium sulfur batteries

NASA Astrophysics Data System (ADS)

Liu, Xiaoyan; Huang, Wenlong; Wang, Dongdong; Tian, Jianhua; Shan, Zhongqiang

2017-07-01

Hybrid nanostructures containing one-dimensional (1D) carbon nanotubes (CNTs) and three-dimensional (3D) mesoporous carbon sphere have many promising applications due to their unique physical chemical properties. In this study, a novel 3D hierarchical carbon material (MCCNT) composed of mesoporous carbon sphere core and nitrogen rich CNTs shell is successfully prepared via an aerosol spray and subsequent chemical vapor deposition (CVD) processes. Owning to its well defined porous structure and favorable conductive framework, MCCNT is used as a potential sulfur host in lithium sulfur batteries through a classic melt-diffusion method. When cycled at a current density of 0.2 C (1 C = 1675 mA h g-1), it delivers an initial capacity as high as 1438.7 mAh g-1. Even if the current density increase to 1 C, the specific capacity still remain up to 534.6 mAh g-1 after 300 cycles. The enhanced electrochemical performance can be attributed to the hybrid structure of MCCNT, in which, the porous core works as a host to confine sulfur and accommodate volume expansion and the external CNTs provide excellent electron and ion conductive frame work. Furthermore, the in-situ doped nitrogen on the surface of CNTs enables effective trapping of lithium polysulfides, leading to a much-improved cycling performance.

Nitrogen fixation rates associated with the invasive macroalgae Sargassum horneri around Catalina Island, CA

NASA Astrophysics Data System (ADS)

DeLiberto, A.

2016-02-01

Nitrogen fixation is an important process which allows organisms access to biologically unavailable dinitrogen gas. Bacteria, known as diazotrophs use the enzyme nitrogenase to convert N2 to NH3. These bacteria, including certain species of heterotrophic bacteria and cyanobacteria, can be symbiotically associated with marine macroalgae, facilitating nutrient cycling in oligotrophic regions. As many species within the genera Sargassum are associated with nitrogen fixation, this study hypothesized that nitrogenase activity would be associated with the benthic invasive Sargassum horneri on Catalina Island. In the past decade, Sargassum horneri, an invasive from Japan, has spread throughout the waters around Catalina Island. Using the acetylene reduction procedure using flame ionization detection, initial nitrogenase activity of S. horneri sampled from Indian Rock was observed. Nitrogen fixation rates increased with decomposition, particularly in dark/anaerobic treatments, suggesting the presence of heterotrophic bacteria. In addition, acetate additions greatly increase nitrogen fixation rates, once again indicating heterotrophic nitrogen fixing bacteria.

Effect of operational cycle time length on nitrogen removal in an alternating oxidation ditch system.

PubMed

Mantziaras, I D; Stamou, A; Katsiri, A

2011-06-01

This paper refers to nitrogen removal optimization of an alternating oxidation ditch system through the use of a mathematical model and pilot testing. The pilot system where measurements have been made has a total volume of 120 m(3) and consists of two ditches operating in four phases during one cycle and performs carbon oxidation, nitrification, denitrification and settling. The mathematical model consists of one-dimensional mass balance (convection-dispersion) equations based on the IAWPRC ASM 1 model. After the calibration and verification of the model, simulation system performance was made. Optimization is achieved by testing operational cycles and phases with different time lengths. The limits of EU directive 91/271 for nitrogen removal have been used for comparison. The findings show that operational cycles with smaller time lengths can achieve higher nitrogen removals and that an "equilibrium" between phase time percentages in the whole cycle, for a given inflow, must be achieved.

Spatial and temporal variability in the nitrogen cyclers of hypereutrophic Lake Taihu.

PubMed

Krausfeldt, Lauren E; Tang, Xiangming; van de Kamp, Jodie; Gao, Guang; Bodrossy, Levente; Boyer, Gregory L; Wilhelm, Steven W

2017-04-01

Harmful cyanobacterial blooms (cyanoHABs) are a major threat to freshwater ecosystems worldwide. Evidence suggests that both nitrogen and phosphorus are important nutrients in the development and proliferation of blooms, yet much less is known about nitrogen cycling dynamics in these systems. To assess the potential nitrogen cycling function of the cyanoHAB community, surface water samples were collected in Lake Tai (Taihu), China over a 5-month bloom event in 2014. The expression of six nitrogen cycling genes (nifH, hzsA, nxrB, nrfA, amoA, nosZ) was surveyed using a targeted microarray with probes designed to provide phylogenetic information. N-Cycling gene expression varied spatially across Taihu, most notably near the mouth of the Dapu River. Expression of nifH was observed across the lake and attributable to both Proteobacteria and Cyanobacteria: Proteobacteria were major contributors to nifH signal near shore. Other N transformations such as anaerobic ammonia oxidation and denitrification were evident in the surface waters as well. Observations in this study highlight the potential importance of heterotrophic bacteria in N-cycling associated with cyanoHABs. © FEMS 2017. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.

Bottom-up synthesis of nitrogen-doped graphene sheets for ultrafast lithium storage

NASA Astrophysics Data System (ADS)

Tian, Lei-Lei; Wei, Xian-Yong; Zhuang, Quan-Chao; Jiang, Chen-Hui; Wu, Chao; Ma, Guang-Yao; Zhao, Xing; Zong, Zhi-Min; Sun, Shi-Gang

2014-05-01

A facile bottom-up strategy was developed to fabricate nitrogen-doped graphene sheets (NGSs) from glucose using a sacrificial template synthesis method. Three main types of nitrogen dopants (pyridinic, pyrrolic and graphitic nitrogens) were introduced into the graphene lattice, and an inimitable microporous structure of NGS with a high specific surface area of 504 m2 g-1 was obtained. Particularly, with hybrid features of lithium ion batteries and Faradic capacitors at a low rate and features of Faradic capacitors at a high rate, the NGS presents a superior lithium storage performance. During electrochemical cycling, the NGS electrode afforded an enhanced reversible capacity of 832.4 mA h g-1 at 100 mA g-1 and an excellent cycling stability of 750.7 mA h g-1 after 108 discharge-charge cycles. Furthermore, an astonishing rate capability of 333 mA h g-1 at 10 000 mA g-1 and a high rate cycle performance of 280.6 mA h g-1 even after 1200 cycles were also achieved, highlighting the significance of nitrogen doping on the maximum utilization of graphene-based materials for advanced lithium storage.

An assessment of the real-world driving gaseous emissions from a Euro 6 light-duty diesel vehicle using a portable emissions measurement system (PEMS)

NASA Astrophysics Data System (ADS)

Luján, José M.; Bermúdez, Vicente; Dolz, Vicente; Monsalve-Serrano, Javier

2018-02-01

Recent investigations demonstrated that real-world emissions usually exceed the levels achieved in the laboratory based type approval processes. By means of on-board emissions measurements, it has been shown that nitrogen oxides emitted by diesel engines substantially exceed the limit imposed by the Euro 6 regulation. Thus, with the aim of complementing the worldwide harmonized light vehicles test cycle, the real driving emissions cycle will be introduced after 1 September 2017 to regulate the vehicle emissions in real-world driving situations. This paper presents on-board gaseous emissions measurements from a Euro 6 light-duty diesel vehicle in a real-world driving route using a portable emissions measurement system. The test route characteristics follow the requirements imposed by the RDE regulation. The analysis of the raw emissions results suggests that the greatest amount of nitrogen oxides and nitrogen dioxide are emitted during the urban section of the test route, confirming that lower speeds with more accelerations and decelerations lead to higher nitrogen oxides emissions levels than constant high speeds. Moreover, the comparison of the two calculation methods proposed by the real driving emissions regulation has revealed emissions rates differences ranging from 10% to 45% depending on the pollutant emission and the trip section considered (urban or total). Thus, the nitrogen oxides emissions conformity factor slightly varies from one method to the other.

Sub-soil microbial activity under rotational cotton crops in Australia

NASA Astrophysics Data System (ADS)

Polain, Katherine; Knox, Oliver; Wilson, Brian; Pereg, Lily

2016-04-01

Soil microbial communities contribute significantly to soil organic matter formation, stabilisation and destabilisation, through nutrient cycling and biodegradation. The majority of soil microbial research examines the processes occurring in the top 0 cm to 30 cm of the soil, where organic nutrients are easily accessible. In soils such as Vertosols, the high clay content causes swelling and cracking. When soil cracking is coupled with rain or an irrigation event, a flush of organic nutrients can move down the soil profile, becoming available for subsoil microbial community use and potentially making a significant contribution to nutrient cycling and biodegradation in soils. At present, the mechanisms and rates of soil nutrient turnover (such as carbon and nitrogen) at depth under cotton rotations are mostly speculative and the process-response relationships remain unclear, although they are undoubtedly underpinned by microbial activity. Our research aims to determine the contribution and role of soil microbiota to the accumulation, cycling and mineralisation of carbon and nitrogen through the whole root profile under continuous cotton (Gossypium hirsutum) and cotton-maize rotations in regional New South Wales, Australia. Through seasonal work, we have established both baseline and potential microbial activity rates from 0 cm to 100 cm down the Vertosol profile, using respiration and colourimetric methods. Further whole soil profile analyses will include determination of microbial biomass and isotopic carbon signatures using phospholipid fatty acid (PLFA) methodology, identification of microbial communities (sequencing) and novel experiments to investigate potential rates of nitrogen mineralisation and quantification of associated genes. Our preliminary observations and the hypotheses tested in this three-year study will be presented.

Assessment of nitrogen and oxygen isotopic fractionation during nitrification and its expression in the marine environment.

PubMed

Casciotti, Karen L; Buchwald, Carolyn; Santoro, Alyson E; Frame, Caitlin

2011-01-01

Nitrification is a microbially-catalyzed process whereby ammonia (NH(3)) is oxidized to nitrite (NO(2)(-)) and subsequently to nitrate (NO(3)(-)). It is also responsible for production of nitrous oxide (N(2)O), a climatically important greenhouse gas. Because the microbes responsible for nitrification are primarily autotrophic, nitrification provides a unique link between the carbon and nitrogen cycles. Nitrogen and oxygen stable isotope ratios have provided insights into where nitrification contributes to the availability of NO(2)(-) and NO(3)(-), and where it constitutes a significant source of N(2)O. This chapter describes methods for determining kinetic isotope effects involved with ammonia oxidation and nitrite oxidation, the two independent steps in the nitrification process, and their expression in the marine environment. It also outlines some remaining questions and issues related to isotopic fractionation during nitrification. Copyright © 2011 Elsevier Inc. All rights reserved.

Role of chemotaxis in the ecology of denitrifiers

NASA Technical Reports Server (NTRS)

Kennedy, M. J.; Lawless, J. G.

1985-01-01

It has been recognized that the process of denitrification represents a major sequence in the nitrogen cycle. It involves the anaerobic reduction of nitrate or nitrite to nitrous oxide or elemental nitrogen. This process is responsible for significant losses of nitrogen from agricultural soils. Up to now, little attention has been paid to the ecology of the organisms responsible for denitrification. It is pointed out that chemotaxis would probably offer a strong competitive mechanism for denitrifiers, since chemotaxis would allow denitrifiers to actively reach nitrate by directed motility, rather than by random movement or diffusion of nitrate. The present investigation was initiated to examine the chemotactic responses of several denitrifiers to nitrate and nitrite. Attention is given to bacterial strains, culture media and cell preparation, chemotaxis assays, and competition experiments. It was found that several denitrifiers, including P. aeruginosa, P. fluorescens, and P. Stutzeri, were strongly attracted to NO3(-) and NO2(-).

Interacting Physical and Biological Processes Affecting Nutrient Transport Through Human Dominated Landscapes

NASA Astrophysics Data System (ADS)

Finlay, J. C.

2015-12-01

Human activities increasingly dominate biogeochemical cycles of limiting nutrients on Earth. Urban and agricultural landscapes represent the largest sources of excess nutrients that drive water quality degradation. The physical structure of both urban and agricultural watersheds has been extensively modified, and these changes have large impacts on water and nutrient transport. Despite strong physical controls over nutrient transport in human dominated landscapes, biological processes play important roles in determining the fates of both nitrogen and phosphorus. This talk uses examples from research in urban and agricultural watersheds in the Midwestern USA to illustrate interactions of physical and biological controls over nutrient cycles that have shifted nitrogen (N) and phosphorus (P) sources and cycling in unexpected ways in response to management changes. In urban watersheds, efforts to improve water quality have been hindered by legacy sources of phosphorus added to storm water through transport to drainage systems by vegetation. Similarly, reductions in field erosion in agricultural watersheds have not led to major reductions in phosphorus transport, because of continued release of biological sources of P. Where management of phosphorus has been most effective in reducing eutrophication of lakes, decreases in N removal processes have led to long term increases in N concentration and transport. Together, these examples show important roles for biological processes affecting nutrient movement in highly modified landscapes. Consideration of the downstream physical and biological responses of management changes are thus critical toward identification of actions that will most effectively reduce excess nutrients watersheds and coastal zones.

Remote sensing of canopy chemistry and nitrogen cycling in temperate forest ecosystems

NASA Technical Reports Server (NTRS)

Wessman, Carol A.; Aber, John D.; Peterson, David L.; Melillo, Jerry M.

1988-01-01

The use of images acquired by the Airborne Imaging Spectrometer, an experimental high-spectral resolution imaging sensor developed by NASA, to estimate the lignin concentration of whole forest canopies in Wisconsin is reported. The observed strong relationship between canopy lignin concentration and nitrogen availability in seven undisturbed forest ecosystems on Blackhawk Island, Wisconsin, suggests that canopy lignin may serve as an index for site nitrogen status. This predictive relationship presents the opportunity to estimate nitrogen-cycling rates across forested landscapes through remote sensing.

Carbon and nitrogen biogeochemistry in the ocean: A study using stable isotope natural abundance

NASA Technical Reports Server (NTRS)

Rau, G. H.; Desmarais, David J.

1985-01-01

Determining the biogeochemical pathways traveled by carbon and nitrogen in the ocean is fundamental to the understanding of how the ocean participates in the cycling of these elements within the biosphere. Because biological production, metabolism, and respiration can significantly alter the natural abundance of C-13 and N-15, these abundances can provide important information about the nature of these biological processes and their variability in the marine environment. The research initially seeks to characterize the spatial and temporal patterns of stable isotope abundances in organic matter, and to relate these abundances to C and N biogeochemical processes within selected areas of the northeastern Pacific Ocean.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hill, Walter R.; Griffiths, Natalie A.

Primary consumers play important roles in the cycling of nutrients in headwater streams, storing assimilated nutrients in growing tissue and recycling them through excretion. Though environmental conditions in most headwater streams and their surrounding terrestrial ecosystems vary considerably over the course of a year, relatively little is known about the effects of seasonality on consumer nutrient recycling these streams. Here, we measured nitrogen accumulated through growth and excreted by the grazing snail Elimia clavaeformis (Pleuroceridae) over the course of 12 months in Walker Branch, identifying close connections between in-stream nitrogen processing and seasonal changes in the surrounding forest.

Dissimilatory nitrate reduction processes in sediments of urban river networks: Spatiotemporal variations and environmental implications.

PubMed

Cheng, Lv; Li, Xiaofei; Lin, Xianbiao; Hou, Lijun; Liu, Min; Li, Ye; Liu, Sai; Hu, Xiaoting

2016-12-01

Urbanizations have increased the loadings of reactive nitrogen in urban riverine environments. However, limited information about dissimilatory nitrate reduction processes and associated contributions to nitrogen removal is available for urban riverine environments. In this study, sediment slurry experiments were conducted with nitrogen isotope-tracing technique to investigate the potential rates of denitrification, anaerobic ammonium oxidation (anammox) and dissimilatory nitrate reduction to ammonium (DNRA) and their contributions to nitrate reduction in sediments of urban river networks, Shanghai. The potential rates of denitrification, anammox and DNRA measured in the study area ranged from 0.193 to 98.7 nmol N g -1  h -1 dry weight (dw), 0.0387-23.7 nmol N g -1  h -1  dw and 0-10.3 nmol N g -1  h -1  dw, respectively. Denitrification and DNRA rates were higher in summer than in winter, while anammox rates were greater in winter than in summer for most sites. Dissolved oxygen, total organic carbon, nitrate, ammonium, sulfide, Fe(II) and Fe(III) were found to have significant influence on these nitrate reduction processes. Denitrification contributed 11.5-99.5%% to total nitrate reduction, as compared to 0.343-81.6% for anammox and 0-52.3% for DNRA. It is estimated that nitrogen loss of approximately 1.33 × 10 5  t N year -1 was linked to both denitrification and anammox processes, which accounted for about 20.1% of total inorganic nitrogen transported annually into the urban river networks of Shanghai. Overall, these results show the potential importance of denitrification and anammox in nitrogen removal and provide new insight into the mechanisms of nitrogen cycles in urban riverine environments. Copyright © 2016 Elsevier Ltd. All rights reserved.

Nucleation, Growth Mechanism, and Controlled Coating of ZnO ALD onto Vertically Aligned N-Doped CNTs.

PubMed

Silva, R M; Ferro, M C; Araujo, J R; Achete, C A; Clavel, G; Silva, R F; Pinna, N

2016-07-19

Zinc oxide thin films were deposited on vertically aligned nitrogen-doped carbon nanotubes (N-CNTs) by atomic layer deposition (ALD) from diethylzinc and water. The study demonstrates that doping CNTs with nitrogen is an effective approach for the "activation" of the CNTs surface for the ALD of metal oxides. Conformal ZnO coatings are already obtained after 50 ALD cycles, whereas at lower ALD cycles an island growth mode is observed. Moreover, the process allows for a uniform growth from the top to the bottom of the vertically aligned N-CNT arrays. X-ray photoelectron spectroscopy demonstrates that ZnO nucleation takes place at the N-containing species on the surface of the CNTs by the formation of the Zn-N bonds at the interface between the CNTs and the ZnO film.

Managing Nitrogen in the anthropocene: integrating social and ecological science

NASA Astrophysics Data System (ADS)

Zhang, X.; Mauzerall, D. L.; Davidson, E. A.; Kanter, D.; Cai, R.; Searchinger, T.

2014-12-01

Human alteration of the global nitrogen cycle by agricultural activities has provided nutritious food to society, but also poses increasing threats to human and ecosystem health through unintended pollution. Managing nitrogen more efficiently in crop production is critical for addressing both food security and environmental challenges. Technologies and management practices have been developed to increase the uptake of applied nitrogen by crops. However, nitrogen use efficiency (NUE, yield per unit nitrogen input) is also affected by social and economic factors. For example, to maximize profit, farmers may change crop choice or their nitrogen application rate, both of which lead to a change in NUE. To evaluate such impacts, we use both theoretical and empirical approaches on micro (farm) and macro (national) scales: 1) We developed a bio-economic model (NUE3) on a farm scale to investigate how market signals (e.g. fertilizer and crop prices), government policies, and nitrogen-efficient technologies affect NUE. We demonstrate that if factors that influence nitrogen inputs (e.g. fertilizer-to-crop price ratios) are not considered, NUE projections will be poorly constrained. The impact of nitrogen-efficient technologies on NUE not only depends on how technology changes the production function, but also relies on the prices of the technologies, fertilizers, and crops. 2) We constructed a database of the nitrogen budget in crop production for major crops and major crop producing countries from 1961 to 2010. Using this database, we investigate historical trends of NUE and its relationship to agronomic, economic, social, and policy factors. We find that NUE in most developed countries follows a "U-shape" relationship with income level, consistent with the Environmental Kuznets Curve theory. According to the dynamics revealed in the NUE3 model, we propose three major pathways by which economic development affects NUE, namely consumption, technology, and public policy. Overall, our research suggests that it is critical to include social and economic processes when studying perturbations of the global nitrogen cycle and crafting environmental and food security policy. Better collaboration across disciplines is essential to improve nitrogen management in the anthropocene.

[Nitrogen pool in northern taiga larch forests of Central Siberia].

PubMed

Shugaleĭ, L S; Vedrova, E F

2004-01-01

The pools of nitrogen in different blocks of forest ecosystems and its cycle in the soil are considered. It is shown that the bulk of nitrogen concentrates in the soil and dead organic matter (necromass) of an ecosystem. The nitrogen pool of forest litters and soils consists by 83-93% of the inert compounds that cannot be involved in the biological cycle. Mineralization of organic nitrogen-containing substances in the litters and soils usually yields ammonium as an end product. The amount of nitrogen mineralized over the growing season is partially expended for annual plant increment (30-65%) and immobilization (12-17%), with its large proportion being found in the soil.

Food, Feed and Fuel: a Story About Nitrogen

NASA Astrophysics Data System (ADS)

Galloway, J. N.; Burke, M. B.; Mooney, H. A.; Steinfeld, H.

2008-12-01

Humans obtain metabolic energy by eating food. Nitrogen is required to grow food, but natural supplies of N for human purposes have been inadequate since the beginning of the twentieth century. The Haber-Bosch process now provides a virtually inexhaustible supply of nitrogen, limited primarily by the cost of energy. However, most nitrogen used in food production is lost to the environment, where it cascades through environmental reservoirs contributing to many of the major environmental issues of the day. Furthermore, growing international trade in nitrogen-containing commodities is increasingly replacing wind and water as an important international transporter of nitrogen around the globe. Finally, the rapid growth in crop-based biofuels, and its attendant effects on the global production and trade of all agricultural commodities, could greatly affect global patterns of N use and loss. In the light of the findings above, this paper examines the role of nitrogen in food, feed and fuel production. It describes the beneficial consequences for food production and the negative consequences associated with the commodity nitrogen cascade and the environmental nitrogen cascade. The paper reviews estimates of future projections of nitrogen demands for food and fuel, including the impact of changing diets in the developing world. The paper concludes by presenting the potential interactions among global change, agricultural production and the nitrogen and carbon cycles.

Regime Shift and Microbial Dynamics in a Sequencing Batch Reactor for Nitrification and Anammox Treatment of Urine ▿†

PubMed Central

Bürgmann, Helmut; Jenni, Sarina; Vazquez, Francisco; Udert, Kai M.

2011-01-01

The microbial population and physicochemical process parameters of a sequencing batch reactor for nitrogen removal from urine were monitored over a 1.5-year period. Microbial community fingerprinting (automated ribosomal intergenic spacer analysis), 16S rRNA gene sequencing, and quantitative PCR on nitrogen cycle functional groups were used to characterize the microbial population. The reactor combined nitrification (ammonium oxidation)/anammox with organoheterotrophic denitrification. The nitrogen elimination rate initially increased by 400%, followed by an extended period of performance degradation. This phase was characterized by accumulation of nitrite and nitrous oxide, reduced anammox activity, and a different but stable microbial community. Outwashing of anammox bacteria or their inhibition by oxygen or nitrite was insufficient to explain reactor behavior. Multiple lines of evidence, e.g., regime-shift analysis of chemical and physical parameters and cluster and ordination analysis of the microbial community, indicated that the system had experienced a rapid transition to a new stable state that led to the observed inferior process rates. The events in the reactor can thus be interpreted to be an ecological regime shift. Constrained ordination indicated that the pH set point controlling cycle duration, temperature, airflow rate, and the release of nitric and nitrous oxides controlled the primarily heterotrophic microbial community. We show that by combining chemical and physical measurements, microbial community analysis and ecological theory allowed extraction of useful information about the causes and dynamics of the observed process instability. PMID:21724875

DOE Office of Scientific and Technical Information (OSTI.GOV)

Scott, Nicole M.; Hess, Matthias; Bouskill, Nick J.

During hydrocarbon exposure, the composition and functional dynamics of marine microbial communities are altered, favoring bacteria that can utilize this rich carbon source. Initial exposure of high levels of hydrocarbons in aerobic surface sediments can enrich growth of heterotrophic microorganisms having hydrocarbon degradation capacity. As a result, there can be a localized reduction in oxygen potential within the surface layer of marine sediments causing anaerobic zones. We hypothesized that increasing exposure to elevated hydrocarbon concentrations would positively correlate with an increase in denitrification processes and the net accumulation of dinitrogen. This hypothesis was tested by comparing the relative abundance ofmore » genes associated with nitrogen metabolism and nitrogen cycling identified in 6 metagenomes from sediments contaminated by polyaromatic hydrocarbons from the Deepwater Horizon (DWH) oil spill in the Gulf of Mexico, and 3 metagenomes from sediments associated with natural oil seeps in the Santa Barbara Channel. An additional 8 metagenomes from uncontaminated sediments from the Gulf of Mexico were analyzed for comparison. We predicted relative changes in metabolite turnover as a function of the differential microbial gene abundances, which showed predicted accumulation of metabolites associated with denitrification processes, including anammox, in the contaminated samples compared to uncontaminated sediments, with the magnitude of this change being positively correlated to the hydrocarbon concentration and exposure duration. Furthermore, these data highlight the potential impact of hydrocarbon inputs on N cycling processes in marine sediments and provide information relevant for system scale models of nitrogen metabolism in affected ecosystems.« less

Atmospheric cycles of nitrogen oxides and ammonia. [source strengths and destruction rates

NASA Technical Reports Server (NTRS)

Bottger, A.; Ehhalt, D. H.; Gravenhorst, G.

1981-01-01

The atmospheric cycles of nitrogenous trace compounds for the Northern and Southern Hemispheres are discussed. Source strengths and destruction rates for the nitrogen oxides: NO, NO2 and HNO3 -(NOX) and ammonia (NH3) are given as a function of latitude over continents and oceans. The global amounts of NOX-N and NH3-N produced annually in the period 1950 to 1975 (34 + 5 x one trillion g NOx-N/yr and 29 + or - 6 x one trillion g NH3-N/yr) are much less than previously assumed. Globally, natural and anthropogenic emissions are of similar magnitude. The NOx emission from anthropogenic sources is 1.5 times that from natural processes in the Northern Hemisphere, whereas in the Southern Hemisphere, it is a factor of 3 or 4 less. More than 80% of atmospheric ammonia seems to be derived from excrements of domestic animals, mostly by bulk deposition: 24 + or - 9 x one trillion g NO3 -N/yr and 21 + or - 9 x one trillion g NH4+-N/yr. Another fraction may be removed by absorption on vegetation and soils.

The impact of post-fire salvage logging on microbial nitrogen cyclers in Mediterranean forest soil.

PubMed

Pereg, Lily; Mataix-Solera, Jorge; McMillan, Mary; García-Orenes, Fuensanta

2018-04-01

Forest fires are a regular occurrence in the Mediterranean basin. High severity fires and post-fire management can affect biological, chemical and physical properties of soil, including the composition and abundance of soil microbial communities. Salvage logging is a post-fire management strategy, which involves the removal of burnt wood from land after a fire. The main objective of this work was to evaluate the impact of post-fire salvage logging and microaggregation on soil microbial communities, specifically on the abundance of nitrogen cyclers and, thus, the potential of the soil for microbial nitrogen cycling. The abundance of nitrogen cyclers was assessed by quantification of microbial nitrogen cycling genes in soil DNA, including nifH (involved in nitrogen fixation), nirS/K and nosZ (involved in denitrification), amoA-B and amoA-Arch (involved in bacterial and archaeal nitrification, respectively). It was demonstrated that salvage logging reduced bacterial load post-fire when compared to tree retention control and resulted in significant changes to the abundance of functional bacteria involved in nitrogen cycling. Microbial gene pools involved in various stages of the nitrogen cycle were larger in control soil than in soil subjected to post-fire salvage logging and were significantly correlated with organic matter, available phosphorous, nitrogen and aggregate stability. The microaggregate fraction of the soil, which has been associated with greater organic carbon, was shown to be a hotspot for nitrogen cyclers particularly under salvage logging. The impact of post-fire management strategies on soil microbial communities needs to be considered in relation to maintaining ecosystem productivity, resilience and potential impact on climate change. Copyright © 2017 Elsevier B.V. All rights reserved.

Biome-scale nitrogen fixation strategies selected by climatic constraints on nitrogen cycle.

PubMed

Sheffer, Efrat; Batterman, Sarah A; Levin, Simon A; Hedin, Lars O

2015-11-23

Dinitrogen fixation by plants (in symbiosis with root bacteria) is a major source of new nitrogen for land ecosystems(1). A long-standing puzzle(2) is that trees capable of nitrogen fixation are abundant in nitrogen-rich tropical forests, but absent or restricted to early successional stages in nitrogen-poor extra-tropical forests. This biome-scale pattern presents an evolutionary paradox(3), given that the physiological cost(4) of nitrogen fixation predicts the opposite pattern: fixers should be out-competed by non-fixers in nitrogen-rich conditions, but competitively superior in nitrogen-poor soils. Here we evaluate whether this paradox can be explained by the existence of different fixation strategies in tropical versus extra-tropical trees: facultative fixers (capable of downregulating fixation(5,6) by sanctioning mutualistic bacteria(7)) are common in the tropics, whereas obligate fixers (less able to downregulate fixation) dominate at higher latitudes. Using a game-theoretic approach, we assess the ecological and evolutionary conditions under which these fixation strategies emerge, and examine their dependence on climate-driven differences in the nitrogen cycle. We show that in the tropics, transient soil nitrogen deficits following disturbance and rapid tree growth favour a facultative strategy and the coexistence of fixers and non-fixers. In contrast, sustained nitrogen deficits following disturbance in extra-tropical forests favour an obligate fixation strategy, and cause fixers to be excluded in late successional stages. We conclude that biome-scale differences in the abundance of nitrogen fixers can be explained by the interaction between individual plant strategies and climatic constraints on the nitrogen cycle over evolutionary time.

Climate Change, Soils, and Human Health

NASA Astrophysics Data System (ADS)

Brevik, Eric C.

2013-04-01

According to the Intergovernmental Panel on Climate Change, global temperatures are expected to increase 1.1 to 6.4 degrees C during the 21st century and precipitation patterns will be altered by climate change (IPCC, 2007). Soils are intricately linked to the atmospheric/climate system through the carbon, nitrogen, and hydrologic cycles. Altered climate will, therefore, have an effect on soil processes and properties. Studies into the effects of climate change on soil processes and properties are still incomplete, but have revealed that climate change will impact soil organic matter dynamics including soil organisms and the multiple soil properties that are tied to organic matter, soil water, and soil erosion. The exact direction and magnitude of those impacts will be dependent on the amount of change in atmospheric gases, temperature, and precipitation amounts and patterns. Recent studies give reason to believe at least some soils may become net sources of atmospheric carbon as temperatures rise; this is particularly true of high latitude regions with permanently frozen soils. Soil erosion by both wind and water is also likely to increase. These soil changes will lead to both direct and indirect impacts on human health. Possible indirect impacts include temperature extremes, food safety and air quality issues, increased and/or expanded disease incidences, and occupational health issues. Potential direct impacts include decreased food security and increased atmospheric dust levels. However, there are still many things we need to know more about. How climate change will affect the nitrogen cycle and, in turn, how the nitrogen cycle will affect carbon sequestration in soils is a major research need, as is a better understanding of soil water-CO2 level-temperature relationships. Knowledge of the response of plants to elevated atmospheric CO2 given limitations in nutrients like nitrogen and phosphorus and how that affects soil organic matter dynamics is a critical need. There is also a great need for a better understanding of how soil organisms will respond to climate change because those organisms are incredibly important in a number of soil processes, including the carbon and nitrogen cycles. All of these questions are important in trying to understand human health impacts. More information on climate change, soils, and human health issues can be found in Brevik (2012). References Brevik, E.C. 2012. Climate change, soils, and human health. In: E.C. Brevik and L. Burgess (Eds). Soils and human health. CRC Press, Boca Raton, FL. in press. IPCC. 2007. Summary for policymakers. pp. 1-18. In S. Solomon, D. Qin, M. Manning, Z. Chen, M. Marquis, K.B. Averyt, M.Tignor and H.L. Miller (eds). Climate change 2007: the physical science basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press, Cambridge, UK.

Nitrogen Cycling in the Mycorrhizosphere: Multipartite Interactions and Plant Nitrogen Uptake Vary with Fertilization Legacy

NASA Astrophysics Data System (ADS)

Hestrin, R.; Lehmann, J.

2017-12-01

Soil microbes play an important role in rhizosphere nutrient cycling and plant productivity. In this study, the contributions of soil microbes to organic matter mineralization and plant nitrogen uptake were investigated using incubation and microcosm experiments. Microbial inocula included arbuscular mycorrhizal fungi and microbial communities sampled across a long-term gradient of nitrogen fertilization. Stable isotopes, nanoSIMS imaging, and phospholipid fatty acid analysis were used to track carbon and nitrogen movement from organic matter into microbes, mycorrhizal fungi, and plants. Results show that multipartite relationships between plants and microbes increased plant growth and access to nitrogen from organic matter, and that nitrogen fertilization history had a lasting effect on microbial contributions to fungal and plant nitrogen uptake. This research links rhizosphere ecology and land management with terrestrial biogeochemistry.

Nitrogen Deposition: A Component of Global Change Analyses

DOE Office of Scientific and Technical Information (OSTI.GOV)

Norby, Richard J.

1997-12-31

The global cycles of carbon and nitrogen are being perturbed by human activities that increase the transfer from large pools of nonreactive forms of the elements to reactive forms that are essential to the functioning of the terrestrial biosphere. The cycles are closely linked at all scales, and global change analyses must consider carbon and nitrogen cycles together. The increasing amount of nitrogen originating from fossil fuel combustion and deposited to terrestrial ecosystems as nitrogen oxides could increase the capacity of ecosystems to sequester carbon thereby removing some of the excess carbon dioxide from the atmosphere and slowing the developmentmore » of greenhouse warming. Several global and ecosystem models have calculated the amount of carbon sequestration that can be attributed to nitrogen deposition based on assumptions about the allocation of nitrogen among ecosystem components with different carbon-nitrogen ratios. They support the premise that nitrogen deposition is responsible for a an increasing terrestrial carbon sink since industrialization began, but there are large uncertainties related to the continued capacity of ecosystems to retain exogenous nitrogen. Whether terrestrial ecosystems continue to sequester additional carbon will depend in part on their response to increasing atmospheric carbon dioxide concentrations, which is widely thought to be constrained by limited nitrogen availability. Ecosystem models generally support the conclusion that the responses of ecosystems to increasing concentrations of carbon dioxide will be larger, and the range of possible responses will be wider, in ecosystems with increased nitrogen inputs originating as atmospheric deposition.« less

Microbial Succession and Nitrogen Cycling in Cultured Biofilms as Affected by the Inorganic Nitrogen Availability.

PubMed

Li, Shuangshuang; Peng, Chengrong; Wang, Chun; Zheng, Jiaoli; Hu, Yao; Li, Dunhai

2017-01-01

Biofilms play important roles in nutrients and energy cycling in aquatic ecosystems. We hypothesized that as eutrophication could change phytoplankton community and decrease phytoplankton diversity, ambient inorganic nitrogen level will affect the microbial community and diversity of biofilms and the roles of biofilms in nutrient cycling. Biofilms were cultured using a flow incubator either with replete inorganic nitrogen (N-rep) or without exogenous inorganic nitrogen supply (N-def). The results showed that the biomass and nitrogen and phosphorous accumulation of biofilms were limited by N deficiency; however, as expected, the N-def biofilms had significantly higher microbial diversity than that of N-rep biofilms. The microbial community of biofilms shifted in composition and abundance in response to ambient inorganic nitrogen level. For example, as compared between the N-def and the N-rep biofilms, the former consisted of more diazotrophs, while the latter consisted of more denitrifying bacteria. As a result of the shift of the functional microbial community, the N concentration of N-rep medium kept decreasing, while that of N-def medium showed an increasing trend in the late stage. This indicates that biofilms can serve as the source or the sink of nitrogen in aquatic ecosystems, and it depends on the inorganic nitrogen availability.

System Response of Metabolic Networks in Chlamydomonas reinhardtii to Total Available Ammonium

PubMed Central

Lee, Do Yup; Park, Jeong-Jin; Barupal, Dinesh K.; Fiehn, Oliver

2012-01-01

Drastic alterations in macronutrients are known to cause large changes in biochemistry and gene expression in the photosynthetic alga Chlamydomonas reinhardtii. However, metabolomic and proteomic responses to subtle reductions in macronutrients have not yet been studied. When ammonium levels were reduced by 25–100% compared with control cultures, ammonium uptake and growth rates were not affected at 25% or 50% nitrogen-reduction for 28 h. However, primary metabolism and enzyme expression showed remarkable changes at acute conditions (4 h and 10 h after ammonium reduction) compared with chronic conditions (18 h and 28 h time points). Responses of 145 identified metabolites were quantified using gas chromatography-time of flight mass spectrometry; 495 proteins (including 187 enzymes) were monitored using liquid chromatography-ion trap mass spectrometry with label-free spectral counting. Stress response and carbon assimilation processes (Calvin cycle, acetate uptake and chlorophyll biosynthesis) were altered first, in addition to increase in enzyme contents for lipid biosynthesis and accumulation of short chain free fatty acids. Nitrogen/carbon balance metabolism was found changed only under chronic conditions, for example in the citric acid cycle and amino acid metabolism. Metabolism in Chlamydomonas readily responds to total available media nitrogen with temporal increases in short-chain free fatty acids and turnover of internal proteins, long before nitrogen resources are depleted. PMID:22787274

Nitrogen-doped graphene aerogel as both a sulfur host and an effective interlayer for high-performance lithium-sulfur batteries

NASA Astrophysics Data System (ADS)

Sui, Zhu-Yin; Yang, Quan-Sheng; Zhou, Hang-Yu; Li, Xin; Sun, Ya-Nan; Xiao, Pei-Wen; Wei, Zhi-Xiang; Han, Bao-Hang

2017-12-01

Lithium-sulfur batteries have attracted great concern because of the high theoretical capacity of sulfur (1675 mA h g-1). However, the poor electrical conductivity and volumetric expansion of sulfur along with the dissolution of lithium polysulfides largely limit their practical application. In this study, nitrogen-doped graphene aerogel (NGA) with high nitrogen content and porosity is used as a host for the impregnation of sulfur. The effects of sulfur impregnation on the specific surface area, pore volume, and microstructure of NGA supported sulfur composite (S@NGA) are well investigated. Furthermore, NGA is also processed into a NGA film, which is sandwiched between a separator and S@NGA cathode. The lithium-sulfur battery with such a configuration delivers a high reversible capacity of 1514 mA h g-1 at 0.1 C, excellent rate performance (822 mA h g-1 at 2.0 C), and good cycling stability (946 mA h g-1 at 0.5 C even after 100 cycles). The enhanced electrochemical performance can be ascribed to the introduction of the NGA interlayer, the unique interconnected porous structure, and strong interaction between the three-dimensional nitrogen-doped graphene network and the homogeneously dispersed sulfur and/or lithium polysulfides.

