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Carbon And Nitrogen Cycling In Permeable Continental Shelf Sediments And Porewater Solute Exchange Across The Sediment Water Interface
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Book Synopsis Carbon and Nitrogen Cycling in Permeable Continental Shelf Sediments and Porewater Solute Exchange Across the Sediment-water Interface by : Alexandra Mina Fernandes Rao
Download or read book Carbon and Nitrogen Cycling in Permeable Continental Shelf Sediments and Porewater Solute Exchange Across the Sediment-water Interface written by Alexandra Mina Fernandes Rao and published by . This book was released on 2006 with total page 249 pages. Available in PDF, EPUB and Kindle. Book excerpt: The results obtained reveal that the benthic and pelagic sub-systems on continental shelves are more dynamically coupled than previously thought because of the rapid biogeochemical reactions and porewater transport rates that characterize most of the shelf seafloor. These findings reveal that a better mechanistic understanding of benthic carbon and nutrient cycling at continental margins is required to advance understanding of marine ecosystems and global biogeochemistry.
Book Synopsis Treatise on Estuarine and Coastal Science by :
Download or read book Treatise on Estuarine and Coastal Science written by and published by Academic Press. This book was released on 2012-03-06 with total page 4604 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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
Book Synopsis Benthic Carbon Cycling on the Antarctic Continental Shelf by : Marwa Baloza
Download or read book Benthic Carbon Cycling on the Antarctic Continental Shelf written by Marwa Baloza and published by . This book was released on 2023 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: The sedimentation of pelagic production makes continental shelf sediments important sites for organic matter (OM) remineralization and nutrient regeneration in the ocean. Consequently, shelf sediments play an important role in the bentho-pelagic coupling by providing essential nutrients for algal growth and maintaining the high primary production of shelf areas and the adjacent open ocean. In Antarctica, changes in sea ice cover have a major impact on surface primary production and the subsequent sinking of organic carbon to the seafloor. Recent observations indicate that global warming has led to substantial changes in sea ice cover, with a significant reduction of one million square kilometers in the annual maximum sea ice extent around Antarctica. These changes in sea ice conditions are expected to trigger significant changes in the pelagic ecosystem, with potentially profound effects on the benthic ecosystem. The imprint of climate-sensitive variables such as sea ice cover can be best studied in shelf sediments, where shallow water depths result in increased OM supply and tighter bentho-pelagic coupling. Therefore, a comprehensive understanding of the current carbon cycle on the Antarctic continental shelf is crucial for assessing the vulnerability of the ecosystem to climate change and for predicting the future trajectory of the carbon cycle in Antarctic waters. This thesis aims to quantify benthic carbon remineralization rates on the Antarctic continental shelf and the release of nutrients, particularly iron, that limit primary production in the Southern Ocean. In addition, the thesis aims to identify the main pathways of OM degradation and associated microbial communities, while contextualizing the above variables within the prevailing sea ice conditions. For this purpose, I first studied the geochemistry of shelf sediments along a gradient of sea ice cover on the eastern shelf of the Antarctic Peninsula (AP) (manuscript 1). The main focus was on carbon and iron fluxes within the sediment and between the water column and the sediment. The results were interpreted in the context of sea ice cover. An increase in carbon remineralization rates was observed as one moved from heavily ice-covered to moderately ice-covered stations where light availability and water column stratification increased. Conversely, the ice-free station displayed lower carbon remineralization rates and was subject to wind-driven mixing of the water column, which can deepen the mixed layer depth below the critical depth, resulting in reduced surface production. In summary, a positive correlation was found between moderate sea ice cover and increased carbon fluxes to the sediment, which followed an exponential increase. The study also revealed significant iron cycling in sediments with increased carbon remineralization, resulting in high dissolved iron fluxes. This finding highlights the importance of sediments underlying the moderate ice cover as a source of limiting nutrients for primary production in this region. A complementary study of benthic microbial communities along the AP transect was conducted using 16S ribosomal RNA (rRNA) gene sequencing (manuscript 2). The results indicate that sea ice cover and its effect on organic carbon fluxes are the main drivers of changes in benthic microbial communities. As sea ice cover decreases, the benthic microbial community shifts towards anaerobic communities of iron and sulfate reducers. These communities were more abundant at low ice cover stations than at high ice cover stations. Furthermore, an increase in the relative abundance of Sva1033, a Desulfuromonadia clade, with dissolved iron concentration at low ice cover stations suggests a putative role for Sva1033 in dissimilatory iron reduction in surface