scholarly journals Flocculation in Estuaries: Modeling, Laboratory and In-situ Studies

2021 ◽  
Author(s):  
Claire Chassagne ◽  
Zeinab Safar ◽  
Zhirui Deng ◽  
Qing He ◽  
Andy Manning
Keyword(s):  
Organic Matter ◽  
Water Column ◽  
Transport Model ◽  
Hydrodynamic Interactions ◽  
Dominant Form ◽  
In Situ Studies ◽  
Complex Particle ◽  
Estuarine Systems ◽  
Recent Laboratory

Modelling the flocculation of particles in a natural environment like an estuary is a challenging task owing to the complex particle-particle and particle-hydrodynamic interactions involved. In this chapter a summary is given of recent laboratory and in-situ studies regarding flocculation. A flocculation model is presented and the way to implement it in an existing sediment transport model is discussed. The model ought to be parametrized, which can be done by performing laboratory experiments which are reviewed. It is found, both from laboratory and in-situ studies, that flocculation between mineral sediment and organic matter is the dominant form of flocculation in estuarine systems. Mineral sediment in the water column is < 20 μm in size and its settling velocity is in the range [0–0.5] mm/s. Flocs can then be categorized in two types: flocs of size [20–200] μm and flocs of size > 200 μm. The origin of these two types is discussed. The two types of flocs are found at different positions in the water column and both have settling velocities in the range [0.5–10] mm/s.

The Carbon:²³⁴Thorium ratios of sinking particles in the California Current Ecosystem 2: Examination of a thorium sorption, desorption, and particle transport model

2019 ◽  
Author(s):  
Michael Stukel ◽  
Thomas Kelly
Keyword(s):  
Organic Carbon ◽  
Water Column ◽  
Particulate Organic Carbon ◽  
Transport Model ◽  
California Current ◽  
In Situ Measurements ◽  
Power Law Distribution ◽  
Sinking Particles ◽  
Organic Carbon Concentration

Thorium-234 (234Th) is a powerful tracer of particle dynamics and the biological pump in the surface ocean; however, variability in carbon:thorium ratios of sinking particles adds substantial uncertainty to estimates of organic carbon export. We coupled a mechanistic thorium sorption and desorption model to a one-dimensional particle sinking model that uses realistic particle settling velocity spectra. The model generates estimates of 238U-234Th disequilibrium, particulate organic carbon concentration, and the C:234Th ratio of sinking particles, which are then compared to in situ measurements from quasi-Lagrangian studies conducted on six cruises in the California Current Ecosystem. Broad patterns observed in in situ measurements, including decreasing C:234Th ratios with depth and a strong correlation between sinking C:234Th and the ratio of vertically-integrated particulate organic carbon (POC) to vertically-integrated total water column 234Th, were accurately recovered by models assuming either a power law distribution of sinking speeds or a double log normal distribution of sinking speeds. Simulations suggested that the observed decrease in C:234Th with depth may be driven by preferential remineralization of carbon by particle-attached microbes. However, an alternate model structure featuring complete consumption and/or disaggregation of particles by mesozooplankton (e.g. no preferential remineralization of carbon) was also able to simulate decreasing C:234Th with depth (although the decrease was weaker), driven by 234Th adsorption onto slowly sinking particles. Model results also suggest that during bloom decays C:234Th ratios of sinking particles should be higher than expected (based on contemporaneous water column POC), because high settling velocities minimize carbon remineralization during sinking.

The excitation of O(1S) and O2 bands in the nightglow: a brief review and preview

1986 ◽  
Vol 64 (12) ◽  
pp. 1626-1630 ◽  
Author(s):  
I. C. McDade ◽  
E. J. Llewellyn
Keyword(s):  
Molecular Oxygen ◽  
Kinetic Data ◽  
Green Line ◽  
Excitation Mechanism ◽  
Precursor State ◽  
In Situ Studies ◽  
Photometric Observations ◽  
Recent Laboratory ◽  
Atmospheric System

Recent laboratory and in situ studies of the processes involved in the excitation of O(1S) and the five strongest systems of molecular oxygen in the terrestrial nightglow are reviewed. In spite of the significant advances that have been made during the last few years, it is not yet possible to reconcile rocket and satellite photometric observations with expectations based on laboratory kinetic data. Even in the most extensively studied O2 system, the Herzberg-I system, serious discrepancies exist between the kinetic parameters measured in the laboratory and those deduced from the airglow observations. It is only in the case of the O2 Atmospheric system that the laboratory and in situ studies have converged on a consistent view of the overall excitation mechanism. In the case of the O(1S) green line, most evidence would now appear to support the Barth mechanism, but progress towards a conclusive identification of the Barth precursor state, or states, is seriously hindered by the inadequacies in current understanding of the molecular oxygen systems.