Nitrogen-doped graphene aerogel as both a sulfur host and an effective interlayer for high-performance lithium-sulfur batteries.

PubMed

Sui, Zhu-Yin; Yang, Quan-Sheng; Zhou, Hang-Yu; Li, Xin; Sun, Ya-Nan; Xiao, Pei-Wen; Wei, Zhi-Xiang; Han, Bao-Hang

2017-12-08

Lithium-sulfur batteries have attracted great concern because of the high theoretical capacity of sulfur (1675 mA h g -1 ). However, the poor electrical conductivity and volumetric expansion of sulfur along with the dissolution of lithium polysulfides largely limit their practical application. In this study, nitrogen-doped graphene aerogel (NGA) with high nitrogen content and porosity is used as a host for the impregnation of sulfur. The effects of sulfur impregnation on the specific surface area, pore volume, and microstructure of NGA supported sulfur composite (S@NGA) are well investigated. Furthermore, NGA is also processed into a NGA film, which is sandwiched between a separator and S@NGA cathode. The lithium-sulfur battery with such a configuration delivers a high reversible capacity of 1514 mA h g -1 at 0.1 C, excellent rate performance (822 mA h g -1 at 2.0 C), and good cycling stability (946 mA h g -1 at 0.5 C even after 100 cycles). The enhanced electrochemical performance can be ascribed to the introduction of the NGA interlayer, the unique interconnected porous structure, and strong interaction between the three-dimensional nitrogen-doped graphene network and the homogeneously dispersed sulfur and/or lithium polysulfides.

Salinity is a key factor driving the nitrogen cycling in the mangrove sediment.

PubMed

Wang, Haitao; Gilbert, Jack A; Zhu, Yongguan; Yang, Xiaoru

2018-08-01

Coastal ecosystems are hotspots for nitrogen cycling, and specifically for nitrogen removal from water and sediment through the coupled nitrification-denitrification process. Salinity is globally important in structuring bacterial and archaeal communities, but the association between salinity and microbially-mediated nitrification and denitrification remains unclear. The denitrification activity and composition and structure of microbial nitrifiers and denitrifiers were characterized across a gradient of manipulated salinity (0, 10, 20 and 30ppt) in a mangrove sediment. Salinity negatively correlated with both denitrifying activity and the abundance of nirK and nosZ denitrifying genes. Ammonia-oxidizing bacteria (AOB), which dominated nitrification, had significantly greater abundance at intermediate salinity (10 and 20ppt). However, a positive correlation between ammonia concentration and salinity suggested that nitrifying activity might also be inhibited at higher salinity. The community structure of ammonia-oxidizing archaea (AOA) and bacteria (AOB), as well as nirK, nirS and nosZ denitrifying communities, were all significantly correlated with salinity. These changes were also associated with structural shifts in phylogeny. These findings provide a strong evidence that salinity is a key factor that influences the nitrogen transformations in coastal wetlands, indicating that salinity intrusion caused by climate change might have a broader impact on the coastal biospheres. Copyright © 2018 Elsevier B.V. All rights reserved.

Nitrogen Bsalance for a Plantation Forest Drainage Canal on the North Carolina Coastal Plain

USDA-ARS?s Scientific Manuscript database

Human alteration of the nitrogen cycle has led to increased riverine nitrogen loads, contributing to the eutrophication of lakes, streams, estuaries, and near-coastal oceans. These riverine nitrogen loads are usually less than the total nitrogen inputs to the system, indicating nitrogen removal duri...

Nitrogen Fate in a Phreatic Fluviokarst Watershed: a Stable Isotope, Sediment Tracing, and Numerical Modeling Approach

NASA Astrophysics Data System (ADS)

Husic, A.; Fox, J.; Ford, W. I., III; Agouridis, C.; Currens, J. C.; Taylor, C. J.

2017-12-01

Sediment tracing tools provide an insight into provenance, fate, and transport of sediment and, when coupled to stable isotopes, can elucidate in-stream biogeochemical processes. Particulate nitrogen fate in fluviokarst systems is a relatively unexplored area of research partially due to the complex hydrodynamics at play in karst systems. Karst topography includes turbulent conduits that transport groundwater and contaminants at speeds more typical of open channel flows than laminar Darcian flows. While it is accepted that karst hydro-geomorphology represents a hybrid surface-subsurface system for fluid, further investigation is needed to determine whether, and to what extent, karst systems behave like surface agricultural streams or porous media aquifers with respect to their role in nitrogen cycling. Our objective is to gain an understanding of in-conduit nitrogen processes and their effect on net nitrogen-exports from karst springs to larger waterbodies. The authors apply water, sediment, carbon, and nitrogen tracing techniques to analyze water for nitrate, sediment carbon and nitrogen, and stable sediment nitrogen isotope (δ15N). Thereafter, a new numerical model is formulated that: simulates dissolved inorganic nitrogen and sediment nitrogen transformations in the phreatic karst conduit; couples carbon turnover and nitrogen transformations in the model structure; and simulates the nitrogen stable isotope mass balance for the dissolved and sediment phases. Nitrogen tracing data results show a significant increase in δ15N of sediment nitrogen at the spring outlet relative to karst inputs indicating the potential for isotope fractionation during dissolved N uptake by bed sediments in the conduit and during denitrification within bed sediments. The new numerical modeling structure is then used to reproduce the data results and provide an estimate of the relative dominance of N uptake and denitrification within the surficial sediments of the karst conduit system. For the first time to our knowledge, results shed light on sediment processes that help control nutrient retention in phreatic karst conduits and tend to suggest that the karst systems behave as an intermediate N conveyor relative to surface agricultural streams and porous media aquifers.

Dual nitrate isotopes clarify the role of biological processing and hydrologic flow paths on nitrogen cycling in subtropical low-gradient watersheds

DOE PAGES

Griffiths, Natalie A.; Jackson, C. Rhett; McDonnell, Jeffrey J.; ...

2016-02-08

Nitrogen (N) is an important nutrient as it often limits productivity but in excess can impair water quality. Most studies on watershed N cycling have occurred in upland forested catchments where snowmelt dominates N export; fewer studies have focused on low-relief watersheds that lack snow. We examined watershed N cycling in three adjacent, low-relief watersheds in the Upper Coastal Plain of the southeastern United States to better understand the role of hydrological flow paths and biological transformations of N at the watershed scale. Groundwater was the dominant source of nitrified N to stream water in two of the three watersheds,more » while atmospheric deposition comprised 28% of stream water nitrate in one watershed. The greater atmospheric contribution may have been due to the larger stream channel area relative to total watershed area or the dominance of shallow subsurface flow paths contributing to stream flow in this watershed. There was a positive relationship between temperature and stream water ammonium concentrations and a negative relationship between temperature and stream water nitrate concentrations in each watershed suggesting that N cycling processes (i.e., nitrification and denitrification) varied seasonally. However, there were no clear patterns in the importance of denitrification in different water pools possibly because a variety of factors (i.e., assimilatory uptake, dissimilatory uptake, and mixing) affected nitrate concentrations. In conclusion, together, these results highlight the hydrological and biological controls on N cycling in low-gradient watersheds and variability in N delivery flow paths among adjacent watersheds with similar physical characteristics.« less

Regulation causes nitrogen cycling discontinuities in Mediterranean rivers.

PubMed

von Schiller, Daniel; Aristi, Ibon; Ponsatí, Lídia; Arroita, Maite; Acuña, Vicenç; Elosegi, Arturo; Sabater, Sergi

2016-01-01

River regulation has fundamentally altered large sections of the world's river networks. The effects of dams on the structural properties of downstream reaches are well documented, but less is known about their effect on river ecosystem processes. We investigated the effect of dams on river nutrient cycling by comparing net uptake of total dissolved nitrogen (TDN), phosphorus (TDP) and organic carbon (DOC) in river reaches located upstream and downstream from three reservoir systems in the Ebro River basin (NE Iberian Peninsula). Increased hydromorphological stability, organic matter standing stocks and ecosystem metabolism below dams enhanced the whole-reach net uptake of TDN, but not that of TDP or DOC. Upstream from dams, river reaches tended to be at biogeochemical equilibrium (uptake≈release) for all nutrients, whereas river reaches below dams acted as net sinks of TDN. Overall, our results suggest that flow regulation by dams may cause relevant N cycling discontinuities in rivers. Higher net N uptake capacity below dams could lead to reduced N export to downstream ecosystems. Incorporating these discontinuities could significantly improve predictive models of N cycling and transport in complex river networks. Copyright © 2015. Published by Elsevier B.V.

Variability of alpha-tocopherol values associated with procurement, storage, and freezing of equine serum and plasma samples.

PubMed

Craig, A M; Blythe, L L; Rowe, K E; Lassen, E D; Barrington, R; Walker, K C

1992-12-01

Recent evidence concerning the pathogenesis of equine degenerative myeloencephalopathy indicated that low blood alpha-tocopherol values are a factor in the disease process. Variables that could be introduced by a veterinarian procuring, transporting, or storing samples were evaluated for effects on alpha-tocopherol concentration in equine blood. These variables included temperature; light; exposure to the rubber stopper of the evacuated blood collection tube; hemolysis; duration of freezing time, with and without nitrogen blanketing; and repeated freeze/thaw cycles. It was found that hemolysis caused the greatest change in high-performance liquid chromatography-measured serum alpha-tocopherol values, with mean decrease of 33% (P < 0.001). Lesser, but significant (P < 0.01) changes in serum alpha-tocopherol values were an approximate 10% decrease when refrigerated blood was left in contact with the red rubber stopper of the blood collection tube for 72 hours and an approximate 5% increase when blood was stored at 20 to 25 C (room temperature) for 72 hours. Repeated freeze/thaw cycles resulted in a significant (P < 0.05) 3% decrease in alpha-tocopherol values in heparinized plasma by the third thawing cycle. Freezer storage for a 3-month period without nitrogen blanketing resulted in slight (2%) decrease in mean serum alpha-tocopherol values, whereas values in serum stored for an identical period under nitrogen blanketing did not change. A significant (P < 0.001) mean decrease (10.3%) in alpha-tocopherol values was associated with freezer (-16 C) storage of nitrogen blanketed serum for 6 months.(ABSTRACT TRUNCATED AT 250 WORDS)

NC10 Bacteria in a Marine Oxygen Minimum Zone

NASA Astrophysics Data System (ADS)

Padilla, C. C.; Bristow, L. A.; Benson, C. R.; Sarode, N. D.; Girguis, P. R.; Glass, J. B.; DiChristina, T. J.; Thamdrup, B.; Stewart, F. J.

2014-12-01

Marine oxygen minimum zones (OMZs) are key regions of nitrogen cycling and nitrogen loss as N2. The potential for methane cycling to influence OMZ nitrogen budgets remains largely unknown. The anaerobic oxidation of methane (AOM) coupled to nitrite or nitrate reduction has been shown to be a potential source of methane consumption, N loss, and oxygen production in freshwater sediments, but has not been described for marine pelagic environments. Nitrite-dependent AOM is performed by bacteria of the candidate division NC10 through an intra-aerobic pathway involving the dismutation of nitric oxide to O2 and N2. We explored the potential that NC10-like bacteria are present and active in the anoxic, nitrite-rich OMZ of the Eastern Tropical North Pacific. Community transcriptome sequencing confirmed the expression of genes with top matches to the NC10 bacterium 'Candidatus Methylomirabilis oxyfera.' NC10-like transcripts increased in relative abundance with depth into the anoxic OMZ core and included genes of aerobic methanotrophy and denitrification, as well as high numbers of transcripts matching norZ nitric oxide reductase, hypothesized to play a role in the O2-yielding dismutation reaction. Phylogenetic analysis of OMZ particulate methane monooxygenase (pmoA) and 16S rRNA gene sequences recovered by PCR revealed multiple clades of NC10 phylotypes in the OMZ. Preliminary data from OMZ enrichments revealed methane-dependent nitrite consumption, but further characterization is required to identify the pathways and organisms mediating this process. These findings expand the known environmental range of NC10 and suggest the possibility of previously uncharacterized linkages between OMZ nitrogen and methane cycles.

Partitioning nitrogen losses by natural abundance nitrogen isotope composition in a process-based statistical modelling framework

NASA Astrophysics Data System (ADS)

Dong, Ning; Wright, Ian; Prentice, Iain Colin

2017-04-01

Natural abundance of the stable isotope 15N is an under-utilized resource for research on the global terrestrial nitrogen cycle. Mass balance considerations suggest that if reactive N inputs have a roughly constant isotopic signature, soil δ15N should be mainly determined by the fraction of N losses by leaching - which barely discriminates against 15N - versus gaseous N losses, which discriminate strongly against 15N. We defined simple process-oriented functions of runoff (frunoff) and soil temperature (ftemp) and investigated the dependencies of soil and foliage δ15N (from global compilations of both types of measurement) on their ratio. Both plant and soil δ15N were found to systematically increase with ftemp/frunoff. Consistent with previous analyses, foliage δ15N was offset (more negative) with respect to soil δ15N, with significant differences in this offset between (from largest to smallest offset) ericoid, ectomycorrhizal, arbuscular mycorrhizal and non-mycorrhizal associated plants. δ15N values tend to be large and positive in the driest environments and to decline as frunoff increases, while also being lower in cold environments and increasing as ftemp increases. The fitted statistical model was used to estimate the gaseous fraction of total N losses from ecosystems (fgas) on a global grid basis. In common with earlier results, the largest values of fgas are predicted in the tropics and semi-arid subtropics. This analysis provides an indirectly estimated global mapping of fgas, which could be used as an improved benchmark for terrestrial nitrogen cycle models.

Global declines in oceanic nitrification rates as a consequence of ocean acidification.

PubMed

Beman, J Michael; Chow, Cheryl-Emiliane; King, Andrew L; Feng, Yuanyuan; Fuhrman, Jed A; Andersson, Andreas; Bates, Nicholas R; Popp, Brian N; Hutchins, David A

2011-01-04

Ocean acidification produced by dissolution of anthropogenic carbon dioxide (CO(2)) emissions in seawater has profound consequences for marine ecology and biogeochemistry. The oceans have absorbed one-third of CO(2) emissions over the past two centuries, altering ocean chemistry, reducing seawater pH, and affecting marine animals and phytoplankton in multiple ways. Microbially mediated ocean biogeochemical processes will be pivotal in determining how the earth system responds to global environmental change; however, how they may be altered by ocean acidification is largely unknown. We show here that microbial nitrification rates decreased in every instance when pH was experimentally reduced (by 0.05-0.14) at multiple locations in the Atlantic and Pacific Oceans. Nitrification is a central process in the nitrogen cycle that produces both the greenhouse gas nitrous oxide and oxidized forms of nitrogen used by phytoplankton and other microorganisms in the sea; at the Bermuda Atlantic Time Series and Hawaii Ocean Time-series sites, experimental acidification decreased ammonia oxidation rates by 38% and 36%. Ammonia oxidation rates were also strongly and inversely correlated with pH along a gradient produced in the oligotrophic Sargasso Sea (r(2) = 0.87, P < 0.05). Across all experiments, rates declined by 8-38% in low pH treatments, and the greatest absolute decrease occurred where rates were highest off the California coast. Collectively our results suggest that ocean acidification could reduce nitrification rates by 3-44% within the next few decades, affecting oceanic nitrous oxide production, reducing supplies of oxidized nitrogen in the upper layers of the ocean, and fundamentally altering nitrogen cycling in the sea.

The nitrogen cycles on Pluto over seasonal and astronomical timescales

NASA Astrophysics Data System (ADS)

Bertrand, T.; Forget, F.; Umurhan, O. M.; Grundy, W. M.; Schmitt, B.; Protopapa, S.; Zangari, A. M.; White, O. L.; Schenk, P. M.; Singer, K. N.; Stern, A.; Weaver, H. A.; Young, L. A.; Ennico, K.; Olkin, C. B.

2018-07-01

Pluto's landscape is shaped by the endless condensation and sublimation cycles of the volatile ices covering its surface. In particular, the Sputnik Planitia ice sheet, which is thought to be the main reservoir of nitrogen ice, displays a large diversity of terrains, with bright and dark plains, small pits and troughs, topographic depressions and evidences of recent and past glacial flows. Outside Sputnik Planitia, New Horizons also revealed numerous nitrogen ice deposits, in the eastern side of Tombaugh Regio and at mid-northern latitudes. These observations suggest a complex history involving volatile and glacial processes occurring on different timescales. We present numerical simulations of volatile transport on Pluto performed with a model designed to simulate the nitrogen cycle over millions of years, taking into account the changes of obliquity, solar longitude of perihelion and eccentricity as experienced by Pluto. Using this model, we first explore how the volatile and glacial activity of nitrogen within Sputnik Planitia has been impacted by the diurnal, seasonal and astronomical cycles of Pluto. Results show that the obliquity dominates the N2 cycle and that over one obliquity cycle, the latitudes of Sputnik Planitia between 25°S-30°N are dominated by N2 condensation, while the northern regions between 30°N and -50°N are dominated by N2 sublimation. We find that a net amount of 1 km of ice has sublimed at the northern edge of Sputnik Planitia during the last 2 millions of years. It must have been compensated by a viscous flow of the thick ice sheet. By comparing these results with the observed geology of Sputnik Planitia, we can relate the formation of the small pits and the brightness of the ice at the center of Sputnik Planitia to the sublimation and condensation of ice occurring at the annual timescale, while the glacial flows at its eastern edge and the erosion of the water ice mountains all around the ice sheet are instead related to the astronomical timescale. We also perform simulations including a glacial flow scheme which shows that the Sputnik Planitia ice sheet is currently at its minimum extent at the northern and southern edges. We also explore the stability of N2 ice deposits outside the latitudes and longitudes of the Sputnik Planitia basin. Results show that N2 ice is not stable at the poles but rather in the equatorial regions, in particular in depressions, where thick deposits may persist over tens of millions of years, before being trapped in Sputnik Planitia. Finally, another key result is that the minimum and maximum surface pressures obtained over the simulated millions of years remain in the range of milli-Pascals and Pascals, respectively. This suggests that Pluto never encountered conditions allowing liquid nitrogen to flow directly on its surface. Instead, we suggest that the numerous geomorphological evidences of past liquid flow observed on Pluto's surface are the result of liquid nitrogen that flowed at the base of thick ancient nitrogen glaciers, which have since disappeared.

Mixtures of macrophyte growth forms promote nitrogen cycling in wetlands.

PubMed

Choudhury, Maidul I; McKie, Brendan G; Hallin, Sara; Ecke, Frauke

2018-09-01

The importance of aquatic plant diversity in regulating nutrient cycling in wetlands remains poorly understood. We investigated how variation in macrophyte growth form (emerging, submerged and bryophyte) combinations and species mixtures affect nitrogen (N) removal from the water and N accumulation in plant biomass. We conducted a wetland mesocosm experiment for 100 days during July-September 2015. Twelve species were grown in mono- and in two-species mixed cultures for a total of 32 single and two-growth form combinations. Nitrogen removal from the water was quantified on three occasions during the experiment, while N accumulation in plant biomass was determined following termination of the experiment. The number of species and growth forms present increased N removal and accumulation. The growth form combinations of emerging and bryophyte species showed the highest N accumulation and N removal from water, followed by combinations of emerging species. By contrast, submerged species growing in the presence of emerging or other submerged species showed the lowest levels of N accumulation and N removal. Temporal variation in N removal also differed among growth form combinations: N removal was highest for emerging-bryophyte combinations in July, but peaked for the emerging-submerged and emerging-bryophyte combinations in August. Indeed, the occurrence of complementarity among macrophyte species, particularly in combinations of bryophyte and emerging species, enhanced N removal and uptake during the entire growing season. Our study highlights the importance of bryophytes, which have been neglected in research on nutrient cycling in wetlands, for aquatic N cycling, especially given their worldwide distribution across biomes. Overall, our findings point towards the potential important role of the diversity of macrophyte growth forms in regulating key ecosystem processes related to N cycling in wetlands. Copyright © 2018 Elsevier B.V. All rights reserved.

Titan's past and future: 3D modeling of a pure nitrogen atmosphere and geological implications

NASA Astrophysics Data System (ADS)

Charnay, Benjamin; Forget, François; Tobie, Gabriel; Sotin, Christophe; Wordsworth, Robin

2014-10-01

Several clues indicate that Titan's atmosphere has been depleted in methane during some period of its history, possibly as recently as 0.5-1 billion years ago. It could also happen in the future. Under these conditions, the atmosphere becomes only composed of nitrogen with a range of temperature and pressure allowing liquid or solid nitrogen to condense. Here, we explore these exotic climates throughout Titan's history with a 3D Global Climate Model (GCM) including the nitrogen cycle and the radiative effect of nitrogen clouds. We show that for the last billion years, only small polar nitrogen lakes should have formed. Yet, before 1 Ga, a significant part of the atmosphere could have condensed, forming deep nitrogen polar seas, which could have flowed and flooded the equatorial regions. Alternatively, nitrogen could be frozen on the surface like on Triton, but this would require an initial surface albedo higher than 0.65 at 4 Ga. Such a state could be stable even today if nitrogen ice albedo is higher than this value. According to our model, nitrogen flows and rain may have been efficient to erode the surface. Thus, we can speculate that a paleo-nitrogen cycle may explain the erosion and the age of Titan's surface, and may have produced some of the present valley networks and shorelines. Moreover, by diffusion of liquid nitrogen in the crust, a paleo-nitrogen cycle could be responsible of the flattening of the polar regions and be at the origin of the methane outgassing on Titan.

Different land use intensities in grassland ecosystems drive ecology of microbial communities involved in nitrogen turnover in soil.

PubMed

Meyer, Annabel; Focks, Andreas; Radl, Viviane; Keil, Daniel; Welzl, Gerhard; Schöning, Ingo; Boch, Steffen; Marhan, Sven; Kandeler, Ellen; Schloter, Michael

2013-01-01

Understanding factors driving the ecology of N cycling microbial communities is of central importance for sustainable land use. In this study we report changes of abundance of denitrifiers, nitrifiers and nitrogen-fixing microorganisms (based on qPCR data for selected functional genes) in response to different land use intensity levels and the consequences for potential turnover rates. We investigated selected grassland sites being comparable with respect to soil type and climatic conditions, which have been continuously treated for many years as intensely used meadows (IM), intensely used mown pastures (IP) and extensively used pastures (EP), respectively. The obtained data were linked to above ground biodiversity pattern as well as water extractable fractions of nitrogen and carbon in soil. Shifts in land use intensity changed plant community composition from systems dominated by s-strategists in extensive managed grasslands to c-strategist dominated communities in intensive managed grasslands. Along the different types of land use intensity, the availability of inorganic nitrogen regulated the abundance of bacterial and archaeal ammonia oxidizers. In contrast, the amount of dissolved organic nitrogen determined the abundance of denitrifiers (nirS and nirK). The high abundance of nifH carrying bacteria at intensive managed sites gave evidence that the amounts of substrates as energy source outcompete the high availability of inorganic nitrogen in these sites. Overall, we revealed that abundance and function of microorganisms involved in key processes of inorganic N cycling (nitrification, denitrification and N fixation) might be independently regulated by different abiotic and biotic factors in response to land use intensity.

Different Land Use Intensities in Grassland Ecosystems Drive Ecology of Microbial Communities Involved in Nitrogen Turnover in Soil

PubMed Central

Meyer, Annabel; Focks, Andreas; Radl, Viviane; Keil, Daniel; Welzl, Gerhard; Schöning, Ingo; Boch, Steffen; Marhan, Sven; Kandeler, Ellen; Schloter, Michael

2013-01-01

Understanding factors driving the ecology of N cycling microbial communities is of central importance for sustainable land use. In this study we report changes of abundance of denitrifiers, nitrifiers and nitrogen-fixing microorganisms (based on qPCR data for selected functional genes) in response to different land use intensity levels and the consequences for potential turnover rates. We investigated selected grassland sites being comparable with respect to soil type and climatic conditions, which have been continuously treated for many years as intensely used meadows (IM), intensely used mown pastures (IP) and extensively used pastures (EP), respectively. The obtained data were linked to above ground biodiversity pattern as well as water extractable fractions of nitrogen and carbon in soil. Shifts in land use intensity changed plant community composition from systems dominated by s-strategists in extensive managed grasslands to c-strategist dominated communities in intensive managed grasslands. Along the different types of land use intensity, the availability of inorganic nitrogen regulated the abundance of bacterial and archaeal ammonia oxidizers. In contrast, the amount of dissolved organic nitrogen determined the abundance of denitrifiers (nirS and nirK). The high abundance of nifH carrying bacteria at intensive managed sites gave evidence that the amounts of substrates as energy source outcompete the high availability of inorganic nitrogen in these sites. Overall, we revealed that abundance and function of microorganisms involved in key processes of inorganic N cycling (nitrification, denitrification and N fixation) might be independently regulated by different abiotic and biotic factors in response to land use intensity. PMID:24039974

Life cycle analysis on fossil energy ratio of algal biodiesel: effects of nitrogen deficiency and oil extraction technology.

PubMed

Jian, Hou; Jing, Yang; Peidong, Zhang

2015-01-01

Life cycle assessment (LCA) has been widely used to analyze various pathways of biofuel preparation from "cradle to grave." Effects of nitrogen supply for algae cultivation and technology of algal oil extraction on life cycle fossil energy ratio of biodiesel are assessed in this study. Life cycle fossil energy ratio of Chlorella vulgaris based biodiesel is improved by growing algae under nitrogen-limited conditions, while the life cycle fossil energy ratio of biodiesel production from Phaeodactylum tricornutum grown with nitrogen deprivation decreases. Compared to extraction of oil from dried algae, extraction of lipid from wet algae with subcritical cosolvents achieves a 43.83% improvement in fossil energy ratio of algal biodiesel when oilcake drying is not considered. The outcome for sensitivity analysis indicates that the algal oil conversion rate and energy content of algae are found to have the greatest effects on the LCA results of algal biodiesel production, followed by utilization ratio of algal residue, energy demand for algae drying, capacity of water mixing, and productivity of algae.

Life Cycle Analysis on Fossil Energy Ratio of Algal Biodiesel: Effects of Nitrogen Deficiency and Oil Extraction Technology

PubMed Central

Jian, Hou; Jing, Yang; Peidong, Zhang

2015-01-01

Life cycle assessment (LCA) has been widely used to analyze various pathways of biofuel preparation from “cradle to grave.” Effects of nitrogen supply for algae cultivation and technology of algal oil extraction on life cycle fossil energy ratio of biodiesel are assessed in this study. Life cycle fossil energy ratio of Chlorella vulgaris based biodiesel is improved by growing algae under nitrogen-limited conditions, while the life cycle fossil energy ratio of biodiesel production from Phaeodactylum tricornutum grown with nitrogen deprivation decreases. Compared to extraction of oil from dried algae, extraction of lipid from wet algae with subcritical cosolvents achieves a 43.83% improvement in fossil energy ratio of algal biodiesel when oilcake drying is not considered. The outcome for sensitivity analysis indicates that the algal oil conversion rate and energy content of algae are found to have the greatest effects on the LCA results of algal biodiesel production, followed by utilization ratio of algal residue, energy demand for algae drying, capacity of water mixing, and productivity of algae. PMID:26000338

Performance comparison of single-stage mixed-refrigerant Joule-Thomson cycle and reverse Brayton cycle for cooling 80 to 120 K temperature-distributed heat loads

NASA Astrophysics Data System (ADS)

Wang, H. C.; Chen, G. F.; Gong, M. Q.; Li, X.

2017-12-01

Thermodynamic performance comparison of single-stage mixed-refrigerant Joule-Thomson cycle (MJTR) and pure refrigerant reverse Brayton cycle (RBC) for cooling 80 to 120 K temperature-distributed heat loads was conducted in this paper. Nitrogen under various liquefaction pressures was employed as the heat load. The research was conducted under nonideal conditions by exergy analysis methods. Exergy efficiency and volumetric cooling capacity are two main evaluation parameters. Exergy loss distribution in each process of refrigeration cycle was also investigated. The exergy efficiency and volumetric cooling capacity of MJTR were obviously superior to RBC in 90 to 120 K temperature zone, but still inferior to RBC at 80 K. The performance degradation of MJTR was caused by two main reasons: The high fraction of neon resulted in large entropy generation and exergy loss in throttling process. Larger duty and WLMTD lead to larger exergy losses in recuperator.

MODELING NITROGEN-CARBON CYCLING AND OXYGEN CONSUMPTION IN BOTTOM SEDIMENTS

EPA Science Inventory

A model framework is presented for simulating nitrogen and carbon cycling at the sediment–water interface, and predicting oxygen consumption by oxidation reactions inside the sediments. Based on conservation of mass and invoking simplifying assumptions, a coupled system of diffus...

News from Online: Digging up Earth Day Resources

ERIC Educational Resources Information Center

Coldwell, Bernadette A.

2006-01-01

The soil science and soil chemistry is incorporated into teaching materials for earth day and beyond. It revealed some of the chemical properties of the soil through color and texture and the chemical processes relevant to soils abound, including the carbon and nitrogen cycles in the soil, acidification of soils through acid deposition, leaching…

STATISTICAL ESTIMATES OF VARIANCE FOR 15N ISOTOPE DILUTION MEASUREMENTS OF GROSS RATES OF NITROGEN CYCLE PROCESSES

EPA Science Inventory

It has been fifty years since Kirkham and Bartholmew (1954) presented the conceptual framework and derived the mathematical equations that formed the basis of the now commonly employed method of 15N isotope dilution. Although many advances in methodology and analysis have been ma...

Comparative Biogeochemical Cycles of Bioenergy Crops Reveal Nitrogen-Fixation and Low GHG Emissions in a Miscanthus x giganteus Agro-ecosystem

USDA-ARS?s Scientific Manuscript database

We evaluated the relative greenhouse gas mitigation potential of plant species considered as biofuel feedstock crops by simulating the biogeochemical processes associated with Miscanthus x giganteus, Panicum virgatum, Zea mays, and a mixed prairie community. DayCent model simulations for Miscanthus ...

A Cu(I)-Catalyzed C-H α-Amination of Aryl Ketones. Direct Synthesis of Imidazolinones

PubMed Central

Zhao, Baoguo; Du, Haifeng; Shi, Yian

2009-01-01

This paper describes an α-amination process of aryl ketones using CuCl as catalyst and di-tert-butyldiaziridinone as the nitrogen source. A variety of imidazolinone derivatives are prepared in moderate yields under mild conditions. A possible catalytic cycle is proposed for this reaction. PMID:19402696

Seasonal and spatial patterns in coupled nitrification-denitrification rates in a large Great Lakes coastal system: The St. Louis River Estuary

EPA Science Inventory

Anthropogenic inputs of excess nitrogen (N) to aquatic systems are detrimental, but aquatic plants and sediments have the potential to mitigate N-loading. Sediment processes are driven by microbially mediated N-cycling. Coastal embayments purportedly play a significant role in N-...

Temporal variation in the importance of a dominant consumer to stream nutrient cycling

DOE PAGES

Griffiths, Natalie A.; Hill, Walter

2014-06-19

Animal excretion can be a significant nutrient flux within ecosystems, where it supports primary production and facilitates microbial decomposition of organic matter. The effects of excretory products on nutrient cycling have been documented for various species and ecosystems, but temporal variation in these processes is poorly understood. We examined variation in excretion rates of a dominant grazing snail, Elimia clavaeformis, and its contribution to nutrient cycling, over the course of 14 months in a well-studied, low-nutrient stream (Walker Branch, east Tennessee, USA). Biomass-specific excretion rates of ammonium varied over twofold during the study, coinciding with seasonal changes in food availabilitymore » (measured as gross primary production) and water temperature (multiple linear regression, R 2 = 0.57, P = 0.053). The contribution of ammonium excretion to nutrient cycling varied with seasonal changes in both biological (that is, nutrient uptake rate) and physical (that is, stream flow) variables. On average, ammonium excretion accounted for 58% of stream water ammonium concentrations, 26% of whole-stream nitrogen demand, and 66% of autotrophic nitrogen uptake. Phosphorus excretion by Elimia was contrastingly low throughout the year, supplying only 1% of total dissolved phosphorus concentrations. The high average N:P ratio (89:1) of snail excretion likely exacerbated phosphorus limitation in Walker Branch. To fully characterize animal excretion rates and effects on ecosystem processes, multiple measurements through time are necessary, especially in ecosystems that experience strong seasonality.« less

Temporal variation in the importance of a dominant consumer to stream nutrient cycling

DOE Office of Scientific and Technical Information (OSTI.GOV)

Griffiths, Natalie A.; Hill, Walter

Animal excretion can be a significant nutrient flux within ecosystems, where it supports primary production and facilitates microbial decomposition of organic matter. The effects of excretory products on nutrient cycling have been documented for various species and ecosystems, but temporal variation in these processes is poorly understood. We examined variation in excretion rates of a dominant grazing snail, Elimia clavaeformis, and its contribution to nutrient cycling, over the course of 14 months in a well-studied, low-nutrient stream (Walker Branch, east Tennessee, USA). Biomass-specific excretion rates of ammonium varied over twofold during the study, coinciding with seasonal changes in food availabilitymore » (measured as gross primary production) and water temperature (multiple linear regression, R 2 = 0.57, P = 0.053). The contribution of ammonium excretion to nutrient cycling varied with seasonal changes in both biological (that is, nutrient uptake rate) and physical (that is, stream flow) variables. On average, ammonium excretion accounted for 58% of stream water ammonium concentrations, 26% of whole-stream nitrogen demand, and 66% of autotrophic nitrogen uptake. Phosphorus excretion by Elimia was contrastingly low throughout the year, supplying only 1% of total dissolved phosphorus concentrations. The high average N:P ratio (89:1) of snail excretion likely exacerbated phosphorus limitation in Walker Branch. To fully characterize animal excretion rates and effects on ecosystem processes, multiple measurements through time are necessary, especially in ecosystems that experience strong seasonality.« less

Towards a community Earth System Model

NASA Astrophysics Data System (ADS)

Blackmon, M.

2003-04-01

The Community Climate System Model, version 2 (CCSM2), was released in June 2002. CCSM2 has several new components and features, which I will discuss briefly. I will also show a few results from a multi-century equilibrium run with this model, emphasizing the improvements over the earlier simulation using the original CSM. A few flaws and inadequacies in CCSM2 have been identified. I will also discuss briefly work underway to improve the model and present results, if available. CCSM2, with improvements, will be the basis for the development of a Community Earth System Model (CESM). The highest priority for expansion of the model involves incorporation of biogeosciences into the coupled model system, with emphasis given to the carbon, nitrogen and iron cycles. The overall goal of the biogeosciences project within CESM is to understand the regulation of planetary energetics, planetary ecology, and planetary metabolism through exchanges of energy, momentum, and materials among atmosphere, land, and ocean, and the response of the climate system through these processes to changes in land cover and land use. In particular, this research addresses how biogeochemical coupling of carbon, nitrogen, and iron cycles affects climate and how human perturbations of these cycles alter climate. To accomplish these goals, the Community Land Model, the land component of CCSM2, is being developed to include river routing, carbon and nitrogen cycles, emissions of mineral aerosols and biogenic volatile organic compounds, dry deposition of various gases, and vegetation dynamics. The carbon and nitrogen cycles are being implemented using parameterizations developed as part of a state-of-the-art ecosystem biogeochemistry model. The primary goal of this research is to provide an accurate net flux of CO2 between the land and the atmosphere so that CESM can be used to study the dynamics of the coupled climate-carbon system. Emissions of biogenic volatile organic compounds are also based on a state-of-the-art emissions model and depend on plant type, leaf area index, photosynthetically active radiation, and leaf temperature. Dust emissions and deposition are being developed to implement a fully coupled dust cycle in CCSM, including the radiative effects of dust and carbon feedbacks related to fertilization of ocean and terrestrial ecosystems. Dust mobilization depends on surface wind speed, soil moisture, plant cover, and soil texture. Dust dry deposition processes include sedimentation and turbulent mix-out. A major research focus is how natural and human-mediated changes in land cover and ecosystem functions alter surface energy fluxes, the hydrological cycle, and biogeochemical cycles. Human land uses include conversion of natural vegetation to cropland, soil degradation, and urbanization. Climate feedbacks associated with natural changes in land cover are being assessed by developing and implementing a model of natural vegetation dynamics for use with the Community Land Model. Development of a marine ecosystem model is also underway. The ecosystem model is based on the global, mixed-layer marine ecosystem model of Moore et al., which includes parameterizations for such things as iron limitation and scavenging, zooplankton grazing, nitrogen fixation, calcification, and ballast-based remineralization. A series of experiments is being planned to assess the coupling of the ecology to the biogeochemistry, to adequately tune some of the model parameters that are poorly constrained by data, to explore new parameterizations and processes (e.g., riverine and atmospheric inputs of nutrients), and to conduct uncoupled application studies (e.g., deliberate carbon sequestration, retrospective historical simulations, iron-dust deposition response). Longer term plans include investigating biogeochemical processes in the coastal zone and how to incorporate these processes into a global ocean model, either through subgrid-scale parameterizations or model nesting. A Whole Atmosphere Community Climate Model(WACCM) is being developed. The vertical extent of the model is 150 km at present, but extension to 500 km is eventually expected. Interactive chemistry is being incorporated. This model will be used as the atmospheric component of CESM for some experiments. One expected application is the study of solar variability and its impact on climate variability in the troposphere and at the atmosphere, ocean, land interface. Preliminary results using some of these model components will be shown. A timeline for development and use of the models will be given.

