Academic literature on the topic 'Redox-stratified systems'
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Journal articles on the topic "Redox-stratified systems"
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Petrash, Daniel A., Ingrid M. Steenbergen, Astolfo Valero, Travis B. Meador, Tomáš Pačes, and Christophe Thomazo. "Aqueous system-level processes and prokaryote assemblages in the ferruginous and sulfate-rich bottom waters of a post-mining lake." Biogeosciences 19, no. 6 (March 24, 2022): 1723–51. http://dx.doi.org/10.5194/bg-19-1723-2022.
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Abstract. In the low-nutrient, redox-stratified Lake Medard (Czechia), reductive Fe(III) dissolution outpaces sulfide generation from microbial sulfate reduction (MSR) and ferruginous conditions occur without quantitative sulfate depletion. The lake currently has marked overlapping C, N, S, Mn and Fe cycles occurring in the anoxic portion of the water column. This feature is unusual in stable, natural, redox-stratified lacustrine systems where at least one of these biogeochemical cycles is functionally diminished or undergoes minimal transformations because of the dominance of another component or other components. Therefore, this post-mining lake has scientific value for (i) testing emerging hypotheses on how such interlinked biogeochemical cycles operate during transitional redox states and (ii) acquiring insight into redox proxy signals of ferruginous sediments underlying a sulfatic and ferruginous water column. An isotopically constrained estimate of the rates of sulfate reduction (SRRs) suggests that despite high genetic potential, this respiration pathway may be limited by the rather low amounts of metabolizable organic carbon. This points to substrate competition exerted by iron- and nitrogen-respiring prokaryotes. Yet, the planktonic microbial succession across the nitrogenous and ferruginous zones also indicates genetic potential for chemolithotrophic sulfur oxidation. Therefore, our SRR estimates could rather be portraying high rates of anoxic sulfide oxidation to sulfate, probably accompanied by microbially induced disproportionation of S intermediates. Near and at the anoxic sediment–water interface, vigorous sulfur cycling can be fuelled by ferric and manganic particulate matter and redeposited siderite stocks. Sulfur oxidation and disproportionation then appear to prevent substantial stabilization of iron monosulfides as pyrite but enable the interstitial precipitation of microcrystalline equant gypsum. This latter mineral isotopically recorded sulfur oxidation proceeding at near equilibrium with the ambient anoxic waters, whilst authigenic pyrite sulfur displays a 38 ‰ to 27 ‰ isotopic offset from ambient sulfate, suggestive of incomplete MSR and open sulfur cycling. Pyrite-sulfur fractionation decreases with increased reducible reactive iron in the sediment. In the absence of ferruginous coastal zones today affected by post-depositional sulfate fluxes, the current water column redox stratification in the post-mining Lake Medard is thought relevant for refining interpretations pertaining to the onset of widespread redox-stratified states across ancient nearshore depositional systems.
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Lassak, Jürgen, Anna-Lena Henche, Lucas Binnenkade, and Kai M. Thormann. "ArcS, the Cognate Sensor Kinase in an Atypical Arc System of Shewanella oneidensis MR-1." Applied and Environmental Microbiology 76, no. 10 (March 26, 2010): 3263–74. http://dx.doi.org/10.1128/aem.00512-10.
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ABSTRACT The availability of oxygen is a major environmental factor for many microbes, in particular for bacteria such as Shewanella species, which thrive in redox-stratified environments. One of the best-studied systems involved in mediating the response to changes in environmental oxygen levels is the Arc two-component system of Escherichia coli, consisting of the sensor kinase ArcB and the cognate response regulator ArcA. An ArcA ortholog was previously identified in Shewanella, and as in Escherichia coli, Shewanella ArcA is involved in regulating the response to shifts in oxygen levels. Here, we identified the hybrid sensor kinase SO_0577, now designated ArcS, as the previously elusive cognate sensor kinase of the Arc system in Shewanella oneidensis MR-1. Phenotypic mutant characterization, transcriptomic analysis, protein-protein interaction, and phosphotransfer studies revealed that the Shewanella Arc system consists of the sensor kinase ArcS, the single phosphotransfer domain protein HptA, and the response regulator ArcA. Phylogenetic analyses suggest that HptA might be a relict of ArcB. Conversely, ArcS is substantially different with respect to overall sequence homologies and domain organizations. Thus, we speculate that ArcS might have adopted the role of ArcB after a loss of the original sensor kinase, perhaps as a consequence of regulatory adaptation to a redox-stratified environment.
