scholarly journals The Impact of Water Column Mixing in a Salt-Wedge Estuary

2018 ◽  
Author(s):  
Joshua Johnson
Keyword(s):  
Water Column ◽  
Salt Wedge ◽  
Water Column Mixing ◽  
The Impact

scholarly journals Computational Evaluation of Shock Wave Interaction with a Cylindrical Water Column

2021 ◽  
Vol 11 (11) ◽  
pp. 4934
Author(s):  
Viola Rossano ◽  
Giuliano De Stefano
Keyword(s):  
Shock Wave ◽  
Water Column ◽  
Wave Interaction ◽  
Navier Stokes ◽  
Plane Shock ◽  
Governing Equations ◽  
Computational Evaluation ◽  
Air Water Interface ◽  
The Mean ◽  
The Impact

Computational fluid dynamics was employed to predict the early stages of the aerodynamic breakup of a cylindrical water column, due to the impact of a traveling plane shock wave. The unsteady Reynolds-averaged Navier–Stokes approach was used to simulate the mean turbulent flow in a virtual shock tube device. The compressible flow governing equations were solved by means of a finite volume-based numerical method, where the volume of fluid technique was employed to track the air–water interface on the fixed numerical mesh. The present computational modeling approach for industrial gas dynamics applications was verified by making a comparison with reference experimental and numerical results for the same flow configuration. The engineering analysis of the shock–column interaction was performed in the shear-stripping regime, where an acceptably accurate prediction of the interface deformation was achieved. Both column flattening and sheet shearing at the column equator were correctly reproduced, along with the water body drift.

Biogeochemical and ecological features of sinking particulate matter in the deep Ionian Sea (E. Mediterranean) during a 10-year time series study: impacts of atmospheric and oceanographic variabilities on carbon production and sequestration

2021 ◽  
Author(s):  
Alexandra Gogou ◽  
Constantine Parinos ◽  
Spyros Stavrakakis ◽  
Emmanouil Proestakis ◽  
Maria Kanakidou ◽  
...  
Keyword(s):  
Particulate Matter ◽  
Organic Carbon ◽  
Carbon Cycle ◽  
Atmospheric Deposition ◽  
Water Column ◽  
Particulate Organic Carbon ◽  
Nutrient Dynamics ◽  
Ionian Sea ◽  
Ecological Features ◽  
The Impact

<p>Biotic and abiotic processes that form, alter, transport, and remineralize particulate organic carbon, silicon, calcium carbonate, and other minor and trace chemical species in the water column are central to the ocean’s ecological and biogeochemical functioning and of fundamental importance to the ocean carbon cycle. Sinking particulate matter is the major vehicle for exporting carbon from the sea surface to the deep sea. During its transit towards the sea floor, most particulate organic carbon (POC) is returned to inorganic form and redistributed in the water column. This redistribution determines the surface concentration of dissolved CO<sub>2</sub>, and hence the rate at which the ocean can absorb CO<sub>2</sub> from the atmosphere. The ability to predict quantitatively the depth profile of remineralization is therefore critical to deciphering the response of the global carbon cycle to natural and human-induced changes.</p><p>Aiming to investigate the significant biogeochemical and ecological features and provide new insights on the sources and cycles of sinking particulate matter, a mooring line of five sediment traps was deployed from 2006 to 2015 (with some gap periods) at 5 successive water column depths (700, 1200, 2000, 3200 and 4300 m) in the SE Ionian Sea, northeastern Mediterranean (‘NESTOR’ site). We have examined the long-term records of downward fluxes for Corg, N<sub>tot</sub>, δ<sup>13</sup>Corg and δ<sup>15</sup>N<sub>tot</sub>, along with the associated ballast minerals (opal, lithogenics and CaCO<sub>3</sub>), lipid biomarkers, Chl-a and PP rates, phytoplankton composition, nutrient dynamics and atmospheric deposition.  </p><p>The satellite-derived seasonal and interannual variability of phytoplankton metrics (biomass and phenology) and atmospheric deposition (meteorology and air masses origin) was examined for the period of the sediment trap experiment. Regarding the atmospheric deposition, synergistic opportunities using Earth Observation satellite lidar and radiometer systems are proposed (e.g. Cloud‐Aerosol Lidar with Orthogonal Polarization - CALIOP, Moderate Resolution Imaging Spectroradiometer - MODIS), aiming towards a four‐dimensional exploitation of atmospheric aerosol loading (e.g. Dust Optical Depth) in the study area.</p><p>Our main goals are to: i) develop a comprehensive knowledge of carbon fluxes and associated mineral ballast fluxes from the epipelagic to the mesopelagic and bathypelagic layers, ii) elucidate the mechanisms governing marine productivity and carbon export and sequestration to depth and iii) shed light on the impact of atmospheric forcing and deposition in respect to regional and large scale circulation patterns and climate variability and the prevailing oceanographic processes (internal variability).</p><p>Acknowledgments</p><p>We acknowledge support of this work by the Action ‘National Network on Climate Change and its Impacts – <strong>CLIMPACT</strong>’, funded by the Public Investment Program of Greece (GSRT, Ministry of Development and Investments).</p>