Terrestrial nitrogen–carbon cycle interactions at the global scale

PubMed Central

Zaehle, S.

2013-01-01

Interactions between the terrestrial nitrogen (N) and carbon (C) cycles shape the response of ecosystems to global change. However, the global distribution of nitrogen availability and its importance in global biogeochemistry and biogeochemical interactions with the climate system remain uncertain. Based on projections of a terrestrial biosphere model scaling ecological understanding of nitrogen–carbon cycle interactions to global scales, anthropogenic nitrogen additions since 1860 are estimated to have enriched the terrestrial biosphere by 1.3 Pg N, supporting the sequestration of 11.2 Pg C. Over the same time period, CO2 fertilization has increased terrestrial carbon storage by 134.0 Pg C, increasing the terrestrial nitrogen stock by 1.2 Pg N. In 2001–2010, terrestrial ecosystems sequestered an estimated total of 27 Tg N yr−1 (1.9 Pg C yr−1), of which 10 Tg N yr−1 (0.2 Pg C yr−1) are due to anthropogenic nitrogen deposition. Nitrogen availability already limits terrestrial carbon sequestration in the boreal and temperate zone, and will constrain future carbon sequestration in response to CO2 fertilization (regionally by up to 70% compared with an estimate without considering nitrogen–carbon interactions). This reduced terrestrial carbon uptake will probably dominate the role of the terrestrial nitrogen cycle in the climate system, as it accelerates the accumulation of anthropogenic CO2 in the atmosphere. However, increases of N2O emissions owing to anthropogenic nitrogen and climate change (at a rate of approx. 0.5 Tg N yr−1 per 1°C degree climate warming) will add an important long-term climate forcing. PMID:23713123

The microbiome of Brazilian mangrove sediments as revealed by metagenomics.

PubMed

Andreote, Fernando Dini; Jiménez, Diego Javier; Chaves, Diego; Dias, Armando Cavalcante Franco; Luvizotto, Danice Mazzer; Dini-Andreote, Francisco; Fasanella, Cristiane Cipola; Lopez, Maryeimy Varon; Baena, Sandra; Taketani, Rodrigo Gouvêa; de Melo, Itamar Soares

2012-01-01

Here we embark in a deep metagenomic survey that revealed the taxonomic and potential metabolic pathways aspects of mangrove sediment microbiology. The extraction of DNA from sediment samples and the direct application of pyrosequencing resulted in approximately 215 Mb of data from four distinct mangrove areas (BrMgv01 to 04) in Brazil. The taxonomic approaches applied revealed the dominance of Deltaproteobacteria and Gammaproteobacteria in the samples. Paired statistical analysis showed higher proportions of specific taxonomic groups in each dataset. The metabolic reconstruction indicated the possible occurrence of processes modulated by the prevailing conditions found in mangrove sediments. In terms of carbon cycling, the sequences indicated the prevalence of genes involved in the metabolism of methane, formaldehyde, and carbon dioxide. With respect to the nitrogen cycle, evidence for sequences associated with dissimilatory reduction of nitrate, nitrogen immobilization, and denitrification was detected. Sequences related to the production of adenylsulfate, sulfite, and H(2)S were relevant to the sulphur cycle. These data indicate that the microbial core involved in methane, nitrogen, and sulphur metabolism consists mainly of Burkholderiaceae, Planctomycetaceae, Rhodobacteraceae, and Desulfobacteraceae. Comparison of our data to datasets from soil and sea samples resulted in the allotment of the mangrove sediments between those samples. The results of this study add valuable data about the composition of microbial communities in mangroves and also shed light on possible transformations promoted by microbial organisms in mangrove sediments.

The Microbiome of Brazilian Mangrove Sediments as Revealed by Metagenomics

PubMed Central

Andreote, Fernando Dini; Jiménez, Diego Javier; Chaves, Diego; Dias, Armando Cavalcante Franco; Luvizotto, Danice Mazzer; Dini-Andreote, Francisco; Fasanella, Cristiane Cipola; Lopez, Maryeimy Varon; Baena, Sandra; Taketani, Rodrigo Gouvêa; de Melo, Itamar Soares

2012-01-01

Here we embark in a deep metagenomic survey that revealed the taxonomic and potential metabolic pathways aspects of mangrove sediment microbiology. The extraction of DNA from sediment samples and the direct application of pyrosequencing resulted in approximately 215 Mb of data from four distinct mangrove areas (BrMgv01 to 04) in Brazil. The taxonomic approaches applied revealed the dominance of Deltaproteobacteria and Gammaproteobacteria in the samples. Paired statistical analysis showed higher proportions of specific taxonomic groups in each dataset. The metabolic reconstruction indicated the possible occurrence of processes modulated by the prevailing conditions found in mangrove sediments. In terms of carbon cycling, the sequences indicated the prevalence of genes involved in the metabolism of methane, formaldehyde, and carbon dioxide. With respect to the nitrogen cycle, evidence for sequences associated with dissimilatory reduction of nitrate, nitrogen immobilization, and denitrification was detected. Sequences related to the production of adenylsulfate, sulfite, and H2S were relevant to the sulphur cycle. These data indicate that the microbial core involved in methane, nitrogen, and sulphur metabolism consists mainly of Burkholderiaceae, Planctomycetaceae, Rhodobacteraceae, and Desulfobacteraceae. Comparison of our data to datasets from soil and sea samples resulted in the allotment of the mangrove sediments between those samples. The results of this study add valuable data about the composition of microbial communities in mangroves and also shed light on possible transformations promoted by microbial organisms in mangrove sediments. PMID:22737213

SEASONAL VARIATION IN THE BIOGEOCHEMICAL CYCLING OF SESTON IN GRAND TRAVERSE BAY, LAKE MICHIGAN. (R825151)

EPA Science Inventory

This study describes the biogeochemical cycling of seston in Grand Traverse Bay, Lake Michigan. Seston was characterized by carbon and nitrogen elemental and isotopic abundances. Fluorescence, temperature, light transmittance, and concentrations of dissolved inorganic nitrogen we...

Effects of Hypoxia on Sedimentary Nitrogen Cycling in the Pensacola Bay Estuary

EPA Science Inventory

Eutrophic-induced hypoxic events pose a serious threat to estuaries in coastal systems. Hypoxic events are becoming more intense and widespread with changes in land use and increased anthropogenic pressures. Microbial communities involved in sedimentary nitrogen (N) cycling may h...

Meiofauna increases bacterial denitrification in marine sediments.

PubMed

Bonaglia, S; Nascimento, F J A; Bartoli, M; Klawonn, I; Brüchert, V

2014-10-16

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.

Microbial extracellular enzymes in biogeochemical cycling of ecosystems.

PubMed

Luo, Ling; Meng, Han; Gu, Ji-Dong

2017-07-15

Extracellular enzymes, primarily produced by microorganisms, affect ecosystem processes because of their essential roles in degradation, transformation and mineralization of organic matter. Extracellular enzymes involved in the cycling of carbon (C), nitrogen (N) and phosphorus (P) have been widely investigated in many different ecosystems, and several enzymes have been recognized as key components in regulating C storage and nutrient cycling. In this review, it was the first time to summarize the specific extracellular enzymes related to C storage and nutrient cycling for better understanding the important role of microbial extracellular enzymes in biogeochemical cycling of ecosystems. Subsequently, ecoenzymatic stoichiometry - the relative ratio of extracellular enzyme, has been reviewed and further provided a new perspective for understanding biogeochemical cycling of ecosystems. Finally, the new insights of using microbial extracellular enzyme in indicating biogeochemical cycling and then protecting ecosystems have been suggested. Copyright © 2017 Elsevier Ltd. All rights reserved.

Nitrogen Oxide Fluxes and Nitrogen Cycling during Postagricultural Succession and Forest Fertilization in the Humid Tropics.

Treesearch

Heather Erickson; Michael Keller; Eric Davidson

2001-01-01

The effects of changes in tropical land use on soil emissions of nitrous oxide (N2O) and nitric oxide (NO) are not well understood. We examined emissions of N2O and NO and their relationships to land use and forest composition, litterfall, soil nitrogen (N) pools and turnover, soil moisture, and patterns of carbon (C) cycling in a lower montane, subtropical wet region...

Nitrogen balance for a plantation forest drainage canal on the North Carolina Coastal Plain

Treesearch

Timothy W. Appelboom; George M. Chescheir; R. Wayne Skaggs; J. Wendell Gilliam; Devendra M. Amatya

2009-01-01

Human alteration of the nitrogen cycle has led to increased riverine nitrogen loads, contributing to the eutrophication of lakes, streams, estuaries, and near-coastal oceans. These riverine nitrogen loads are usually less...

Global climate change and terrestrial net primary production

NASA Technical Reports Server (NTRS)

Melillo, Jerry M.; Mcguire, A. D.; Kicklighter, David W.; Moore, Berrien, III; Vorosmarty, Charles J.; Schloss, Annette L.

1993-01-01

A process-based model was used to estimate global patterns of net primary production and soil nitrogen cycling for contemporary climate conditions and current atmospheric CO2 concentration. Over half of the global annual net primary production was estimated to occur in the tropics, with most of the production attributable to tropical evergreen forest. The effects of CO2 doubling and associated climate changes were also explored. The responses in tropical and dry temperate ecosystems were dominated by CO2, but those in northern and moist temperate ecosystems reflected the effects of temperature on nitrogen availability.

The development of a new technical platform to measure soil organic nitrogen cycling processes by microbes

NASA Astrophysics Data System (ADS)

Hu, Yuntao; Richter, Andreas; Wanek, Wolfgang

2016-04-01

Soil organic matter (SOM) decomposition is one of the most important processes of the global nitrogen cycle, having strong implications on soil N availability, terrestrial carbon cycling and soil carbon sequestration. During SOM decomposition low-molecular weight organic nitrogen (LMWON) is released which can be taken up by microbes (and plants). The breakdown of high-molecular weight organic nitrogen (HMWON, e.g. proteins, peptidoglycan, chitin, nucleic acids) represents the bottleneck of soil HMWON decomposition and is performed by extracellular enzymes released mainly by soil microorganisms. Despite that, the current understanding of the controls of these processes is incomplete. The only way to measure gross decomposition rates of these polymers is to use isotope pool dilution (IPD) techniques. In IPD approaches the product pool is isotopically enriched (by e.g. 15N) and the isotope dilution of this pool is measured over time. We have pioneered an IPD for protein and cellulose depolymerization, but IPD approaches for other polymers, specifically for important microbial necromass components such as chitin (fungi) and peptidoglycan (bacteria), or nucleic acids have not yet been developed. Here we present a workflow based on a universally applicable technical platform that allows to estimate the gross depolymerization rate of SOM (HMWON) at the molecular level, using ultra high performance liquid chromatography/high resolution Orbitrap mass spectrometry (UPLC/HRMS) combined with IPD techniques. The necessary isotopically labeled organic polymers (chitin, peptidoglycan and others) are extracted from laboratory bacterial and fungal cultures grown in fully isotopically labeled nutrient media (15N, 13C or both). A purification scheme for the different polymers is currently established. Labeled potential decomposition products (e.g. amino sugars and muropeptides from peptidoglycan, amino sugars and chitooligosaccharides from chitin, nucleotides and nucleosides from nucleic acids) are prepared by enzymatic and/or acid digestion of the polymers. Different UPLC separation columns (Hypercarb, HiliC and C18) make it possible to separate more than 100 related monomers and oligomers produced during polymer decomposition, a prerequisite for analyzing the concentrations and isotope kinetics of decomposition products in complex soil samples. The benchtop Orbitrap mass analyzer has a nominal mass resolving power of 100,000 (FWHM at m/z 200), which enables us to separate compounds that are 13C- and 15N-labelled (mass difference: 0.00632) in the same compound, allowing tracing carbon and nitrogen isotopes in the same compound in IPD experiments. With the accurate masses, retention times and the isotopic pattern we can quantify and qualify the target decomposition products and their isotope kinetics during soil incubation experiments. This will enable us to estimate in situ decomposition rates of the major organic nitrogen polymers in soils, allowing new insights into the major controls of the most important step in soil organic nitrogen recycling.

Marine Bioinorganic Chemistry: The Role of Trace Metals in the Oceanic Cycles of Major Nutrients

NASA Astrophysics Data System (ADS)

Morel, F. M. M.; Milligan, A. J.; Saito, M. A.

2003-12-01

The bulk of living biomass is chiefly made up of only a dozen "major" elements - carbon, hydrogen, oxygen, nitrogen, phosphorus, sodium, potassium, chlorine, calcium, magnesium, sulfur (and silicon in diatoms) - whose proportions vary within a relatively narrow range in most organisms. A number of trace elements, particularly first row transition metals - manganese, iron, nickel, cobalt, copper, and zinc - are also "essential" for the growth of organisms. At the molecular level, the chemical mechanisms by which such elements function as active centers or structural factors in enzymes and by which they are accumulated and stored by organisms is the central topic of bioinorganic chemistry. At the scale of ocean basins, the interplay of physical, chemical, and biological processes that govern the cycling of biologically essential elements in seawater is the subject of marine biogeochemistry. For those interested in the growth of marine organisms, particularly in the one-half of the Earth's primary production contributed by marine phytoplankton, bioinorganic chemistry and marine biogeochemistry are critically linked by the extraordinary paucity of essential trace elements in surface seawater, which results from their biological utilization and incorporation in sinking organic matter. How marine organisms acquire elements that are present at nano- or picomolar concentrations in surface seawater; how they perform critical enzymatic functions when necessary metal cofactors are almost unavailable are the central topics of "marine bioinorganic chemistry." The central aim of this field is to elucidate at the molecular level the metal-dependent biological processes involved in the major biogeochemical cycles.By examining the solutions that emerged from the problems posed by the scarcity of essential trace elements, marine bioinorganic chemists bring to light hitherto unknown ways to take up or utilize trace elements, new molecules, and newer "essential" elements. Focusing on molecular mechanisms involved in such processes as inorganic carbon fixation, organic carbon respiration, or nitrogen transformation, they explain how the cycles of trace elements are critically linked to those of major nutrients such as carbon or nitrogen. But we have relatively little understanding of the binding molecules and the enzymes that mediate the biochemical role of trace metals in the marine environment. In this sense, this chapter is more a "preview" than a review of the field of marine bioinorganic chemistry. To exemplify the concepts and methods of this field, we have chosen to focus on one of its most important topics: the potentially limiting role of trace elements in primary marine production. As a result we center our discussion on particular subsets of organisms, biogeochemical cycles, and trace elements. Our chief actors are marine phytoplankton, particularly eukaryotes, while heterotrophic bacteria make only cameo appearances. The biogeochemical cycles that will serve as our plot are those of the elements involved in phytoplankton growth, the major algal nutrients - carbon, nitrogen, phosphorus, and silicon - leaving aside, e.g., the interesting topic of the marine sulfur cycle. Seven trace metals provide the intrigue: manganese, iron, nickel, cobalt, copper, zinc, and cadmium. But several other trace elements such as selenium, vanadium, molybdenum, and tungsten (and, probably, others not yet identified) will assuredly add further twists in future episodes.We begin this chapter by discussing what we know of the concentrations of trace elements in marine microorganisms and of the relevant mechanisms and kinetics of trace-metal uptake. We then review the biochemical role of trace elements in the marine cycles of carbon, nitrogen, phosphorus, and silicon. Using this information, we examine the evidence, emanating from both laboratory cultures and field measurements, relevant to the mechanisms and the extent of control by trace metals of marine biogeochemical cycles. Before concluding with a wistful glimpse of the future of marine bioinorganic chemistry we discuss briefly some paleoceanographic aspects of this new field: how the chemistry of the planet "Earth" - particularly the concentrations of trace elements in the oceans - has evolved since its origin, chiefly as a result of biological processes and how the evolution of life has, in turn, been affected by the availability of essential trace elements.

Spatially explicit simulation of hydrologically controlled carbon and nitrogen cycles and associated feedback mechanisms in a boreal ecosystem in Eastern Canada.

NASA Astrophysics Data System (ADS)

Govind, A.; Chen, J. M.; Margolis, H.

2007-12-01

Current estimates of terrestrial carbon overlook the effects of topographically-driven lateral flow of soil water. We hypothesize that this component, which occur at a landscape or watershed scale have significant influences on the spatial distribution of carbon, due to its large contribution to the local water balance. To this end, we further developed a spatially explicit ecohydrological model, BEPS-TerrainLab V2.0. We simulated the coupled hydrological and carbon cycle processes in a black spruce-moss ecosystem in central Quebec, Canada. The carbon stocks were initialized using a long term carbon cycling model, InTEC, under a climate change and disturbance scenario, the accuracy of which was determined with inventory plot measurements. Further, we simulated and validated several ecosystem indicators such as ET, GPP, NEP, water table, snow depth and soil temperature, using the measurements for two years, 2004 and 2005. After gaining confidence in the model's ability to simulate ecohydrological processes, we tested the influence of lateral water flow on the carbon cycle. We made three hydrological modeling scenarios 1) Explicit, were realistic lateral water routing was considered 2) Implicit where calculations were based on a bucket modeling approach 3) NoFlow, where the lateral water flow was turned off in the model. The results showed that pronounced anomalies exist among the scenarios for the simulated GPP, ET and NEP. In general, Implicit calculation overestimated GPP and underestimated NEP, as opposed to Explicit simulation. NoFlow underestimated GPP and overestimated NEP. The key processes controlling GPP were manifested through stomatal conductance which reduces under conditions of rapid soil saturation ( NoFlow ) or increases in the Implicit case, and, nitrogen availability which affects Vcmax, the maximum carboxylation rate. However, for NEP, the anomalies were attributed to differences in soil carbon pool decomposition, which determine the heterotrophic respiration and the resultant nitrogen mineralization which affects GPP and several other feedback mechanisms. These results suggest that lateral water flow does play a significant role in the terrestrial carbon distribution. Therefore, regional or global scale terrestrial carbon estimates could have significant errors if proper hydrological constrains are not considered for modeling ecological processes due to large topographic variations on the Earth's surface. For more info please visit: http://ajit.govind.googlepages.com/agu2007

A post-Cassini view of Titan's methane-based hydrologic cycle

NASA Astrophysics Data System (ADS)

Hayes, Alexander G.; Lorenz, Ralph D.; Lunine, Jonathan I.

2018-05-01

The methane-based hydrologic cycle on Saturn's largest moon, Titan, is an extreme analogue to Earth's water cycle. Titan is the only planetary body in the Solar System, other than Earth, that is known to have an active hydrologic cycle. With a surface pressure of 1.5 bar and temperatures of 90 to 95 K, methane and ethane condense out of a nitrogen-based atmosphere and flow as liquids on the moon's surface. Exchange processes between atmospheric, surface and subsurface reservoirs produce methane and ethane cloud systems, as well as erosional and depositional landscapes that have strikingly similar forms to their terrestrial counterparts. Over its 13-year exploration of the Saturn system, the Cassini-Huygens mission revealed that Titan's hydrocarbon-based hydrology is driven by nested methane cycles that operate over a range of timescales, including geologic, orbital (for example, Croll-Milankovitch cycles), seasonal and that of a single convective storm. In this Review Article, we describe the dominant exchange processes that operate over these timescales and present a post-Cassini view of Titan's methane-based hydrologic system.

Effects of Bromus tectorum invasion on microbial carbon and nitrogen cycling in two adjacent undisturbed arid grassland communities

USGS Publications Warehouse

Schaeffer, Sean M.; Ziegler, Susan E.; Belnap, Jayne; Evans, R.D.

2012-01-01

Soil nitrogen (N) is an important component in maintaining ecosystem stability, and the introduction of non-native plants can alter N cycling by changing litter quality and quantity, nutrient uptake patterns, and soil food webs. Our goal was to determine the effects of Bromus tectorum (C3) invasion on soil microbial N cycling in adjacent non-invaded and invaded C3 and C4 native arid grasslands. We monitored resin-extractable N, plant and soil δ13C and δ15N, gross rates of inorganic N mineralization and consumption, and the quantity and isotopic composition of microbial phospholipid biomarkers. In invaded C3 communities, labile soil organic N and gross and net rates of soil N transformations increased, indicating an increase in overall microbial N cycling. In invaded C4 communities labile soil N stayed constant, but gross N flux rates increased. The δ13C of phospholipid biomarkers in invaded C4 communities showed that some portion of the soil bacterial population preferentially decomposed invader C3-derived litter over that from the native C4 species. Invasion in C4 grasslands also significantly decreased the proportion of fungal to bacterial phospholipid biomarkers. Different processes are occurring in response to B. tectorum invasion in each of these two native grasslands that: 1) alter the size of soil N pools, and/or 2) the activity of the microbial community. Both processes provide mechanisms for altering long-term N dynamics in these ecosystems and highlight how multiple mechanisms can lead to similar effects on ecosystem function, which may be important for the construction of future biogeochemical process models.

Abiotic versus biotic controls on soil nitrogen cycling in drylands along a 3200 km transect

NASA Astrophysics Data System (ADS)

Liu, Dongwei; Zhu, Weixing; Wang, Xiaobo; Pan, Yuepeng; Wang, Chao; Xi, Dan; Bai, Edith; Wang, Yuesi; Han, Xingguo; Fang, Yunting

2017-03-01

Nitrogen (N) cycling in drylands under changing climate is not well understood. Our understanding of N cycling over larger scales to date relies heavily on the measurement of bulk soil N, and the information about internal soil N transformations remains limited. The 15N natural abundance (δ15N) of ammonium and nitrate can serve as a proxy record for the N processes in soils. To better understand the patterns and mechanisms of N cycling in drylands, we collected soils along a 3200 km transect at about 100 km intervals in northern China, with mean annual precipitation (MAP) ranging from 36 to 436 mm. We analyzed N pools and δ15N of ammonium, dual isotopes (15N and 18O) of nitrate, and the microbial gene abundance associated with soil N transformations. We found that N status and its driving factors were different above and below a MAP threshold of 100 mm. In the arid zone with MAP below 100 mm, soil inorganic N accumulated, with a large fraction being of atmospheric origin, and ammonia volatilization was strong in soils with high pH. In addition, the abundance of microbial genes associated with soil N transformations was low. In the semiarid zone with MAP above 100 mm, soil inorganic N concentrations were low and were controlled mainly by biological processes (e.g., plant uptake and denitrification). The preference for soil ammonium over nitrate by the dominant plant species may enhance the possibility of soil nitrate losses via denitrification. Overall, our study suggests that a shift from abiotic to biotic controls on soil N biogeochemistry under global climate changes would greatly affect N losses, soil N availability, and other N transformation processes in these drylands in China.

Beneficial effects of aluminum enrichment on nitrogen-fixing cyanobacteria in the South China Sea.

PubMed

Liu, Jiaxing; Zhou, Linbin; Ke, Zhixin; Li, Gang; Shi, Rongjun; Tan, Yehui

2018-04-01

Few studies focus on the effects of aluminum (Al) on marine nitrogen-fixing cyanobacteria, which play important roles in the ocean nitrogen cycling. To examine the effects of Al on the nitrogen-fixing cyanobacteria, bioassay experiments in the oligotrophic South China Sea (SCS) and culture of Crocosphaera watsonii in the laboratory were conducted. Field data showed that 200 nM Al stimulated the growth and the nitrogenase gene expression of Trichodesmium and unicellular diazotrophic cyanobacterium group A, and the nitrogen fixation rates of the whole community. Laboratory experiments demonstrated that Al stimulated the growth and nitrogen fixation of C. watsonii under phosphorus limited conditions. Both field and laboratory results indicated that Al could stimulate the growth of diazotrophs and nitrogen fixation in oligotrophic oceans such as the SCS, which is likely related to the utilization of phosphorus, implying that Al plays an important role in the ocean nitrogen and carbon cycles by influencing nitrogen fixation. Copyright © 2018 Elsevier Ltd. All rights reserved.

Terrestrial ecosystem process model Biome-BGCMuSo v4.0: summary of improvements and new modeling possibilities

NASA Astrophysics Data System (ADS)

Hidy, Dóra; Barcza, Zoltán; Marjanović, Hrvoje; Zorana Ostrogović Sever, Maša; Dobor, Laura; Gelybó, Györgyi; Fodor, Nándor; Pintér, Krisztina; Churkina, Galina; Running, Steven; Thornton, Peter; Bellocchi, Gianni; Haszpra, László; Horváth, Ferenc; Suyker, Andrew; Nagy, Zoltán

2016-12-01

The process-based biogeochemical model Biome-BGC was enhanced to improve its ability to simulate carbon, nitrogen, and water cycles of various terrestrial ecosystems under contrasting management activities. Biome-BGC version 4.1.1 was used as a base model. Improvements included addition of new modules such as the multilayer soil module, implementation of processes related to soil moisture and nitrogen balance, soil-moisture-related plant senescence, and phenological development. Vegetation management modules with annually varying options were also implemented to simulate management practices of grasslands (mowing, grazing), croplands (ploughing, fertilizer application, planting, harvesting), and forests (thinning). New carbon and nitrogen pools have been defined to simulate yield and soft stem development of herbaceous ecosystems. The model version containing all developments is referred to as Biome-BGCMuSo (Biome-BGC with multilayer soil module; in this paper, Biome-BGCMuSo v4.0 is documented). Case studies on a managed forest, cropland, and grassland are presented to demonstrate the effect of model developments on the simulation of plant growth as well as on carbon and water balance.

A dynamic nitrogen budget model of a Pacific Northwest salt ...

EPA Pesticide Factsheets

The role of salt marshes as either nitrogen sinks or sources in relation to their adjacent estuaries has been a focus of ecosystem service research for many decades. The complex hydrology of these systems is driven by tides, upland surface runoff, precipitation, evapotranspiration, and groundwater inputs, all of which can vary significantly on timescales ranging from sub-daily to seasonal. Additionally, many of these hydrologic drivers may vary with a changing climate. Due to this temporal variation in hydrology, it is difficult to represent salt marsh nitrogen budgets as steady-state models. A dynamic nitrogen budget model that varies based on hydrologic conditions may more accurately describe the role of salt marshes in nitrogen cycling. In this study we aim to develop a hydrologic model that is coupled with a process-based nitrogen model to simulate nitrogen dynamics at multiple temporal scales. To construct and validate our model we will use hydrologic and nitrogen species data collected from 2010 to present, from a 1.8 hectare salt marsh in the Yaquina Estuary, OR, USA. Hydrologic data include water table levels at two transects, upland tributary flow, tidal channel stage and flow, and vertical hydraulic head gradients. Nitrogen pool data include concentrations of nitrate and ammonium in porewater, tidal channel water, and extracted from soil cores. Nitrogen flux data include denitrification rates, nitrogen concentrations in upland runoff, and tida

Novel Metabolic Attributes of the Genus Cyanothece, Comprising a Group of Unicellular Nitrogen-Fixing Cyanobacteria

PubMed Central

Bandyopadhyay, Anindita; Elvitigala, Thanura; Welsh, Eric; Stöckel, Jana; Liberton, Michelle; Min, Hongtao; Sherman, Louis A.; Pakrasi, Himadri B.

2011-01-01

ABSTRACT The genus Cyanothece comprises unicellular cyanobacteria that are morphologically diverse and ecologically versatile. Studies over the last decade have established members of this genus to be important components of the marine ecosystem, contributing significantly to the nitrogen and carbon cycle. System-level studies of Cyanothece sp. ATCC 51142, a prototypic member of this group, revealed many interesting metabolic attributes. To identify the metabolic traits that define this class of cyanobacteria, five additional Cyanothece strains were sequenced to completion. The presence of a large, contiguous nitrogenase gene cluster and the ability to carry out aerobic nitrogen fixation distinguish Cyanothece as a genus of unicellular, aerobic nitrogen-fixing cyanobacteria. Cyanothece cells can create an anoxic intracellular environment at night, allowing oxygen-sensitive processes to take place in these oxygenic organisms. Large carbohydrate reserves accumulate in the cells during the day, ensuring sufficient energy for the processes that require the anoxic phase of the cells. Our study indicates that this genus maintains a plastic genome, incorporating new metabolic capabilities while simultaneously retaining archaic metabolic traits, a unique combination which provides the flexibility to adapt to various ecological and environmental conditions. Rearrangement of the nitrogenase cluster in Cyanothece sp. strain 7425 and the concomitant loss of its aerobic nitrogen-fixing ability suggest that a similar mechanism might have been at play in cyanobacterial strains that eventually lost their nitrogen-fixing ability. PMID:21972240

Curriculum Development of an inquiry lesson for grades 6-12 using real time core data from the JOIDES Resolution for analysis by students for the Cretaceous-Paleogene (K-Pg)

NASA Astrophysics Data System (ADS)

Cohen, E.

2013-12-01

The mass extinction event at the Cretaceous-Paleogene (K-Pg) boundary was the result of a bolide impact, and is popularly known for the extinction of the dinosaurs, but is also one of the largest Paleogene mass extinctions identified. In addition, it was followed by a period of drastic changes in ecological conditions, including a complete alteration of the global carbon cycle; the root cause of this change is still debated. Little information is known regarding changes in the nitrogen cycle during these periods of mass extinction and recovery. Given the importance of the nitrogen cycle to primary production and its relationship to the redox state of the local environment, determining changes in the nitrogen cycle will provide important information as to the processes of global mass extinction and the subsequent recovery. Data from the JOIDES Resolution is used to introduce students to authentic data analysis. Students are asked to analyze if standards are consistent, is there anomalous data, how are significant figures used, and how consistent is the method which then, in turn effects data collection. Students are provided data from one core sample and asked to represent the data using technology. Students use Infograms, a technology which not only includes graphs but also visuals and texts in order to represent information in a meaningful way. Students create correlation between the data of nitrogen isotopes, foraminifera, oxygen isotopes, age of the earth and depth of collections. The lesson aligned to standards for students' grade 6-12 were created to support the content surrounding: National Science Education Content Standards: Standard A: Science as Inquiry Standard D: Earth and Space Science Ocean Literacy Essential Principles: 3. The ocean is a major influence on weather and climate 7. The ocean is largely unexplored.

Plant traits related to nitrogen uptake influence plant-microbe competition.

PubMed

Moreau, Delphine; Pivato, Barbara; Bru, David; Busset, Hugues; Deau, Florence; Faivre, Céline; Matejicek, Annick; Strbik, Florence; Philippot, Laurent; Mougel, Christophe

2015-08-01

Plant species are important drivers of soil microbial communities. However, how plant functional traits are shaping these communities has received less attention though linking plant and microbial traits is crucial for better understanding plant-microbe interactions. Our objective was to determine how plant-microbe interactions were affected by plant traits. Specifically we analyzed how interactions between plant species and microbes involved in nitrogen cycling were affected by plant traits related to 'nitrogen nutrition in interaction with soil nitrogen availability. Eleven plant species, selected along an oligotrophic-nitrophilic gradient, were grown individually in a nitrogen-poor soil with two levels of nitrate availability. Plant traits for both carbon and nitrogen nutrition were measured and the genetic structure and abundance of rhizosphere. microbial communities, in particular the ammonia oxidizer and nitrate reducer guilds, were analyzed. The structure of the bacterial community in the rhizosphere differed significantly between plant species and these differences depended on nitrogen availability. The results suggest that the rate of nitrogen uptake per unit of root biomass and per day is a key plant trait, explaining why the effect of nitrogen availability on the structure of the bacterial community depends on the plant species. We also showed that the abundance of nitrate reducing bacteria always decreased with increasing nitrogen uptake per unit of root biomass per day, indicating that there was competition for nitrate between plants and nitrate reducing bacteria. This study demonstrates that nitrate-reducing microorganisms may be adversely affected by plants with a high nitrogen uptake rate. Our work puts forward the role of traits related to nitrogen in plant-microbe interactions, whereas carbon is commonly considered as the main driver. It also suggests that plant traits related to ecophysiological processes, such as nitrogen uptake rates, are more relevant for understanding plant-microbe interactions than composite traits, such as nitrophily, which are related to a number of ecophysiological processes.

Global scale analysis and evaluation of an improved mechanistic representation of plant nitrogen and carbon dynamics in the Community Land Model (CLM)

NASA Astrophysics Data System (ADS)

Ghimire, B.; Riley, W. J.; Koven, C. D.; Randerson, J. T.; Mu, M.; Kattge, J.; Rogers, A.; Reich, P. B.

2014-12-01

In many ecosystems, nitrogen is the most limiting nutrient for plant growth and productivity. However mechanistic representation of nitrogen uptake linked to root traits, and functional nitrogen allocation among different leaf enzymes involved in respiration and photosynthesis is currently lacking in Earth System models. The linkage between nitrogen availability and plant productivity is simplistically represented by potential photosynthesis rates, and is subsequently downregulated depending on nitrogen supply and other nitrogen consumers in the model (e.g., nitrification). This type of potential photosynthesis rate calculation is problematic for several reasons. Firstly, plants do not photosynthesize at potential rates and then downregulate. Secondly, there is considerable subjectivity on the meaning of potential photosynthesis rates. Thirdly, there exists lack of understanding on modeling these potential photosynthesis rates in a changing climate. In addition to model structural issues in representing photosynthesis rates, the role of plant roots in nutrient acquisition have been largely ignored in Earth System models. For example, in CLM4.5, nitrogen uptake is linked to leaf level processes (e.g., primarily productivity) rather than root scale process involved in nitrogen uptake. We present a new plant model for CLM with an improved mechanistic presentation of plant nitrogen uptake based on root scale Michaelis Menten kinetics, and stronger linkages between leaf nitrogen and plant productivity by inferring relationships observed in global databases of plant traits (including the TRY database and several individual studies). We also incorporate improved representation of plant nitrogen leaf allocation, especially in tropical regions where significant over-prediction of plant growth and productivity in CLM4.5 simulations exist. We evaluate our improved global model simulations using the International Land Model Benchmarking (ILAMB) framework. We conclude that mechanistic representation of leaf-level nitrogen allocation and a theoretically consistent treatment of competition with belowground consumers leads to overall improvements in CLM4.5's global carbon cycling predictions.

Rational design of metal nitride redox materials for solar-driven ammonia synthesis.

PubMed

Michalsky, Ronald; Pfromm, Peter H; Steinfeld, Aldo

2015-06-06

Fixed nitrogen is an essential chemical building block for plant and animal protein, which makes ammonia (NH3) a central component of synthetic fertilizer for the global production of food and biofuels. A global project on artificial photosynthesis may foster the development of production technologies for renewable NH3 fertilizer, hydrogen carrier and combustion fuel. This article presents an alternative path for the production of NH3 from nitrogen, water and solar energy. The process is based on a thermochemical redox cycle driven by concentrated solar process heat at 700-1200°C that yields NH3 via the oxidation of a metal nitride with water. The metal nitride is recycled via solar-driven reduction of the oxidized redox material with nitrogen at atmospheric pressure. We employ electronic structure theory for the rational high-throughput design of novel metal nitride redox materials and to show how transition-metal doping controls the formation and consumption of nitrogen vacancies in metal nitrides. We confirm experimentally that iron doping of manganese nitride increases the concentration of nitrogen vacancies compared with no doping. The experiments are rationalized through the average energy of the dopant d-states, a descriptor for the theory-based design of advanced metal nitride redox materials to produce sustainable solar thermochemical ammonia.