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Schulz, T. J., and D. Barnes. "The Stratified Facultative Lagoon for the Treatment and Storage of High Strength Agricultural Wastewaters." Water Science and Technology 22, no. 9 (September 1, 1990): 43–50. http://dx.doi.org/10.2166/wst.1990.0065.
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A research and development programme at The University of New South Wales and a large intensive piggery located on the outskirts of Sydney, Australia, has culminated in the successful commissioning of an odour control process for the storage and treatment of wastewaters from the piggery. The stratified facultative lagoon utilises surface aeration of an otherwise anaerobic lagoon to provide a non-odorous cover for the anaerobic contents. The process has filled a need in the pig industry for a non-odorous cost effective alternative to conventional treatment systems, prior to wastewater re-use or disposal by land application. Critical design parameters include lagoon depth, specific energy input and aeration system design. Mean removal efficiencies of biochemical oxygen demand of 75 per cent have been achieved consistently. The development of the process was facilitated by the use of wastewater redox potential testing to indicate the likely presence of odorous compounds in the liquid on the surface of the lagoon and in the surrounding atmosphere. Surface redox potential readings (Eh) greater than −76 mV resulted in non-odorous operation of the process.
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Thote, Prashant, and Gowri S. "OUTCOME BASED LEARNING: A PANACEA FOR QUALITY EDUCATION." International Journal of Research -GRANTHAALAYAH 9, no. 5 (May 14, 2021): 8–23. http://dx.doi.org/10.29121/granthaalayah.v9.i5.2021.3909.
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The curriculum framework asserts learner to debate, dissent form individual opinion on ideas, systems, practices by nurturing skills to think and reason independently. Participatory learning activity is envisioned as a process whereby learners construct concept through assimilation, absorption, interaction and reflection. In the present paper experiential learning activity are designed to ensure that the students are encouraged to seek out knowledge from their hands-on activity than the text book in their own experiences. In the present paper attempt is made to investigate the impact of conventional method of teaching and experiential learning activities on attainment of knowledge and retention of knowledge in learning redox reaction. Data is collected by using pre-test, post-test and retention test. Instrument is validated by experts. Stratified random method is applied to draw the sample. Totally 50 students participate in the study. Sample is separated into two: control and the study group. Control group is exposed to the conventional chalk and talk method while the students from the study group are exposed to Experiential Learning Activities. The result of the study reveals that there is noteworthy difference in the mean score in learning redox reaction in the scores of pre-test, post-test and retention test between the study group and the control group.
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Regnier, P., P. Jourabchi, and C. P. Slomp. "Reactive-Transport modeling as a technique for understanding coupled biogeochemical processes in surface and subsurface environments." Netherlands Journal of Geosciences - Geologie en Mijnbouw 82, no. 1 (April 2003): 5–18. http://dx.doi.org/10.1017/s0016774600022757.
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AbstractReactive-transport models contribute significantly to the field of modern geosciences. A general mathematical approach to solving models of complex biogeochemical systems is introduced. It is argued that even though mathematical models for reactive-transport simulations can be developed at various levels of approximation, the approach for their construction and application to the various compartments of the hydrosphere is fundamentally the same. The workings of coupled transport-reaction systems are described in more detail by means of examples, which demonstrate the similarities in the approach. Three models of the carbon dynamics in redox-stratified environments are compared: porous media flow problems in a coastal sediment and in a contaminated groundwater system; and a surface flow problem in a eutrophic estuary. Considering the interdisciplinary nature of such models, a Knowledge Base System for biogeochemical processes is proposed. Incorporation of the proposed knowledge base in an appropriate modeling framework, such as the Biogeochemical Reaction Network Simulator, proves an effective approach to the modeling of complex natural systems. This methodology allows for construction of multi-component reactive-transport models applicable to a wide range of problems of interest to the geoscientist.
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Hartland, Adam, Martin S. Andersen, and David P. Hamilton. "Phosphorus and arsenic distributions in a seasonally stratified, iron- and manganese-rich lake: microbiological and geochemical controls." Environmental Chemistry 12, no. 6 (2015): 708. http://dx.doi.org/10.1071/en14094.