scholarly journals The mass impacts on chemosynthetic primary producers: potential implications on anammox communities and their consequences

2018 ◽  
Vol 18 (05) ◽  
pp. 440-444
Author(s):  
Noel Pérez ◽  
Jorge Luis Velazco-Vargas ◽  
Osmel Martin ◽  
Rolando Cardenas ◽  
Jesús Martínez-Frías
Keyword(s):  
Water Column ◽  
Deposition Rate ◽  
Extreme Case ◽  
Chemical Compounds ◽  
Global Scale ◽  
Biogeochemical Cycle ◽  
Potential Influence ◽  
Asteroid Impact ◽  
Global Cooling ◽  
The Impact

AbstractThe potential of a mass asteroid impact on Earth to disturb the chemosynthetic communities at global scale is discussed. Special emphasis is made on the potential influence on anammox communities and their implications in the nitrogen biogeochemical cycle. According to our preliminary estimates, anammox communities could be seriously affected as a consequence of global cooling and the large process of acidification usually associated with the occurrence of this kind of event. The scale of affectations could vary in a scenario like the Chicxulub as a function of the amount of soot, depth of the water column and the deposition rate for sulphates assumed in each case. The most severe affectations take place where the amount of soot and sulphates produced during the event is higher and the scale of time of settlements for sulphates is short, of the order of 10 h. In this extreme case, the activity of anammox is considerably reduced, a condition that may persist for several years after the impact. Furthermore, the impact of high levels of other chemical compounds like sulphates and nitrates associated with the occurrence of this kind of event are also discussed.

Uncertainty in Wave Basin Testing of a Fixed Oscillating Water Column Wave Energy Converter

2021 ◽  
Author(s):  
Frances M. Judge ◽  
Eoin Lyden ◽  
Michael O'Shea ◽  
Brian Flannery ◽  
Jimmy Murphy
Keyword(s):  
Water Column ◽  
Wave Energy ◽  
Wave Energy Converter ◽  
Width Ratio ◽  
Oscillating Water Column ◽  
Energy Converter ◽  
The Monte Carlo Method ◽  
Wave Basin ◽  
Measurement Location ◽  
The Impact

Abstract This research presents a methodology for carrying out uncertainty analysis on measurements made during wave basin testing of an oscillating water column wave energy converter. Values are determined for Type A and Type B uncertainty for each parameter of interest, and uncertainty is propagated using the Monte Carlo method to obtain an overall Expanded Uncertainty with a 95% confidence level associated with the Capture Width Ratio of the device. An analysis into the impact of reflections on the experimental results reveals the importance of identifying the incident and combined wave field at each measurement location used to determine device performance, in order to avoid misleading results.