Rational design of metal nitride redox materials for solar-driven ammonia synthesis

PubMed Central

Michalsky, Ronald; Pfromm, Peter H.; Steinfeld, Aldo

2015-01-01

Fixed nitrogen is an essential chemical building block for plant and animal protein, which makes ammonia (NH3) a central component of synthetic fertilizer for the global production of food and biofuels. A global project on artificial photosynthesis may foster the development of production technologies for renewable NH3 fertilizer, hydrogen carrier and combustion fuel. This article presents an alternative path for the production of NH3 from nitrogen, water and solar energy. The process is based on a thermochemical redox cycle driven by concentrated solar process heat at 700–1200°C that yields NH3 via the oxidation of a metal nitride with water. The metal nitride is recycled via solar-driven reduction of the oxidized redox material with nitrogen at atmospheric pressure. We employ electronic structure theory for the rational high-throughput design of novel metal nitride redox materials and to show how transition-metal doping controls the formation and consumption of nitrogen vacancies in metal nitrides. We confirm experimentally that iron doping of manganese nitride increases the concentration of nitrogen vacancies compared with no doping. The experiments are rationalized through the average energy of the dopant d-states, a descriptor for the theory-based design of advanced metal nitride redox materials to produce sustainable solar thermochemical ammonia. PMID:26052421

Forest Soil Bacteria: Diversity, Involvement in Ecosystem Processes, and Response to Global Change

PubMed Central

Lladó, Salvador; López-Mondéjar, Rubén

2017-01-01

SUMMARY The ecology of forest soils is an important field of research due to the role of forests as carbon sinks. Consequently, a significant amount of information has been accumulated concerning their ecology, especially for temperate and boreal forests. Although most studies have focused on fungi, forest soil bacteria also play important roles in this environment. In forest soils, bacteria inhabit multiple habitats with specific properties, including bulk soil, rhizosphere, litter, and deadwood habitats, where their communities are shaped by nutrient availability and biotic interactions. Bacteria contribute to a range of essential soil processes involved in the cycling of carbon, nitrogen, and phosphorus. They take part in the decomposition of dead plant biomass and are highly important for the decomposition of dead fungal mycelia. In rhizospheres of forest trees, bacteria interact with plant roots and mycorrhizal fungi as commensalists or mycorrhiza helpers. Bacteria also mediate multiple critical steps in the nitrogen cycle, including N fixation. Bacterial communities in forest soils respond to the effects of global change, such as climate warming, increased levels of carbon dioxide, or anthropogenic nitrogen deposition. This response, however, often reflects the specificities of each studied forest ecosystem, and it is still impossible to fully incorporate bacteria into predictive models. The understanding of bacterial ecology in forest soils has advanced dramatically in recent years, but it is still incomplete. The exact extent of the contribution of bacteria to forest ecosystem processes will be recognized only in the future, when the activities of all soil community members are studied simultaneously. PMID:28404790

Forest Soil Bacteria: Diversity, Involvement in Ecosystem Processes, and Response to Global Change.

PubMed

Lladó, Salvador; López-Mondéjar, Rubén; Baldrian, Petr

2017-06-01

The ecology of forest soils is an important field of research due to the role of forests as carbon sinks. Consequently, a significant amount of information has been accumulated concerning their ecology, especially for temperate and boreal forests. Although most studies have focused on fungi, forest soil bacteria also play important roles in this environment. In forest soils, bacteria inhabit multiple habitats with specific properties, including bulk soil, rhizosphere, litter, and deadwood habitats, where their communities are shaped by nutrient availability and biotic interactions. Bacteria contribute to a range of essential soil processes involved in the cycling of carbon, nitrogen, and phosphorus. They take part in the decomposition of dead plant biomass and are highly important for the decomposition of dead fungal mycelia. In rhizospheres of forest trees, bacteria interact with plant roots and mycorrhizal fungi as commensalists or mycorrhiza helpers. Bacteria also mediate multiple critical steps in the nitrogen cycle, including N fixation. Bacterial communities in forest soils respond to the effects of global change, such as climate warming, increased levels of carbon dioxide, or anthropogenic nitrogen deposition. This response, however, often reflects the specificities of each studied forest ecosystem, and it is still impossible to fully incorporate bacteria into predictive models. The understanding of bacterial ecology in forest soils has advanced dramatically in recent years, but it is still incomplete. The exact extent of the contribution of bacteria to forest ecosystem processes will be recognized only in the future, when the activities of all soil community members are studied simultaneously. Copyright © 2017 American Society for Microbiology.

Responses of the terrestrial carbon cycle to drought: modeling sensitivities of the interactive nitrogen and dynamic vegetation

NASA Astrophysics Data System (ADS)

Jia, B.; Wang, Y.; Xie, Z.

2016-12-01

Drought can trigger both immediate and time-lagged responses of terrestrial ecosystems and even cause sizeable positive feedbacks to climate warming. In this study, the influences of interactive nitrogen (N) and dynamic vegetation (DV) on the response of the carbon cycle in terrestrial ecosystems of China to drought were investigated using the Community Land Model version 4.5 (CLM4.5). Model simulations from three configurations of CLM4.5 (C, carbon cycle only; CN, dynamic carbon and nitrogen cycle; CNDV, dynamic carbon and nitrogen cycle as well as dynamic vegetation) between 1961 and 2010 showed that the incorporation of a prognostic N cycle and DV into CLM4.5 reduce the predicted annual means and inter-annual variability of predicted gross primary production (GPP) and net ecosystem production (NEP), except for a slight increase in NEP for CNDV compared to CN. These model improvements resulted in better agreement with observations (7.0 PgC yr-1) of annual GPP over the terrestrial ecosystems in China for CLM45-CN (7.5 PgC yr-1) and CLM45-CNDV (7.3 PgC yr-1) than for CLM45-C (10.9 PgC yr-1). Compared to the CLM45-C, the carbon-nitrogen coupling strengthened the predicted response of GPP to drought, resulting in a higher correlation with the standardized precipitation index (SPI; rC = 0.62, rCN = 0.67), but led to a weaker sensitivity of NEP to SPI (rC = 0.51, rCN = 0.45). The CLM45-CNDV had the longest lagged responses of GPP to drought among the three configurations. These results enhance our understanding of the response of the terrestrial carbon cycle to drought.

Fabrication of Nitrogen-Doped Hollow Mesoporous Spherical Carbon Capsules for Supercapacitors.

PubMed

Chen, Aibing; Xia, Kechan; Zhang, Linsong; Yu, Yifeng; Li, Yuetong; Sun, Hexu; Wang, Yuying; Li, Yunqian; Li, Shuhui

2016-09-06

A novel "dissolution-capture" method for the fabrication of nitrogen-doped hollow mesoporous spherical carbon capsules (N-HMSCCs) with high capability for supercapacitor is developed. The fabrication process is performed by depositing mesoporous silica on the surface of the polyacrylonitrile nanospheres, followed by a dissolution-capture process occurring in the polyacrylonitrile core and silica shell. The polyacrylonitrile core is dissolved by dimethylformamide treatment to form a hollow cavity. Then, the polyacrylonitrile is captured into the mesochannel of silica. After carbonization and etching of silica, N-HMSCCs with uniform mesopore size are produced. The N-HMSCCs show a high specific capacitance of 206.0 F g(-1) at a current density of 1 A g(-1) in 6.0 M KOH due to its unique hollow nanostructure, high surface area, and nitrogen content. In addition, 92.3% of the capacitance of N-HMSCCs still remains after 3000 cycles at 5 A g(-1). The "dissolution-capture" method should give a useful enlightenment for the design of electrode materials for supercapacitor.

Ecosystem services altered by human changes in the nitrogen cycle: A new perspective for assessment

EPA Science Inventory

Human alteration of the nitrogen (N) cycle has produced benefits for health and well-being, but excess N has altered many ecosystems and degraded air and water quality. US regulations mandate protection of the environment in terms that directly connect to ecosystem services. Here...

Size-fraction partitioning of community gene transcription and nitrogen metabolism in a marine oxygen minimum zone.

PubMed

Ganesh, Sangita; Bristow, Laura A; Larsen, Morten; Sarode, Neha; Thamdrup, Bo; Stewart, Frank J

2015-12-01

The genetic composition of marine microbial communities varies at the microscale between particle-associated (PA; >1.6 μm) and free-living (FL; 0.2-1.6 μm) niches. It remains unclear, however, how metabolic activities differ between PA and FL fractions. We combined rate measurements with metatranscriptomics to quantify PA and FL microbial activity in the oxygen minimum zone (OMZ) of the Eastern Tropical North Pacific, focusing on dissimilatory processes of the nitrogen (N) cycle. Bacterial gene counts were 8- to 15-fold higher in the FL compared with the PA fraction. However, rates of all measured N cycle processes, excluding ammonia oxidation, declined significantly following particle (>1.6 μm) removal. Without particles, rates of nitrate reduction to nitrite (1.5-9.4nMNd(-1)) fell to zero and N2 production by denitrification (0.5-1.7nMNd(-1)) and anammox (0.3-1.9nMNd(-1)) declined by 53-85%. The proportional representation of major microbial taxa and N cycle gene transcripts in metatranscriptomes followed fraction-specific trends. Transcripts encoding nitrate reductase were uniform among PA and FL fractions, whereas anammox-associated transcripts were proportionately enriched up to 15-fold in the FL fraction. In contrast, transcripts encoding enzymes for N2O and N2 production by denitrification were enriched up to 28-fold in PA samples. These patterns suggest that the majority of N cycle activity, excluding N2O and N2 production by denitrification, is confined to a FL majority that is critically dependent on access to particles, likely as a source of organic carbon and inorganic N. Variable particle distributions may drive heterogeneity in N cycle activity and gene expression in OMZs.

Size-fraction partitioning of community gene transcription and nitrogen metabolism in a marine oxygen minimum zone

PubMed Central

Ganesh, Sangita; Bristow, Laura A; Larsen, Morten; Sarode, Neha; Thamdrup, Bo; Stewart, Frank J

2015-01-01

The genetic composition of marine microbial communities varies at the microscale between particle-associated (PA; >1.6 μm) and free-living (FL; 0.2–1.6 μm) niches. It remains unclear, however, how metabolic activities differ between PA and FL fractions. We combined rate measurements with metatranscriptomics to quantify PA and FL microbial activity in the oxygen minimum zone (OMZ) of the Eastern Tropical North Pacific, focusing on dissimilatory processes of the nitrogen (N) cycle. Bacterial gene counts were 8- to 15-fold higher in the FL compared with the PA fraction. However, rates of all measured N cycle processes, excluding ammonia oxidation, declined significantly following particle (>1.6 μm) removal. Without particles, rates of nitrate reduction to nitrite (1.5–9.4nMNd−1) fell to zero and N2 production by denitrification (0.5–1.7nMNd−1) and anammox (0.3–1.9nMNd−1) declined by 53–85%. The proportional representation of major microbial taxa and N cycle gene transcripts in metatranscriptomes followed fraction-specific trends. Transcripts encoding nitrate reductase were uniform among PA and FL fractions, whereas anammox-associated transcripts were proportionately enriched up to 15-fold in the FL fraction. In contrast, transcripts encoding enzymes for N2O and N2 production by denitrification were enriched up to 28-fold in PA samples. These patterns suggest that the majority of N cycle activity, excluding N2O and N2 production by denitrification, is confined to a FL majority that is critically dependent on access to particles, likely as a source of organic carbon and inorganic N. Variable particle distributions may drive heterogeneity in N cycle activity and gene expression in OMZs. PMID:25848875

Biochar decelerates soil organic nitrogen cycling but stimulates soil nitrification in a temperate arable field trial.

PubMed

Prommer, Judith; Wanek, Wolfgang; Hofhansl, Florian; Trojan, Daniela; Offre, Pierre; Urich, Tim; Schleper, Christa; Sassmann, Stefan; Kitzler, Barbara; Soja, Gerhard; Hood-Nowotny, Rebecca Clare

2014-01-01

Biochar production and subsequent soil incorporation could provide carbon farming solutions to global climate change and escalating food demand. There is evidence that biochar amendment causes fundamental changes in soil nutrient cycles, often resulting in marked increases in crop production, particularly in acidic and in infertile soils with low soil organic matter contents, although comparable outcomes in temperate soils are variable. We offer insight into the mechanisms underlying these findings by focusing attention on the soil nitrogen (N) cycle, specifically on hitherto unmeasured processes of organic N cycling in arable soils. We here investigated the impacts of biochar addition on soil organic and inorganic N pools and on gross transformation rates of both pools in a biochar field trial on arable land (Chernozem) in Traismauer, Lower Austria. We found that biochar increased total soil organic carbon but decreased the extractable organic C pool and soil nitrate. While gross rates of organic N transformation processes were reduced by 50-80%, gross N mineralization of organic N was not affected. In contrast, biochar promoted soil ammonia-oxidizer populations (bacterial and archaeal nitrifiers) and accelerated gross nitrification rates more than two-fold. Our findings indicate a de-coupling of the soil organic and inorganic N cycles, with a build-up of organic N, and deceleration of inorganic N release from this pool. The results therefore suggest that addition of inorganic fertilizer-N in combination with biochar could compensate for the reduction in organic N mineralization, with plants and microbes drawing on fertilizer-N for growth, in turn fuelling the belowground build-up of organic N. We conclude that combined addition of biochar with fertilizer-N may increase soil organic N in turn enhancing soil carbon sequestration and thereby could play a fundamental role in future soil management strategies.

Encapsulating micro-nano Si/SiO x into conjugated nitrogen-doped carbon as binder-free monolithic anodes for advanced lithium ion batteries

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Jing; Zhou, Meijuan; Tan, Guoqiang

2015-01-01

Silicon monoxide, a promising silicon-based anode candidate for lithium-ion batteries, has recently attracted much attention for its high theoretical capacity, good cycle stability, low cost, and environmental benignity. Currently, the most critical challenge is to improve its low initial coulombic efficiency and significant volume changes during the charge–discharge processes. Herein, we report a binder-free monolithic electrode structure based on directly encapsulating micro-nano Si/SiOx particles into conjugated nitrogen-doped carbon frameworks to form monolithic, multi-core, cross-linking composite matrices. We utilize micro-nano Si/SiOx reduced by high-energy ball-milling SiO as active materials, and conjugated nitrogen-doped carbon formed by the pyrolysis of polyacrylonitrile both asmore » binders and conductive agents. Owing to the high electrochemical activity of Si/SiOx and the good mechanical resiliency of conjugated nitrogen-doped carbon backbones, this specific composite structure enhances the utilization efficiency of SiO and accommodates its large volume expansion, as well as its good ionic and electronic conductivity. The annealed Si/SiOx/polyacrylonitrile composite electrode exhibits excellent electrochemical properties, including a high initial reversible capacity (2734 mA h g-1 with 75% coulombic efficiency), stable cycle performance (988 mA h g-1 after 100 cycles), and good rate capability (800 mA h g-1 at 1 A g-1 rate). Because the composite is naturally abundant and shows such excellent electrochemical performance, it is a promising anode candidate material for lithium-ion batteries. The binder-free monolithic architectural design also provides an effective way to prepare other monolithic electrode materials for advanced lithium-ion batteries.« less

Carbon associated nitrate (CAN) in the Ediacaran Johnnie Formation, Death Valley, California and links to the Shuram negative carbon isotope excursion

NASA Astrophysics Data System (ADS)

Dilles, Z. Y. G.; Prokopenko, M. G.; Bergmann, K.; Loyd, S. J.; Corsetti, F. A.; Berelson, W.; Gaines, R. R.

2014-12-01

Nitrogen, a major nutrient of marine primary production whose many redox states are linked through biological processes to O2, may afford better understanding of changes in post-Great Oxidation Event (GOE) environmental redox conditions. Using a novel approach to quantify nitrate content in carbonates, we identified a trend of CAN increase in the late-Proterozoic, including several distinct peaks within a carbonate succession of the Sonora province, Mexico, deposited ~630-500 Ma. The goal of the current study was to investigate CAN variability in the context of the global "Shuram" event, a large negative δ13C excursion expressed in Rainstorm member carbonates of the Johnnie Formation in Death Valley, CA. The lower Rainstorm Member "Johnnie Oolite", a time-transgressive, regionally extensive, shallow dolomitic oolite, was sampled. CAN concentrations ranged from 7.31 to 127.36 nmol/g, with higher values measured toward the base of the bed. This trend held at each sampled locality, along with a tendency towards decreasing CAN with larger magnitude negative δ13C excursions. Modern analog ooids formed in low-latitude marine environments lack CAN, consistent with their formation in low-nitrate waters of the euphotic zone characteristic of the modern ocean nitrogen cycling. In contrast, maximum values within the Johnnie oolite exceed by a factor of five to seven CAN measured in carbonates deposited below the main nitracline in the modern ocean, implying high nitrate content within shallow depositional environments. Johnnie oolite data, broadly consistent with the Sonora sequence findings, may indicate large perturbations in the Ediacaran nitrogen cycle immediately preceding the negative δ13C excursion. The implication of these findings for possible changes in the Ediacaran nitrogen, oxygen and carbon biogeochemical cycling will be further discussed.

Spatial and Temporal Patterns of Nitrification Rates in Forested Floodplain Wetland Soils of Upper Mississippi River Pool 8, Journal Article

EPA Science Inventory

Overbank flooding is thought to be a critical process controlling nitrogen retention and cycling. In this study we investigated the effects of season and flood frequency on soil nitrification rates at ten sites in forested floodplains of Upper Mississippi River, Pool 8...A rough ...

Integrating a process-based ecosystem model with Landsat imagery to assess impacts of forest disturbance on terrestrial carbon dynamics: Case studies in Alabama and Mississippi

USDA-ARS?s Scientific Manuscript database

Forest ecosystems in the southern United States are dramatically altered by three major 26 disturbances: timber harvesting, hurricane, and permanent land conversion. Understanding and quantifying effects of disturbance on forest carbon, nitrogen, and water cycles is critical for sustainable forest m...

Oxygen at Nanomolar Levels Reversibly Suppresses Process Rates and Gene Expression in Anammox and Denitrification in the Oxygen Minimum Zone off Northern Chile

PubMed Central

Stewart, Frank J.; Thamdrup, Bo; De Brabandere, Loreto; Revsbech, Niels Peter; Ulloa, Osvaldo; Canfield, Don E.; DeLong, Edward F.

2014-01-01

ABSTRACT A major percentage (20 to 40%) of global marine fixed-nitrogen loss occurs in oxygen minimum zones (OMZs). Concentrations of O2 and the sensitivity of the anaerobic N2-producing processes of anammox and denitrification determine where this loss occurs. We studied experimentally how O2 at nanomolar levels affects anammox and denitrification rates and the transcription of nitrogen cycle genes in the anoxic OMZ off Chile. Rates of anammox and denitrification were reversibly suppressed, most likely at the enzyme level. Fifty percent inhibition of N2 and N2O production by denitrification was achieved at 205 and 297 nM O2, respectively, whereas anammox was 50% inhibited at 886 nM O2. Coupled metatranscriptomic analysis revealed that transcripts encoding nitrous oxide reductase (nosZ), nitrite reductase (nirS), and nitric oxide reductase (norB) decreased in relative abundance above 200 nM O2. This O2 concentration did not suppress the transcription of other dissimilatory nitrogen cycle genes, including nitrate reductase (narG), hydrazine oxidoreductase (hzo), and nitrite reductase (nirK). However, taxonomic characterization of transcripts suggested inhibition of narG transcription in gammaproteobacteria, whereas the transcription of anammox narG, whose gene product is likely used to oxidatively replenish electrons for carbon fixation, was not inhibited. The taxonomic composition of transcripts differed among denitrification enzymes, suggesting that distinct groups of microorganisms mediate different steps of denitrification. Sulfide addition (1 µM) did not affect anammox or O2 inhibition kinetics but strongly stimulated N2O production by denitrification. These results identify new O2 thresholds for delimiting marine nitrogen loss and highlight the utility of integrating biogeochemical and metatranscriptomic analyses. PMID:25352619

Global declines in oceanic nitrification rates as a consequence of ocean acidification

PubMed Central

Beman, J. Michael; Chow, Cheryl-Emiliane; King, Andrew L.; Feng, Yuanyuan; Fuhrman, Jed A.; Andersson, Andreas; Bates, Nicholas R.; Popp, Brian N.; Hutchins, David A.

2011-01-01

Ocean acidification produced by dissolution of anthropogenic carbon dioxide (CO2) emissions in seawater has profound consequences for marine ecology and biogeochemistry. The oceans have absorbed one-third of CO2 emissions over the past two centuries, altering ocean chemistry, reducing seawater pH, and affecting marine animals and phytoplankton in multiple ways. Microbially mediated ocean biogeochemical processes will be pivotal in determining how the earth system responds to global environmental change; however, how they may be altered by ocean acidification is largely unknown. We show here that microbial nitrification rates decreased in every instance when pH was experimentally reduced (by 0.05–0.14) at multiple locations in the Atlantic and Pacific Oceans. Nitrification is a central process in the nitrogen cycle that produces both the greenhouse gas nitrous oxide and oxidized forms of nitrogen used by phytoplankton and other microorganisms in the sea; at the Bermuda Atlantic Time Series and Hawaii Ocean Time-series sites, experimental acidification decreased ammonia oxidation rates by 38% and 36%. Ammonia oxidation rates were also strongly and inversely correlated with pH along a gradient produced in the oligotrophic Sargasso Sea (r2 = 0.87, P < 0.05). Across all experiments, rates declined by 8–38% in low pH treatments, and the greatest absolute decrease occurred where rates were highest off the California coast. Collectively our results suggest that ocean acidification could reduce nitrification rates by 3–44% within the next few decades, affecting oceanic nitrous oxide production, reducing supplies of oxidized nitrogen in the upper layers of the ocean, and fundamentally altering nitrogen cycling in the sea. PMID:21173255

Available nitrogen is the key factor influencing soil microbial functional gene diversity in tropical rainforest.

PubMed

Cong, Jing; Liu, Xueduan; Lu, Hui; Xu, Han; Li, Yide; Deng, Ye; Li, Diqiang; Zhang, Yuguang

2015-08-20

Tropical rainforests cover over 50% of all known plant and animal species and provide a variety of key resources and ecosystem services to humans, largely mediated by metabolic activities of soil microbial communities. A deep analysis of soil microbial communities and their roles in ecological processes would improve our understanding on biogeochemical elemental cycles. However, soil microbial functional gene diversity in tropical rainforests and causative factors remain unclear. GeoChip, contained almost all of the key functional genes related to biogeochemical cycles, could be used as a specific and sensitive tool for studying microbial gene diversity and metabolic potential. In this study, soil microbial functional gene diversity in tropical rainforest was analyzed by using GeoChip technology. Gene categories detected in the tropical rainforest soils were related to different biogeochemical processes, such as carbon (C), nitrogen (N) and phosphorus (P) cycling. The relative abundance of genes related to C and P cycling detected mostly derived from the cultured bacteria. C degradation gene categories for substrates ranging from labile C to recalcitrant C were all detected, and gene abundances involved in many recalcitrant C degradation gene categories were significantly (P < 0.05) different among three sampling sites. The relative abundance of genes related to N cycling detected was significantly (P < 0.05) different, mostly derived from the uncultured bacteria. The gene categories related to ammonification had a high relative abundance. Both canonical correspondence analysis and multivariate regression tree analysis showed that soil available N was the most correlated with soil microbial functional gene structure. Overall high microbial functional gene diversity and different soil microbial metabolic potential for different biogeochemical processes were considered to exist in tropical rainforest. Soil available N could be the key factor in shaping the soil microbial functional gene structure and metabolic potential.

Controls of nitrogen cycling evaluated along a well-characterized climate gradient.

PubMed

von Sperber, Christian; Chadwick, Oliver A; Casciotti, Karen L; Peay, Kabir G; Francis, Christopher A; Kim, Amy E; Vitousek, Peter M

2017-04-01

The supply of nitrogen (N) constrains primary productivity in many ecosystems, raising the question "what controls the availability and cycling of N"? As a step toward answering this question, we evaluated N cycling processes and aspects of their regulation on a climate gradient on Kohala Volcano, Hawaii, USA. The gradient extends from sites receiving <300 mm/yr of rain to those receiving >3,000 mm/yr, and the pedology and dynamics of rock-derived nutrients in soils on the gradient are well understood. In particular, there is a soil process domain at intermediate rainfall within which ongoing weathering and biological uplift have enriched total and available pools of rock-derived nutrients substantially; sites at higher rainfall than this domain are acid and infertile as a consequence of depletion of rock-derived nutrients, while sites at lower rainfall are unproductive and subject to wind erosion. We found elevated rates of potential net N mineralization in the domain where rock-derived nutrients are enriched. Higher-rainfall sites have low rates of potential net N mineralization and high rates of microbial N immobilization, despite relatively high rates of gross N mineralization. Lower-rainfall sites have moderately low potential net N mineralization, relatively low rates of gross N mineralization, and rates of microbial N immobilization sufficient to sequester almost all the mineral N produced. Bulk soil δ 15 N also varied along the gradient, from +4‰ at high rainfall sites to +14‰ at low rainfall sites, indicating differences in the sources and dynamics of soil N. Our analysis shows that there is a strong association between N cycling and soil process domains that are defined using soil characteristics independent of N along this gradient, and that short-term controls of N cycling can be understood in terms of the supply of and demand for N. © 2017 by the Ecological Society of America.

[Research progress on the mechanisms and influence factors of nitrogen retention and transformation in riparian ecosystems.

PubMed

Yang, Dan; Fan, Da Yong; Xie, Zong Qiang; Zhang, Ai Ying; Xiong, Gao Ming; Zhao, Chang Ming; Xu, Wen Ting

2016-03-01

Riparian zone, the ecological transition buffer between terrestrial and aquatic ecosystems (rivers, lakes, reservoirs, wetlands, and other specific water bodies) with unique eco-hydrological and biogeochemical processes, is the last ecological barrier to prevent ammonium, nitrate and other non-point nitrogen pollutants from adjacent water bodies. Based on a summary of current progress of related studies, we found there were two major mechanisms underpinning the nitrogen retention/removal by the riparian ecosystems: 1) the relative locations of nitrogen in the soil-plant-atmosphere continuum system could be altered by riparian vegetation; 2) nitrogen could also be denitrified and then removed permanently by microorganisms in riparian soil. However, which process is more critical for the nitrogen removal remains elusive. Due to large variances of hydro-dynamic, vegetation, microbial, and soil substrate properties in nitrogen retention and transformation with various watersheds, it's difficult to identify which factor is the most important one driving nitrogen cycle in the riparian ecosystems. It is also found that the limitation of study methods, paucity of data at large spatial and temporal scale, and no consensus on the riparian width, are the three major reasons leading to large variances of the results among studies. In conclusion, it is suggested that further efforts should be focused on: 1) the detailed analysis on the successive environmental factors with long-term; 2) the application of a comprehensive method combining mathematical models, geographic information system, remote sensing and quantified technique (such as the coupled technique of the isotopic tracer and gas exchange measurement); 3) the implementation of studies at large temporal and spatial scales. It is sure that, these efforts can help to optimize the nitrogen removal pathways in the riparian ecosystems and provide scientific basis for ecosystem management.

A chronology of human understanding of the nitrogen cycle†

PubMed Central

Galloway, James N.; Leach, Allison M.; Bleeker, Albert; Erisman, Jan Willem

2013-01-01

Nitrogen over the ages! It was discovered in the eighteenth century. The following century, its importance in agriculture was documented and the basic components of its cycle were elucidated. In the twentieth century, a process to provide an inexhaustible supply of reactive N (Nr; all N species except N2) for agricultural, industrial and military uses was invented. This discovery and the extensive burning of fossil fuels meant that by the beginning of the twenty-first century, anthropogenic sources of newly created Nr were two to three times that of natural terrestrial sources. This caused a fundamental change in the nitrogen cycle; for the first time, there was the potential for enough food to sustain growing populations and changing dietary patterns. However, most Nr created by humans is lost to the environment, resulting in a cascade of negative earth systems impacts—including enhanced acid rain, smog, eutrophication, greenhouse effect and stratospheric ozone depletion, with associated impacts on human and ecosystem health. The impacts continue and will be magnified, as Nr is lost to the environment at an even greater rate. Thus, the challenge for the current century is how to optimize the uses of N while minimizing the negative impacts. PMID:23713118

Volcanism and the atmosphere: the potential role of the atmosphere in unlocking the reactivity of volcanic emissions.

PubMed

Mather, Tamsin A

2008-12-28

Recent measurements of reactive trace gas species in volcanic plumes have offered intriguing hints at the chemistry occurring in the hot environment at volcanic vents. This has led to the recognition that volcanic vents should be regarded not only as passive sources of volcanic gases to the atmosphere, but also as 'reaction vessels' that unlock otherwise inert volcanic and atmospheric gas species. The atypical conditions created by the mixing of ambient atmosphere with the hot gases emitted from magma give rise to elevated concentrations of otherwise unexpected chemical compounds. Rapid cooling of this mixture allows these species to persist into the environment, with important consequences for gas plume chemistry and impacts. This paper discusses some examples of the implications of these high-temperature interactions in terms of nitrogen, halogen and sulphur chemistry, and their consequences in terms of the global fixed nitrogen budget, volcanically induced ozone destruction and particle fluxes to the atmosphere. Volcanically initiated atmospheric chemistry was likely to have been particularly important before biological (and latterly anthropogenic) processes started to dominate many geochemical cycles, with important consequences in terms of the evolution of the nitrogen cycle and the role of particles in modulating the Earth's climate.

Short-term effects of tidal flooding on soil nitrogen mineralization in a Chinese tidal salt marsh

NASA Astrophysics Data System (ADS)

Gao, Haifeng; Bai, Junhong; Deng, Xiaoya; Lu, Qiongqiong; Ye, Xiaofei

2018-02-01

Tidal flooding is an important control of nitrogen biogeochemistry in wetland ecosystems of Yellow River Delta, China. Variations in hydrology could change soil redox dynamics and conditions for microorganisms living. A tidal simulation experiment was designed to extract tidal flooding effect on nitrogen mineralization of salt marsh soil. Inorganic nitrogen and relevant enzyme were measured during the 20-day incubation period. Considering the variation of both inorganic N and enzymes, nitrogen mineralization process in tidal salt marsh could be divided into 2 phases of short term response and longtime adaption by around 12th incubation day as the inflection point. Soil ammonium nitrogen (NH4+-N) and volatilized ammonia (NH3) occupied the mineralization process since nitrate nitrogen (NO3--N) was not detected over whole incubation period. NH4+-N varied fluctuant and increased significantly after 12 day's incubation. Released NH3 reached to peak value of 14.24 mg m-2 d-1 at the inflection point and declined thereafter. Inorganic nitrogen released according to net nitrogen mineralization rate (RM) under the tidal flooding condition without plant uptake except first 2 days. However, during the transitional period of 6-12 days, RM decreased notably to almost 0 and increased again after inflection point with the value of 0.182 mg kg-1 d-1. It might be due to the change of microbial composition and function when soil shifted from oxic to anoxic, which were reflected by arylamidase, urease and fluorescein diacetate. Fluorescein diacetate hydrolysis and arylamidase had the similar variation of U style with decreasing activities before 12 days' incubation. All the enzymes measured in this experiment increased after inflection point. Whereas, urease activity kept constant from 2 to 12 days. Alternant oxidation reduction condition would increase N loss through denitrification and ammonia volatilization during the transitional period, while more inorganic nitrogen would be available in reductive environment of long-term tidal flooding. Therefore, hydrological process regulation has great influence on nitrogen cycling and further influence on wetland productivity.

In Situ One-Step Synthesis of Hierarchical Nitrogen-Doped Porous Carbon for High Performance Supercapacitors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jeon, Ju Won; Sharma, Ronish; Meduri, Praveen

2014-04-30

Electrochemical performance of the existing state-of-the art capacitors is not very high, key scientific barrier is that its charge storage mechanism wholly depends on adsorption of electrolyte on electrode. We present a novel method for the synthesis of nitrogen -doped porous carbons and address the drawback by precisely controlling composition and surface area. Nitrogen-doped porous carbon was synthesized using a self-sacrificial template technique without any additional nitrogen and carbon sources. They exhibited exceptionally high capacitance (239 Fg-1) due to additional pseudocapacitance originating from doped nitrogen. Cycling tests showed no obvious capacitance decay even after 10,000 cycles, which meets the requirementmore » of commercial supercapacitors. Our method is simple and highly efficient for the production of large quantities of nitrogen-doped porous carbons.« less

Mechanical properties of a nitrogen-bearing austenitic steel during static and cycle deformation

NASA Astrophysics Data System (ADS)

Blinov, E. V.; Terent'ev, V. F.; Prosvirnin, D. V.

2016-09-01

The mechanical properties of a nitrogen-bearing corrosion-resistant austenitic steel containing 0.311% nitrogen have been studied during static and cyclic deformation. It is found that the steel having an ultimate strength of 930 MPa exhibits a plasticity of 33%. The endurance limit under repeated tension at 106 loading cycles is 400 MPa. The propagation of a fatigue crack at low and high amplitudes of cyclic deformation follows a ductile fracture mechanism with the presence of fatigue grooves.

Distribution of iron, copper and manganese in the Arabian Sea

NASA Astrophysics Data System (ADS)

Moffett, James

2014-05-01

The distribution of iron, copper and manganese was studied on a zonal transect of the Arabian Sea during the SW monsoon in 2007. The distribution of metals in the eastern and western ends of the transect are completely different, with concentrations of Fe and Mn higher in the east, but copper much higher in the west. Redox cycling in the east, and enhanced ventilation in the west contributes to these processes. It seems likely that blooms of Phaeocystis sp. contribute to the pronounced surface depletion and oxicline regeneration we observe, particularly for copper. The results are very different than similar surveys in the Peru upwelling, indicating controls by very different processes. These results have important implications for carbon and nitrogen cycling, particularly for processes mediated by key Cu and Fe metalloenzymes.

Long-Term Cultivation and Metagenomics Reveal Ecophysiology of Previously Uncultivated Thermophiles Involved in Biogeochemical Nitrogen Cycle

PubMed Central

Kato, Shingo; Sakai, Sanae; Hirai, Miho; Tasumi, Eiji; Nishizawa, Manabu; Suzuki, Katsuhiko; Takai, Ken

2018-01-01

Many thermophiles thriving in a natural high-temperature environment remain uncultivated, and their ecophysiological functions in the biogeochemical cycle remain unclear. In the present study, we performed long-term continuous cultivation at 65°C and 70°C using a microbial mat sample, collected from a subsurface geothermal stream, as the inoculum, and reconstructed the whole genome of the maintained populations using metagenomics. Some metagenome-assembled genomes (MAGs), affiliated into phylum-level bacterial and archaeal clades without cultivated representatives, contained genes involved in nitrogen metabolism including nitrification and denitrification. Our results show genetic components and their potential interactions for the biogeochemical nitrogen cycle in a subsurface geothermal environment. PMID:29459499

Capturing interactions between nitrogen and hydrological cycles under historical climate and land use: Susquehanna watershed analysis with the GFDL land model LM3-TAN

USGS Publications Warehouse

Lee, M.; Malyshev, S.; Shevliakova, E.; Milly, Paul C. D.; Jaffé, P. R.

2014-01-01

We developed a process model LM3-TAN to assess the combined effects of direct human influences and climate change on terrestrial and aquatic nitrogen (TAN) cycling. The model was developed by expanding NOAA's Geophysical Fluid Dynamics Laboratory land model LM3V-N of coupled terrestrial carbon and nitrogen (C-N) cycling and including new N cycling processes and inputs such as a soil denitrification, point N sources to streams (i.e., sewage), and stream transport and microbial processes. Because the model integrates ecological, hydrological, and biogeochemical processes, it captures key controls of the transport and fate of N in the vegetation–soil–river system in a comprehensive and consistent framework which is responsive to climatic variations and land-use changes. We applied the model at 1/8° resolution for a study of the Susquehanna River Basin. We simulated with LM3-TAN stream dissolved organic-N, ammonium-N, and nitrate-N loads throughout the river network, and we evaluated the modeled loads for 1986–2005 using data from 16 monitoring stations as well as a reported budget for the entire basin. By accounting for interannual hydrologic variability, the model was able to capture interannual variations of stream N loadings. While the model was calibrated with the stream N loads only at the last downstream Susquehanna River Basin Commission station Marietta (40°02' N, 76°32' W), it captured the N loads well at multiple locations within the basin with different climate regimes, land-use types, and associated N sources and transformations in the sub-basins. Furthermore, the calculated and previously reported N budgets agreed well at the level of the whole Susquehanna watershed. Here we illustrate how point and non-point N sources contributing to the various ecosystems are stored, lost, and exported via the river. Local analysis of six sub-basins showed combined effects of land use and climate on soil denitrification rates, with the highest rates in the Lower Susquehanna Sub-Basin (extensive agriculture; Atlantic coastal climate) and the lowest rates in the West Branch Susquehanna Sub-Basin (mostly forest; Great Lakes and Midwest climate). In the re-growing secondary forests, most of the N from non-point sources was stored in the vegetation and soil, but in the agricultural lands most N inputs were removed by soil denitrification, indicating that anthropogenic N applications could drive substantial increase of N2O emission, an intermediate of the denitrification process.

'Trophic' and 'source' amino acids in trophic estimation: a likely metabolic explanation.

PubMed

O'Connell, T C

2017-06-01

Amino acid nitrogen isotopic analysis is a relatively new method for estimating trophic position. It uses the isotopic difference between an individual's 'trophic' and 'source' amino acids to determine its trophic position. So far, there is no accepted explanation for the mechanism by which the isotopic signals in 'trophic' and 'source' amino acids arise. Yet without a metabolic understanding, the utility of nitrogen isotopic analyses as a method for probing trophic relations, at either bulk tissue or amino acid level, is limited. I draw on isotopic tracer studies of protein metabolism, together with a consideration of amino acid metabolic pathways, to suggest that the 'trophic'/'source' groupings have a fundamental metabolic origin, to do with the cycling of amino-nitrogen between amino acids. 'Trophic' amino acids are those whose amino-nitrogens are interchangeable, part of a metabolic amino-nitrogen pool, and 'source' amino acids are those whose amino-nitrogens are not interchangeable with the metabolic pool. Nitrogen isotopic values of 'trophic' amino acids will reflect an averaged isotopic signal of all such dietary amino acids, offset by the integrated effect of isotopic fractionation from nitrogen cycling, and modulated by metabolic and physiological effects. Isotopic values of 'source' amino acids will be more closely linked to those of equivalent dietary amino acids, but also modulated by metabolism and physiology. The complexity of nitrogen cycling suggests that a single identifiable value for 'trophic discrimination factors' is unlikely to exist. Greater consideration of physiology and metabolism should help in better understanding observed patterns in nitrogen isotopic values.

