Author: Lisa Bohlen
Publisher:
ISBN:
Category :
Languages : en
Pages : 0

Get Book Here

Book Description

Author: Elizabeth W. Boyer
Publisher: Springer Science & Business Media
ISBN: 9401734054
Category : Science
Languages : en
Pages : 520

Get Book Here

Book Description
This issue is the final report from the International SCOPE Project on Nitrogen Transport and Transformations: A Regional and Global Analysis. SCOPE (the Scientific Committee on Problems of the Environment, ICSU) authorized the Nitrogen Project as an 8-year effort between 1994 and 2002 because of the need to better understand how humans have altered nitrogen cyc1ing globally and at the scale of large regions. Human activity has more than doubled the rate of formation of reactive nitrogen on the land surface of the earth, and the nitrogen cyc1e continues to accelerate. The distribution of this reactive nitrogen is not uniform, though, and some regions such as Europe and Asia have seen massive increases in reactive nitrogen, while other regions have seen little change. The SCOPE Nitrogen Project has synthesized detailed information on the nature of the human alteration of the nitrogen cyc1e through aseries of workshops over the past 8 years. These cumulatively have involved over 250 of previous workshops scientists from over 20 different nations. The results have been published in aseries of special journal issues and reports that synthesize information on nitrogen in the North Atlantic Ocean and its water sheds (Howarth 1996), nitrogen cycling in Asia (Hong-Chi Lin et al. 1996; Mosier et al.

Author: Edward J. Carpenter
Publisher: Elsevier
ISBN: 1483288293
Category : Science
Languages : en
Pages : 919

Get Book Here

Book Description
Nitrogen in the Marine Environment provides information pertinent to the many aspects of the nitrogen cycle. This book presents the advances in ocean productivity research, with emphasis on the role of microbes in nitrogen transformations with excursions to higher trophic levels. Organized into 24 chapters, this book begins with an overview of the abundance and distribution of the various forms of nitrogen in a number of estuaries. This text then provides a comparison of the nitrogen cycling of various ecosystems within the marine environment. Other chapters consider chemical distributions and methodology as an aid to those entering the field. This book discusses as well the enzymology of the initial steps of inorganic nitrogen assimilation. The final chapter deals with the philosophy and application of modeling as an investigative method in basic research on nitrogen dynamics in coastal and open-ocean marine environments. This book is a valuable resource for plant biochemists, microbiologists, aquatic ecologists, and bacteriologists.

Author: Zahra Akbarzadeh
Publisher:
ISBN:
Category : Groundwater
Languages : en
Pages : 142

Get Book Here

Book Description
The vast release of anthropogenically produced reactive nitrogen (N) into the environment, by agricultural activities, energy production and municipal wastewater, has led to a variety of consequences for atmospheric, terrestrial, and aquatic ecosystems and human health. In particular, elevated loadings of N have been documented in many rivers worldwide. However, the fate of this reactive N in the different biogeochemical compartments of the river system is yet to be fully investigated. Elevated concentrations of N in the river system influence the interactions at the sediment-water interface (SWI), which can significantly impact the water quality and primary productivity in the river system and receiving water bodies. In addition, humans have impacted the N cycling in rivers by dam construction. The damming of rivers represents one of the most profound human interventions in the freshwater cycle, with substantial implications for water security, energy production, biodiversity and aquatic ecosystem functioning. River damming, on the rise during the last 60 years, shows no sign of abating in the coming decades. However, since the beginning of the 20th century, the geographical locations of the new dams have increasingly spread to the rapidly developing parts of the world, in particular, Southeast Asia and South America. This thesis aims to simulate the biogeochemical cycling of N along the river continuum across different scales so as to quantitatively predict the modifications caused by anthropogenic activities. At the local to regional scale, the role of bottom sediments in the nitrite budget of a European river system, impacted by urban and agricultural activities, is investigated using an early diagenesis model. At the global scale, the changes in the past, present and future riverine fluxes of N due to river damming are estimated and analyzed. To describe the fate of reactive N in streambed sediments, a comprehensive reactive-transport model is developed. The model explicitly represents the production and consumption of nitrite, a reactive intermediate in the N cycle, through nitrification, denitrification, dissimilatory nitrate reduction to ammonium (DNRA) and anammox. Although nitrite is typically considered to be a short-lived compound, elevated concentrations of it have been observed at relatively high concentrations in freshwaters aquatic systems, raising concerns due to its toxicity for humans, animals and plants. Among other impacted rivers, nitrite accumulation has been observed in the Seine, a N polluted river with high agricultural and urban inputs in France, raising questions about its sources and fate. The early diagenetic model is employed to assess the role of sediments in releasing nitrite to the overlying water or removing it at two different sampling locations and two different times of the year. Four datasets collected in summer and fall, upstream and downstream of the largest wastewater treatment plant (WWTP) serving the Paris conurbation area, are used to test the model. The datasets include pore water profiles plus benthic exchange fluxes of nitrate, nitrite and ammonium at the SWI, measured during core incubation experiments. The model results emphasize the major role of the WWTP for the nitrite budget in river, not only due to the direct release of nitrite through effluent discharges, but also by supplying the high loads of labile organic carbon (C) that enhance heterotrophic activity in the sediments. In the next step, the reactive-transport model is expanded by incorporating the N isotopic compositions of nitrate, nitrite, ammonium and organic N, and accounting for the isotopic fractionations along the N transformation pathways. The model is used to simulate the temporal variation in isotopic composition of N species under non-steady state conditions at the SWI during incubation experiments. A sensitivity analysis is performed, by applying different scenarios, to provide insight into the main controls on the nitrite isotopic compositions at the SWI. The results highlight the major role of oxygen on the variations of the isotopic values of N species and illustrate the effects of different N transformations on the isotopic compositions of N species at the SWI. The model will be applied in upcoming sediment incubation experiments with Seine River sediments that will be carried out by our French colleagues. Finally, I assess the impacts of damming on the global riverine nitrogen fluxes by estimating N burial in sediments of dam reservoirs and gaseous emissions through denitrification. Moreover, I estimate global N fixation in reservoirs as a source of new N to these systems. A process-based N mass balance model is developed to represent the biogeochemical cycling of N in reservoirs. Using Monte Carlo simulations, the model is scaled up to generate a virtual database of dams. From this dataset, I derive two global relationships between N elimination in reservoirs, by either denitrification or burial, and the hydraulic residence time. These relationships are then combined with N loads to rivers obtained from the Global-NEWS model and N fixation fluxes calculated for dams included in databases for existing and future reservoirs. The results demonstrate that, globally, denitrification and burial in dam reservoirs exceed N fixation, and dam reservoirs therefore act as a sink of N worldwide. I estimate that denitrification and burial in reservoirs eliminated 7% of N loading to the global river network in the year 2000. This percentage is predicted to double by 2030, mainly because of the current boom in dam building. This thesis provides new tools to make more detailed assessments of the role of bottom sediments in the nitrite budget of rivers and give insights on the processes that affect the direction and magnitude of the nitrite fluxes at the SWI. Additionally, I present the first estimation of global N fixation in dam reservoirs. By coupling my results to those of the earlier work on phosphorus (P), I further show that dams increase the N:P ratio of riverine discharge, thereby reducing the magnitude of N limitation for primary production in receiving lentic and coastal marine environments. This information should be taken into consideration when developing strategies to lessen the impacts of cultural eutrophication.