The Carbon:²³⁴Thorium ratios of sinking particles in the California Current Ecosystem 2: Examination of a thorium sorption, desorption, and particle transport model

2019 ◽  
Author(s):  
Michael Stukel ◽  
Thomas Kelly
Keyword(s):  
Organic Carbon ◽  
Water Column ◽  
Particulate Organic Carbon ◽  
Transport Model ◽  
California Current ◽  
In Situ Measurements ◽  
Power Law Distribution ◽  
Sinking Particles ◽  
Organic Carbon Concentration

Thorium-234 (234Th) is a powerful tracer of particle dynamics and the biological pump in the surface ocean; however, variability in carbon:thorium ratios of sinking particles adds substantial uncertainty to estimates of organic carbon export. We coupled a mechanistic thorium sorption and desorption model to a one-dimensional particle sinking model that uses realistic particle settling velocity spectra. The model generates estimates of 238U-234Th disequilibrium, particulate organic carbon concentration, and the C:234Th ratio of sinking particles, which are then compared to in situ measurements from quasi-Lagrangian studies conducted on six cruises in the California Current Ecosystem. Broad patterns observed in in situ measurements, including decreasing C:234Th ratios with depth and a strong correlation between sinking C:234Th and the ratio of vertically-integrated particulate organic carbon (POC) to vertically-integrated total water column 234Th, were accurately recovered by models assuming either a power law distribution of sinking speeds or a double log normal distribution of sinking speeds. Simulations suggested that the observed decrease in C:234Th with depth may be driven by preferential remineralization of carbon by particle-attached microbes. However, an alternate model structure featuring complete consumption and/or disaggregation of particles by mesozooplankton (e.g. no preferential remineralization of carbon) was also able to simulate decreasing C:234Th with depth (although the decrease was weaker), driven by 234Th adsorption onto slowly sinking particles. Model results also suggest that during bloom decays C:234Th ratios of sinking particles should be higher than expected (based on contemporaneous water column POC), because high settling velocities minimize carbon remineralization during sinking.

scholarly journals Bacterial degradation activity in the eastern tropical South Pacific oxygen minimum zone

2020 ◽  
Vol 17 (1) ◽  
pp. 215-230 ◽  
Author(s):  
Marie Maßmig ◽  
Jan Lüdke ◽  
Gerd Krahmann ◽  
Anja Engel
Keyword(s):  
Organic Matter ◽  
Water Column ◽  
Microbial Degradation ◽  
Bacterial Production ◽  
Leucine Aminopeptidase ◽  
Extracellular Enzyme ◽  
Bacterial Degradation ◽  
Oxygen Loss ◽  
Oxygen Minimum

Abstract. Oxygen minimum zones (OMZs) show distinct biogeochemical processes that relate to microorganisms being able to thrive under low or even absent oxygen. Microbial degradation of organic matter is expected to be reduced in OMZs, although quantitative evidence is low. Here, we present heterotrophic bacterial production (3H leucine incorporation), extracellular enzyme rates (leucine aminopeptidase/β-glucosidase) and bacterial cell abundance for various in situ oxygen concentrations in the water column, including the upper and lower oxycline, of the eastern tropical South Pacific off Peru. Bacterial heterotrophic activity in the suboxic core of the OMZ (at in situ ≤ 5 µmol O2 kg−1) ranged from 0.3 to 281 µmol C m−3 d−1 and was not significantly lower than in waters of 5–60 µmol O2 kg−1. Moreover, bacterial abundance in the OMZ and leucine aminopeptidase activity were significantly higher in suboxic waters compared to waters of 5–60 µmol O2 kg−1, suggesting no impairment of bacterial organic-matter degradation in the core of the OMZ. Nevertheless, high cell-specific bacterial production was observed in samples from oxyclines, and cell-specific extracellular enzyme rates were especially high at the lower oxycline, corroborating earlier findings of highly active and distinct micro-aerobic bacterial communities. To assess the impact of bacterial degradation of dissolved organic matter (DOM) for oxygen loss in the Peruvian OMZ, we compared diapycnal fluxes of oxygen and dissolved organic carbon (DOC) and their microbial uptake within the upper 60 m of the water column. Our data indicate low bacterial growth efficiencies of 1 %–21 % at the upper oxycline, resulting in a high bacterial oxygen demand that can explain up to 33 % of the observed average oxygen loss over depth. Our study therewith shows that microbial degradation of DOM has a considerable share in sustaining the OMZ off Peru.