A graphene barristor using nitrogen profile controlled ZnO Schottky contacts.

PubMed

Hwang, Hyeon Jun; Chang, Kyoung Eun; Yoo, Won Beom; Shim, Chang Hoo; Lee, Sang Kyung; Yang, Jin Ho; Kim, So-Young; Lee, Yongsu; Cho, Chunhum; Lee, Byoung Hun

2017-02-16

We have successfully demonstrated a graphene-ZnO:N Schottky barristor. The barrier height between graphene and ZnO:N could be modulated by a buried gate electrode in the range of 0.5-0.73 eV, and an on-off ratio of up to 10 7 was achieved. By using a nitrogen-doped ZnO film as a Schottky contact material, the stability problem of previously reported graphene barristors could be greatly alleviated and a facile route to build a top-down processed graphene barristor was realized with a very low heat cycle. This device will be instrumental when implementing logic functions in systems requiring high-performance logic devices fabricated with a low temperature fabrication process such as back-end integrated logic devices or flexible devices on soft substrates.

Nitrogen-doped carbon spheres: A new high-energy-density and long-life pseudo-capacitive electrode material for electrochemical flow capacitor.

PubMed

Hou, Shujin; Wang, Miao; Xu, Xingtao; Li, Yandong; Li, Yanjiang; Lu, Ting; Pan, Likun

2017-04-01

One of the most challenging issues in developing electrochemical flow capacitor (EFC) technology is the design and synthesis of active electrode materials with high energy density and long cycle life. However, in practical cases, the energy density and cycle ability obtained currently cannot meet the practical need. In this work, we propose a new active material, nitrogen-doped carbon spheres (NCSs), as flowable electrodes for EFC application. The NCSs were prepared via one-pot hydrothermal synthesis in the presence of resorcinol/formaldehyde as carbon precursors and melamine as nitrogen precursor, followed by carbonization in nitrogen flow at various temperatures. The results of EFC experiments demonstrate that NCSs obtained at 800°C exhibit a high energy density of 13.5Whkg -1 and an excellent cycle ability, indicating the superiority of NCSs for EFC application. Copyright © 2016 Elsevier Inc. All rights reserved.

Microbial Metagenomics Reveals Climate-Relevant Subsurface Biogeochemical Processes.

PubMed

Long, Philip E; Williams, Kenneth H; Hubbard, Susan S; Banfield, Jillian F

2016-08-01

Microorganisms play key roles in terrestrial system processes, including the turnover of natural organic carbon, such as leaf litter and woody debris that accumulate in soils and subsurface sediments. What has emerged from a series of recent DNA sequencing-based studies is recognition of the enormous variety of little known and previously unknown microorganisms that mediate recycling of these vast stores of buried carbon in subsoil compartments of the terrestrial system. More importantly, the genome resolution achieved in these studies has enabled association of specific members of these microbial communities with carbon compound transformations and other linked biogeochemical processes-such as the nitrogen cycle-that can impact the quality of groundwater, surface water, and atmospheric trace gas concentrations. The emerging view also emphasizes the importance of organism interactions through exchange of metabolic byproducts (e.g., within the carbon, nitrogen, and sulfur cycles) and via symbioses since many novel organisms exhibit restricted metabolic capabilities and an associated extremely small cell size. New, genome-resolved information reshapes our view of subsurface microbial communities and provides critical new inputs for advanced reactive transport models. These inputs are needed for accurate prediction of feedbacks in watershed biogeochemical functioning and their influence on the climate via the fluxes of greenhouse gases, CO2, CH4, and N2O. Copyright © 2016 Elsevier Ltd. All rights reserved.

Effects of Land Use Change on C-N cycling: Microbes Matter.

NASA Astrophysics Data System (ADS)

Hofmockel, K.

2012-12-01

Large swaths of the terrestrial landscape have been altered by human actions on Earth's biophysical systems, resulting in the homogenization of Earth's biota, while simultaneously increasing greenhouse gases and reactive nitrogen (N). This is especially poignant in grasslands that have been largely replaced by managed agricultural systems with substantial N inputs, or by unmanaged grasslands that are dominated by exotic species. Impacted ecosystems may be important for global C models, because they comprise a major portion of the global land area, terrestrial NPP and the world's soil C stocks. This research investigates how anthropogenic changes in plant community composition and agricultural management systems influence the composition and function of microbial communities that mediate key aspects of belowground C and N cycling and storage. Data from agroecology and grassland climate change experiments are used to illustrate how microbial responses can have important implications for large scale coupling of C and N cycles. In this study exotic plant species significantly decreased root inputs, causing shifts in microbial community composition, including both specific taxa and functional guilds of bacteria. By contrast, climate change (precipitation manipulation) caused functional responses (increased carbon and phosphorus cycling) that were not detected in the microbial community composition. Mycorrhizal fungi in managed systems were responsive to both root biomass and nitrogen inputs, significantly altering hydrolytic enzyme activity and aggregate turnover. Collectively small-scale processes can alter the ecosystem biogeochemical cycles. Together theses results suggest that linking microbial communities to coupled C-N cycles may have important implications for terrestrial C cycling feedbacks that are an integral part of the anthropocene era.

Nitrogen cycling following mountain pine beetle disturbance in lodgepole pine forests of Greater Yellowstone

Treesearch

Jacob M. Griffin; Monica G. Turner; Martin Simard

2011-01-01

Widespread bark beetle outbreaks are currently affecting multiple conifer forest types throughout western North America, yet many ecosystem-level consequences of this disturbance are poorly understood. We quantified the effect of mountain pine beetle (Dendroctonus ponderosae) outbreak on nitrogen (N) cycling through litter, soil, and vegetation in...

Tightly-coupled plant-soil nitrogen cycling: Implications for multiple ecosystem services on organic farms across an intensively managed agricultural landscape

USDA-ARS?s Scientific Manuscript database

Variability among farms across an agricultural landscape may reveal diverse biophysical contexts and experiences that show innovations and insights to improve nitrogen (N) cycling and yields, and thus the potential for multiple ecosystem services. In order to assess potential tradeoffs between yield...

Long-life Li/polysulphide batteries with high sulphur loading enabled by lightweight three-dimensional nitrogen/sulphur-codoped graphene sponge

PubMed Central

Zhou, Guangmin; Paek, Eunsu; Hwang, Gyeong S.; Manthiram, Arumugam

2015-01-01

Lithium–sulphur batteries with a high theoretical energy density are regarded as promising energy storage devices for electric vehicles and large-scale electricity storage. However, the low active material utilization, low sulphur loading and poor cycling stability restrict their practical applications. Herein, we present an effective strategy to obtain Li/polysulphide batteries with high-energy density and long-cyclic life using three-dimensional nitrogen/sulphur codoped graphene sponge electrodes. The nitrogen/sulphur codoped graphene sponge electrode provides enough space for a high sulphur loading, facilitates fast charge transfer and better immobilization of polysulphide ions. The hetero-doped nitrogen/sulphur sites are demonstrated to show strong binding energy and be capable of anchoring polysulphides based on first-principles calculations. As a result, a high specific capacity of 1,200 mAh g−1 at 0.2C rate, a high-rate capacity of 430 mAh g−1 at 2C rate and excellent cycling stability for 500 cycles with ∼0.078% capacity decay per cycle are achieved. PMID:26182892

Nitrogen biogeochemistry in tropical peatlands: nitrogen gas emissions and metagenomic insights into related microbial groups

NASA Astrophysics Data System (ADS)

Kasak, Kuno; Espenberg, Mikk; Oopkaup, Kristjan; Ligi, Teele; Truu, Marika; Truu, Jaak; Maddison, Martin; Järveoja, Järvi; Teemusk, Alar; Mander, Ülo

2017-04-01

Tropical peatlands constitute considerable amount of global peatland areas and are one of the most important and vulnerable terrestrial ecosystems in terms of impact on the atmospheric greenhouse gas composition. Anthropogenic actions, especially drainage and agriculture, are transforming biochemical cycles in tropical peatlands substantially. It is well known that drainage of tropical peatlands will result in huge amount of carbon loss, however a comprehensive study of the nitrogen cycling genetic potential in tropical areas is still less known. In the current study, nitrogen gas (N2, N2O) emissions from tropical peatlands (French Guiana, South America) were measured and their relationships with the soil chemical parameters, water regime, and abundances and diversity of genes in nitrogen cycle was assessed. The measurements and soil sampling were carried out in October 2013 in two sites (undisturbed and drainage influenced) of the northern part of French Guiana. At both sampling sites, N2O emissions were measured in six sessions during three days using static closed chambers. N2 and N2O emission from the top soil samples were measured in the laboratory applying He-O (N2) method. Soil pHKCl, NO3-N, NH4-N, soluble P, K, Ca and Mg, totN and soil organic matter content were determined from the collected samples. The bacterial and archaeal 16S rRNA genes and functional genes involved in nitrogen cycle (nirS, nirK, nosZI, nosZII, bacterial and archaeal amoA, nifH, nrfA, ANAMMOX bacteria specific 16S rRNA genes) in soil were quantified by using quantitative PCR method. DNA extracted from soil samples was sequenced on Illumina NextSeq system. Metagenomes were used for microbial profiling, identifying functional genes and relating them to biogeochemical cycles and biological processes. N2O emissions were significantly lower and N2 emissions higher (p<0.05 in both cases) in natural site (mean values -0.3 and 9.9 μg m-2 h-1 for N2O, and 1477.3 and 637.2 μg m-2 h-1 for N2 in natural and drained sites, respectively). Results from molecular analyses showed that drainage had a clear impact on the communities of nirS, nirK, nosZ, amoA archaea and nifH gene possessing microorganisms and the structure of these communities were mainly related to different nitrogen forms in tropical peatlands. The bacterial community was more abundant in the natural site while the N2O production potential (by the abundance of nir genes) was not different between the two sites. N2O reduction potential (by the abundance of nosZ genes) was higher in the natural area where also the lower mineral N content and high groundwater level was detected. A systematic variation in nir and nosZ genes abundances along the groundwater depth gradient in both areas was notable.

Sliding mode control of dissolved oxygen in an integrated nitrogen removal process in a sequencing batch reactor (SBR).

PubMed

Muñoz, C; Young, H; Antileo, C; Bornhardt, C

2009-01-01

This paper presents a sliding mode controller (SMC) for dissolved oxygen (DO) in an integrated nitrogen removal process carried out in a suspended biomass sequencing batch reactor (SBR). The SMC performance was compared against an auto-tuning PI controller with parameters adjusted at the beginning of the batch cycle. A method for cancelling the slow DO sensor dynamics was implemented by using a first order model of the sensor. Tests in a lab-scale reactor showed that the SMC offers a better disturbance rejection capability than the auto-tuning PI controller, furthermore providing reasonable performance in a wide range of operation. Thus, SMC becomes an effective robust nonlinear tool to the DO control in this process, being also simple from a computational point of view, allowing its implementation in devices such as industrial programmable logic controllers (PLCs).

Cost-effectiveness of nitrogen mitigation by alternative household wastewater management technologies.

PubMed

Wood, Alison; Blackhurst, Michael; Hawkins, Troy; Xue, Xiaobo; Ashbolt, Nicholas; Garland, Jay

2015-03-01

Household wastewater, especially from conventional septic systems, is a major contributor to nitrogen pollution. Alternative household wastewater management technologies provide similar sewerage management services but their life cycle costs and nitrogen flow implications remain uncertain. This paper addresses two key questions: (1) what are the total costs, nitrogen mitigation potential, and cost-effectiveness of a range of conventional and alternative municipal wastewater treatment technologies, and (2) what uncertainties influence these outcomes and how can we improve our understanding of these technologies? We estimate a household nitrogen mass balance for various household wastewater treatment systems and combine this mass balance with life cycle cost assessment to calculate the cost-effectiveness of nitrogen mitigation, which we define as nitrogen removed from the local watershed. We apply our methods to Falmouth, MA, where failing septic systems have caused heightened eutrophication in local receiving water bodies. We find that flushing and dry (composting) urine-diversion toilets paired with conventional septic systems for greywater management demonstrate the lowest life cycle cost and highest cost-effectiveness (dollars per kilogram of nitrogen removed from the watershed). Composting toilets are also attractive options in some cases, particularly best-case nitrogen mitigation. Innovative/advanced septic systems designed for high-level nitrogen removal are cost-competitive options for newly constructed homes, except at their most expensive. A centralized wastewater treatment plant is the most expensive and least cost-effective option in all cases. Using a greywater recycling system with any treatment technology increases the cost without adding any nitrogen removal benefits. Sensitivity analysis shows that these results are robust considering a range of cases and uncertainties. Copyright © 2014 The Authors. Published by Elsevier Ltd.. All rights reserved.

U.S. nitrogen science plan focuses collaborative efforts

NASA Astrophysics Data System (ADS)

Holland, E. A.; Guenther, A.; Lee-Taylor, J.; Bertman, S. B.; Carroll, M. A.; Shepson, P. B.; Sparks, J. P.

Nitrogen is a major nutrient in terrestrial ecosystems and an important catalyst in tropospheric photochemistry. Over the last century human activities have dramatically increased inputs of reactive nitrogen (Nr, the combination of oxidized, reduced, and organically bound nitrogen) to the Earth system (Figure 1). Nitrogen cycle perturbations have compromised air quality and human health, acidified ecosystems, and degraded and eutrophied lakes and coastal estuaries [Vitousek et al., 1997a, 1997b; Rabalais, 2002; Howarth et al., 2003; Townsend et al., 2003; Galloway et al., 2004].Increased Nr affects global climate. Use of agricultural fertilizers such as ammonium nitrate leads to increased soil production of nitrous oxide (N2O), which has 320 times the global warming potential of carbon dioxide (CO2). Emission of nitrogen oxides (NOx = nitric oxide, NO + nitrogen dioxide, NO2) from fossil fuel burning leads to increases in tropospheric ozone, another greenhouse gas. Ozone is phytotoxic, and may reduce terrestrial CO2 sequestration. To predict the effects of nitrogen cycling changes under changing climatic conditions, there needs to be a better understanding of the global nitrogen budget.

Organic forms dominate hydrologic nitrogen export from a lowland tropical watershed.

PubMed

Taylor, Philip G; Wieder, William R; Weintraub, Samantha; Cohen, Sagy; Cleveland, Cory C; Townsend, Alan R

2015-05-01

Observations of high dissolved inorganic nitrogen (DIN) concentrations in stream water have reinforced the notion that primary tropical rain forests cycle nitrogen (N) in relative excess compared to phosphorus. Here we test this notion by evaluating hydrologic N export from a small watershed on the Osa Peninsula, Costa Rica, where prior research has shown multiple indicators of conservative N cycling throughout the ecosystem. We repeatedly measured a host of factors known to influence N export for one year, including stream water chemistry and upslope litterfall, soil N availability and net N processing rates, and soil solution chemistry at the surface, 15- and 50-cm depths. Contrary to prevailing assumptions about the lowland N cycle, we find that dissolved organic nitrogen (DON) averaged 85% of dissolved N export for 48 of 52 consecutive weeks. For most of the year stream water nitrate (NO3-) export was very low, which reflected minimal net N processing and DIN leaching from upslope soils. Yet, for one month in the dry season, NO3- was the major component of N export due to a combination of low flows and upslope nitrification that concentrated NO3- in stream water. Particulate organic N (PON) export was much larger than dissolved forms at 14.6 kg N x ha(-1) x yr(-1), driven by soil erosion during storms. At this rate, PON export was slightly greater than estimated inputs from free-living N fixation and atmospheric N deposition, which suggests that erosion-driven PON export could constrain ecosystem level N stocks over longer timescales. This phenomenon is complimentary to the "DON leak" hypothesis, which postulates that the long-term accumulation of ecosystem N in unpolluted ecosystems is constrained by the export of organic N independently of biological N demand. Using an established global sediment generation model, we illustrate that PON erosion may be an important vector for N loss in tropical landscapes that are geomorphically active. This study supports an emerging view that landscape geomorphology influences nutrient biogeochemistry and limitation, though more research is needed to understand the mechanisms and spatial significance of erosional N loss from terrestrial ecosystems.

The nitrogen isotopic composition in soils and plants: Its use in environmental studies (A Review)

NASA Astrophysics Data System (ADS)

Makarov, M. I.

2009-12-01

The results of studying the isotopic composition of the nitrogen in soils and plants and its use for characterizing the nitrogen cycle in ecosystems, the transformation of nitrogen compounds in soils, the sources of nitrogen nutrition for plants, and the assessment of the symbiotic nitrogen fixation’s contribution to the nitrogen budget of ecosystems were considered for a wide variety of natural and agricultural ecosystems.

Microbial oceanography of anoxic oxygen minimum zones.

PubMed

Ulloa, Osvaldo; Canfield, Donald E; DeLong, Edward F; Letelier, Ricardo M; Stewart, Frank J

2012-10-02

Vast expanses of oxygen-deficient and nitrite-rich water define the major oxygen minimum zones (OMZs) of the global ocean. They support diverse microbial communities that influence the nitrogen economy of the oceans, contributing to major losses of fixed nitrogen as dinitrogen (N(2)) and nitrous oxide (N(2)O) gases. Anaerobic microbial processes, including the two pathways of N(2) production, denitrification and anaerobic ammonium oxidation, are oxygen-sensitive, with some occurring only under strictly anoxic conditions. The detection limit of the usual method (Winkler titrations) for measuring dissolved oxygen in seawater, however, is much too high to distinguish low oxygen conditions from true anoxia. However, new analytical technologies are revealing vanishingly low oxygen concentrations in nitrite-rich OMZs, indicating that these OMZs are essentially anoxic marine zones (AMZs). Autonomous monitoring platforms also reveal previously unrecognized episodic intrusions of oxygen into the AMZ core, which could periodically support aerobic metabolisms in a typically anoxic environment. Although nitrogen cycling is considered to dominate the microbial ecology and biogeochemistry of AMZs, recent environmental genomics and geochemical studies show the presence of other relevant processes, particularly those associated with the sulfur and carbon cycles. AMZs correspond to an intermediate state between two "end points" represented by fully oxic systems and fully sulfidic systems. Modern and ancient AMZs and sulfidic basins are chemically and functionally related. Global change is affecting the magnitude of biogeochemical fluxes and ocean chemical inventories, leading to shifts in AMZ chemistry and biology that are likely to continue well into the future.

Microbial oceanography of anoxic oxygen minimum zones

PubMed Central

Ulloa, Osvaldo; Canfield, Donald E.; DeLong, Edward F.; Letelier, Ricardo M.; Stewart, Frank J.

2012-01-01

Vast expanses of oxygen-deficient and nitrite-rich water define the major oxygen minimum zones (OMZs) of the global ocean. They support diverse microbial communities that influence the nitrogen economy of the oceans, contributing to major losses of fixed nitrogen as dinitrogen (N2) and nitrous oxide (N2O) gases. Anaerobic microbial processes, including the two pathways of N2 production, denitrification and anaerobic ammonium oxidation, are oxygen-sensitive, with some occurring only under strictly anoxic conditions. The detection limit of the usual method (Winkler titrations) for measuring dissolved oxygen in seawater, however, is much too high to distinguish low oxygen conditions from true anoxia. However, new analytical technologies are revealing vanishingly low oxygen concentrations in nitrite-rich OMZs, indicating that these OMZs are essentially anoxic marine zones (AMZs). Autonomous monitoring platforms also reveal previously unrecognized episodic intrusions of oxygen into the AMZ core, which could periodically support aerobic metabolisms in a typically anoxic environment. Although nitrogen cycling is considered to dominate the microbial ecology and biogeochemistry of AMZs, recent environmental genomics and geochemical studies show the presence of other relevant processes, particularly those associated with the sulfur and carbon cycles. AMZs correspond to an intermediate state between two “end points” represented by fully oxic systems and fully sulfidic systems. Modern and ancient AMZs and sulfidic basins are chemically and functionally related. Global change is affecting the magnitude of biogeochemical fluxes and ocean chemical inventories, leading to shifts in AMZ chemistry and biology that are likely to continue well into the future. PMID:22967509

Microbial mediated iron redox cycling in Fe (hydr)oxides for nitrite removal.

PubMed

Lu, Yongsheng; Xu, Lu; Shu, Weikang; Zhou, Jizhi; Chen, Xueping; Xu, Yunfeng; Qian, Guangren

2017-01-01

Nitrite, at an environmentally relevant concentration, was significantly reduced with iron (hydr)oxides mediated by Shewanella oneidensis MR-1. The average nitrite removal rates of 1.28±0.08 and 0.65±0.02(mgL -1 )h -1 were achieved with ferrihydrite and magnetite, respectively. The results showed that nitrite removal was able to undergo multiple redox cycles with iron (hydr)oxides mediated by Shewanella oneidensis MR-1. During the bioreduction of the following cycles, biogenic Fe(II) was subsequently chemically oxidized to Fe(III), which is associated with nitrite reduction. There was 11.18±1.26mgL -1 of NH 4 + -N generated in the process of redox cycling of ferrihydrite. Additionally, results obtained by using X-ray diffraction showed that ferrihydrite and magnetite remained mainly stable in the system. This study indicated that redox cycling of Fe in iron (hydr)oxides was a potential process associated with NO 2 - -N removal from solution, and reduced most nitrite abiotically to gaseous nitrogen species. Copyright © 2016 Elsevier Ltd. All rights reserved.

Carbon-nitrogen-water interactions: is model parsimony fruitful?

NASA Astrophysics Data System (ADS)

Puertes, Cristina; González-Sanchis, María; Lidón, Antonio; Bautista, Inmaculada; Lull, Cristina; Francés, Félix

2017-04-01

It is well known that carbon and nitrogen cycles are highly intertwined and both should be explained through the water balance. In fact, in water-controlled ecosystems nutrient deficit is related to this water scarcity. For this reason, the present study compares the capability of three models in reproducing the interaction between the carbon and nitrogen cycles and the water cycle. The models are BIOME-BGCMuSo, LEACHM and a simple carbon-nitrogen model coupled to the hydrological model TETIS. Biome-BGCMuSo and LEACHM are two widely used models that reproduce the carbon and nitrogen cycles adequately. However, their main limitation is that these models are quite complex and can be too detailed for watershed studies. On the contrary, the TETIS nutrient sub-model is a conceptual model with a vertical tank distribution over the active soil depth, dividing it in two layers. Only the input of the added litter and the losses due to soil respiration, denitrification, leaching and plant uptake are considered as external fluxes. Other fluxes have been neglected. The three models have been implemented in an experimental plot of a semi-arid catchment (La Hunde, East of Spain), mostly covered by holm oak (Quercus ilex). Plant transpiration, soil moisture and runoff have been monitored daily during nearly two years (26/10/2012 to 30/09/2014). For the same period, soil samples were collected every two months and taken to the lab in order to obtain the concentrations of dissolved organic carbon, microbial biomass carbon, ammonium and nitrate. In addition, between field trips soil samples were placed in PVC tubes with resin traps and were left incubating (in situ buried cores). Thus, mineralization and nitrification accumulated fluxes for two months, were obtained. The ammonium and nitrate leaching accumulated for two months were measured using ion-exchange resin cores. Soil respiration was also measured every field trip. Finally, water samples deriving from runoff, were collected to obtain the concentrations of dissolved organic carbon, dissolved organic nitrogen, ammonium and nitrate. The comparison shows a better performance of the complex models reproducing carbon and nitrogen cycles. However, the TETIS nutrient sub-model, even simpler than BIOME-BGCMuSo and LEACHM, reproduces the water balance adequately and it obtains a suitable representation of the carbon and nitrogen cycles.

Surface disturbances: their role in accelerating desertification

USGS Publications Warehouse

Belnap, Jayne

1995-01-01

Maintaining soil stability and normal water and nutrient cycles in desert systems is critical to avoiding desertification. These particular ecosystem processes are threatened by trampling of livestock and people, and by off-road vehicle use. Soil compaction and disruption of cryptobiotic soil surfaces (composed of cyanobacteria, lichens, and mosses) can result in decreased water availability to vascular plants through decreased water infiltration and increased albedo with possible decreased precipitation. Surface disturbance may also cause accelerated soil loss through wind and water erosion and decreased diversity and abundance of soil biota. In addition, nutrient cycles can be altered through lowered nitrogen and carbon inputs and slowed decomposition of soil organic matter, resulting in lower nutrient levels in associated vascular plants. Some cold desert systems may be especially susceptible to these disruptions due to the paucity of surface-rooting vascular plants for soil stabilization, fewer nitrogen-fixing higher plants, and lower soil temperatures, which slow nutrient cycles. Desert soils may recover slowly from surface disturbances, resulting in increased vulnerability to desertification. Recovery from compaction and decreased soil stability is estimated to take several hundred years. Re-establishment rates for soil bacterial and fungal populations are not known. The nitrogen fixation capability of soil requires at least 50 years to recover. Recovery of crusts can be hampered by large amounts of moving sediment, and re-establishment can be extremely difficult in some areas. Given the sensitivity of these resources and slow recovery times, desertification threatens million of hectares of semiarid lands in the United States.

Changes in Nitrogen Cycling during Tropical Forest Secondary Succession on Abandoned Pastures

NASA Astrophysics Data System (ADS)

Mirza, S.; Rivera, R. J.; Marin-Spiotta, E.

2017-12-01

Nitrogen (N) plays two important roles in Earth's climate. As a plant nutrient, the availability of N affects plant growth and the uptake of carbon (C) from the atmosphere into plant biomass. The accumulation of C in long-lived biomass and in soils contributes to reducing the amount of CO2 in the atmosphere. Secondly, excess N can lead to the production of N2O, which is a more potent greenhouse than CO2. Humans have altered the cycling of N in terrestrial ecosystems, affecting their potential to sequester C and help mitigate climate change. Land-use change, specifically deforestation and reforestation, can affect N availability for plant growth and N2O production. Long-term agricultural use can deplete nitrogen sources, even in tropical soils where N is not expected to limit productivity. Secondary succession and reforestation can allow for the recovery of N stocks and fluxes, with implications for C cycling and N2O emissions. N limitation in pastures and early successional forests increases the demand for N-fixing tree species, but previous research has shown that there is a greater abundance of N-fixing species in older forests (Batterman et. al 2013). Successional trends in N mineralization and denitrification vary across studies, with some showing greater rates in agricultural soils or in mature forest soils, compared to early successional sites. Here we examine changes in N-fixing species, above and belowground N pools, and N cycling rates in secondary forests on former pastures on Oxisols in the wet tropical forest life zone of Puerto Rico. The availability of a long-term well-replicated chronosequence provides us with the opportunity to study decadal trends in N processes during forest recovery after agricultural abandonment.

Processes regulating progressive nitrogen limitation under elevated carbon dioxide: a meta-analysis

NASA Astrophysics Data System (ADS)

Liang, Junyi; Qi, Xuan; Souza, Lara; Luo, Yiqi

2016-05-01

The nitrogen (N) cycle has the potential to regulate climate change through its influence on carbon (C) sequestration. Although extensive research has explored whether or not progressive N limitation (PNL) occurs under CO2 enrichment, a comprehensive assessment of the processes that regulate PNL is still lacking. Here, we quantitatively synthesized the responses of all major processes and pools in the terrestrial N cycle with meta-analysis of CO2 experimental data available in the literature. The results showed that CO2 enrichment significantly increased N sequestration in the plant and litter pools but not in the soil pool, partially supporting one of the basic assumptions in the PNL hypothesis that elevated CO2 results in more N sequestered in organic pools. However, CO2 enrichment significantly increased the N influx via biological N fixation and the loss via N2O emission, but decreased the N efflux via leaching. In addition, no general diminished CO2 fertilization effect on plant growth was observed over time up to the longest experiment of 13 years. Overall, our analyses suggest that the extra N supply by the increased biological N fixation and decreased leaching may potentially alleviate PNL under elevated CO2 conditions in spite of the increases in plant N sequestration and N2O emission. Moreover, our syntheses indicate that CO2 enrichment increases soil ammonium (NH4+) to nitrate (NO3-) ratio. The changed NH4+/NO3- ratio and subsequent biological processes may result in changes in soil microenvironments, above-belowground community structures and associated interactions, which could potentially affect the terrestrial biogeochemical cycles. In addition, our data synthesis suggests that more long-term studies, especially in regions other than temperate ones, are needed for comprehensive assessments of the PNL hypothesis.

Impact of Vitamin B12 and Nitrate on Transcript and Metabolite Abundances in Marine Diatoms.

NASA Astrophysics Data System (ADS)

Pound, H. L.; Schanke, N. L.; Penta, W. B.; Zavala, J.; Casu, F.; Bearden, D. W.; Lee, P. A.

2016-02-01

Phytoplankton play countless roles in the support and regulation of marine ecosystems, as well as in global biogeochemical cycling processes. They are also, to varying extents, reliant on other physical and biological processes to supply their nutrient demands, such as the production of vitamin B12 by bacteria and archaea or the regeneration and upwelling of nitrate. One such process in the global biogeochemical sulfur cycle is the pathway that begins with the production of dimethylsulfoniopropionate (DMSP) by marine phytoplankton and leads to the atmospheric formation of sulfate-based cloud condensation nuclei, which contribute to the Earth's albedo. Nutrient limitation is thought to play a major role in the amount of DMSP produced by phytoplankton. Vitamin B12 and nitrate are of particular interest due to their involvement as a co-factor and nitrogen source, respectively, in the synthesis of methionine, the precursor for DMSP. Laboratory-based nutrient limitation experiments have been performed on cultures of the diatom Phaeodactylum tricornutum. In addition to the B12-dependent methionine synthase (MetH) P. tricornutum has a unique B12-independent methionine synthase gene (MetE). Based on classic techniques, B12 limitation had little impact on cell growth, whereas nitrate limitation had a significant effect on both culture health and DMSP concentration. Yet, targeted transcriptomic analysis (using Nanostring nCounter technology) and metabolomics analysis (using Nuclear Magnetic Resonance (NMR)) revealed complex changes in transcript abundance towards upregulated gene expression associated with the MetE gene in B12 limited cultures, and shifts away from nitrogen-based metabolites towards DMSP in nitrate-limited cultures. These experiments help verify the role of B12 in DMSP production and link the underlying metabolic pathways that drive the cellular portion of the sulfur cycle to ecosystem and global scale processes.

Multivariate Analysis of Multi-tracer and Climatological Data in an Urbanizing, Drought-impacted Watershed

NASA Astrophysics Data System (ADS)

Creech, L. T.; Donahoe, R. J.

2009-12-01

This paper documents water quality conditions of the Lake Tuscaloosa, Alabama water-supply reservoir and its watershed under two end-members of hydrologic and climatic variability. These data afford the opportunity to view water quality in the context of both land use and drought, facilitating the development of coupled hydrologic and water-quality forecast models to guide watershed management decisions. This study demonstrates that even the region’s normal 10-year drought cycle holds the capacity to significantly impact water quality and should be incorporated into watershed models and decision-making. To accomplish the goals of this project, a multi-tracer approach has been adopted to assess solute sources and water-quality impairments induced by land use. The biogeochemical tracers include: Major- and minor-ions, trace metals, nutrient speciation and stable-isotope tracers at natural abundance levels. These tracers are also vital to understand the role of climate variability in the context of a heterogeneous landscape. Eight seasonal sampling events across 23 sample locations and two water years yield 184 discrete water-quality samples representative of a range of landscape variability and climatological conditions. Each sample was analyzed for 27 solute species and relevant indicators of water quality. Climatological data was obtained from public repositories (NCDC, USDA); hydrologic data from stream and precipitation gages within the watershed (USGS). Multivariate statistics are used to facilitate the numerical analysis and interpretation of the resulting data. Measurements of nitrogen speciation were collected to document patterns of nutrient loading and nitrogen cycling. These data are augmented by the analysis of nitrogen and oxygen isotopes of nitrate. These data clarify the extent to which nitrogen is being loaded in the non-growing season as well as the capacity of the lake to assimilate nutrients. Under drought conditions the lake becomes nitrogen-limited at most locations. Yet, despite these low concentrations of dissolved nitrogen, Diel measurements reveal that the lake achieves a eutrophic state (due to algal productivity and decomposition). This ecological state is also associated with elevated coliform bacteria in the lake, at times exceeding regulatory limits. Although the lake assimilates excess dissolved nitrogen via enhanced productivity, the process constitutes a water-resource impairment. In this context, the stable-isotope tracer component of the project both: 1) accounts for nitrogen sources and mixing, and 2) clarifies the relative importance of nitrogen assimilation vs. biogeochemical cycling. Multivariate analyses of nutrient data, plus that of metals and rock-weathering solutes further clarify the fate of nitrogen at times and locations that nitrogen flux is less than in most river basins, and less than existing models might predict. By extension, these data may also afford deeper understanding of the larger Mobile River Basin’s 'missing' nitrogen loads under variable flow conditions. This phenomenon offers a protective effect against even faster eutrophication rates (than already exist) in our coastal waters, yet is incompletely understood.

Cyanobacterial crusts linked to soil productivity under different grazing management practices in Northern Australia

NASA Astrophysics Data System (ADS)

Alchin, Bruce; Williams, Wendy

2015-04-01

In arid and semi-arid Australia, the central role of healthy soil ecosystems in broad-acre grazing lands may be attributed to the widespread presence of cyanobacterial crusts. In terms of soil nutrient cycling and stability their role is particularly crucial in a climate dominated by annual dry seasons and variable wet seasons. In this study, we aimed to measure the contribution of cyanobacteria to soil nutrient cycling under contrasting levels of disturbance associated with grazing management. Field sampling was carried out on six paired sites (twelve properties) located across an east-west 3,000 km transect that covered different rangeland types on grazing properties in northern Australia (Queensland, Northern Territory and Western Australia). At each location paired sites were established and two different management systems were assessed, cell-paddock rotations (25-400 ha) and continuous grazing (200-2,000 ha). Cyanobacterial soil crusts were recorded from all of the twelve sites and cyanobacteria with the capacity to fix nitrogen were found at ten of the twelve sites. The overall diversity of cyanobacteria varied from three to ten species under any type of grazing system. As field work was conducted in the dry season, it is likely that the diversity may be greater in the wet season than the initial data may indicate. The average cyanobacterial soil crust cover across soil surfaces, between grass tussocks, during the dry season was estimated to be 50.9% and, 42.6% in the early wet season. This reflected longer established crust cover (dry season) versus newly established crusts. There was a high level of variability in the biomass of cyanobacteria however; the grazing system did not have any marked effect on the biomass for any one rangeland type. The grazing system differences did not appear to significantly influence the diversity at any location except on a floodplain in the Pilbara (WA). Biological nitrogen fixation by cyanobacteria was recorded at all sites. Nitrogen fixation rates were significantly higher in the wet season samples compared to the dry season. Rates of nitrogen fixation, mineralisable nitrogen and cyanobacterial biomass were comparative to other studies both in Australia and globally. Eleven of the twelve sites had higher plant-available (mineralisable) nitrogen in the 0-1 cm depth compared to the 1-5 cm depth. Nitrogen isotopes showed that the nitrogen concentration found in the surface soils (0-1 cm) from five sites originated from cyanobacterial nitrogen fixation. At the remaining sites the isotopic signatures were slightly more positive, indicative of fractionation. The results have substantiated the link between cyanobacteria and their contribution to carbon and nitrogen cycling across the northern Australian rangelands. The data also highlights the variability between sites and management practices that influence biogeochemical processes that affect soil productivity.

Hydration status and diurnal trophic interactions shape microbial community function in desert biocrusts

NASA Astrophysics Data System (ADS)

Kim, Minsu; Or, Dani

2017-12-01

Biological soil crusts (biocrusts) are self-organised thin assemblies of microbes, lichens, and mosses that are ubiquitous in arid regions and serve as important ecological and biogeochemical hotspots. Biocrust ecological function is intricately shaped by strong gradients of water, light, oxygen, and dynamics in the abundance and spatial organisation of the microbial community within a few millimetres of the soil surface. We report a mechanistic model that links the biophysical and chemical processes that shape the functioning of biocrust representative microbial communities that interact trophically and respond dynamically to cycles of hydration, light, and temperature. The model captures key features of carbon and nitrogen cycling within biocrusts, such as microbial activity and distribution (during early stages of biocrust establishment) under diurnal cycles and the associated dynamics of biogeochemical fluxes at different hydration conditions. The study offers new insights into the highly dynamic and localised processes performed by microbial communities within thin desert biocrusts.

Methane emission from natural wetlands: interplay between emergent macrophytes and soil microbial processes. A mini-review

PubMed Central

Laanbroek, Hendrikus J.