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Environmental context Despite being present at trace concentrations, arsenic and phosphorus are among the most important of freshwater contaminants. This research highlights the biogeochemical coupling of both elements in a New Zealand lake. We find that the mineralisation of organic residues coupled to the dissolution of colloidal iron and manganese hydroxides may be an important driver of the bioavailability of phosphorus and arsenic. Abstract Seasonal stratification in temperate lakes greater than a few metres deep provides conditions amenable to pronounced vertical zonation of redox chemistry. Such changes are particularly evident in eutrophic systems where high phytoplankton biomass often leads to seasonally established anaerobic hypolimnia and profound changes in geochemical conditions. In this study, we investigated the behaviour of trace elements in the water column of a seasonally stratified, eutrophic lake. Two consecutive years of data from Lake Ngapouri, North Island, New Zealand, demonstrate the occurrence of highly correlated profiles of phosphorus, arsenic, iron and manganese, all of which increased in concentration by 1–2 orders of magnitude within the anaerobic hypolimnion. Stoichiometric and mass-balance considerations demonstrate that increases in alkalinity in hypolimnetic waters were consistent with observed changes in sulfate, Fe and Mn concentrations with depth, corresponding to dissimilatory reduction of sulfate, FeIII and MnIV hydroxides. Thermodynamic constraints on Fe, Mn and Al solubility indicate that amorphous FeIII, MnIV hydroxides most probably controlled Fe and Mn in the surface mixed layer (~0 to 8m) whereas AlIII hydroxides were supersaturated throughout the entire system. Surface complexation modelling indicated that iron hydroxides (HFO) potentially dominated As speciation in the lake. It is likely that other colloidal phases such as allophanic clays also limited HPO42– activity, reducing competition for HAsO42– adsorption to iron hydroxides. This research highlights the coupling of P, As, Fe and Mn in Lake Ngapouri, and the apparent role of multiple colloidal phases in affecting P and As activity within overarching microbiological and geochemical processes.
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Friedrich, J., F. Janssen, D. Aleynik, H. W. Bange, N. Boltacheva, M. N. Çagatay, A. W. Dale, et al. "Investigating hypoxia in aquatic environments: diverse approaches to addressing a complex phenomenon." Biogeosciences 11, no. 4 (February 27, 2014): 1215–59. http://dx.doi.org/10.5194/bg-11-1215-2014.
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Abstract. In this paper we provide an overview of new knowledge on oxygen depletion (hypoxia) and related phenomena in aquatic systems resulting from the EU-FP7 project HYPOX ("In situ monitoring of oxygen depletion in hypoxic ecosystems of coastal and open seas, and landlocked water bodies", http://www.hypox.net). In view of the anticipated oxygen loss in aquatic systems due to eutrophication and climate change, HYPOX was set up to improve capacities to monitor hypoxia as well as to understand its causes and consequences. Temporal dynamics and spatial patterns of hypoxia were analyzed in field studies in various aquatic environments, including the Baltic Sea, the Black Sea, Scottish and Scandinavian fjords, Ionian Sea lagoons and embayments, and Swiss lakes. Examples of episodic and rapid (hours) occurrences of hypoxia, as well as seasonal changes in bottom-water oxygenation in stratified systems, are discussed. Geologically driven hypoxia caused by gas seepage is demonstrated. Using novel technologies, temporal and spatial patterns of water-column oxygenation, from basin-scale seasonal patterns to meter-scale sub-micromolar oxygen distributions, were resolved. Existing multidecadal monitoring data were used to demonstrate the imprint of climate change and eutrophication on long-term oxygen distributions. Organic and inorganic proxies were used to extend investigations on past oxygen conditions to centennial and even longer timescales that cannot be resolved by monitoring. The effects of hypoxia on faunal communities and biogeochemical processes were also addressed in the project. An investigation of benthic fauna is presented as an example of hypoxia-devastated benthic communities that slowly recover upon a reduction in eutrophication in a system where naturally occurring hypoxia overlaps with anthropogenic hypoxia. Biogeochemical investigations reveal that oxygen intrusions have a strong effect on the microbially mediated redox cycling of elements. Observations and modeling studies of the sediments demonstrate the effect of seasonally changing oxygen conditions on benthic mineralization pathways and fluxes. Data quality and access are crucial in hypoxia research. Technical issues are therefore also addressed, including the availability of suitable sensor technology to resolve the gradual changes in bottom-water oxygen in marine systems that can be expected as a result of climate change. Using cabled observatories as examples, we show how the benefit of continuous oxygen monitoring can be maximized by adopting proper quality control. Finally, we discuss strategies for state-of-the-art data archiving and dissemination in compliance with global standards, and how ocean observations can contribute to global earth observation attempts.
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Magnall, Joseph M., Sarah A. Gleeson, and Suzanne Paradis. "A NEW SUBSEAFLOOR REPLACEMENT MODEL FOR THE MACMILLAN PASS CLASTIC-DOMINANT Zn-Pb ± Ba DEPOSITS (YUKON, CANADA)." Economic Geology 115, no. 5 (August 1, 2020): 953–59. http://dx.doi.org/10.5382/econgeo.4719.