sediments. In addition to Sva1033, this study successfully identified other taxa that could potentially contribute to dissimilatory iron reduction or have syntrophic partnerships and/or common metabolic preferences with iron reducers. The focus was extended towards the southern shelf of the Weddell Sea, a region characterized by heavy sea ice cover (manuscript 3). Benthic oxygen uptake rates were measured at stations with different water depths and sediment compositions. Benthic measurements also revealed a dependence of carbon fluxes on sediment grain size and water depth. In general, diffusive oxygen uptake (DOU) rates on the southern Weddell Sea shelf were low. DOU showed a positive correlation with preserved total organic carbon (TOC) at stations with fine-grained sediments, whereas stations with typical of coarse-grained sediments showed a markedly different correlation of DOU with TOC. Common to all stations is that dissolved iron and manganese concentrations in pore water were found only at greater depths, suggesting very limited release of these nutrients back into the water column. The strong dependence of benthic carbon fluxes on sea ice cover and water depth was then combined to derive a simple empirical model, which was validated by all available DOU measurements reported in the literature for the Antarctic seasonal ice zone (manuscript 4). The model allows extrapolation and budgeting of benthic carbon remineralization for the entire seasonal ice zone (16 million km2), yielding a total of 46 Tg C yr-1. Notably, although the Antarctic continental shelf represents only 15% of the total area, it contributes a significant 71% (33 Tg C yr-1) of the total benthic carbon remineralization. Furthermore, the total organic carbon supply to the sediments and the carbon burial in the sediments were estimated to amount to 52 Tg C yr-1 and 6 Tg C yr-1, respectively. Overall, the thesis highlights the pivotal role of sea ice cover in controlling the benthic carbon and iron cycling on the Antarctic continental shelf. Through extensive data correlation and empirical modeling, the thesis has provided, for the first time, a quantitative framework for the relationship between sea ice cover and benthic carbon fluxes. It also emphasizes the substantial contribution of Antarctic shelf sediments to the marine carbon remineralization, allowing a better assessment of the carbon cycling and related CO2 sequestration across the Southern Ocean. Furthermore, it has improved our understanding of the main drivers of change in benthic microbial communities and, ultimately, nutrient fluxes across the sediment-water interface. These findings make a significant contribution to our understanding of the complex Antarctic ecosystem, which is necessary to assess the future trajectory of the Southern Ocean and its impact on the global carbon cycle.
Book Synopsis Nitrogen Cycling in the North Atlantic Ocean and its Watersheds by : Robert W. Howarth
Download or read book Nitrogen Cycling in the North Atlantic Ocean and its Watersheds written by Robert W. Howarth and published by Springer Science & Business Media. This book was released on 2012-12-06 with total page 300 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.
Book Synopsis Dissertation Abstracts International by :
Download or read book Dissertation Abstracts International written by and published by . This book was released on 2007 with total page 924 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Oxygen and Dissolved Organic Carbon Dynamics in Permeable Coastal Sediments by : Lindsay Chipman
Download or read book Oxygen and Dissolved Organic Carbon Dynamics in Permeable Coastal Sediments written by Lindsay Chipman and published by . This book was released on 2011 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: ABSTRACT: A large fraction of the continental shelf is covered by permeable sediments that are flushed by wave, wind, and tide generated bottom currents. Elevated dissolved organic carbon (DOC) concentrations in coastal zones, a diverse and abundant sediment microbial community, and advective filtration of seawater through the surface layers of permeable sediments, make these environments important zones for the cycling of organic matter. This research investigates the role of permeable sediments in the dynamics of two central components of the carbon cycle: DOC and oxygen. In Chapter 2, published in Limnology & Oceanography, I investigate decomposition rates and compositional changes of DOC when filtered through permeable sediments contained in laboratory column reactors. Substantial amounts of DOC were mineralized in the sediments and could be linked to incorporation by aerobic and anaerobic microbes. In DOC pore-water profiles measured at two study sites with permeable sediment, we observed a concave shape of the profiles in the upper 10 cm of permeable sediment resulting from transport of DOC with advective pore water flows into the sand, and DOC decomposition in the subsurface layers. We found that the flushed sand layer between the water column and deeper anoxic sediment layers acts as an effective DOC filter, with subsurface horizontal pore-water flows promoting decomposition of DOC, suggesting that permeable sediments play a key role in the cycling of organic matter. In Chapter 3, submitted to Continental Shelf Research, I use the findings of Chapter 2 for the interpretation of field time series data of DOC, DIC, and TN concentrations in the water column and coastal sediment pore waters. We use these time series to investigate the spatial and temporal dynamics of dissolved organic matter and how