2010-01-01

Background According to the Intergovernmental Panel on Climate Change (IPCC) 2007, natural wetlands contribute 20–39 % to the global emission of methane. The range in the estimated percentage of the contribution of these systems to the total release of this greenhouse gas is large due to differences in the nature of the emitting vegetation including the soil microbiota that interfere with the production and consumption of methane. Scope Methane is a dominant end-product of anaerobic mineralization processes. When all electron acceptors except carbon dioxide are used by the microbial community, methanogenesis is the ultimate pathway to mineralize organic carbon compounds. Emergent wetland plants play an important role in the emission of methane to the atmosphere. They produce the carbon necessary for the production of methane, but also facilitate the release of methane by the possession of a system of interconnected internal gas lacunas. Aquatic macrophytes are commonly adapted to oxygen-limited conditions as they prevail in flooded or waterlogged soils. By this system, oxygen is transported to the underground parts of the plants. Part of the oxygen transported downwards is released in the root zone, where it sustains a number of beneficial oxidation processes. Through the pores from which oxygen escapes from the plant into the root zone, methane can enter the plant aerenchyma system and subsequently be emitted into the atmosphere. Part of the oxygen released into the root zone can be used to oxidize methane before it enters the atmosphere. However, the oxygen can also be used to regenerate alternative electron acceptors. The continuous supply of alternative electron acceptors will diminish the role of methanogenesis in the anaerobic mineralization processes in the root zone and therefore repress the production and emission of methane. The role of alternative element cycles in the inhibition of methanogenesis is discussed. Conclusions The role of the nitrogen cycle in repression of methane production is probably low. In contrast to wetlands particularly created for the purification of nitrogen-rich waste waters, concentrations of inorganic nitrogen compounds are low in the root zones in the growing season due to the nitrogen-consuming behaviour of the plant. Therefore, nitrate hardly competes with other electron acceptors for reduced organic compounds, and repression of methane oxidation by the presence of higher levels of ammonium will not be the case. The role of the iron cycle is likely to be important with respect to the repression of methane production and oxidation. Iron-reducing and iron-oxidizing bacteria are ubiquitous in the rhizosphere of wetland plants. The cycling of iron will be largely dependent on the size of the oxygen release in the root zone, which is likely to be different between different wetland plant species. The role of the sulfur cycle in repression of methane production is important in marine, sulfate-rich ecosystems, but might also play a role in freshwater systems where sufficient sulfate is available. Sulfate-reducing bacteria are omnipresent in freshwater ecosystems, but do not always react immediately to the supply of fresh sulfate. Hence, their role in the repression of methanogenesis is still to be proven in freshwater marshes. PMID:19689973

In situ self-sacrificed template synthesis of vanadium nitride/nitrogen-doped graphene nanocomposites for electrochemical capacitors.

PubMed

Liu, Hong-Hui; Zhang, Hong-Ling; Xu, Hong-Bin; Lou, Tai-Ping; Sui, Zhi-Tong; Zhang, Yi

2018-03-15

Vanadium nitride and graphene have been widely used as pseudo-capacitive and electric double-layer capacitor electrode materials for electrochemical capacitors, respectively. However, the poor cycling stability of vanadium nitride and the low capacitance of graphene impeded their practical applications. Herein, we demonstrated an in situ self-sacrificed template method for the synthesis of vanadium nitride/nitrogen-doped graphene (VN/NGr) nanocomposites by the pyrolysis of a mixture of dicyandiamide, glucose, and NH 4 VO 3 . Vanadium nitride nanoparticles of the size in the range of 2 to 7 nm were uniformly embedded into the nitrogen-doped graphene skeleton. Furthermore, the VN/NGr nanocomposites with a high specific surface area and pore volume showed a high specific capacitance of 255 F g -1 at 10 mV s -1 , and an excellent cycling stability (94% capacitance retention after 2000 cycles). The excellent capacitive properties were ascribed to the excellent conductivity of nitrogen-doped graphene, high surface area, high pore volume, and the synergistic effect between vanadium nitride and nitrogen-doped graphene.

Cost-Effectiveness of Nitrogen Mitigation by Alternative Household Wastewater Management Technologies

EPA Science Inventory

Household wastewater, especially from conventional septic systems, is a major contributor to nitrogen pollution. Alternative household wastewater management technologies provide similar sewerage management services but their life cycle costs and nitrogen flow implications remain ...

Carbon cycle: Nitrogen's carbon bonus

NASA Astrophysics Data System (ADS)

Janssens, Ivan A.; Luyssaert, Sebastiaan

2009-05-01

Atmospheric deposition of nitrogen can, but does not always, speed up the sequestration of carbon in trees and forest soil. This complexity may arise from the spatial variations in each of the three mechanisms by which nitrogen affects carbon storage.

Nitrogen-Doped Mesoporous Carbon: A Top-Down Strategy to Promote Sulfur Immobilization for Lithium-Sulfur Batteries.

PubMed

Zhao, Xiaohui; Liu, Ying; Manuel, James; Chauhan, Ghanshyam S; Ahn, Hyo-Jun; Kim, Ki-Won; Cho, Kwon-Koo; Ahn, Jou-Hyeon

2015-10-12

The loss of active sulfur material is a challenge in the application of lithium-sulfur (Li-S) batteries. To immobilize sulfur, a nitrogen-doped mesoporous carbon (PMC) was synthesized with polyaniline (PANi) as the carbon source, which was used for development of Li-S batteries. The nitrogen content and pore system of the PMCs were modulated by varying the pyrolysis temperature to impart good electrochemical properties to the Li-S cells. As a result, the optimal capacity reversibility was obtained with the PMC synthesized at 700 °C that consisted of 12.8 % nitrogen. The enhanced cycle performance of Li-S cells was also validated at high sulfur contents up to 70 % and high C-rates up to 2 C. Furthermore, such sulfur/PMC cathodes could alleviate volume expansion during the discharge process. The results suggest that our synthesized nitrogen-doped PMCs prepared by this top-down strategy are promising materials to immobilize active sulfur in Li-S batteries. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Key ecological responses to nitrogen are altered by climate ...

EPA Pesticide Factsheets

Here we review the effects of nitrogen and climate (e.g. temperature and precipitation) on four aspects of ecosystem structure and function including hydrologic-coupled nitrogen cycling, carbon cycling, acidification and biodiversity. Ecosystems are simultaneously exposed to multiple stressors; two dominant drivers threatening ecosystems are anthropogenic nitrogen loading and climate change. Evaluating the cumulative effects of these stressors provides a holistic view of ecosystem vulnerability, which would better inform policy decisions aimed to protect the sustainability of ecosystems. Our current knowledge of the cumulative effects of these stressors is growing, but limited. The goal of this paper is to synthesize the state of scientific knowledge on how ecosystems are affected by the interactions of meteorlogic/climatic factors (e.g., temperature and precipitation) and nitrogen addition. Understanding the interactions of meteorlogic/climatic factors and nitrogen will help to inform how current and projected variability may affect ecosystem response.

N cycling in SPRUCE (Spruce Peatlands Response Under ...

EPA Pesticide Factsheets

Peatlands located in boreal regions make up a third of global wetland area and are expected to have the highest temperature increases in response to climate change. As climate warms, we expect peat decomposition may accelerate, altering the cycling of nitrogen. Alterations in the nitrogen cycle can have consequences on NO3, NH4 availability or pollution, and potentially increase nitrous oxide (N2O) emissions, a persistent greenhouse gas (GHG). These consequences can cascade to altering whole ecosystem functions and effecting human health.We are investigating nitrogen cycling response to elevated temperature and CO2 in a boreal peatland. Spruce and Peatland Responses Under Climate and Environmental Change (SPRUCE) project initiated soil warming in 2014 in ten peatland mesocosms (five temperature treatments from ambient (+0°C) to +9°C) and elevated CO2 in half of the mesocosms in 2016. Peat cores at three depths (acrotelm, catotelm, deep peat) were analyzed in the laboratory for denitrification, nitrification, and ammonification. We expect denitrification, nitrification, and ammonification rates to increase, and denitrification efficiency to decrease with rising temperatures- potentially contaminating water resources with NO3, NH4 and increase N2O concentrations in our atmosphere. This research will enhance the scientific understanding of how nitrogen cycling, an important functional eco-service, responds under environmental conditions including elevated CO2

Changes in biogeochemical cycling following forest defoliation by pine wilt disease in Kiryu experimental catchment in Japan

NASA Astrophysics Data System (ADS)

Tokuchi, Naoko; Ohte, Nobuhito; Hobara, Satoru; Kim, Su-Jin; Masanori, Katsuyama

2004-10-01

Changes in nutrient budgets and hydrological processes due to the natural disturbance of pine wilt disease (PWD) were monitored in a small, forested watershed in Japan. The disturbance caused changes in soil nitrogen transformations. Pre-disturbance, mineralized nitrogen remained in the form of NH4+, whereas in disturbed areas most mineralized nitrogen was nitrified. Stream NO3- concentrations increased following PWD. There was a delay between time of disturbance and the increase of NO3- in ground and stream waters. Stream concentrations of NO3- and cations (Ca2+ + Mg2+) were significantly correlated from 1994 to 1996, whereas the correlation among NO3-, H+, and SO42- was significant only in 1995. Although both cation exchange and SO42- adsorption buffered protons, cation exchange was the dominant and continuous mechanism for acid buffering. SO42- adsorption was variable and highly pH dependent. The disturbance also resulted in slight delayed changes of input-output nutrient balances. The nitrogen contribution to PWD litter inputs was 7.39 kmol ha-1, and nitrogen loss from streamwater was less than 0.5 kmol ha-1 year-1 throughout the observation period. This large discrepancy suggested substantial nitrogen immobilization.

Applying modeling Results in designing a global tropospheric experiment

NASA Technical Reports Server (NTRS)

1982-01-01

A set of field experiments and advanced modeling studies which provide a strategy for a program of global tropospheric experiments was identified. An expanded effort to develop space applications for trospheric air quality monitoring and studies was recommended. The tropospheric ozone, carbon, nitrogen, and sulfur cycles are addressed. Stratospheric-tropospheric exchange is discussed. Fast photochemical processes in the free troposphere are considered.

Biogeochemical cycling and chemical fluxes in a managed northern forested wetland, Michigan, USA

Treesearch

James McLaughlin; Emily Calhoon; Margaret Gale; Martin Jurgensen; Carl Trettin

2011-01-01

Forest harvesting and subsequent regeneration treatments may cause changes in soil and solution chemistry that adversely affect forest productivity and environmental quality. The objective of this study was to assess soil carbon (C), nitrogen (N), and base cation pools and fluxes, and to construct a hydrogen ion (H+) mass balance to identify major processes controlling...

Stream nitrogen responses to fire in the Southeastern U.S.

Treesearch

James M. Vose; Stephanie H. Laseter; Steve G. McNulty

2005-01-01

Fire can play a significant role in runoff, sediment yield, and nitrate transport in aquatic and terrestrial ecosystems in the southeast US. The typical impact of fire is an immediate change in the physical properties of the soil and forest floor surface, followed by mid- and long-term changes in biological pools and cycling processes. Depending upon the severity of...

Ecoenzymatic stoichiometry and microbial processing of organic matter in northern bogs and fens reveals a common P-limitation between peatland types

Treesearch

Brian H. Hill; Colleen M. Elonen; Terri M. Jicha; Randall K. Kolka; LaRae L.P. Lehto; Stephen D. Sebestyen; Lindsey R. Seifert-Monson

2014-01-01

We compared carbon (C), nitrogen (N), and phosphorus (P) concentrations in atmospheric deposition, runoff, and soils with microbial respiration [dehydrogenase (DHA)] and ecoenzyme activity (EEA) in an ombrotrophic bog and a minerotrophic fen to investigate the environmental drivers of biogeochemical cycling in peatlands at the Marcell Experimental Forest in northern...

The response of streambed nitrogen cycling to spatial and temporal hyporheic vertical flux patterns and associated residence times

NASA Astrophysics Data System (ADS)

Briggs, M. A.; Lautz, L. K.; Hare, D. K.

2011-12-01

Small beaver dams enhance the development of patchy micro-environments along the stream corridor by trapping sediment and creating complex streambed morphologies. This generates intricate hyporheic flux patterns that govern the exchange of oxygen and redox sensitive solutes between the water column and the streambed, and exert control on the biogeochemical cycling of nitrogen. Specifically, flowpaths from the stream into the subsurface with low residence times create oxic conditions that favor nitrification, while flowpaths with longer residence times become anoxic and favor denitrification. To investigate these processes we collected vertical profiles of pore water upstream of two beaver dams in Wyoming, USA at nine locations with varied morphology. We sampled pore water to the 0.55 m depth every week for five weeks as stream discharge dropped by 45% and subsequently measured concentrations of dissolved oxygen and several redox sensitive solutes, including nitrate. Additionally, estimates of hyporheic flux along these nine vertical profiles through time were made using high-resolution heat data combined with 1-D heat transport modeling. The data show that areas of rapid, deep hyporheic flux at the glides immediately upstream of the dams were oxygen rich, and were generally sites of moderate net nitrification to at least the 0.35 m depth. These conditions were relatively steady over the study period. Hyporheic zones at sediment bars closest to the dams were hotspots of nitrate production to a depth of 0.35 m, with nitrate concentrations increasing by as much as 400% as vertical flux fell sharply and residence times increased over the study period. In contrast, shallow bars farther upstream from the dams showed increasing fluxes and decreased residence times, which caused a shift from net denitrification to net nitrification over the period at shallow depths. These results support previous work indicating threshold behavior of nitrogen cycling in response to flowpath residence time. Furthermore the threshold between oxic and anoxic conditions, and subsequently the zone of peak net nitrification, can be approached from either end of the redox spectrum simultaneously within the same system in response to complex temporal changes in vertical flux. Finally, pools were sites of weak hyporheic flux, overall anoxic conditions and net denitrification. These patterns offer more evidence of the complicated spatial and temporal patterns of nitrogen cycling in the hyporheic zone, but also show that flux patterns measured with 1-D heat transport models may be used to develop predictive relationships regarding streambed biogeochemical conditions and hot spots of nitrogen cycling.

Nitrogen cycling in a forest stream determined by a 15N tracer addition

Treesearch

Patrick J. Mullholland; Jennifer L. Tank; Diane M. Sanzone; Wilfred M. Wollheim; Bruce J. Peterson; Jackson R. Webster; Judy L. Meyer

2000-01-01

Nitrogen uptake and cycling was examined using a six-week tracer addition of 15N-labeled ammonium in early spring in Waer Branch, a first-order deciduous forest stream in eastern Tennessee. Prior to the 15N addition, standing stocks of N were determined for the major biomass compartments. During and after the addition,

Ecosystem services altered by human changes in the nitrogen cycle: a new perspective for US decision making Ecology Letters

EPA Science Inventory

The human alteration of the nitrogen (N) cycle has yielded many benefits, but also has altered ecosystems and degraded air and water quality in many areas. Here we explore the science available to connect the effects of increasing N on ecosystem structure and function to ecosyst...

Nitrogen Fixation by Gliding Arc Plasma: Better Insight by Chemical Kinetics Modelling.

PubMed

Wang, Weizong; Patil, Bhaskar; Heijkers, Stjin; Hessel, Volker; Bogaerts, Annemie

2017-05-22

The conversion of atmospheric nitrogen into valuable compounds, that is, so-called nitrogen fixation, is gaining increased interest, owing to the essential role in the nitrogen cycle of the biosphere. Plasma technology, and more specifically gliding arc plasma, has great potential in this area, but little is known about the underlying mechanisms. Therefore, we developed a detailed chemical kinetics model for a pulsed-power gliding-arc reactor operating at atmospheric pressure for nitrogen oxide synthesis. Experiments are performed to validate the model and reasonable agreement is reached between the calculated and measured NO and NO 2 yields and the corresponding energy efficiency for NO x formation for different N 2 /O 2 ratios, indicating that the model can provide a realistic picture of the plasma chemistry. Therefore, we can use the model to investigate the reaction pathways for the formation and loss of NO x . The results indicate that vibrational excitation of N 2 in the gliding arc contributes significantly to activating the N 2 molecules, and leads to an energy efficient way of NO x production, compared to the thermal process. Based on the underlying chemistry, the model allows us to propose solutions on how to further improve the NO x formation by gliding arc technology. Although the energy efficiency of the gliding-arc-based nitrogen fixation process at the present stage is not comparable to the world-scale Haber-Bosch process, we believe our study helps us to come up with more realistic scenarios of entering a cutting-edge innovation in new business cases for the decentralised production of fertilisers for agriculture, in which low-temperature plasma technology might play an important role. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Rice Ferredoxin-Dependent Glutamate Synthase Regulates Nitrogen-Carbon Metabolomes and Is Genetically Differentiated between japonica and indica Subspecies.

PubMed

Yang, Xiaolu; Nian, Jinqiang; Xie, Qingjun; Feng, Jian; Zhang, Fengxia; Jing, Hongwei; Zhang, Jian; Dong, Guojun; Liang, Yan; Peng, Juli; Wang, Guodong; Qian, Qian; Zuo, Jianru

2016-11-07

Plants assimilate inorganic nitrogen absorbed from soil into organic forms as Gln and Glu through the glutamine synthetase/glutamine:2-oxoglutarate amidotransferase (GS/GOGAT) cycle. Whereas GS catalyzes the formation of Gln from Glu and ammonia, GOGAT catalyzes the transfer of an amide group from Gln to 2-oxoglutarate to produce two molecules of Glu. However, the regulatory role of the GS/GOGAT cycle in the carbon-nitrogen balance is not well understood. Here, we report the functional characterization of rice ABNORMAL CYTOKININ RESPONSE 1 (ABC1) gene that encodes a ferredoxin-dependent (Fd)-GOGAT. The weak mutant allele abc1-1 mutant shows a typical nitrogen-deficient syndrome, whereas the T-DNA insertional mutant abc1-2 is seedling lethal. Metabolomics analysis revealed the accumulation of an excessive amount of amino acids with high N/C ratio (Gln and Asn) and several intermediates in the tricarboxylic acid cycle in abc1-1, suggesting that ABC1 plays a critical role in nitrogen assimilation and carbon-nitrogen balance. Five non-synonymous single-nucleotide polymorphisms were identified in the ABC1 coding region and characterized as three distinct haplotypes, which have been highly and specifically differentiated between japonica and indica subspecies. Collectively, these results suggest that ABC1/OsFd-GOGAT is essential for plant growth and development by modulating nitrogen assimilation and the carbon-nitrogen balance. Copyright © 2016 The Author. Published by Elsevier Inc. All rights reserved.

Excess nitrogen in the U.S. environment: Trends, risks, and solutions

USGS Publications Warehouse

Davidson, E.A.; David, M.B.; Galloway, J.N.; Goodale, C.L.; Haeuber, R.; Harrison, J.A.; Howarth, R.W.; Jaynes, D.B.; Lowrance, R.R.; Thomas, Nolan B.; Peel, J.L.; Pinder, R.W.; Porter, E.; Snyder, C.S.; Townsend, A.R.; Ward, M.H.

2011-01-01

It is not surprising that humans have profoundly altered the global nitrogen (N) cycle in an effort to feed 7 billion people, because nitrogen is an essential plant and animal nutrient. Food and energy production from agriculture, combined with industrial and energy sources, have more than doubled the amount of reactive nitrogen circulating annually on land. Humanity has disrupted the nitrogen cycle even more than the carbon (C) cycle. We present new research results showing widespread effects on ecosystems, biodiversity, human health, and climate, suggesting that in spite of decades of research quantifying the negative consequences of too much available nitrogen in the biosphere, solutions remain elusive. There have been important successes in reducing nitrogen emissions to the atmosphere and this has improved air quality. Effective solutions for reducing nitrogen losses from agriculture have also been identified, although political and economic impediments to their adoption remain. Here, we focus on the major sources of reactive nitrogen for the United States (U.S.), their impacts, and potential mitigation options. Sources: ??? Intensive development of agriculture, industry, and transportation has profoundly altered the U.S. nitrogen cycle. ??? Nitrogen emissions from the energy and transportation sectors are declining, but agricultural emissions are increasing. ??? Approximately half of all nitrogen applied to boost agricultural production escapes its intended use and is lost to the environment. Impacts: ??? Two-thirds of U.S. coastal systems are moderately to severely impaired due to nutrient loading; there are now approximately 300 hypoxic (low oxygen) zones along the U.S. coastline and the number is growing. One third of U.S. streams and two fifths of U.S. lakes are impaired by high nitrogen concentrations. ??? Air pollution continues to reduce biodiversity. A nation-wide assessment has documented losses of nitrogen-sensitive native species in favor of exotic, invasive species. ??? More than 1.5 million Americans drink well water contaminated with too much (or close to too much) nitrate (a regulated drinking water pollutant), potentially placing them at increased risk of birth defects and cancer. More research is needed to deepen understanding of these health risks. ??? Several pathogenic infections, including coral diseases, bird die-offs, fish diseases, and human diarrheal diseases and vector-borne infections are associated with nutrient losses from agriculture and from sewage entering ecosystems. ??? Nitrogen is intimately linked with the carbon cycle and has both warming and cooling effects on the climate. Mitigation Options: ??? Regulation of nitrogen oxide (NOX) emissions from energy and transportation sectors has greatly improved air quality, especially in the eastern U.S. Nitrogen oxide is expected to decline further as stronger regulations take effect, but ammonia remains mostly unregulated and is expected to increase unless better controls on ammonia emissions from livestock operations are implemented. ??? Nitrogen loss from farm and livestock operations can be reduced 30-50% using current practices and technologies and up to 70-90% with innovative applications of existing methods. Current U.S. agricultural policies and support systems, as well as declining investments in agricultural extension, impede the adoption of these practices. Society faces profound challenges to meet demands for food, fiber, and fuel while minimizing unintended environmental and human health impacts. While our ability to quantify transfers of nitrogen across land, water, and air has improved since the first publication of this series in 1997, an even bigger challenge remains: using the science for effective management policies that reduce climate change, improve water quality, and protect human and environmental health. ?? The Ecological Society of America.

The life sulfuric: microbial ecology of sulfur cycling in marine sediments

PubMed Central

Wasmund, Kenneth; Mußmann, Marc

2017-01-01

Summary Almost the entire seafloor is covered with sediments that can be more than 10 000 m thick and represent a vast microbial ecosystem that is a major component of Earth's element and energy cycles. Notably, a significant proportion of microbial life in marine sediments can exploit energy conserved during transformations of sulfur compounds among different redox states. Sulfur cycling, which is primarily driven by sulfate reduction, is tightly interwoven with other important element cycles (carbon, nitrogen, iron, manganese) and therefore has profound implications for both cellular‐ and ecosystem‐level processes. Sulfur‐transforming microorganisms have evolved diverse genetic, metabolic, and in some cases, peculiar phenotypic features to fill an array of ecological niches in marine sediments. Here, we review recent and selected findings on the microbial guilds that are involved in the transformation of different sulfur compounds in marine sediments and emphasise how these are interlinked and have a major influence on ecology and biogeochemistry in the seafloor. Extraordinary discoveries have increased our knowledge on microbial sulfur cycling, mainly in sulfate‐rich surface sediments, yet many questions remain regarding how sulfur redox processes may sustain the deep‐subsurface biosphere and the impact of organic sulfur compounds on the marine sulfur cycle. PMID:28419734

Stable isotope fractionation related to microbial nitrogen turnover in constructed wetlands treating contaminated groundwater

NASA Astrophysics Data System (ADS)

Voloshchenko, O.; Knoeller, K.

2013-12-01

To improve the efficiency of ground- and wastewater treatment in constructed wetlands (CWs), better understanding of the occurring processes is necessary. This research explores N-isotope fractionations associated with the removal of ammonium from contaminated groundwater in pilot-scale CWs downstream of the chemical industrial area Leuna, Germany. The groundwater at the site is contaminated mainly by organic (BTEX, MTBE) and inorganic compounds (ammonium). We assume that the anaerobic ammonium oxidation (ANAMMOX) plays an important role in nitrogen removal in these CWs. However, to date, interactions between processes of aerobic and anaerobic ammonium oxidation in CWs still have not been well explored. Especially, the importance of the ANAMMOX process for the nitrogen removal is generally accepted, but its role in CWs is quite unknown. For this aim, three CWs were chosen: planted horizontal subsurface flow (HSSF); unplanted HSSF, and floating plant root mat (FPRM). Water samples were taken at the inflow and outflow as well as from the pore space at different distances (1, 2.5 and 4 m) from the inlet and at different depths (20, 30 and 40 cm in the HSSF-CWs, 30 cm in the FPRM). Samples were collected in a time interval of 1 to 6 weeks during 1 year with the exception of the winter season. Physicochemical parameters, nitrogen isotope signatures of ammonium, as well as nitrogen and oxygen isotope signatures of nitrate were analysed. Within the CWs, spatial concentration gradients of the nitrogen species (ammonium and nitrate) are observed. N-isotope variations of ammonium and nitrate are interpreted according to the prevailing processes of the N-transformations. Based on isotope mass-balance approach microbial processes such as nitrification, denitrification, and ANAMMOX are quantified. DNA from biofilms at roots and gravel was extracted using FastDNA Spin Kit For Soil (MP Biomedicals). PCR, quantitative PCR, cloning, and sequencing were applied with the purpose of getting information about the abundance and the community of key players of the N-cycle. Pyrosequencing and specific FISH probes in connection with confocal laser scanning microscopy will give information about structure and spatial distribution of the microbial nitrogen transforming community.

Experimental and mathematical modeling of the consumer’s influence on productivity of algae in a model aquatic ecosystem

NASA Astrophysics Data System (ADS)

Pisman, T. I.; Galayda, Ya. V.; Shirobokova, I. M.

A "producer-consumer" ( Chlorella vulgaris- Paramecium caudatum) closed aquatic system has been investigated experimentally and theoretically. It has been found that there is a direct relationship between the growth of the paramecia population and their release of ammonia nitrogen, which is the best form of nitrogen for Chlorella growth. The theoretical study of a model of a "producer-consumer" aquatic biotic cycle with spatially separated compartments has confirmed the contribution of paramecia to nitrogen cycling. It has been shown that an increase in the concentration of nitrogen released as metabolites of paramecia is accompanied by an increase in the productivity of microalgae.

The pitcher plant Sarracenia purpurea can directly acquire organic nitrogen and short-circuit the inorganic nitrogen cycle.

PubMed

Karagatzides, Jim D; Butler, Jessica L; Ellison, Aaron M

2009-07-07

Despite the large stocks of organic nitrogen in soil, nitrogen availability limits plant growth in many terrestrial ecosystems because most plants take up only inorganic nitrogen, not organic nitrogen. Although some vascular plants can assimilate organic nitrogen directly, only recently has organic nitrogen been found to contribute significantly to the nutrient budget of any plant. Carnivorous plants grow in extremely nutrient-poor environments and carnivory has evolved in these plants as an alternative pathway for obtaining nutrients. We tested if the carnivorous pitcher plant Sarracenia purpurea could directly take up intact amino acids in the field and compared uptake of organic and inorganic forms of nitrogen across a gradient of nitrogen deposition. We hypothesized that the contribution of organic nitrogen to the nitrogen budget of the pitcher plant would decline with increasing nitrogen deposition. At sites in Canada (low nitrogen deposition) and the United States (high nitrogen deposition), individual pitchers were fed two amino acids, glycine and phenylalanine, and inorganic nitrogen (as ammonium nitrate), individually and in mixture. Plants took up intact amino acids. Acquisition of each form of nitrogen provided in isolation exceeded uptake of the same form in mixture. At the high deposition site, uptake of organic nitrogen was higher than uptake of inorganic nitrogen. At the low deposition site, uptake of all three forms of nitrogen was similar. Completeness of the associated detritus-based food web that inhabits pitcher-plant leaves and breaks down captured prey had no effect on nitrogen uptake. By taking up intact amino acids, Sarracenia purpurea can short-circuit the inorganic nitrogen cycle, thus minimizing potential bottlenecks in nitrogen availability that result from the plant's reliance for nitrogen mineralization on a seasonally reconstructed food web operating on infrequent and irregular prey capture.

Stable carbon and nitrogen isotopes in vertical peat profiles of natural and drained boreal peatlands

NASA Astrophysics Data System (ADS)

Nykänen, Hannu; Mpamah, Promise; Rissanen, Antti; Pitkänen, Aki; Turunen, Jukka; Simola, Heikki

2015-04-01

Peatlands form a significant carbon pool in the global carbon cycle. Change in peat hydrology, due to global warming is projected to change microbiological processes and peat carbon pool. We tested if bulk stable carbon and nitrogen isotopes serve as indicators of severe long term drying in peatlands drained for forestry. Depth profile analysis of peat, for their carbon and nitrogen content as well as their carbon and nitrogen stable isotopic signatures, were conducted for peatlands in southern and eastern Finland, having ombrotrophic and minerotrophic natural and corresponding drained pairs or separate drained sites. The selection of sites allowed us to compare changes due to different fertility and changes due to long term artificial drying. Drainage lasting over 40 years has led to changes in hydrology, vegetation, nutrient mineralization and respiration. Furthermore, increased nutrient uptake and possible recycling of peat nitrogen and carbon trough vegetation back to the peat surface, also possibly has an effect on the stable isotopic composition of peat carbon and nitrogen. We think that drainage induced changes somehow correspond to those caused by changed hydrology due to climate change. We will present data from these measurements and discuss their implications for carbon and nitrogen flows in peatlands.

Influence of different Sinorhizobium meliloti inocula on abundance of genes involved in nitrogen transformations in the rhizosphere of alfalfa (Medicago sativa L.).

PubMed

Babić, Katarina Huić; Schauss, Kristina; Hai, Brigitte; Sikora, Sanja; Redzepović, Sulejman; Radl, Viviane; Schloter, Michael

2008-11-01

Inoculation of leguminous seeds with selected rhizobial strains is practised in agriculture to ameliorate the plant yield by enhanced root nodulation and nitrogen uptake of the plant. However, effective symbiosis between legumes and rhizobia does not only depend on the capacity of nitrogen fixation but also on the entire nitrogen turnover in the rhizosphere. We investigated the influence of seed inoculation with two indigenous Sinorhizobium meliloti strains exhibiting different efficiency concerning plant growth promotion on nitrogen turnover processes in the rhizosphere during the growth of alfalfa. Quantification of six target genes (bacterial amoA, nirK, nirS, nosZ, nifH and archaeal amoA) within the nitrogen cycle was performed in rhizosphere samples before nodule formation, at bud development and at the late flowering stage. The results clearly demonstrated that effectiveness of rhizobial inocula is related to abundance of nifH genes in the late flowering phase of alfalfa. Moreover, other genes involved in nitrogen turnover had been affected by the inocula, e.g. higher numbers of amoA copies were observed during flowering when the more effective strain had been inoculated. However, the respective gene abundances differed overall to a greater extent between the three plant development stages than between the inoculation variants.

Nitride stabilized core/shell nanoparticles

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kuttiyiel, Kurian Abraham; Sasaki, Kotaro; Adzic, Radoslav R.

Nitride stabilized metal nanoparticles and methods for their manufacture are disclosed. In one embodiment the metal nanoparticles have a continuous and nonporous noble metal shell with a nitride-stabilized non-noble metal core. The nitride-stabilized core provides a stabilizing effect under high oxidizing conditions suppressing the noble metal dissolution during potential cycling. The nitride stabilized nanoparticles may be fabricated by a process in which a core is coated with a shell layer that encapsulates the entire core. Introduction of nitrogen into the core by annealing produces metal nitride(s) that are less susceptible to dissolution during potential cycling under high oxidizing conditions.

Biophysical and socio-economic assessments of the coastal zone: The LOICZ approach

USGS Publications Warehouse

Talaue-McManus, L.; Smith, S.V.; Buddemeier, R.W.

2003-01-01

The Land-Ocean Interactions in the Coastal Zone Project of the International Geosphere-Biosphere Programme focused on quantifying the role of the global coastal zone in the cycling of carbon and nutrients. From 1993 to date, it has developed protocols and tools that allow for site-specific and global assessments of coastal processes and their drivers. Indicators used in coastal assessments include the contribution of population and economic activities to waste load generation, and the resulting coastal system states relative to net production and nitrogen cycling. ?? 2003 Elsevier Science Ltd. All rights reserved.

Feasibility of nitrification/denitrification in a sequencing batch biofilm reactor with liquid circulation applied to post-treatment.

PubMed

Andrade do Canto, Catarina Simone; Rodrigues, José Alberto Domingues; Ratusznei, Suzana Maria; Zaiat, Marcelo; Foresti, Eugênio

2008-02-01

An investigation was performed on the biological removal of ammonium nitrogen from synthetic wastewater by the simultaneous nitrification/denitrification (SND) process, using a sequencing batch biofilm reactor (SBBR). System behavior was analyzed as to the effects of sludge type used as inoculum (autotrophic/heterotrophic), wastewater feed strategy (batch/fed-batch) and aeration strategy (continuous/intermittent). The presence of an autotrophic aerobic sludge showed to be essential for nitrification startup, despite publications stating the existence of heterotrophic organisms capable of nitrifying organic and inorganic nitrogen compounds at low dissolved oxygen concentrations. As to feed strategy, batch operation (synthetic wastewater containing 100 mg COD/L and 50 mg N-NH(4)(+)/L) followed by fed-batch (synthetic wastewater with 100 mg COD/L) during a whole cycle seemed to be the most adequate, mainly during the denitrification phase. Regarding aeration strategy, an intermittent mode, with dissolved oxygen concentration of 2.0mg/L in the aeration phase, showed the best results. Under these optimal conditions, 97% of influent ammonium nitrogen (80% of total nitrogen) was removed at a rate of 86.5 mg N-NH(4)(+)/Ld. In the treated effluent only 0.2 mg N-NO(2)(-)/L,4.6 mg N-NO(3)(-)/L and 1.0 mg N-NH(4)(+)/L remained, demonstrating the potential viability of this process in post-treatment of wastewaters containing ammonium nitrogen.

The effect of millennial-scale changes in Arabian Sea denitrification on atmospheric CO2.

PubMed

Altabet, Mark A; Higginson, Matthew J; Murray, David W

2002-01-10

Most global biogeochemical processes are known to respond to climate change, some of which have the capacity to produce feedbacks through the regulation of atmospheric greenhouse gases. Marine denitrification-the reduction of nitrate to gaseous nitrogen-is an important process in this regard, affecting greenhouse gas concentrations directly through the incidental production of nitrous oxide, and indirectly through modification of the marine nitrogen inventory and hence the biological pump for CO2. Although denitrification has been shown to vary with glacial-interglacial cycles, its response to more rapid climate change has not yet been well characterized. Here we present nitrogen isotope ratio, nitrogen content and chlorin abundance data from sediment cores with high accumulation rates on the Oman continental margin that reveal substantial millennial-scale variability in Arabian Sea denitrification and productivity during the last glacial period. The detailed correspondence of these changes with Dansgaard-Oeschger events recorded in Greenland ice cores indicates rapid, century-scale reorganization of the Arabian Sea ecosystem in response to climate excursions, mediated through the intensity of summer monsoonal upwelling. Considering the several-thousand-year residence time of fixed nitrogen in the ocean, the response of global marine productivity to changes in denitrification would have occurred at lower frequency and appears to be related to climatic and atmospheric CO2 oscillations observed in Antarctic ice cores between 20 and 60 kyr ago.

THE FATE AND RETENTION OF ORGANIC AND INORGANIC 15N-NITROGEN IN AN OLD-GROWTH FOREST SOIL IN WESTERN OREGON

EPA Science Inventory

Forests in the Pacific northwestern region of North America receive very little nitrogen through atmospheric deposition and thus can provide insights into how the nitrogen cycle functioned before heavy atmospheric deposition of inorganic nitrogen began in other regions. Our obje...

Diurnal variability in carbon and nitrogen pools within Chesapeake Bay and northern Gulf of Mexico: implications for future ocean color satellite sensors

NASA Astrophysics Data System (ADS)

Mannino, A.; Novak, M. G.; Tzortziou, M.; Salisbury, J.

2016-02-01

Relative to their areal extent, estuaries and coastal ocean ecosystems contribute disproportionately more to global biogeochemical cycling of carbon, nitrogen and other elements compared to the open ocean. Applying ocean color satellite data to study biological and biogeochemical processes within coastal ecosystems is challenging due to the complex mixtures of aquatic constituents derived from terrestrial, anthropogenic, and marine sources, human-impacted atmospheric properties, presence of clouds during satellite overpass, fine-scale spatial gradients, and time-varying processes on diurnal scales that cannot be resolved with current sensors. On diurnal scales, biological, photochemical, and biogeochemical processes are regulated by the variation in solar radiation. Other physical factors, such as tides, river discharge, estuarine and coastal ocean circulation, wind-driven mixing, etc., impart further variability on biological and biogeochemical processes on diurnal to multi-day time scales. Efforts to determine the temporal frequency required from a NASA GEO-CAPE ocean color satellite sensor to discern diurnal variability C and N stocks, fluxes and productivity culminated in field campaigns in the Chesapeake Bay and northern Gulf of Mexico. Near-surface drogues were released and tracked in quasi-lagrangian space to monitor hourly changes in community production, C and N stocks, and optical properties. While only small diurnal changes were observed in dissolved organic carbon (DOC) and colored dissolved organic matter (CDOM) absorption in Chesapeake Bay, substantial variation in particulate organic carbon (POC) and nitrogen (PN), chlorophyll-a, and inorganic nitrogen (DIN) were measured. Similar or greater diurnal changes in POC, PN, chlorophyll-a and DIN were found in Gulf of Mexico nearshore and offshore sites. These results suggest that satellite observations at hourly frequency are desirable to capture diurnal variability in carbon and nitrogen stocks, fluxes and productivity within coastal ecosystems.