An Overview of Dynamics and Biotoxicity of Metals in the Freshwater Environment

1993 ◽  
Vol 28 (1) ◽  
pp. 1-6 ◽  
Author(s):  
P.M. Huang
Keyword(s):  
Water Column ◽  
Interstitial Water ◽  
Dynamic Equilibrium ◽  
Kinetic Studies ◽  
Integrated Approach ◽  
Freshwater Ecosystem ◽  
Overlying Water ◽  
Freshwater Environment ◽  
Particulate Materials ◽  
The Impact

Abstract The toxic metals, including metalloids, in the freshwater ecosystem are largely associated with surficial sediments and suspended particulate materials. These metals are in dynamic equilibrium with interstitial water and the overlying water column. The bioavailability and toxicity of metals in the freshwater environment are influenced by their speciation and dynamics. Our current understanding of the nature of metal partitioning in particulate materials, interstitial water and the overlying water column is quite limited because of the limitations of the metal fractionation methods and difficulties in obtaining thermodynamic information which approaches the realities in streams, rivers and lakes. Little is known about the in situ metal dynamics. Kinetic studies of metal reactions, thus, warrant in-depth research for years to come. Besides inorganic and organic colloids, microbes contribute to metal transformations. The impact of the interactions of microbes with minerals and organic components on the dynamics and biotoxicity of metals merits attention. Over the last decade, there has been much research on the development of hydrochemical models for better understanding and predicting metal transport in the freshwater system, yet little research has been focused on how well they describe field data. The supply of biologically available metals in the freshwater environment is governed by a series of physical, physicochemical, biochemical and biological processes. To date, there are very few studies on the subject in which an integrated approach has been taken. The roles of these interacting processes in affecting metal dynamics and their impacts on freshwater toxicology deserve increasing attention.

Controls on oxygen response to climate change on the Northwest European Continental Shelf

2020 ◽  
Author(s):  
Sarah L. Wakelin ◽  
Yuri Artioli ◽  
Momme Butenschön ◽  
Jason Holt ◽  
Jeremy Blackford
Keyword(s):  
Climate Change ◽  
Continental Shelf ◽  
Water Column ◽  
Ecosystem Processes ◽  
Phytoplankton Production ◽  
Biogeochemical Model ◽  
Biological Cycling ◽  
Increasing Temperature ◽  
The Impact ◽  
Oxygen Concentrations

<p>Dissolved oxygen in the ocean is an indicator of water quality and low concentrations can threaten ecosystem health. The main sources of marine oxygen are diffusion from the atmosphere and phytoplankton photosynthesis. Biological respiration and decomposition act to reduce oxygen concentrations. Under conditions of vertical stratification, the water column below the pycnocline is isolated from oxygen exchange with the atmosphere, photosynthesis may be limited by light availability and oxygen concentrations decrease. Climate change influences the oxygen cycle in two ways: 1) changing the hydrodynamic climate and 2) affecting rates of biogeochemical processes. The hydrodynamic climate affects the nutrient supply and so controls phytoplankton production while changes to water column stratification affects vertical mixing. Gas solubility decreases with increasing temperature so that oxygen uptake from the atmosphere is expected to decrease under increasing oceanic temperatures. Biological cycling rates increase with increasing temperature affecting photosynthesis, respiration and bacterial decomposition. It is not obvious whether changes in oxygen concentrations due to changing ecosystem processes will mitigate or reinforce the projected reduction from solubility changes.</p><p>The Northwest European Continental shelf (NWES) is a region of the northeast Atlantic that experiences seasonal stratification. We use the physics-biogeochemical model NEMO-ERSEM to study near-bed oxygen concentrations on the NWES under a high greenhouse gas emissions scenario (Representative Concentration Pathway (RCP) 8.5). We show that much of the NWES could experience low oxygen concentrations by 2100 and assess the relative impacts of changing temperature and ecosystem processes. Until about 2040 the impact of solubility dominates the oxygen change. The mean near-bed oxygen concentration is projected to decrease by 6.3% by 2100, of which 73% is due to solubility changes and the remainder to changes in the ecosystem. In the oxygen-depleted region in the eastern North Sea, 77% of the near-bed oxygen reduction is due to ecosystem processes.</p>

scholarly journals Organic matter mineralization and trace element post-depositional redistribution in Western Siberia thermokarst lake sediments

2011 ◽  
Vol 8 (11) ◽  
pp. 3341-3358 ◽  
Author(s):  
S. Audry ◽  
O. S. Pokrovsky ◽  
L. S. Shirokova ◽  
S. N. Kirpotin ◽  
B. Dupré
Keyword(s):  
Trace Elements ◽  
Organic Matter ◽  
Organic Carbon ◽  
Lake Sediments ◽  
Water Column ◽  
Western Siberia ◽  
Ecosystem Development ◽  
Thermokarst Lake ◽  
Fe And Mn ◽  
The Impact