benthic pelagic coupling influences DOC concentrations in the permeable sediments. Our results reveal that DOC in the upper layer (0-12 cm) of the shallow sands is controlled by benthic-pelagic coupling facilitated by advective pore water filtration modulated by the regional wave climate. For the quantification of oxygen fluxes in the permeable coastal sands resulting from the benthic organic matter production and consumption and the current-induced sediment flushing, I deployed the eddy correlation technique. In order to make this technique more suitable for our shallow coastal zone with relatively rough hydrodynamic conditions (as compared to deeper marine environments), we adapted existing eddy correlation instruments for use with more durable and repairable oxygen optodes. This development is described in detail in Chapter 4 that has been submitted for publication in Limnology and Oceanography Methods. Our results show that optodes have a comparable response time to electrodes, produce similar fluxes in field deployments, and are a viable alternative for use with the eddy correlation measurement in coastal environments with strong currents and wave action. These hydrodynamic conditions are an important factor controlling production and decomposition processes at the sediment-water interface and within the sediment because they can largely control the availability of DOC and oxygen to microbial communities in the sediments. In Chapter 5, which is presently is being prepared for submission to Marine Ecology - Progress Series, we investigate the relationship between flow, wave height, DOC concentration, temperature, light, and the benthic oxygen fluxes. The results reveal a large range of production and consumption rates in the permeable coastal sediments with distinct seasonal changes. The latter are caused by the availability of degradable organic matter and the magnitude of the pore water flushing process that carries these organic substrates and oxygen into the permeable coastal sands. We conclude that the highly degradable DOC produced by pelagic and benthic primary producers enhances water column - sediment biogeochemical coupling in the coastal zone thereby increasing the contribution of the sediment surface layer in the cycling of carbon and nutrients.
Book Synopsis Selected Water Resources Abstracts by :
Download or read book Selected Water Resources Abstracts written by and published by . This book was released on 1990 with total page 710 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Polarographic Oxygen Sensors by : E. Gnaiger
Download or read book Polarographic Oxygen Sensors written by E. Gnaiger and published by Springer Science & Business Media. This book was released on 2012-12-06 with total page 378 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Marine Carbon Biogeochemistry by : Jack J. Middelburg
Download or read book Marine Carbon Biogeochemistry written by Jack J. Middelburg and published by Springer. This book was released on 2019-01-25 with total page 126 pages. Available in PDF, EPUB and Kindle. Book excerpt: This open access book discusses biogeochemical processes relevant to carbon and aims to provide readers, graduate students and researchers, with insight into the functioning of marine ecosystems. A carbon centric approach has been adopted, but other elements are included where relevant or needed. The book focuses on concepts and quantitative understanding of primary production, organic matter mineralization and sediment biogeochemistry. The impact of biogeochemical processes on inorganic carbon dynamics and organic matter transformation are also discussed.
Book Synopsis Carbon and Nutrient Fluxes in Continental Margins by : Kon-Kee Liu
Download or read book Carbon and Nutrient Fluxes in Continental Margins written by Kon-Kee Liu and published by Springer Science & Business Media. This book was released on 2010-02-11 with total page 757 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book is a product of the joint JGOFS (Joint Global Ocean Flux Study)/LOICZ (Land–Ocean Interactions in the Coastal Zone) Continental Margins Task Team which was established to facilitate continental margins research in the two projects. It contains signi cant information on the physical, biogeochemical, and ecosystems of continental margins nationally and regionally and provides a very valuable synthesis of this information and the physical, biogeochemical and ecosystem processes which occur on continental margins. The publication of this book is timely as it provides a very strong foundation for the development of the joint IMBER (Integrated Marine Biogeochemistry and Ecosystems Research)/LOICZ Science Plan and Implemen- tion Strategy for biogeochemical and ecosystems research in the continental margins and the impacts of global change on these systems. This initiative will move forward integrated biogeochemical and ecosystems research in the continental margins. We thank all the contributors to this volume and especially Kon-Kee Liu who has dedicated a great deal of time to ensuring a high-quality book is published. IMBER Scienti c Steering Committee Julie Hall LOICZ Scienti c Steering Committee Jozef Pacyna v 1 Preface In general, interfaces between the Earth’s larger material reservoirs (i. e. , the land, atmosphere, ocean, and sediments) are important in the control of the biogeoche- cal dynamics and cycling of the major bio-essential elements, including carbon (C), nitrogen (N), phosphorus (P), sulfur (S), and silicon (Si), found in organic matter and the inorganic skeletons, shells, and tests of benthic and marine organisms.