A Multiscale Approach to Modeling Carbon and Nitrogen Cycling within a High Elevation Watershed

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lawrence, Corey

This funding represents a small sub-award related the larger project titled: A Multiscale Approach to Modeling Carbon and Nitrogen Cycling within a High Elevation Watershed. The goal of the sub-award was to facilitate the characterization of carbon and radiocarbon data collected from the East River watershed outside Gothic, Colorado USA. During the period of funding from 8/1/15 until 7/31/17, we sampled 40 soil profiles and collected ~325 soil samples. This funding supported the collection, processing, and elemental analysis of each of these samples. In addition, the funding allowed for the further density separation of a subset of soil resulting inmore » 60 measurements of 13C and 14C of bulk soil and density separates. Funding also supported installation of temperature and moisture data sensors arrays, soil gas wells, and soil water lysimeters. From this infrastructure, a steady stream data including soil gas, water, and physical information have been generated to support the larger research project.« less

Nitrogen cycling in an extreme hyperarid environment inferred from δ(15)N analyses of plants, soils and herbivore diet.

PubMed

Díaz, Francisca P; Frugone, Matías; Gutiérrez, Rodrigo A; Latorre, Claudio

2016-03-09

Climate controls on the nitrogen cycle are suggested by the negative correlation between precipitation and δ(15)N values across different ecosystems. For arid ecosystems this is unclear, as water limitation among other factors can confound this relationship. We measured herbivore feces, foliar and soil δ(15)N and δ(13)C values and chemically characterized soils (pH and elemental composition) along an elevational/climatic gradient in the Atacama Desert, northern Chile. Although very positive δ(15)N values span the entire gradient, soil δ(15)N values show a positive correlation with aridity as expected. In contrast, foliar δ(15)N values and herbivore feces show a hump-shaped relationship with elevation, suggesting that plants are using a different N source, possibly of biotic origin. Thus at the extreme limits of plant life, biotic interactions may be just as important as abiotic processes, such as climate in explaining ecosystem δ(15)N values.

Nitrogen nutrition of poplar trees.

PubMed

Rennenberg, H; Wildhagen, H; Ehlting, B

2010-03-01

Many forest ecosystems have evolved at sites with growth-limiting nitrogen (N) availability, low N input from external sources and high ecosystem internal cycling of N. By contrast, many poplar species are frequent constituents of floodplain forests where they are exposed to a significant ecosystem external supply of N, mainly nitrate, in the moving water table. Therefore, nitrate is much more important for N nutrition of these poplar species than for many other tree species. We summarise current knowledge of nitrate uptake and its regulation by tree internal signals, as well as acquisition of ammonium and organic N from the soil. Unlike herbaceous plants, N nutrition of trees is sustained by seasonal, tree internal cycling. Recent advances in the understanding of seasonal storage and mobilisation in poplar bark and regulation of these processes by temperature and daylength are addressed. To explore consequences of global climate change on N nutrition of poplar trees, responses of N uptake and metabolism to increased atmospheric CO(2) and O(3) concentrations, increased air and soil temperatures, drought and salt stress are highlighted.

Nitrogen cycling in an extreme hyperarid environment inferred from δ15N analyses of plants, soils and herbivore diet

NASA Astrophysics Data System (ADS)

Díaz, Francisca P.; Frugone, Matías; Gutiérrez, Rodrigo A.; Latorre, Claudio

2016-03-01

Climate controls on the nitrogen cycle are suggested by the negative correlation between precipitation and δ15N values across different ecosystems. For arid ecosystems this is unclear, as water limitation among other factors can confound this relationship. We measured herbivore feces, foliar and soil δ15N and δ13C values and chemically characterized soils (pH and elemental composition) along an elevational/climatic gradient in the Atacama Desert, northern Chile. Although very positive δ15N values span the entire gradient, soil δ15N values show a positive correlation with aridity as expected. In contrast, foliar δ15N values and herbivore feces show a hump-shaped relationship with elevation, suggesting that plants are using a different N source, possibly of biotic origin. Thus at the extreme limits of plant life, biotic interactions may be just as important as abiotic processes, such as climate in explaining ecosystem δ15N values.

Nitrogen cycling in an extreme hyperarid environment inferred from δ15N analyses of plants, soils and herbivore diet

PubMed Central

Díaz, Francisca P.; Frugone, Matías; Gutiérrez, Rodrigo A.; Latorre, Claudio

2016-01-01

Climate controls on the nitrogen cycle are suggested by the negative correlation between precipitation and δ15N values across different ecosystems. For arid ecosystems this is unclear, as water limitation among other factors can confound this relationship. We measured herbivore feces, foliar and soil δ15N and δ13C values and chemically characterized soils (pH and elemental composition) along an elevational/climatic gradient in the Atacama Desert, northern Chile. Although very positive δ15N values span the entire gradient, soil δ15N values show a positive correlation with aridity as expected. In contrast, foliar δ15N values and herbivore feces show a hump-shaped relationship with elevation, suggesting that plants are using a different N source, possibly of biotic origin. Thus at the extreme limits of plant life, biotic interactions may be just as important as abiotic processes, such as climate in explaining ecosystem δ15N values. PMID:26956399

Placing an upper limit on cryptic marine sulphur cycling.

PubMed

Johnston, D T; Gill, B C; Masterson, A; Beirne, E; Casciotti, K L; Knapp, A N; Berelson, W

2014-09-25

A quantitative understanding of sources and sinks of fixed nitrogen in low-oxygen waters is required to explain the role of oxygen-minimum zones (OMZs) in controlling the fixed nitrogen inventory of the global ocean. Apparent imbalances in geochemical nitrogen budgets have spurred numerous studies to measure the contributions of heterotrophic and autotrophic N2-producing metabolisms (denitrification and anaerobic ammonia oxidation, respectively). Recently, 'cryptic' sulphur cycling was proposed as a partial solution to the fundamental biogeochemical problem of closing marine fixed-nitrogen budgets in intensely oxygen-deficient regions. The degree to which the cryptic sulphur cycle can fuel a loss of fixed nitrogen in the modern ocean requires the quantification of sulphur recycling in OMZ settings. Here we provide a new constraint for OMZ sulphate reduction based on isotopic profiles of oxygen ((18)O/(16)O) and sulphur ((33)S/(32)S, (34)S/(32)S) in seawater sulphate through oxygenated open-ocean and OMZ-bearing water columns. When coupled with observations and models of sulphate isotope dynamics and data-constrained model estimates of OMZ water-mass residence time, we find that previous estimates for sulphur-driven remineralization and loss of fixed nitrogen from the oceans are near the upper limit for what is possible given in situ sulphate isotope data.

Effects of global change during the 21st century onthe nitrogen cycle

NASA Astrophysics Data System (ADS)

Fowler, D.; Steadman, C. E.; Stevenson, D.; Coyle, M.; Rees, R. M.; Skiba, U. M.; Sutton, M. A.; Cape, J. N.; Dore, A. J.; Vieno, M.; Simpson, D.; Zaehle, S.; Stocker, B. D.; Rinaldi, M.; Facchini, M. C.; Flechard, C. R.; Nemitz, E.; Twigg, M.; Erisman, J. W.; Butterbach-Bahl, K.; Galloway, J. N.

2015-12-01

The global nitrogen (N) cycle at the beginning of the 21st century has been shown to be strongly influenced by the inputs of reactive nitrogen (Nr) from human activities, including combustion-related NOx, industrial and agricultural N fixation, estimated to be 220 Tg N yr-1 in 2010, which is approximately equal to the sum of biological N fixation in unmanaged terrestrial and marine ecosystems. According to current projections, changes in climate and land use during the 21st century will increase both biological and anthropogenic fixation, bringing the total to approximately 600 Tg N yr-1 by around 2100. The fraction contributed directly by human activities is unlikely to increase substantially if increases in nitrogen use efficiency in agriculture are achieved and control measures on combustion-related emissions implemented. Some N-cycling processes emerge as particularly sensitive to climate change. One of the largest responses to climate in the processing of Nr is the emission to the atmosphere of NH3, which is estimated to increase from 65 Tg N yr-1 in 2008 to 93 Tg N yr-1 in 2100 assuming a change in global surface temperature of 5 °C in the absence of increased anthropogenic activity. With changes in emissions in response to increased demand for animal products the combined effect would be to increase NH3 emissions to 135 Tg N yr-1. Another major change is the effect of climate changes on aerosol composition and specifically the increased sublimation of NH4NO3 close to the ground to form HNO3 and NH3 in a warmer climate, which deposit more rapidly to terrestrial surfaces than aerosols. Inorganic aerosols over the polluted regions especially in Europe and North America were dominated by (NH4)2SO4 in the 1970s to 1980s, and large reductions in emissions of SO2 have removed most of the SO42- from the atmosphere in these regions. Inorganic aerosols from anthropogenic emissions are now dominated by NH4NO3, a volatile aerosol which contributes substantially to PM10 and human health effects globally as well as eutrophication and climate effects. The volatility of NH4NO3 and rapid dry deposition of the vapour phase dissociation products, HNO3 and NH3, is estimated to be reducing the transport distances, deposition footprints and inter-country exchange of Nr in these regions. There have been important policy initiatives on components of the global N cycle. These have been regional or country-based and have delivered substantial reductions of inputs of Nr to sensitive soils, waters and the atmosphere. To date there have been no attempts to develop a global strategy to regulate human inputs to the nitrogen cycle. However, considering the magnitude of global Nr use, potential future increases, and the very large leakage of Nr in many forms to soils, waters and the atmosphere, international action is required. Current legislation will not deliver the scale of reductions globally for recovery from the effects of Nr deposition on sensitive ecosystems, or a decline in N2O emissions to the global atmosphere. Such changes would require substantial improvements in nitrogen use efficiency across the global economy combined with optimization of transport and food consumption patterns. This would allow reductions in Nr use, inputs to the atmosphere and deposition to sensitive ecosystems. Such changes would offer substantial economic and environmental co-benefits which could help motivate the necessary actions.

A program in global biology. [biota-environment interaction important to life

NASA Technical Reports Server (NTRS)

Mooneyhan, D. W.

1983-01-01

NASA's Global Biology Research Program and its goals for greater understanding of planetary biological processes are discussed. Consideration is given to assessing major pathways and rates of exchange of elements such as carbon and nitrogen, extrapolating local rates of anaerobic activities, determining exchange rates of ocean nutrients, and developing models for the global cycles of carbon, nitrogen, sulfur, and phosphorus. Satellites and sensors operating today are covered: the Nimbus, NOAA, and Landsat series. Block diagrams of the software and hardware for a typical ground data processing and analysis system are provided. Samples of the surface cover data achieved with the Advanced Very High Resolution Radiometer, the Multispectral Scanner, and the Thematic Mapper are presented, as well as a productive capacity model for coastal wetlands. Finally, attention is given to future goals, their engineering requirements, and the necessary data analysis system.

An Overview of Nitrogen Cycling in a Semiarid Savanna: Some Implications for Management and Conservation in a Large African Park

NASA Astrophysics Data System (ADS)

Coetsee, Corli; Jacobs, Shayne; Govender, Navashni

2012-02-01

Nitrogen (N) is a major control on primary productivity and hence on the productivity and diversity of secondary producers and consumers. As such, ecosystem structure and function cannot be understood without a comprehensive understanding of N cycling and dynamics. This overview describes the factors that govern N distribution and dynamics and the consequences that variable N dynamics have for structure, function and thresholds of potential concern (TPCs) for management of a semiarid southern African savanna. We focus on the Kruger National Park (KNP), a relatively intact savanna, noted for its wide array of animal and plant species and a prized tourist destination. KNP's large size ensures integrity of most ecosystem processes and much can be learned about drivers of ecosystem structure and function using this park as a baseline. Our overview shows that large scale variability in substrates exists, but do not necessarily have predictable consequences for N cycling. The impact of major drivers such as fire is complex; at a landscape scale little differences in stocks and cycling were found, though at a smaller scale changes in woody cover can lead to concomitant changes in total N. Contrasting impacts of browsers and grazers on N turnover has been recorded. Due to the complexity of this ecosystem, we conclude that it will be complicated to draw up TPCs for most transformations and pools involved with the N cycle. However, we highlight in which cases the development of TPCs will be possible.

Ammonia oxidizer populations vary with nitrogen cycling across a tropical montane mean annual temperature gradient

Treesearch

S. Pierre; I. Hewson; J. P. Sparks; C. M. Litton; C. Giardina; P. M. Groffman; T. J. Fahey

2017-01-01

Functional gene approaches have been used to better understand the roles of microbes in driving forest soil nitrogen (N) cycling rates and bioavailability. Ammonia oxidation is a rate limiting step in nitrification, and is a key area for understanding environmental constraints on N availability in forests. We studied how increasing temperature affects the role of...

Effects of forest harvest on stream-water quality and nitrogen cycling in the Caspar Creek watershed

Treesearch

Randy A. Dahlgren

1998-01-01

The effects of forest harvest on stream-water quality and nitrogen cycling were examined for a redwood/Douglas-fir ecosystem in the North Fork, Caspar Creek experimental watershed in northern California. Stream-water samples were collected from treated (e.g., clearcut) and reference (e.g., noncut) watersheds, and from various locations downstream from the treated...

Awakening of a Dormant Cyanobacterium from Nitrogen Chlorosis Reveals a Genetically Determined Program.

PubMed

Klotz, Alexander; Georg, Jens; Bučinská, Lenka; Watanabe, Satoru; Reimann, Viktoria; Januszewski, Witold; Sobotka, Roman; Jendrossek, Dieter; Hess, Wolfgang R; Forchhammer, Karl

2016-11-07

The molecular and physiological mechanisms involved in the transition of microbial cells from a resting state to the active vegetative state are critically relevant for solving problems in fields ranging from microbial ecology to infection microbiology. Cyanobacteria that cannot fix nitrogen are able to survive prolonged periods of nitrogen starvation as chlorotic cells in a dormant state. When provided with a usable nitrogen source, these cells re-green within 48 hr and return to vegetative growth. Here we investigated the resuscitation of chlorotic Synechocystis sp. PCC 6803 cells at the physiological and molecular levels with the aim of understanding the awakening process of a dormant bacterium. Almost immediately upon nitrate addition, the cells initiated a highly organized resuscitation program. In the first phase, they suppressed any residual photosynthetic activity and activated respiration to gain energy from glycogen catabolism. Concomitantly, they restored the entire translational apparatus, ATP synthesis, and nitrate assimilation. After only 12-16 hr, the cells re-activated the synthesis of the photosynthetic apparatus and prepared for metabolic re-wiring toward photosynthesis. When the cells reached full photosynthetic capacity after ∼48 hr, they resumed cell division and entered the vegetative cell cycle. An analysis of the transcriptional dynamics during the resuscitation process revealed a perfect match to the observed physiological processes, and it suggested that non-coding RNAs play a major regulatory role during the lifestyle switch in awakening cells. This genetically encoded program ensures rapid colonization of habitats in which nitrogen starvation imposes a recurring growth limitation. Copyright © 2016 Elsevier Ltd. All rights reserved.

Dominance of organic nitrogen from headwater streams to large rivers across the conterminous United States

USGS Publications Warehouse

Scott, D.; Harvey, J.; Alexander, R.; Schwarz, G.

2007-01-01

The frequency and magnitude of hypoxic areas in coastal waterbodies are increasing across the globe, partially in response to the increase in nitrogen delivery from the landscape (Diaz, 2001; Rabalais et al., 2002). Although studies of annual total nitrogen and nitrate yields have greatly improved understanding of the contaminant sources that contribute to riverine nitrogen loads (Alexander et al., 2000; Caraco and Cole, 1999), the emphasis of these studies on annual timescales and selected nitrogen forms is not sufficient to understand the factors that control the cycling, transport, and fate of reactive nitrogen. Here we use data from 850 river stations to calculate long-term mean-annual and interannual loads of organic, ammonia, and nitrate-nitrite nitrogen suitable for spatial analysis. We find that organic nitrogen is the dominant nitrogen pool within rivers across most of the United States and is significant even in basins with high anthropogenic sources of nitrogen. Downstream organic nitrogen patterns illustrate that organic nitrogen is an abundant fraction of the nitrogen loads in all regions. Although the longitudinal patterns are not consistent across regions, these patterns are suggestive of cycling between ON and NO3- on seasonal timescales influenced by land use, stream morphology, and riparian connectivity with active floodplains. Future regional studies need to incorporate multinitrogen species at intraannual timescales, as well as stream characteristics beyond channel depth, to elucidate the roles of nitrogen sources and in-stream transformations on the fate and reactivity of riverine nitrogen transported to coastal seas.

Dominance of organic nitrogen from headwater streams to large rivers across the conterminous United States

NASA Astrophysics Data System (ADS)

Scott, Durelle; Harvey, Judson; Alexander, Richard; Schwarz, Gregory

2007-03-01

The frequency and magnitude of hypoxic areas in coastal waterbodies are increasing across the globe, partially in response to the increase in nitrogen delivery from the landscape (Diaz, 2001; Rabalais et al., 2002). Although studies of annual total nitrogen and nitrate yields have greatly improved understanding of the contaminant sources that contribute to riverine nitrogen loads (Alexander et al., 2000; Caraco and Cole, 1999), the emphasis of these studies on annual timescales and selected nitrogen forms is not sufficient to understand the factors that control the cycling, transport, and fate of reactive nitrogen. Here we use data from 850 river stations to calculate long-term mean-annual and interannual loads of organic, ammonia, and nitrate-nitrite nitrogen suitable for spatial analysis. We find that organic nitrogen is the dominant nitrogen pool within rivers across most of the United States and is significant even in basins with high anthropogenic sources of nitrogen. Downstream organic nitrogen patterns illustrate that organic nitrogen is an abundant fraction of the nitrogen loads in all regions. Although the longitudinal patterns are not consistent across regions, these patterns are suggestive of cycling between ON and NO3- on seasonal timescales influenced by land use, stream morphology, and riparian connectivity with active floodplains. Future regional studies need to incorporate multinitrogen species at intraannual timescales, as well as stream characteristics beyond channel depth, to elucidate the roles of nitrogen sources and in-stream transformations on the fate and reactivity of riverine nitrogen transported to coastal seas.

Cascading costs: an economic nitrogen cycle.

PubMed

Moomaw, William R; Birch, Melissa B L

2005-09-01

The chemical nitrogen cycle is becoming better characterized in terms of fluxes and reservoirs on a variety of scales. Galloway has demonstrated that reactive nitrogen can cascade through multiple ecosystems causing environmental damage at each stage before being denitrified to N(2). We propose to construct a parallel economic nitrogen cascade (ENC) in which economic impacts of nitrogen fluxes can be estimated by the costs associated with each stage of the chemical cascade. Using economic data for the benefits of damage avoided and costs of mitigation in the Chesapeake Bay basin, we have constructed an economic nitrogen cascade for the region. Since a single ton of nitrogen can cascade through the system, the costs also cascade. Therefore evaluating the benefits of mitigating a ton of reactive nitrogen released needs to consider the damage avoided in all of the ecosystems through which that ton would cascade. The analysis reveals that it is most cost effective to remove a ton of nitrogen coming from combustion since it has the greatest impact on human health and creates cascading damage through the atmospheric, terrestrial, aquatic and coastal ecosystems. We will discuss the implications of this analysis for determining the most cost effective policy option for achieving environmental quality goals.

Cascading costs: an economic nitrogen cycle.

PubMed

Moomaw, William R; Birch, Melissa B L

2005-12-01

The chemical nitrogen cycle is becoming better characterized in terms of fluxes and reservoirs on a variety of scales. Galloway has demonstrated that reactive nitrogen can cascade through multiple ecosystems causing environmental damage at each stage before being denitrified to N2. We propose to construct a parallel economic nitrogen cascade (ENC) in which economic impacts of nitrogen fluxes can be estimated by the costs associated with each stage of the chemical cascade. Using economic data for the benefits of damage avoided and costs of mitigation in the Chesapeake Bay basin, we have constructed an economic nitrogen cascade for the region. Since a single tonne of nitrogen can cascade through the system, the costs also cascade. Therefore evaluating the benefits of mitigating a tonne of reactive nitrogen released needs to consider the damage avoided in all of the ecosystems through which that tonne would cascade. The analysis reveals that it is most cost effective to remove a tonne of nitrogen coming from combustion since it has the greatest impact on human health and creates cascading damage through the atmospheric, terrestrial, aquatic and coastal ecosystems. We will discuss the implications of this analysis for determining the most cost effective policy option for achieving environmental quality goals.

Sagebrush carrying out hydraulic lift enhances surface soil nitrogen cycling and nitrogen uptake into inflorescences.

PubMed

Cardon, Zoe G; Stark, John M; Herron, Patrick M; Rasmussen, Jed A

2013-11-19

Plant roots serve as conduits for water flow not only from soil to leaves but also from wetter to drier soil. This hydraulic redistribution through root systems occurs in soils worldwide and can enhance stomatal opening, transpiration, and plant carbon gain. For decades, upward hydraulic lift (HL) of deep water through roots into dry, litter-rich, surface soil also has been hypothesized to enhance nutrient availability to plants by stimulating microbially controlled nutrient cycling. This link has not been demonstrated in the field. Working in sagebrush-steppe, where water and nitrogen limit plant growth and reproduction and where HL occurs naturally during summer drought, we slightly augmented deep soil water availability to 14 HL+ treatment plants throughout the summer growing season. The HL+ sagebrush lifted greater amounts of water than control plants and had slightly less negative predawn and midday leaf water potentials. Soil respiration was also augmented under HL+ plants. At summer's end, application of a gas-based (15)N isotopic labeling technique revealed increased rates of nitrogen cycling in surface soil layers around HL+ plants and increased uptake of nitrogen into HL+ plants' inflorescences as sagebrush set seed. These treatment effects persisted even though unexpected monsoon rainstorms arrived during assays and increased surface soil moisture around all plants. Simulation models from ecosystem to global scales have just begun to include effects of hydraulic redistribution on water and surface energy fluxes. Results from this field study indicate that plants carrying out HL can also substantially enhance decomposition and nitrogen cycling in surface soils.

Coupling of oceanic carbon and nitrogen facilitates spatially resolved quantitative reconstruction of nitrate inventories.

PubMed

Glock, Nicolaas; Erdem, Zeynep; Wallmann, Klaus; Somes, Christopher J; Liebetrau, Volker; Schönfeld, Joachim; Gorb, Stanislav; Eisenhauer, Anton

2018-03-23

Anthropogenic impacts are perturbing the global nitrogen cycle via warming effects and pollutant sources such as chemical fertilizers and burning of fossil fuels. Understanding controls on past nitrogen inventories might improve predictions for future global biogeochemical cycling. Here we show the quantitative reconstruction of deglacial bottom water nitrate concentrations from intermediate depths of the Peruvian upwelling region, using foraminiferal pore density. Deglacial nitrate concentrations correlate strongly with downcore δ 13 C, consistent with modern water column observations in the intermediate Pacific, facilitating the use of δ 13 C records as a paleo-nitrate-proxy at intermediate depths and suggesting that the carbon and nitrogen cycles were closely coupled throughout the last deglaciation in the Peruvian upwelling region. Combining the pore density and intermediate Pacific δ 13 C records shows an elevated nitrate inventory of >10% during the Last Glacial Maximum relative to the Holocene, consistent with a δ 13 C-based and δ 15 N-based 3D ocean biogeochemical model and previous box modeling studies.

Multi-stage combustion using nitrogen-enriched air

DOEpatents

Fischer, Larry E.; Anderson, Brian L.

2004-09-14

Multi-stage combustion technology combined with nitrogen-enriched air technology for controlling the combustion temperature and products to extend the maintenance and lifetime cycles of materials in contact with combustion products and to reduce pollutants while maintaining relatively high combustion and thermal cycle efficiencies. The first stage of combustion operates fuel rich where most of the heat of combustion is released by burning it with nitrogen-enriched air. Part of the energy in the combustion gases is used to perform work or to provide heat. The cooled combustion gases are reheated by additional stages of combustion until the last stage is at or near stoichiometric conditions. Additional energy is extracted from each stage to result in relatively high thermal cycle efficiency. The air is enriched with nitrogen using air separation technologies such as diffusion, permeable membrane, absorption, and cryogenics. The combustion method is applicable to many types of combustion equipment, including: boilers, burners, turbines, internal combustion engines, and many types of fuel including hydrogen and carbon-based fuels including methane and coal.

Isotopic composition of skeleton-bound organic nitrogen in reef-building symbiotic corals: A new method and proxy evaluation at Bermuda

NASA Astrophysics Data System (ADS)

Wang, X. T.; Sigman, D. M.; Cohen, A. L.; Sinclair, D. J.; Sherrell, R. M.; Weigand, M. A.; Erler, D. V.; Ren, H.

2015-01-01

The skeleton-bound organic nitrogen in reef-building symbiotic corals may be a high-resolution archive of ocean nitrogen cycle dynamics and a tool for understanding coral biogeochemistry and physiological processes. However, the existing methods for measuring the isotopic composition of coral skeleton-bound organic nitrogen (hereafter, CS-δ15N) either require too much skeleton material or have low precision, limiting the applications of this relatively new proxy. In addition, the controlling factors on CS-δ15N remain poorly understood: the δ15N of source nitrogen and the internal nitrogen cycle of the coral/zooxanthellae symbiosis may both be important. Here, we describe a new ("persulfate/denitrifier"-based) method for measuring CS-δ15N, requiring only 5 mg of skeleton material and yielding a long-term precision better than 0.2‰ (1σ). Using this new method, we investigate CS-δ15N at Bermuda. Ten modern Diploria labyrinthiformis coral cores/colonies from 4 sampling sites were measured for CS-δ15N. Nitrogen concentrations (nitrate + nitrite, ammonium, and dissolved organic nitrogen) and δ15N of plankton were also measured at these coral sites. Among the 4 sampling sites, CS-δ15N shows an increase with proximity to the island, from ∼3.8‰ to ∼6.8‰ vs. atmospheric N2, with the northern offshore site having a CS-δ15N 1-2‰ higher than the δ15N of thermocline nitrate in the surrounding Sargasso Sea. Two annually resolved CS-δ15N time series suggest that the offshore-inshore CS-δ15N gradient has persisted since at least the 1970s. Plankton δ15N among these 4 sites also has an inshore increase, but of only ∼1‰. Coral physiological change must explain the remaining (∼2‰) inshore increase in CS-δ15N, and previous work points to the coral/zooxanthellae N cycle as a control on host tissue (and thus carbonate skeletal) δ15N. The CS-δ15N gradient is hypothesized to result mainly from varying efficiency in the internal nitrogen recycling of the coral/zooxanthellae symbiosis. It is proposed that, in more productive inshore waters, greater food uptake by the coral causes a greater fraction of its low-δ15N regenerated ammonium to be excreted rather than assimilated by zooxanthellae, raising the δ15N of the inshore corals. If so, coral tissue- and CS-δ15N may prove of use to reconstruct and monitor the state of the coral/zooxanthellae symbiosis over space and time.

Nitrogen removal and intentional nitrous oxide production from reject water in a coupled nitritation/nitrous denitritation system under real feed-stream conditions.

PubMed

Weißbach, Max; Thiel, Paul; Drewes, Jörg E; Koch, Konrad

2018-05-01

A Coupled Aerobic-anoxic Nitrous Decomposition Operation (CANDO) was performed over five months to investigate the performance and dynamics of nitrogen elimination and nitrous oxide production from digester reject water under real feed-stream conditions. A 93% conversion of ammonium to nitrite could be maintained for adapted seed sludge in the first stage (nitritation). The second stage (nitrous denitritation), inoculated with conventional activated sludge, achieved a conversion of 70% of nitrite to nitrous oxide after only 12 cycles of operation. The development of an alternative feeding strategy and the addition of a coagulant (FeCl 3 ) facilitated stable operation and process intensification. Under steady-state conditions, nitrite was reliably eliminated and different nitrous oxide harvesting strategies were assessed. Applying continuous removal increased N 2 O yields by 16% compared to the application of a dedicated stripping phase. These results demonstrate the feasible application of the CANDO process for nitrogen removal and energy recovery from ammonia rich wastewater. Copyright © 2018 Elsevier Ltd. All rights reserved.

Nitrogen and Phosphorus Budgets in the Northwestern Mediterranean Deep Convection Region

NASA Astrophysics Data System (ADS)

Kessouri, Faycal; Ulses, Caroline; Estournel, Claude; Marsaleix, Patrick; Severin, Tatiana; Pujo-Pay, Mireille; Caparros, Jocelyne; Raimbault, Patrick; Pasqueron de Fommervault, Orens; D'Ortenzio, Fabrizio; Taillandier, Vincent; Testor, Pierre; Conan, Pascal

2017-12-01

The aim of this study is to understand the biogeochemical cycles of the northwestern Mediterranean Sea (NW Med), where a recurrent spring bloom related to dense water formation occurs. We used a coupled physical-biogeochemical model at high resolution to simulate realistic 1 year period and analyze the nitrogen (N) and phosphorus (P) cycles. First, the model was evaluated using cruises carried out in winter, spring, and summer and a Bio-Argo float deployed in spring. Then, the annual cycle of meteorological and hydrodynamical forcing and nutrients stocks in the upper layer were analyzed. Third, the effect of biogeochemical and physical processes on N and P was quantified. Fourth, we quantified the effects of the physical and biological processes on the seasonal changes of the molar NO3:PO4 ratio, particularly high compared to the global ocean. The deep convection reduced the NO3:PO4 ratio of upper waters, but consumption by phytoplankton increased it. Finally, N and P budgets were estimated. At the annual scale, this area constituted a sink of inorganic and a source of organic N and P for the peripheral area. NO3 and PO4 were horizontally advected from the peripheral regions into the intermediate waters (130-800 m) of the deep convection area, while organic matter was exported throughout the whole water column toward the surrounding areas. The annual budget suggests that the NW Med deep convection constitutes a major source of nutrients for the photic zone of the Mediterranean Sea.

Water column biogeochemistry of oxygen minimum zones in the eastern tropical North Atlantic and eastern tropical South Pacific Oceans

NASA Astrophysics Data System (ADS)

Löscher, C. R.; Bange, H. W.; Schmitz, R. A.; Callbeck, C. M.; Engel, A.; Hauss, H.; Kanzow, T.; Kiko, R.; Lavik, G.; Loginova, A.; Melzner, F.; Neulinger, S. C.; Pahlow, M.; Riebesell, U.; Schunck, H.; Thomsen, S.; Wagner, H.

2015-03-01

Recent modeling results suggest that oceanic oxygen levels will decrease significantly over the next decades to centuries in response to climate change and altered ocean circulation. Hence the future ocean may experience major shifts in nutrient cycling triggered by the expansion and intensification of tropical oxygen minimum zones (OMZs). There are numerous feedbacks between oxygen concentrations, nutrient cycling and biological productivity; however, existing knowledge is insufficient to understand physical, chemical and biological interactions in order to adequately assess past and potential future changes. We investigated the pelagic biogeochemistry of OMZs in the eastern tropical North Atlantic and eastern tropical South Pacific during a series of cruise expeditions and mesocosm studies. The following summarizes the current state of research on the influence of low environmental oxygen conditions on marine biota, viruses, organic matter formation and remineralization with a particular focus on the nitrogen cycle in OMZ regions. The impact of sulfidic events on water column biogeochemistry, originating from a specific microbial community capable of highly efficient carbon fixation, nitrogen turnover and N2O production is further discussed. Based on our findings, an important role of sinking particulate organic matter in controlling the nutrient stochiometry of the water column is suggested. These particles can enhance degradation processes in OMZ waters by acting as microniches, with sharp gradients enabling different processes to happen in close vicinity, thus altering the interpretation of oxic and anoxic environments.

Modeling Nitrogen Fate and Transport at the Sediment-Water ...

EPA Pesticide Factsheets

Diffusive mass transfer at media interfaces exerts control on the fate and transport of pollutants originating from agricultural and urban landscapes and affects the con-ditions of water bodies. Diffusion is essentially a physical process affecting the distribution and fate of various environmental pollutants such as nutrients, pesticides, metals, PCBs, PAHs, etc. Environmental problems caused by excessive use of agricultural chemicals (e.g., pesticides and fertilizers) and improper discharge of industrial waste and fuel leaks are all influenced by the diffusive nature of pollutants in the environment. Eutrophication is one such environmental problem where the sediment-water interface exerts a significant physical and geochemical control on the eutrophic condition of the stressed water body. Exposure of streams and lakes to contaminated sediment is another common environmental problem whereby transport of the contaminant (PCBs, PAHs, and other organic contaminants) across the sediment water can increase the risk for exposure to the chemicals and pose a significant health hazard to aquatic life and human beings. This chapter presents analytical and numerical models describing fate and transport phenomena at the sediment-water interface in freshwater ecosystems, with the primary focus on nitrogen cycling and the applicability of the models to real-world environmental problems and challenges faced in their applications. The first model deals with nitrogen cycling

Synthesis and characterization of nitrogen-doped graphene hollow spheres as electrode material for supercapacitors

NASA Astrophysics Data System (ADS)

Xia, Kechan; Wang, Guoxu; Zhang, Hongliang; Yu, Yifeng; Liu, Lei; Chen, Aibing

2017-07-01

Recently, the rapid development of graphene industry in the world, especially in China, provides more opportunities for the further extension of the application field of graphene-based materials. Graphene has also been considered as a promising candidate for use in supercapacitors. Here, nitrogen-doped graphene hollow spheres (NGHS) have been successfully synthesized by using industrialized and pre-processed graphene oxide (GO) as raw material, SiO2 spheres as hard templates, and urea as reducing-doping agents. The results demonstrate that the content and pretreatment of GO sheets have important effect on the uniform spherical morphologies of the obtained samples. Industrialized GO and low-cost urea are used to prepare graphene hollow spheres, which can be a promising route to achieve mass production of NGHS. The obtained NGHS have a cavity of about 270 nm, specific surface area of 402.9 m2 g-1, ultrathin porous shells of 2.8 nm, and nitrogen content of 6.9 at.%. As electrode material for supercapacitors, the NGHS exhibit a specific capacitance of 159 F g-1 at a current density of 1 A g-1 in 6 M KOH aqueous electrolyte. Moreover, the NGHS exhibit superior cycling stability with 99.24% capacitive retention after 5000 charge/discharge cycles at a current density of 5 A g-1.

Former land-use and tree species affect nitrogen oxide emissions from a tropical dry forest.

Treesearch

Heather Erickson; Eric A. Davidson; Michael Keller

2002-01-01

Species composition in successional dry forests in the tropics varies widely, but the effect of this variation on biogeochemical processes is not well known. We examined fluxes of N oxides (nitrous and nitric oxide), soil N cycling, and litter chemistry (C/N ratio) in four successional dry forests on similar soils in western Puerto Rico with differing species...

Enhanced litter input rather than changes in litter chemistry drive soil carbon and nitrogen cycles under elevated CO2: a microcosm study

Treesearch

Lingli Lui; John S. King; Fitzgerald L. Booker; Christian P. Giardina; H. Lee Allen; Shuijin Hu

2009-01-01

Elevated CO2 has been shown to stimulate plant productivity and change litter chemistry. These changes in substrate availability may then alter soil microbial processes and possibly lead to feedback effects on N availability. However, the strength of this feedback, and even its direction, remains unknown. Further, uncertainty remains whether...

Mycorrhizal Controls on Nitrogen Uptake Drive Carbon Cycling at the Global Scale

NASA Astrophysics Data System (ADS)

Shi, M.; Fisher, J. B.; Brzostek, E. R.; Phillips, R.

2015-12-01

Nearly all plants form symbiotic relationships with one of two types of mycorrhizal fungi—arbuscular mycorrhizae (AM) and ectomycorrhizal (ECM) fungi, which are essential to global biogeochemical cycling of nutrient elements. In soils with higher rates of nitrogen and phosphorus mineralization from organic matter, AM-associated plants can be better adapted than ECM-associated plants. Importantly, the photosynthate costs of nutrient uptake for AM-associated plants are usually lower than that for ECM-associated plants. Thus, the global carbon cycle is closely coupled with mycorrhizal controls on N uptake. To investigate the potential climate dependence of terrestrial environments from AM- and ECM-associated plants, this study uses the Community Atmosphere Model (CAM) with a plant productivity-optimized N acquisition model—the Fixation and Uptake of Nitrogen (FUN) model—integrated into its land model—the Community Land Model (CLM). This latest version of CLM coupled with FUN allows for the assessment of mycorrhizal controls on global biogeochemical cycling. Here, we show how the historical evolution of AM- and ECM-associations altered regional and global biogeochemical cycling and climate, and future projections over the next century.

Conversion of uniform graphene oxide/polypyrrole composites into functionalized 3D carbon nanosheet frameworks with superior supercapacitive and sodium-ion storage properties

NASA Astrophysics Data System (ADS)

Wang, Huanwen; Zhang, Yu; Sun, Wenping; Tan, Hui Teng; Franklin, Joseph B.; Guo, Yuanyuan; Fan, Haosen; Ulaganathan, Mani; Wu, Xing-Long; Luo, Zhong-Zhen; Madhavi, Srinivasan; Yan, Qingyu

2016-03-01

Two-dimensional (2D) graphene oxide/polypyrrole (GO/PPy) hybrid materials derived from in-situ polymerization are used as precursors for constructing functionalized three-dimensional (3D) porous nitrogen-doped carbon nanosheet frameworks (FT-PNCNFs) through a one-step activation strategy. In the formation process of FT-PNCNFs, PPY is directly converted into hierarchical porous nitrogen-doped carbon layers, while GO is simultaneously reduced to become electrically conductive. The complementary functions of individual components endow the FT-PNCNFs with excellent properties for both supercapacitors (SCs) and sodium ion batteries (SIBs) applications. When tested in symmetrical SC, the FT-PNCNFs demonstrate superior energy storage behaviour. At an extremely high scan rate of 3000 mV s-1, the cyclic voltammetry (CV) curve retains an inspiring quasi-rectangle shape in KOH solution. Meanwhile, high capacitances (∼247 F g-1 at 10 mV s-1; ∼146 F g-1 at 3000 mV s-1) and good cycling stability (∼95% retention after 8000 cycles) are achieved. In addition, an attractive SIB anode performance could be achieved. The FT-PNCNFs electrode delivers a reversible capacity of 187 mAh g-1 during 160th cycle at 100 mA g-1. Its reversible capacity retains 144 mAh g-1 after extending the number of cycles to 500 at 500 mA g-1.