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Abstract Sedimentary exhalative (SEDEX) deposits are a subset of sediment-hosted massive sulfide deposits and provide our dominant resource of Zn. In the SEDEX model, base metals (Zn, Pb, Fe) are hydrothermally vented into sulfidic (euxinic) seawater and deposited coevally with the organic-rich mudstone host rock, resulting in laterally extensive layered mineralization. In the Selwyn Basin (Canada) at Macmillan Pass, two deposits (Tom, Jason) are well preserved in a succession of Upper Devonian mudstones and are considered type-characteristic examples of the SEDEX deposit model. As with a number of SEDEX deposits, at Macmillan Pass barite is abundant in the succession hosting hydrothermal mineralization. Early work presented a hydrothermal model for barite formation, in which barite coprecipitated with base metal sulfides in a redox-stratified water column. Recently, however, studies have both proposed an alternative diagenetic model for barite formation and provided more precise constraints on the chemistry of the hydrothermal fluid that entered the vent complexes. Here, we present a new model for Macmillan Pass in which sulfide mineralization occurred entirely within the subsurface. The introduction of hot (300°C) hydrothermal fluids into the shallow subsurface (<1-km depth) resulted in the thermal degradation of organic matter and generated CO2; this promoted barite dissolution, which both provided a source of sulfate for thermochemical sulfate reduction and increased the porosity and permeability within the system. Importantly, there was clear potential for the development of positive feedbacks and self-organization between diagenetic and hydrothermal processes, resulting in highly efficient ore-forming systems. In contrast to the SEDEX model, alteration footprints will be controlled by the mass transfer involved in (barite) replacement reactions rather than hydrothermal venting, and exploration criteria at a district scale should strongly favor highly productive continental margins.
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Friedrich, J., F. Janssen, D. Aleynik, H. W. Bange, N. Boltacheva, M. N. Çağatay, A. W. Dale, et al. "Investigating hypoxia in aquatic environments: diverse approaches to addressing a complex phenomenon." Biogeosciences Discussions 10, no. 8 (August 5, 2013): 12655–772. http://dx.doi.org/10.5194/bgd-10-12655-2013.
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Abstract. In this paper we synthesize the new knowledge on oxygen and oxygen-related phenomena in aquatic systems, resulting from the EU-FP7 project HYPOX ("In situ monitoring of oxygen depletion in hypoxic ecosystems of coastal and open seas, and land-locked water bodies", www.hypox.net). In view of the anticipated oxygen loss in aquatic systems due to eutrophication and climate change, HYPOX was set up to improve capacities to monitor hypoxia as well as to understand its causes and consequences. Temporal dynamics and spatial patterns of hypoxia were analysed in field studies in various aquatic environments, including the Baltic Sea, the Black Sea, Scottish and Scandinavian fjords, Ionian Sea lagoons and embayments, and in Swiss lakes. Examples of episodic and rapid (hours) occurrences of hypoxia as well as seasonal changes in bottom-water oxygenation in stratified systems are discussed. Geologically-driven hypoxia caused by gas seepage is demonstrated. Using novel technologies, temporal and spatial patterns of water-column oxygenation, from basin-scale seasonal patterns to meter-scale submicromolar oxygen distributions were resolved. Existing multi-decadal monitoring data were used to demonstrate the imprint of climate change and eutrophication on long-term oxygen distributions. Organic and inorganic proxies were used to extend investigations on past oxygen conditions to centennial and even longer timescales not resolved by monitoring. The effects of hypoxia on faunal communities and biogeochemical processes were also addressed in the project. An investigation of benthic fauna is presented as an example of hypoxia-devastated benthic communities that slowly recover upon a reduction in eutrophication in a system where natural and anthropogenic hypoxia overlap. Biogeochemical investigations reveal that oxygen intrusions have a strong effect on microbially-mediated redox cycling of elements. Observations and modeling studies of the sediments demonstrate the effect of seasonally changing oxygen conditions on benthic mineralization pathways and fluxes. Data quality and access are crucial in hypoxia research. Therefore, technical issues are addressed, including the availability of suitable sensor technology to resolve gradual changes in bottom-water oxygen that can be expected as a result of climate change in deep-sea waters. Using cabled observatories as examples, we show how the benefit of continuous oxygen monitoring can be maximized by adopting proper quality control. Finally, we discuss strategies for state-of-the-art data archiving and dissemination in compliance with global standards and how ocean observations may contribute to global earth observation attempts.