Author: Michael J.R. Fasham
Publisher: Springer Science & Business Media
ISBN: 3642558445
Category : Science
Languages : en
Pages : 324

Get Book Here

Book Description
Oceans account for 50% of the anthropogenic CO2 released into the atmosphere. During the past 15 years an international programme, the Joint Global Ocean Flux Study (JGOFS), has been studying the ocean carbon cycle to quantify and model the biological and physical processes whereby CO2 is pumped from the ocean's surface to the depths of the ocean, where it can remain for hundreds of years. This project is one of the largest multi-disciplinary studies of the oceans ever carried out and this book synthesises the results. It covers all aspects of the topic ranging from air-sea exchange with CO2, the role of physical mixing, the uptake of CO2 by marine algae, the fluxes of carbon and nitrogen through the marine food chain to the subsequent export of carbon to the depths of the ocean. Special emphasis is laid on predicting future climatic change.

Author: Christopher J. Somes
Publisher:
ISBN:
Category : Denitrification
Languages : en
Pages : 144

Get Book Here

Book Description
We present a new nitrogen isotope model incorporated into the three-dimensional ocean component of a global Earth System Climate Model designed for millennial timescale simulations. The model includes prognostic tracers for the stable nitrogen isotopes, 14N and 15N, in the nitrate (NO3−), phytoplankton, zooplankton, and detritus variables of the marine ecosystem model. The isotope effects of algal NO3− assimilation, water column denitrification, and zooplankton excretion are considered as well as the input of newly fixed nitrogen by diazotrophs. A global database of [delta]15NO3− observations is compiled from previous studies and compared to the model results on a regional basis where sufficient observations exist. The model is able to qualitatively and quantitatively reproduce the observed patterns such as high subsurface values in denitrification zones, the meridional and vertical gradients in the Southern Ocean, and the meridional gradient in the Central Equatorial Pacific. The observed subsurface minimum in the Atlantic is underestimated presumably owing to too little nitrogen fixation there. Sensitivity experiments show that algal NO3− assimilation, nitrogen fixation and water column denitrification have strong effects on the simulated distribution of nitrogen isotopes, whereas the effect from zooplankton excretion is weaker. Both water column and sedimentary denitrification also have important indirect effects on the nitrogen isotopes distribution by reducing the fixed nitrogen inventory, which creates an ecological niche for diazotrophs and stimulates additional nitrogen fixation. Water column denitrification has a strong but rather localized effect on the nitrogen isotope distribution in model versions without iron limitation of diazotrophy, in which a tight coupling of nitrogen fixation exists. However, including iron limitation of diazotrophy inhibits a tight coupling between water column denitrification and nitrogen fixation in the Eastern Pacific and shifts the main location of nitrogen fixation from the Eastern Tropical Pacific to the Western Tropical Pacific, which results in a better agreement with N' = NO3−-16PO43− and [delta]15NO3− observations. Thus, our model results suggest that iron limitation of diazotrophy can modulate the feedback between denitrification and nitrogen fixation in the ocean. We speculate that a feedback response time on the centennial to millennial time scale may exist between denitrification and nitrogen fixation, producing imbalances in the global oceanic fixed nitrogen cycle, which may well have contributed to past changes of atmospheric CO2 via the biological pump.