Abstract. This study reports the very first results on high-resolution sampling of sediments and their porewaters from three thermokarst (thaw) lakes representing different stages of ecosystem development located within the Nadym-Pur interfluve of the Western Siberia plain. Up to present time, the lake sediments of this and other permafrost-affected regions remain unexplored regarding their biogeochemical behavior. The aim of this study was to (i) document the early diagenesic processes in order to assess their impact on the organic carbon stored in the underlying permafrost, and (ii) characterize the post-depositional redistribution of trace elements and their impact on the water column. The estimated organic carbon (OC) stock in thermokarst lake sediments of 14 ± 2 kg m−2 is low compared to that reported for peat soils from the same region and denotes intense organic matter (OM) mineralization. Mineralization of OM in the thermokarst lake sediments proceeds under anoxic conditions in all the three lakes. In the course of the lake development, a shift in mineralization pathways from nitrate and sulfate to Fe- and Mn-oxyhydroxides as the main terminal electron acceptors in the early diagenetic reactions was suggested. This shift was likely promoted by the diagenetic consumption of nitrate and sulfate and their gradual depletion in the water column due to progressively decreasing frozen peat lixiviation occurring at the lake's borders. Trace elements were mobilized from host phases (OM and Fe- and Mn-oxyhydroxides) and partly sequestered in the sediment in the form of authigenic Fe-sulfides. Arsenic and Sb cycling was also closely linked to that of OM and Fe- and Mn-oxyhydroxides. Shallow diagenetic enrichment of particulate Sb was observed in the less mature stages. As a result of authigenic sulfide precipitation, the sediments of the early stage of ecosystem development were a sink for water column Cu, Zn, Cd, Pb and Sb. In contrast, at all stages of ecosystem development, the sediments were a source of dissolved Co, Ni and As to the water column. However, the concentrations of these trace elements remained low in the bottom waters, indicating that sorption processes on Fe-bounding particles and/or large-size organo-mineral colloids could mitigate the impact of post-depositional redistribution of toxic elements on the water column.

scholarly journals Community Shift from Phototrophic to Chemotrophic Sulfide Oxidation following Anoxic Holomixis in a Stratified Seawater Lake

2014 ◽  
Vol 81 (1) ◽  
pp. 298-308 ◽  
Author(s):  
Petra Pjevac ◽  
Marino Korlević ◽  
Jasmine S. Berg ◽  
Elvira Bura-Nakić ◽  
Irena Ciglenečki ◽  
...  
Keyword(s):  
Water Column ◽  
Sulfide Oxidation ◽  
Water Layer ◽  
Tight Coupling ◽  
Phototrophic Sulfur Bacteria ◽  
Community Shift ◽  
Sulfur Bacteria ◽  
Microbiological Methods ◽  
Culture Independent ◽  
The Impact

ABSTRACTMost stratified sulfidic holomictic lakes become oxygenated after annual turnover. In contrast, Lake Rogoznica, on the eastern Adriatic coast, has been observed to undergo a period of water column anoxia after water layer mixing and establishment of holomictic conditions. Although Lake Rogoznica's chemistry and hydrography have been studied extensively, it is unclear how the microbial communities typically inhabiting the oxic epilimnion and a sulfidic hypolimnion respond to such a drastic shift in redox conditions. We investigated the impact of anoxic holomixis on microbial diversity and microbially mediated sulfur cycling in Lake Rogoznica with an array of culture-independent microbiological methods. Our data suggest a tight coupling between the lake's chemistry and occurring microorganisms. During stratification, anoxygenic phototrophic sulfur bacteria were dominant at the chemocline and in the hypolimnion. After an anoxic mixing event, the anoxygenic phototrophic sulfur bacteria entirely disappeared, and the homogeneous, anoxic water column was dominated by a bloom of gammaproteobacterial sulfur oxidizers related to the GSO/SUP05 clade. This study is the first report of a community shift from phototrophic to chemotrophic sulfide oxidizers as a response to anoxic holomictic conditions in a seasonally stratified seawater lake.

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