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Hohl, Simon V., Shao-Yong Jiang, Sebastian Viehmann, Wei Wei, Qian Liu, Hai-Zhen Wei, and Stephen J. G. Galer. "Trace Metal and Cd Isotope Systematics of the Basal Datangpo Formation, Yangtze Platform (South China) Indicate Restrained (Bio)Geochemical Metal Cycling in Cryogenian Seawater." Geosciences 10, no. 1 (January 19, 2020): 36. http://dx.doi.org/10.3390/geosciences10010036.
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The behaviour of bioavailable trace metals and their stable isotopes in the modern oceans is controlled by uptake into phototrophic organisms and adsorption on and incorporation into marine authigenic minerals. Among other bioessential metals, Cd and its stable isotopes have recently been used in carbonate lithologies as novel tracer for changes in the paleo primary productivity and (bio)geochemical cycling. However, many marine sediments that were deposited during geologically highly relevant episodes and which, thus, urgently require study for a better understanding of the paleo environment are rather composed of a mixture of organic matter (OM), and detrital and authigenic minerals. In this study, we present Cd concentrations and their isotopic compositions as well as trace metal concentrations from sequential leachates of OM-rich shales of the Cryogenian basal Datangpo Formation, Yangtze Platform (South China). Our study shows variable distribution of conservative and bioavailable trace metals as well as Cd isotope compositions between sequential leachates of carbonate, OM, sulphide, and silicate phases. We show that the Cd isotope compositions obtained from OM leachates can be used to calculate the ambient Cryogenian surface seawater of the restricted Nanhua Basin by applying mass balance calculations. By contrast, early diagenetic Mn carbonates and sulphides incorporated the residual Cd from dissolved organic matter that was in isotopic equilibrium with deep/pore waters of the Nanhua Basin. Our model suggests that the Cd isotopic composition of surface seawater at that time reached values of modern oxygenated surface oceans. However, the deep water Cd isotope composition was substantially heavier than that of modern fully oxygenated oceans and rather resembles deep waters with abundant sulphide precipitation typical for modern oxygen minimum zones. This argues for incomplete recycling of Cd and other bioavailable metals shortly after the Sturtian glaciation in the redox stratified Cryogenian Nanhua Basin. Our study highlights the importance of sequential leaching procedures when dealing with impure authigenic sediments such as OM-rich carbonates, mudstones, or shales to achieve reliable trace metal concentrations and Cd isotope compositions as proxies for (bio)geochemical metal cycling in past aquatic systems.
Dissertations / Theses on the topic "Redox-stratified systems"
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Liebelt, S. R. "Testing the redox coupling between chromium and nitrogen isotopes in modern and ancient redox-stratified depositional systems: the Coorong Lagoon and the Greater McArthur Basin." Thesis, 2019. https://hdl.handle.net/2440/136963.
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This item is only available electronically.The history of Earth’s atmospheric oxidation following the Great Oxidation Event (GOE) is widely debated and currently poorly constrained. This uncertainty is largely because the use of different geochemical proxies provides a broad range of possible palaeo-redox conditions during the mid-Proterozoic. Such proxies include nitrogen (δ15N) and chromium (δ53Cr) isotopes, which are the focus of this study. These redox-sensitive proxies have recently demonstrated coupled behaviour in both modern seawaters and recent marine sediments, suggesting isotopic fractionation of Cr could result from biologically mediated redox cycling of N. This concept is opposed to Cr isotope fractionation being purely representative of oxidative weathering on continents, thus challenging the reliability of the δ53Cr proxy as a direct tracer for past atmospheric O2 levels. The aim of this study is to test the purported redox coupling of the δ53Cr and δ15N proxies in two redox-stratified depositional systems, specifically investigating (i) modern waters and organic matter from the Coorong Lagoon of South Australia, and (ii) organic-rich shales from the greater McArthur Basin in the Northern Territory (including the Velkerri, Mainoru, Barney Creek and Fraynes Formations). These marine settings display notable redox gradients, allowing insight into the isotopic behaviour of N and Cr through a variety of conditions. Contrary to published data, this study revealed no positive co-variance between δ53Cr and δ15N records. Rather, δ15N changes in both waters and shales are interpreted to largely result from pH-driven volatilisation of NH3, while δ53Cr variations in shales exhibit a systematic temporal increase. This increase likely reflects progressive basin oxygenation, linked to gradually increasing atmospheric O2 during the mid-Proterozoic (i.e. from 1.64 to 1.31 Ga). Thus, the validity of δ53Cr values in marine archives as a palaeo-redox proxy are supported in this instance, with no direct evidence for biologically driven redox cycling of Cr coupled to local N cycling.
Thesis (B.Sc.(Hons)) -- University of Adelaide, School of Physical Sciences, 2019