Book Synopsis Life at Interfaces and Under Extreme Conditions by : Gerd Liebezeit
Download or read book Life at Interfaces and Under Extreme Conditions written by Gerd Liebezeit and published by Springer Science & Business Media. This book was released on 2012-12-06 with total page 211 pages. Available in PDF, EPUB and Kindle. Book excerpt: Interfaces between media, whether air-water or sediment-water interfaces or organisms themselves, pose considerable problems to marine organisms attempting to live at these boundaries. In the present volume, a number of authors address various aspects of these two topics. Locations under scrutiny range from intertidal areas to the deep sea, while both macro-and meiofaunal organisms are investigated. Distribution patterns and effects of variable temperatures, pressures, and salinities are analysed. Aspects of fouling induction and prevention are also addressed. This book is intended as a progress report from the 33rd European Marine Biology Symposium held in Wilhelmshaven, Germany, in September 1998.
Book Synopsis The Benthic Boundary Layer by : Bernard P. Boudreau
Download or read book The Benthic Boundary Layer written by Bernard P. Boudreau and published by Oxford University Press. This book was released on 2001-03-22 with total page 430 pages. Available in PDF, EPUB and Kindle. Book excerpt: The benthic boundary layer is the zone of water and sediment immediately adjacent to the bottom of a sea, lake, or river. This zone is of considerable interest to biologists, geochemists, sedimentologists, and engineers because of very strong gradients of energy, dissolved and solid chemical components, suspended matter, and the number of organisms that live there. It is, for example, the sink for anthropogenic substances and the home of microscopic plant life that provides the nutrients that determine fish populations--and ultimately the size of the fisheries. This book of original chapters edited by Professors Boudreau and Jorgensen, both leading researchers in the field, will meet the need for an up-to-date, definitive text/reference on measurements, techniques, and models for transport and biochemical processes in the benthic boundary layer. Each chapter provides a comprehensive review of a selected field, with illustrated examples from the authors' own work. The book will appeal to professionals and researchers in marine biology, marine chemistry, marine engineering, and sedimentology.
Book Synopsis The Ocean Carbon Cycle and Climate by : Mick Follows
Download or read book The Ocean Carbon Cycle and Climate written by Mick Follows and published by Springer Science & Business Media. This book was released on 2012-12-06 with total page 401 pages. Available in PDF, EPUB and Kindle. Book excerpt: Our desire to understand the global carbon cycle and its link to the climate system represents a huge challenge. These overarching questions have driven a great deal of scientific endeavour in recent years: What are the basic oceanic mechanisms which control the oceanic carbon reservoirs and the partitioning of carbon between ocean and atmosphere? How do these mechanisms depend on the state of the climate system and how does the carbon cycle feed back on climate? What is the current rate at which fossil fuel carbon dioxide is absorbed by the oceans and how might this change in the future? To begin to answer these questions we must first understand the distribution of carbon in the ocean, its partitioning between different ocean reservoirs (the "solubility" and "biological" pumps of carbon), the mechanisms controlling these reservoirs, and the relationship of the significant physical and biological processes to the physical environment. The recent surveys from the JGOFS and WOCE (Joint Global Ocean Flux Study and World Ocean Circulation Ex periment) programs have given us a first truly global survey of the physical and biogeochemical properties of the ocean. These new, high quality data provide the opportunity to better quantify the present oceans reservoirs of carbon and the changes due to fossil fuel burning. In addition, diverse process studies and time-series observations have clearly revealed the complexity of interactions between nutrient cycles, ecosystems, the carbon-cycle and the physical envi ronment.