Reactive nitrogen deposition to South East Asian rainforest

NASA Astrophysics Data System (ADS)

di Marco, Chiara F.; Phillips, Gavin J.; Thomas, Rick; Tang, Sim; Nemitz, Eiko; Sutton, Mark A.; Fowler, David; Lim, Sei F.

2010-05-01

The supply of reactive nitrogen (N) to global terrestrial ecosystems has doubled since the 1960s as a consequence of human activities, such as fertilizer application and production of nitrogen oxides by fossil-fuel burning. The deposition of atmospheric N species constitutes a major nutrient input to the biosphere. Tropical forests have been undergoing a radical land use change by increasing cultivation of sugar cane and oil palms and the remaining forests are increasingly affected by anthropogenic activities. Yet, quantifications of atmospheric nitrogen deposition to tropical forests, and nitrogen cycling under near-pristine and polluted conditions are rare. The OP3 project ("Oxidant and Particle Photochemical Processes above a Southeast Asian Tropical Rainforest") was conceived to study how emissions of reactive trace gases from a tropical rain forest mediate the regional scale production and processing of oxidants and particles, and to better understand the impact of these processes on local, regional and global scale atmospheric composition, chemistry and climate. As part of this study we have measured reactive, nitrogen containing trace gas (ammonia, nitric acid) and the associated aerosol components (ammonium, nitrate) at monthly time resolution using a simple filter / denuder for 16 months. These measurements were made at the Bukit Atur Global Atmospheric Watch tower near Danum Valley in the Malaysian state of Sabah, Borneo. In addition, the same compounds were measured at hourly time-resolution during an intensive measurement period, with a combination of a wet-chemistry system based on denuders and steam jet aerosol collectors and an aerosol mass spectrometer (HR-ToF-AMS), providing additional information on the temporal controls. During this period, concentrations and fluxes of NO, NO2 and N2O were also measured. The measurements are used for inferential dry deposition modelling and combined with wet deposition data from the South East Asian Acid Deposition Network to estimate the total annual atmospheric reactive nitrogen deposition to this tropical forest ecosystem and to quantify the relative contribution of the different chemical compounds.

Nitrogen-doped porous graphitic carbon as an excellent electrode material for advanced supercapacitors.

PubMed

Sun, Li; Tian, Chungui; Fu, Yu; Yang, Ying; Yin, Jie; Wang, Lei; Fu, Honggang

2014-01-07

An advanced supercapacitor material based on nitrogen-doped porous graphitic carbon (NPGC) with high a surface area was synthesized by means of a simple coordination-pyrolysis combination process, in which tetraethyl orthosilicate (TEOS), nickel nitrate, and glucose were adopted as porogent, graphitic catalyst precursor, and carbon source, respectively. In addition, melamine was selected as a nitrogen source owing to its nitrogen-enriched structure and the strong interaction between the amine groups and the glucose unit. A low-temperature treatment resulted in the formation of a NPGC precursor by combination of the catalytic precursor, hydrolyzed TEOS, and the melamine-glucose unit. Following pyrolysis and removal of the catalyst and porogent, the NPGC material showed excellent electrical conductivity owing to its high crystallinity, a large Brunauer-Emmett-Teller surface area (SBET =1027 m(2)  g(-1) ), and a high nitrogen level (7.72 wt %). The unusual microstructure of NPGC materials could provide electrochemical energy storage. The NPGC material, without the need for any conductive additives, showed excellent capacitive behavior (293 F g(-1) at 1 A g(-1) ), long-term cycling stability, and high coulombic efficiency (>99.9 % over 5000 cycles) in KOH when used as an electrode. Notably, in a two-electrode symmetric supercapacitor, NPGC energy densities as high as 8.1 and 47.5 Wh kg(-1) , at a high power density (10.5 kW kg(-1) ), were achieved in 6 M KOH and 1 M Et4 NBF4 -PC electrolytes, respectively. Thus, the synthesized NPGC material could be a highly promising electrode material for advanced supercapacitors and other conversion devices. Copyright © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Complementary Constraints from Carbon (13C) and Nitrogen (15N) Isotopes on the Efficiency of the Glacial Ocean's Soft-Tissue Biological Pump

NASA Astrophysics Data System (ADS)

Schmittner, A.; Somes, C. J.

2016-12-01

A three-dimensional, process-based model of the ocean's carbon and nitrogen cycles, including 13C and 15N isotopes, is used to explore effects of idealized changes in the soft-tissue biological pump. Results are presented from one preindustrial control run and six simulations of the Last Glacial Maximum (LGM) with increasing values of the spatially constant maximum phytoplankton growth rate μmax, which mimicks iron fertilization. The default LGM simulation, without increasing μmax and with a shallower and weaker Atlantic Meridional Overturning Circulation and increased sea ice cover, leads to 280 Pg more respired organic carbon (Corg) than the pre-industrial control. Dissolved oxygen in the thermocline increase, which reduces water column denitrification and nitrogen fixation, thus increasing the ocean's fixed nitrogen inventory and decreasing δ15NNO3. This simulation already fits observed carbon and nitrogen isotopes relatively well, but it overestimates deep ocean δ13CDIC and underestimates δ15NNO3 at high latitudes. Increasing μmax enhances Corg and lowers deep ocean δ13CDIC, improving the fit. Modest increases in μmax result in higher subpolar δ15NNO3 due to enhanced local nutrient utilization, and better agreement with reconstructions. Large increases in nutrient utilization are inconsistent with nitrogen isotopes although they still fit the carbon isotopes reasonably well. The best fitting models with modest increases in μmax reproduce major features of the glacial δ13CDIC, δ15N, and oxygen reconstructions while simulating increased Corg by 510-670 Pg. These results are consistent with the idea that the soft-tissue pump was more efficient during the LGM. Both circulation and biological nutrient utilization contribute. However, these conclusions are preliminary given our idealized experiments, which do not consider changes in benthic denitrification and spatially inhomogenous changes in aeolian iron fluxes. The analysis illustrates interactions between the carbon and nitrogen cycles as well as the complementary constraints provided by their isotopes. Whereas carbon isotopes are sensitive to circulation changes and indicate well the three-dimensional Corg distribution, nitrogen isotopes are more sensitive to biological nutrient utilization.

Stimulation of microbial nitrogen cycling in aquatic ecosystems by benthic macrofauna: mechanisms and environmental implications

NASA Astrophysics Data System (ADS)

Stief, P.

2013-12-01

Invertebrate animals that live at the bottom of aquatic ecosystems (i.e., benthic macrofauna) are important mediators between nutrients in the water column and microbes in the benthos. The presence of benthic macrofauna stimulates microbial nutrient dynamics through different types of animal-microbe interactions, which potentially affect the trophic status of aquatic ecosystems. This review contrasts three types of animal-microbe interactions in the benthos of aquatic ecosystems: (i) ecosystem engineering, (ii) grazing, and (iii) symbiosis. Their specific contributions to the turnover of fixed nitrogen (mainly nitrate and ammonium) and the emission of the greenhouse gas nitrous oxide are evaluated. Published data indicate that ecosystem engineering by sediment-burrowing macrofauna stimulates benthic nitrification and denitrification, which together allows fixed nitrogen removal. However, the release of ammonium from sediments is enhanced more strongly than the sedimentary uptake of nitrate. Ecosystem engineering by reef-building macrofauna increases nitrogen retention and ammonium concentrations in shallow aquatic ecosystems, but allows organic nitrogen removal through harvesting. Grazing by macrofauna on benthic microbes apparently has small or neutral effects on nitrogen cycling. Animal-microbe symbioses provide abundant and distinct benthic compartments for a multitude of nitrogen-cycle pathways. Recent studies reveal that ecosystem engineering, grazing, and symbioses of benthic macrofauna significantly enhance nitrous oxide emission from shallow aquatic ecosystems. The beneficial effect of benthic macrofauna on fixed nitrogen removal through coupled nitrification-denitrification can thus be offset by the concurrent release of (i) ammonium that stimulates aquatic primary production and (ii) nitrous oxide that contributes to global warming. Overall, benthic macrofauna intensifies the coupling between benthos, pelagial, and atmosphere through enhanced turnover and transport of nitrogen.

Stimulation of microbial nitrogen cycling in aquatic ecosystems by benthic macrofauna: mechanisms and environmental implications

NASA Astrophysics Data System (ADS)

Stief, P.

2013-07-01

Invertebrate animals that live at the bottom of aquatic ecosystems (i.e., benthic macrofauna) are important mediators between nutrients in the water column and microbes in the benthos. The presence of benthic macrofauna stimulates microbial nutrient dynamics through different types of animal-microbe interactions, which potentially affect the trophic status of aquatic ecosystems. This review contrasts three types of animal-microbe interactions in the benthos of aquatic ecosystems: (i) ecosystem engineering, (ii) grazing, and (iii) symbiosis. Their specific contributions to the turnover of fixed nitrogen (mainly nitrate and ammonium) and the emission of the greenhouse gas nitrous oxide are evaluated. Published data indicate that ecosystem engineering by sediment-burrowing macrofauna stimulates benthic nitrification and denitrification, which together allows fixed nitrogen removal. However, the release of ammonium from sediments often is enhanced even more than the sedimentary uptake of nitrate. Ecosystem engineering by reef-building macrofauna increases nitrogen retention and ammonium concentrations in shallow aquatic ecosystems, but allows organic nitrogen removal through harvesting. Grazing by macrofauna on benthic microbes apparently has small or neutral effects on nitrogen cycling. Animal-microbe symbioses provide abundant and distinct benthic compartments for a multitude of nitrogen-cycle pathways. Recent studies revealed that ecosystem engineering, grazing, and symbioses of benthic macrofauna significantly enhance nitrous oxide emission from shallow aquatic ecosystems. The beneficial effect of benthic macrofauna on fixed nitrogen removal through coupled nitrification-denitrification can thus be offset by the concurrent release of (i) ammonium that stimulates aquatic primary production and (ii) nitrous oxide that contributes to global warming. Overall, benthic macrofauna intensifies the coupling between benthos, pelagial, and atmosphere through enhanced turnover and transport of nitrogen.

Genome-to-Watershed Predictive Understanding of Terrestrial Environments

NASA Astrophysics Data System (ADS)

Hubbard, S. S.; Agarwal, D.; Banfield, J. F.; Beller, H. R.; Brodie, E.; Long, P.; Nico, P. S.; Steefel, C. I.; Tokunaga, T. K.; Williams, K. H.

2014-12-01

Although terrestrial environments play a critical role in cycling water, greenhouse gasses, and other life-critical elements, the complexity of interactions among component microbes, plants, minerals, migrating fluids and dissolved constituents hinders predictive understanding of system behavior. The 'Sustainable Systems 2.0' project is developing genome-to-watershed scale predictive capabilities to quantify how the microbiome affects biogeochemical watershed functioning, how watershed-scale hydro-biogeochemical processes affect microbial functioning, and how these interactions co-evolve with climate and land-use changes. Development of such predictive capabilities is critical for guiding the optimal management of water resources, contaminant remediation, carbon stabilization, and agricultural sustainability - now and with global change. Initial investigations are focused on floodplains in the Colorado River Basin, and include iterative model development, experiments and observations with an early emphasis on subsurface aspects. Field experiments include local-scale experiments at Rifle CO to quantify spatiotemporal metabolic and geochemical responses to O2and nitrate amendments as well as floodplain-scale monitoring to quantify genomic and biogeochemical response to natural hydrological perturbations. Information obtained from such experiments are represented within GEWaSC, a Genome-Enabled Watershed Simulation Capability, which is being developed to allow mechanistic interrogation of how genomic information stored in a subsurface microbiome affects biogeochemical cycling. This presentation will describe the genome-to-watershed scale approach as well as early highlights associated with the project. Highlights include: first insights into the diversity of the subsurface microbiome and metabolic roles of organisms involved in subsurface nitrogen, sulfur and hydrogen and carbon cycling; the extreme variability of subsurface DOC and hydrological controls on carbon and nitrogen cycling; geophysical identification of floodplain hotspots that are useful for model parameterization; and GEWaSC demonstration of how incorporation of identified microbial metabolic processes improves prediction of the larger system biogeochemical behavior.

Positive responses of belowground C dynamics to nitrogen enrichment in China.

PubMed

Deng, Lei; Peng, Changhui; Zhu, Guangyu; Chen, Lei; Liu, Yulin; Shangguan, Zhouping

2018-03-01

Determining how nitrogen (N) impacts ecosystem carbon (C) cycling is critical to using C sequestration to offset anthropogenic CO 2 emissions. The N deposition rate in China is higher than the global average; however, many results of N enrichment experiments in China have not been included in global syntheses. In this study, we assembled a large dataset that comprised 124 published studies concerning N addition experiments, including 570 observations at 127 sites across China, to quantify the responses of belowground C dynamics to N enrichment in terrestrial ecosystems in China by a meta-analysis. The results showed that overall soil organic C, dissolved organic C (DOC) and soil microbial biomass C (MBC) increased by 1.8, 7.4, and 8.8%, respectively (P<0.05), in response to N enrichment; belowground biomass and litter increased by 14.6 and 24.4%, respectively (P<0.05); and soil respiration increased by 6.1% (P<0.05). N enrichment promoted C inputs into the soil mainly by increasing litter and belowground biomass inputs. Additionally, N enrichment increased C output by increasing soil respiration. Land use type and N addition level had different impacts on the soil C pool and on soil respiration. DOC, MBC, and litter exhibited more positive responses to N deposition in cooler and more arid regions than in other regions. The meta-analysis indicated that N enrichment had a positive impact on belowground C cycles in China. Climate played a greater role than did N deposition level in affecting processes of ecosystem C cycling. Moreover, belowground C cycle processes are determined by complicated interactions among land use type, N enrichment, and climate. Copyright © 2017 Elsevier B.V. All rights reserved.

Terrestrial N Cycling And C Storage: Some Insights From A Process-based Land Surface Model

NASA Astrophysics Data System (ADS)

Zaehle, S.; Friend, A. D.; Friedlingstein, P.

2008-12-01

We present results of a new land surface model, O-CN, which includes a process-based coupling between the terrestrial cycling of energy, water, carbon, and nitrogen. The model represents the controls of the terrestrial nitrogen (N) cycling on carbon (C) pools and fluxes through photosynthesis, respiration, changes in allocation, and soil organic matter decomposition, and explicitly accounts for N leaching and gaseous losses. O-CN has been shown to give realistic results in comparison to observations at a wide range of scales, including in situ flux measurements, productivity databases, and atmospheric CO2 concentration data. O-CN is run for three free air carbon dioxide enrichment (FACE) sites (Duke, Oak Ridge, Aspen), and reproduces observed magnitudes of changes in net primary productivity, foliage area and foliage N content. Several alternative hypotheses concerning the control of N on vegetation growth and decomposition, including effects of diluting foliage N concentrations, down-regulation of photosynthesis and respiration, acclimation of C allocation patterns and biological N fixation, are tested with respect to their effect on long- term C sequestration estimate. Differences in initial N availability, small transient changes in N inputs and the assumed plasticity of C:N stoichiometry can lead to substantial differences in the simulated long-term changes in productivity and C sequestration. We discuss the capacity of observations obtained at FACE sites to evaluate these alternative hypotheses, and investigate implications of a transient versus instantaneous increase in atmospheric carbon dioxide for the magnitude of the simulated limiting effect of N on C cycling. Finally, we re-examine earlier model-based assessments of the terrestrial C sequestration potential using a global transient O-CN simulation driven by increases in atmospheric CO2, N deposition and climatic changes over the 21st century.

Controllable embedding of sulfur in high surface area nitrogen doped three dimensional reduced graphene oxide by solution drop impregnation method for high performance lithium-sulfur batteries

NASA Astrophysics Data System (ADS)

Zegeye, Tilahun Awoke; Tsai, Meng-Che; Cheng, Ju-Hsiang; Lin, Ming-Hsien; Chen, Hung-Ming; Rick, John; Su, Wei-Nien; Kuo, Chung-Feng Jeffrey; Hwang, Bing-Joe

2017-06-01

High capacity lithium-sulfur batteries with stable cycle performance and sulfur loadings greater than 70 wt% are regarded as promising candidates for energy storage devices. However, it has been challenged to achieving practical application of sulfur cathode because of low loading of active sulfur and poor cycle performance. Herein, we design novel nanocomposite cathode materials consist of sulfur (80 wt%) embedded within nitrogen doped three-dimensional reduced graphene oxide (N-3D-rGO) by controllable sulfur-impregnation method. Nitrogen doping helps increase the surface area by ten times from pristine graphene, and pore volume by seven times. These structural features allow the cathode to hold more sulfur. It also adsorbs polysulfides and prevents their detachment from the host materials; thereby achieving stable cycle performance. The solution drop sulfur-impregnation method provides uniform distribution of nano-sulfur in controlled manner. The material delivers a high initial discharge capacity of 1042 mAhg-1 and 916 mAhg-1 with excellent capacity retention of 94.8% and 81.9% at 0.2 C and 0.5 C respectively after 100 cycles. Thus, the combination of solution drop and nitrogen doping opens a new chapter for resolving capacity fading as well as long cycling problems and creates a new strategy to increase sulfur loading in controlled mechanism.

Identification and quantification of nitrogen cycling processes in cryptogamic covers

NASA Astrophysics Data System (ADS)

Weber, Bettina; Wu, Dianming; Lenhart, Katharina; Tamm, Alexandra; Ruckteschler, Nina; Rodríguez-Caballero, Emilio; Elbert, Wolfgang; Burrows, Susannah; Clough, Tim; Steinkamp, Jörg; Meusel, Hannah; Behrendt, Thomas; Büdel, Burkhard; Andreae, Meinrat O.; Sörgel, Matthias; Cheng, Yafang; Crutzen, Paul; Keppler, Frank; Su, Hang; Pöschl, Ulrich

2016-04-01

Cryptogamic covers (CC) comprise communities of photoautotrophic cyanobacteria, lichens, algae, and bryophytes together with heterotrophic bacteria, microfungi, and archaea in varying proportions. Depending on their habitat, cryptogamic rock covers, cryptogamic plant covers, and cryptogamic soil covers are distinguished. The latter comprise biological soil crusts (biocrusts), which globally occur under dryland conditions. In a first assessment of their global role, we quantified that CC fix ˜49 Tg of nitrogen (N) per year (Elbert et al., 2013), corresponding to ˜1/2 of the maximum terrestrial biological N fixation determined in the latest IPCC report. The fixed N is used for biomass formation and partially leached into the ground, where it can be taken up by plants or transformed into N oxides, being emitted into the atmosphere. We show that biocrusts release nitric oxide (NO) and nitrous acid (HONO), which are key species in the global cycling of nitrogen and in the production of ozone and hydroxyl radicals, regulating the oxidizing power and self-cleaning capacity of the atmosphere. Based on laboratory, field and satellite measurement data, we obtained a best estimate of 1.1 Tg a-1 of NO-N and 0.6 Tg a-1 of HONO-N being globally emitted by biocrusts, corresponding to ˜20% of the global nitrogen oxide emissions from soils under natural vegetation (Weber et al., 2015). During full wetting and drying cycles, emissions peaked at low water contents suggesting NO- and HONO-formation under aerobic conditions during nitrification. Other measurements revealed that cryptogamic organisms release nitrous oxide (N2O), a greenhouse gas of crucial importance for climate change. The emission rates varied with temperature, humidity, and N deposition, but divided by respiratory CO2 emission they formed an almost constant ratio, which allowed upscaling on the global scale. We estimated annual N2O emissions of 0.3 - 0.6 Tg by cryptogams, accounting for 4-9% of the global N2O budget from natural terrestrial sources (Lenhart et al., 2015). 15N isotope labeling experiments revealed that nitrate (NO3-) was a precursor of N2O, suggesting that N2O may be formed during denitrification. Thus, our experiments revealed that CC play a prominent role in different steps of the N cycle, being relevant in terrestrial biogeochemistry, atmospheric chemistry and air quality. Literature Elbert W, Weber B, Burrows S, Steinkamp J, Büdel B, Andreae MO, Pöschl U (2012) Contribution of cryptogamic covers to the global cycles of carbon and nitrogen. Nature Geosciences 5: 459-462. Lenhart K, Weber B, Elbert W, Steinkamp J, Clough T, Crutzen P, Pöschl U, Keppler F (2015) Nitrous oxide and methane emissions from cryptogamic covers. Global Change Biology 21(10): 3889-3900. Weber B, Wu D, Tamm A, Ruckteschler N, Rodríguez-Caballero E, Steinkamp J, Meusel H, Elbert W, Behrendt T, Sörgel M, Cheng Y, Crutzen P, Su H, Pöschl U (2015) Biological soil crusts accelerate the nitrogen cycle through large NO and HONO emissions in drylands. Proceedings of the National Academy of Sciences 112(50): 15384-15389.

Nitrogen-Doped Holey Graphene as an Anode for Lithium-Ion Batteries with High Volumetric Energy Density and Long Cycle Life.

PubMed

Xu, Jiantie; Lin, Yi; Connell, John W; Dai, Liming

2015-12-01

Nitrogen-doped holey graphene (N-hG) as an anode material for lithium-ion batteries has delivered a maximum volumetric capacity of 384 mAh cm(-3) with an excellent long-term cycling life up to 6000 cycles, and as an electrochemical capacitor has delivered a maximum volumetric energy density of 171.2 Wh L(-1) and a volumetric capacitance of 201.6 F cm(-3) . © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Palladium-Catalyzed [3 + 2]-C-C/N-C Bond-Forming Annulation.

PubMed

Liu, Yang; Mao, Zhongyi; Pradal, Alexandre; Huang, Pei-Qiang; Oble, Julie; Poli, Giovanni

2018-06-13

The synthesis of bi- and tricyclic structures incorporating pyrrolidone rings is disclosed, starting from resonance-stabilized acetamides and cyclic α,β-unsaturated-γ-oxycarbonyl derivatives. This process involves an intermolecular Tsuji-Trost allylation/intramolecular nitrogen 1,4-addition sequence. Crucial for the success of this bis-nucleophile/bis-electrophile [3 + 2] annulation is its well-defined step chronology in combination with the total chemoselectivity of the former step. When the newly formed annulation product carries a properly located o-haloaryl moiety at the nitrogen substituent, a further intramolecular keto α-arylation can join the cascade, thereby forming two new cycles and three new bonds in the same synthetic operation.

A missing link in the estuarine nitrogen cycle?: Coupled nitrification-denitrification mediated by suspended particulate matter.

PubMed

Zhu, Weijing; Wang, Cheng; Hill, Jaclyn; He, Yangyang; Tao, Bangyi; Mao, Zhihua; Wu, Weixiang

2018-02-02

In estuarine and coastal ecosystems, the majority of previous studies have considered coupled nitrification-denitrification (CND) processes to be exclusively sediment based, with little focus on suspended particulate matter (SPM) in the water column. Here, we present evidence of CND processes in the water column of Hangzhou Bay, one of the largest macrotidal embayments in the world. Spearman's correlation analysis showed that SPM was negatively correlated with nitrate (rho = -0.372, P = 0.018) and marker genes for nitrification and denitrification in the water column were detected by quantitative PCR analysis. The results showed that amoA and nir gene abundances strongly correlated with SPM (all P < 0.01) and the ratio of amoA/nir strongly correlated with nitrate (rho = -0.454, P = 0.003). Furthermore, aggregates consisting of nitrifiers and denitrifiers on SPM were also detected by fluorescence in situ hybridization. Illumina MiSeq sequencing further showed that ammonia oxidizers mainly belonged to the genus Nitrosomonas, while the potential denitrifying genera Bradyrhizobium, Comamonas, Thauera, Stenotrophomonas, Acinetobacter, Anaeromyxobacter, Sulfurimonas, Paenibacillus and Sphingobacterium showed significant correlations with SPM (all P < 0.01). This study suggests that SPM may provide a niche for CND processes to occur, which has largely been missing from our understanding of nitrogen cycling in estuarine waters.

Nitrogen trading tool

USDA-ARS?s Scientific Manuscript database

The nitrogen cycle is impacted by human activities, including those that increase the use of nitrogen in agricultural systems, and this impact can be seen in effects such as increased nitrate (NO3) levels in groundwater or surface water resources, increased concentration of nitrous oxide (N2O) in th...

Linking Nitrogen-Cycling Microbial Communities to Environmental Fluctuations and Biogeochemical Activity in a Large, Urban Estuary: the San Francisco Bay-Delta

NASA Astrophysics Data System (ADS)

Francis, C.

2015-12-01

Nitrogen (N) availability is an important factor controlling productivity and thus carbon cycling in estuaries. The fate of N in estuaries depends on the activities of the microbes that carry out the N-cycle, which in turn depend on factors such as organic matter availability, dissolved inorganic N, salinity, oxygen, and temperature. Key microbial N transformations include nitrification (the aerobic oxidation of ammonia to nitrite and nitrate) and denitrification (the anaerobic reduction of nitrate to dinitrogen gas). While denitrification leads to N loss, nitrification is the only link between reduced N (produced by decomposition) and oxidized N (substrates for N loss processes), and both processes are known to produce nitrous oxide (N2O), a potent greenhouse gas. Understanding controls of N-cycling in the San Francisco Bay-Delta (SFBD)—the largest estuary on the west coast of North America—is particularly important, as this urban estuary is massively polluted with N, even compared to classic "eutrophic" systems. Interestingly, the SFBD has been spared the detrimental consequences of nutrient enrichment, largely due to high suspended sediment concentrations (and thus low light penetration) throughout the water column, combined with high grazing pressure. However, the recent "clearing" of SFBD waters due to a sharp decrease in suspended sediments may significantly alter the ecology of the estuary, by increasing phytoplankton growth. Thus, the SFBD may be losing its historical resilience to eutrophication, and may soon be "high-nutrient, low-chlorophyll" no more. Elucidating the environmental factors affecting the community structure, activity, and functioning of N-cycling microbes in SFBD is crucial for determining how changes in turbidity and productivity will be propagated throughout the ecosystem. While substantial ecological research in the SFBD has focused on phytoplankton and food webs, bacterial and archaeal communities have received far less attention. Using a combination of molecular, biogeochemical, and 'omics' approaches, we have been examining how N-cycling microbial communities throughout the SFBD change in relation to environmental fluctuations—a critical step in understanding how microbial populations drive biogeochemical cycling in this estuary.

Soil organic matter and nitrogen cycling in response to harvesting, mechanical site preparation, and fertilization in a wetland with a mineral substrate

Treesearch

James W. McLaughlin; Margaret R. Gale; Martin F. Jurgensen; Carl C. Trettin

2000-01-01

Forested wetlands are becoming an important timber resource in the Upper Great Lakes Region of the US. However, there is limited information on soil nutrient cycling responses to harvesting and post-harvest manipulations (site preparation and fertilization). The objective of this study was to examine cellulose decomposition, nitrogen mineralization, and soil solution...

Vegetation controls on carbon and nitrogen cycling and retention: contrasts in spruce and hardwood watershed budgets

Treesearch

Charlene N. Kelly; Stephen H. Schoenholtz; Mary Beth Adams

2010-01-01

Anthropogenic sources of nitrogen (N) have altered the global N cycle to such an extent as to nearly double the rate of N that enters many terrestrial ecosystems. However, predicting the fate of N inputs continues to present challenges, as a multitude of environmental factors play major roles in determining N pathways. This research investigates the role of specific...

Nitrous oxide fluxes and nitrogen cycling along a pasturechronosequence in Central Amazonia, Brazil

Treesearch

B. Wick; E. Veldkamp; W. Z. de Mello; M. Keller; P. Crill

2005-01-01

We studied nitrous oxide (N2O) fluxes and soil nitrogen (N) cycling following forest conversion to pasture in the central Amazon near Santarém, Pará, Brazil. Two undisturbed forest sites and 27 pasture sites of 0.5 to 60 years were sampled once each during wet and dry seasons. In addition to soil-atmosphere fluxes of N...

Effects of nitrogen additions on above- and belowground carbon dynamics in two tropical forests

Treesearch

Daniela F. Cusack; Whendee L. Silver; Margaret S. Torn; William H. McDowell

2011-01-01

Anthropogenic nitrogen (N) deposition is increasing rapidly in tropical regions, adding N to ecosystems that often have high background N availability. Tropical forests play an important role in the global carbon (C) cycle, yet the effects of N deposition on C cycling in these ecosystems are poorly understood. We used a field N-fertilization experiment in lower and...

Diverse Responses of Belowground Internal Nitrogen Cycling to Increasing Aridity

NASA Astrophysics Data System (ADS)

Kou, D.; Peng, Y.; Wang, G.; Ding, J.; Chen, Y.; Yang, G.; Fang, K.; Liu, L.; Zhang, B.; Müller, C.; Zhang, J.; Yang, Y.

2017-12-01

Belowground microbial nitrogen (N) dynamics play key roles in regulating structure and function of terrestrial ecosystems, however, our understanding on their responses to global change remains limited. This gap is particularly true for drylands, which constitute the largest biome in terrestrial ecosystems and are sensitive to predicted increase in aridity. Here, responding patterns and controls of six gross N transformation rates were explored along an aridity gradient in Tibetan drylands. Our results showed that gross N rates responded diversely to the changing aridity. Both mineralization (MN) and ammonium immobilization (INH4) declined as aridity increased. Aridity affected MN through its association with plant cover, clay content, soil organic matter (SOM), dissolved organic nitrogen (DON) and total microbial biomass, while regulated INH4 mainly through its effects on SOM and NH4+. Autotrophic nitrification (ONH4) exhibited a bell-shaped pattern along the gradient with a tipping point at aridity index = 0.47. Such a pattern was induced by aridity effects on the abundance of ammonia oxidizing archaea (AOA) and ammonia supplying capacity. Different from above N transformations, rates of nitrate immobilization (INO3) and dissimilatory nitrate reduction to ammonium (DNRA) had no responses to changing aridity, largely regulated by soil DON availability and clay content, respectively. Overall, these results suggest that predicted increase in aridity will exert different effects on various soil internal N cycling processes. The diverse patterns point to different responses of ecosystem N cycle with respect to aridity, and thus potentially have profound impact on structure and function of dryland ecosystems.

The nitrogen budget for different forest types in the central Congo Basin

NASA Astrophysics Data System (ADS)

Bauters, Marijn; Verbeeck, Hans; Cizungu, Landry; Boeckx, Pascal

2016-04-01

Characterization of fundamental processes in different forest types is vital to understand the interaction of forests with their changing environment. Recent data analyses, as well as modeling activities have shown that the CO2 uptake by terrestrial ecosystems strongly depends on site fertility, i.e. nutrient availability. Accurate projections of future net forest growth and terrestrial CO2 uptake thus necessitate an improved understanding on nutrient cycles and how these are coupled to the carbon (C) cycle in forests. This holds especially for tropical forests, since they represent about 40-50% of the total carbon that is stored in terrestrial vegetation, with the Amazon basin and the Congo basin being the largest two contiguous blocks. However, due to political instability and reduced accessibility in the central Africa region, there is a strong bias in scientific research towards the Amazon basin. Consequently, central African forests are poorly characterized and their role in global change interactions shows distinct knowledge gaps, which is important bottleneck for all efforts to further optimize Earth system models explicitly including this region. Research in the Congo Basin region should combine assessments of both carbon stocks and the underlying nutrient cycles which directly impact the forest productivity. We set up a monitoring network for carbon stocks and nitrogen fluxes in four different forest types in the Congo Basin, which is now operative. With the preliminary data, we can get a glimpse of the differences in nitrogen budget and biogeochemistry of African mixed lowland rainforest, monodominant lowland forest, mixed montane forest and eucalypt plantations.

Consequences of simulating terrestrial N dynamics for projecting future terrestrial C storage

NASA Astrophysics Data System (ADS)

Zaehle, S.; Friend, A. D.; Friedlingstein, P.

2009-04-01

We present results of a new land surface model, O-CN, which includes a process-based coupling between the terrestrial cycling of energy, water, carbon, and nitrogen. The model represents the controls of the terrestrial nitrogen (N) cycling on carbon (C) pools and fluxes through photosynthesis, respiration, changes in allocation patterns, as well as soil organic matter decomposition, and explicitly accounts for N leaching and gaseous losses. O-CN has been shown to give realistic results in comparison to observations at a wide range of scales, including in situ flux measurements, productivity databases, and atmospheric CO2 concentration data. Notably, O-CN simulates realistic responses of net primary productivity, foliage area, and foliage N content to elevated atmospheric [CO2] as evidenced at free air carbon dioxide enrichment (FACE) sites (Duke, Oak Ridge). We re-examine earlier model-based assessments of the terrestrial C sequestration potential using a global transient O-CN simulation driven by increases in atmospheric [CO2], N deposition and climatic changes over the 21st century. We find that accounting for terrestrial N cycling about halves the potential to store C in response to increases in atmospheric CO2 concentrations; mainly due to a reduction of the net C uptake in temperate and boreal forests. Nitrogen deposition partially alleviates the effect of N limitation, but is by far not sufficient to compensate for the effect completely. These findings underline the importance of an accurate representation of nutrient limitations in future projections of the terrestrial net CO2 exchanges and therefore land-climate feedback studies.

The History and Impact of the CNO Cycles in Nuclear Astrophysics

NASA Astrophysics Data System (ADS)

Wiescher, Michael

2018-03-01

The carbon cycle, or Bethe-Weizsäcker cycle, plays an important role in astrophysics as one of the most important energy sources for quiescent and explosive hydrogen burning in stars. This paper presents the intellectual and historical background of the idea of the correlation between stellar energy production and the synthesis of the chemical elements in stars on the example of this cycle. In particular, it addresses the contributions of Carl Friedrich von Weizsäcker and Hans Bethe, who provided the first predictions of the carbon cycle. Further, the experimental verification of the predicted process as it developed over the following decades is discussed, as well as the extension of the initial carbon cycle to the carbon-nitrogen-oxygen (CNO) multi-cycles and the hot CNO cycles. This development emerged from the detailed experimental studies of the associated nuclear reactions over more than seven decades. Finally, the impact of the experimental and theoretical results on our present understanding of hydrogen burning in different stellar environments is presented, as well as the impact on our understanding of the chemical evolution of our universe.

Stochastic Controls on Nitrate Transport and Cycling

NASA Astrophysics Data System (ADS)

Botter, G.; Settin, T.; Alessi Celegon, E.; Marani, M.; Rinaldo, A.

2005-12-01

In this paper, the impact of nutrient inputs on basin-scale nitrates losses is investigated in a probabilistic framework by means of a continuous, geomorphologically based, Montecarlo approach, which explicitly tackles the random character of the processes controlling nitrates generation, transformation and transport in river basins. This is obtained by coupling the stochastic generation of climatic and rainfall series with simplified hydrologic and biogeochemical models operating at the hillslope scale. Special attention is devoted to the spatial and temporal variability of nitrogen sources of agricultural origin and to the effect of temporally distributed rainfall fields on the ensuing nitrates leaching. The influence of random climatic variables on bio-geochemical processes affecting the nitrogen cycle in the soil-water system (e.g. plant uptake, nitrification and denitrification, mineralization), is also considered. The approach developed has been applied to a catchment located in North-Eastern Italy and is used to provide probabilistic estimates of the NO_3 load transferred downstream, which is received and accumulated in the Venice lagoon. We found that the nitrogen load introduced by fertilizations significantly affects the pdf of the nitrates content in the soil moisture, leading to prolonged risks of increased nitrates leaching from soil. The model allowed the estimation of the impact of different practices on the probabilistic structure of the basin-scale hydrologic and chemical response. As a result, the return period of the water volumes and of the nitrates loads released into the Venice lagoon has been linked directly to the ongoing climatic, pluviometric and agricultural regimes, with relevant implications for environmental planning activities aimed at achieving sustainable management practices.

Effect of nitrogen on high temperature low cycle fatigue behaviors in type 316L stainless steel

NASA Astrophysics Data System (ADS)

Kim, Dae Whan; Ryu, Woo-Seog; Hong, Jun Hwa; Choi, Si-Kyung

1998-04-01

Strain-controlled low cycle fatigue (LCF) tests were conducted in the temperature range of RT-600°C and air atmosphere to investigate the nitrogen effect on LCF behavior of type 316L stainless steels with different nitrogen contents (0.04-0.15%). The waveform of LCF was a symmetrical triangle with a strain amplitude of ±0.5% and a constant strain rate of 2×10 -3/s was employed for most tests. Cyclic stress response of the alloys exhibited a gradual cyclic softening at RT, but a cyclic hardening at an early stage of fatigue life at 300-600°C. The hardening at high temperature was attributed to dynamic strain aging (DSA). Nitrogen addition decreased hardening magnitude (maximum cyclic stress — first cyclic stress) because nitrogen retarded DSA for these conditions. The dislocation structures were changed from cell to planar structure with increasing temperature and nitrogen addition by DSA and short range order (SRO). Fatigue life was a maximum at 0.1% nitrogen content, which was attributed to the balance between DSA and SRO.