Author: Robert W. Howarth
Publisher: Springer Science & Business Media
ISBN: 9400917767
Category : Science
Languages : en
Pages : 300

Get Book Here

Book Description
Human activity has dramatically altered the global nitrogen cycle in recent decades. These changes are not evenly distributed around the world; rather, they are greatest in regions of significant industrial and agricultural activity, as the synthesis and use of inorganic fertilizers, cultivation of legumes, burning of fossil fuels, and the simple act of concentrating humans and animals in dense populations all lead to the release of excess, reactive forms of nitrogen into the environment. In part because reactive nitrogen is frequently a limiting nutrient in many terrestrial and aquatic systems, an excess can lead to a variety of adverse effects on both environmental and human health. The North Atlantic Ocean and its contributing watersheds constitute a region which has seen perhaps the greatest increase in anthropogenically-derived nitrogen. In May of 1994, the International Scope Nitrogen Project, with funding from the Andrew Mellon Foundation, the United Nations Environment Program, and the World Meteorological Organization, sponsored a workshop held on Block Island, RI, USA, entitled `Nitrogen Dynamics of the North Atlantic Basin'. More than 50 scientists from 12 different countries convened with a unique set of goals: an integrated and comprehensive estimate of the current nitrogen cycle of the ocean, coastal systems, and contributing watersheds of the North Atlantic region; an analysis of human-induced changes to those cycles; and an assessment of the current and future effects of human-induced changes to nitrogen cycling throughout the globe.

Author: Trelita de Sousa
Publisher: Cambridge Scholars Publishing
ISBN: 152755676X
Category : Nature
Languages : en
Pages : 478

Get Book Here

Book Description
Nitrogen constitutes 78% of the Earth’s atmosphere and inevitably occupies a predominant role in marine and terrestrial nutrient biogeochemistry and the global climate. Callous human activities, like the excessive industrial nitrogen fixation and the incessant burning of fossil fuels, have caused a massive acceleration of the nitrogen cycle, which has, in turn, led to an increasing trend in eutrophication, smog formation, acid rain, and emission of nitrous oxide, which is a potent greenhouse gas, 300 times more powerful in warming the Earth’s atmosphere than carbon dioxide. This book comprehensively reviews the biotransformation of nitrogen, its ecological significance and the consequences of human interference. It will appeal to environmentalists, ecologists, marine biologists, and microbiologists worldwide, and will serve as a valuable guide to graduates, post-graduates, research scholars, scientists, and professors.

Author:
Publisher: Academic Press
ISBN: 0080878857
Category : Science
Languages : en
Pages : 4604

Get Book Here

Book Description
The study of estuaries and coasts has seen enormous growth in recent years, since changes in these areas have a large effect on the food chain, as well as on the physics and chemistry of the ocean. As the coasts and river banks around the world become more densely populated, the pressure on these ecosystems intensifies, putting a new focus on environmental, socio-economic and policy issues. Written by a team of international expert scientists, under the guidance of Chief Editors Eric Wolanski and Donald McClusky, the Treatise on Estuarine and Coastal Science, Ten Volume Set examines topics in depth, and aims to provide a comprehensive scientific resource for all professionals and students in the area of estuarine and coastal science Most up-to-date reference for system-based coastal and estuarine science and management, from the inland watershed to the ocean shelf Chief editors have assembled a world-class team of volume editors and contributing authors Approach focuses on the physical, biological, chemistry, ecosystem, human, ecological and economics processes, to show how to best use multidisciplinary science to ensure earth's sustainability Provides a comprehensive scientific resource for all professionals and students in the area of estuarine and coastal science Features up-to-date chapters covering a full range of topics

Author: Jonathan P. Zehr
Publisher: Springer Nature
ISBN: 303067746X
Category : Science
Languages : en
Pages : 191

Get Book Here

Book Description
This book aims to serve as a centralized reference document for students and researchers interested in aspects of marine nitrogen fixation. Although nitrogen is a critical element in both terrestrial and aquatic productivity, and nitrogen fixation is a key process that balances losses due to denitrification in both environments, most resources on the subject focuses on the biochemistry and microbiology of such processes and the organisms involved in the terrestrial environment on symbiosis in terrestrial systems, or on largely ecological aspects in the marine environment. This book is intended to provide an overview of N2 fixation research for marine researchers, while providing a reference on marine research for researchers in other fields, including terrestrial N2 fixation. This book bridges this knowledge gap for both specialists and non-experts, and provides an in-depth overview of the important aspects of nitrogen fixation as it relates to the marine environment. This resource will be useful for researchers in the specialized field, but also useful for scientists in other disciplines who are interested in the topic. It would provide a possible text for upper division classes or graduate seminars.