Book Synopsis Carbon and Nitrogen Cycling Across the Bathyal Continental Margins by : William Ross Hunter
Download or read book Carbon and Nitrogen Cycling Across the Bathyal Continental Margins written by William Ross Hunter and published by . This book was released on 2012 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: The thesis also investigates the differential fates of marine and terrigenous phytodetritus in the sediments of the Whittard canyon (NE Atlantic). In situ pulse-chase experiments reveal nitrogen demand to control macrofaunal feeding responses, inhibiting the utilisation of the nitrogen-poor terrigenous phytodetritus. Bacteria exhibit similar feeding responses to the fauna, whilst bacterial biomass was negatively correlated to increasing faunal activity. This demonstrates that increased inputs of terrigenous organic matter may alter ecosystem-scale carbon cycling pathways and trophic interactions within continental margin sediments.
Book Synopsis Quantitative Modeling of Nitrogen Cycling Along the River Continuum by : Zahra Akbarzadeh
Download or read book Quantitative Modeling of Nitrogen Cycling Along the River Continuum written by Zahra Akbarzadeh and published by . This book was released on 2018 with total page 142 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.
Book Synopsis Cycling of Carbon, Nitrogen, Sulfur and Phosphorus in Terrestrial and Aquatic Ecosystems by : J. R. Freney
Download or read book Cycling of Carbon, Nitrogen, Sulfur and Phosphorus in Terrestrial and Aquatic Ecosystems written by J. R. Freney and published by Springer. This book was released on 1982-07 with total page 168 pages. Available in PDF, EPUB and Kindle. Book excerpt: The papers published in this volume were presented to that workshop which was held in Canberra on 29-30 April and 1 May 1981.
Book Synopsis The Role of Labile Dissolved Organic Carbon in Influencing Fluxes Across the Sediment-water Interface by : Deborah J. Read
Download or read book The Role of Labile Dissolved Organic Carbon in Influencing Fluxes Across the Sediment-water Interface written by Deborah J. Read and published by . This book was released on 2008 with total page 156 pages. Available in PDF, EPUB and Kindle. Book excerpt: Sediment diagenesis in aquatic systems is usually understood to be controlled by the concentrations of both organic carbon and the oxidant. However, the concept that sediment respiration may be limited by the supply of organic carbon, even in systems with moderate concentrations of organic carbon in the water column, has yet to be fully explored. Typically we assume that a direct coupling between water column and sediment diagenesis processes occurs and the chemical evolution of porewater and surface water are linked through fluxes of chemical species across the sediment-water interface. While the dynamics of supply of particulate organic carbon (POC) to the sediments via plankton deposition and resuspension, has previously been examined, the fate of dissolved organic carbon (DOC) once in the sediments, has rarely been investigated. A series of experiments comprising batch tests, microcosms and sediment cores were conducted on sediment and water from four diverse field sites in which sediment respiration was considered to be carbon limited. Three sites were oligotrophic, acidic lakes and the fourth an oligotrophic coastal embayment. During each experiment dissolved organic carbon was added and measurements were undertaken of solutes that were considered participants in diagenetic processes. While each system differed in its chemical, biological and geological makeup, a key commonality was the rapid onset of anoxic conditions in the sediments irrespective of the overlying water oxygen concentrations, indicating lack of direct coupling between biogeochemical processes in the water column and sediments. Also, similar apparent DOC remineralisation rates were observed, measured solute fluxes after the addition of DOC indicated adherence to the ecological redox sequence, and increased ammonium concentrations were measured in the overlying waters of the acidic microcosms. In marine system experiments it was noted that diagenetic respiration, as indicated by decreasing concentrations of oxygen in the overlying water, increased rapidly after labile DOC was added. To explore the influence of geochemical processes on sediment respiration, a diagenetic model was tested against the laboratory data. The model was able to capture the rapid changes observed in the microcosms after addition of DOC in both the marine and acidic systems experiments. The model has the potential to serve as an essential tool for quantifying sediment organic matter decomposition and dissolved chemical fluxes. This work has focussed our attention on the control of DOC availability on sediment respiration and thus its ultimate control on solute fluxes across the sediment water interface. The results highlight the need to understand and quantify the supply of DOC to the sediment (as POC or already as the dissolved form), its transport through the sediment and its eventual remineralisation. This understanding is critical for improved management of aquatic systems, possibly even in systems where water column organic carbon is plentiful but sediment respiration is constrained by high organic carbon turnover rates in the water column and a resulting low flux of organic carbon to the sediment.