scholarly journals Modelling the Influence from Biota and Organic Matter on the Transport Dynamics of Microplastics in the Water Column and Bottom Sediments in the Oslo Fjord

Water ◽  
2021 ◽  
Vol 13 (19) ◽  
pp. 2690
Author(s):  
Anfisa Berezina ◽  
Evgeniy Yakushev ◽  
Oleg Savchuk ◽  
Christian Vogelsang ◽  
André Staalstrom
Keyword(s):  
Organic Matter ◽  
Dissolved Organic Matter ◽  
Water Column ◽  
Seasonal Changes ◽  
Transport Model ◽  
Biogeochemical Model ◽  
Baseline Scenario ◽  
Fecal Pellets ◽  
Transport Dynamics ◽  
Different Seasons

The fate of microplastics (MP) in seawater is heavily influenced by the biota: the density of MP particles can be changed due to biofouling, which affects sinking, or MP can be digested by zooplankton and transferred into fecal pellets with increased sinking rate. We hypothesize that seasonal production and degradation of organic matter, and corresponding changes in the plankton ecosystem affect the MP capacity for transportation and burying in sediments in different seasons. This is simulated with a coupled hydrodynamical-biogeochemical model that provides a baseline scenario of the seasonal changes in the planktonic ecosystem and changes in the availability of particulate and dissolved organic matter. In this work, we use a biogeochemical model OxyDep that simulates seasonal changes of phytoplankton (PHY), zooplankton (HET), dissolved organic matter (DOM) and detritus (POM). A specifically designed MP module considers MP particles as free particles (MPfree), particles with biofouling (MPbiof), particles consumed by zooplankton (MPhet) and particles in detritus, including fecal pellets (MPdet). A 2D coupled benthic-pelagic vertical transport model 2DBP was applied to study the effect of seasonality on lateral transport of MP and its burying in the sediments. OxyDep and MP modules were coupled with 2DBP using Framework for Aquatic Biogeochemical Modelling (FABM). A depletion of MP from the surface water and acceleration of MP burying in summer period compared to the winter was simulated numerically. The calculations confirm the observations that the “biological pump” can be one of the important drivers controlling the quantity and the distribution of MP in the water column.

Sedimentation of suspensions in the Vistula River mouth

2013 ◽  
Vol 42 (2) ◽  
Author(s):  
Ewa Szymczak ◽  
Dorota Galińska
Keyword(s):  
Organic Matter ◽  
Water Column ◽  
Size Fraction ◽  
River Mouth ◽  
Spatial Location ◽  
Hydrodynamic Conditions ◽  
Suspension Concentration ◽  
Vistula River ◽  
The Relationship

AbstractThe aim of this study was to analyze the variability of the suspension concentration in the area where the Vistula River discharges into the Gulf of Gdańsk. While analyzing the relationship between suspension concentration and the distance from the river mouth and the spatial location in the water column, a number of other important factors were considered, i.e. salinity, temperature, the composition of suspension and in situ hydrodynamic conditions. The samples of surficial sediment were analyzed with regard to the content of organic matter and <0.063 mm size fraction.

scholarly journals High bacterial organic carbon uptake in the Eastern Tropical South Pacific oxygen minimum zone

2019 ◽  
Author(s):  
Marie Maßmig ◽  
Jan Lüdke ◽  
Gerd Krahmann ◽  
Anja Engel
Keyword(s):  
Organic Matter ◽  
Organic Carbon ◽  
Water Column ◽  
Microbial Degradation ◽  
Bacterial Production ◽  
Leucine Aminopeptidase ◽  
Extracellular Enzyme ◽  
Oxygen Loss ◽  
Oxygen Minimum

Abstract. Oxygen minimum zones (OMZs) show distinct biogeochemical processes that relate to microorganisms being able to thrive under low or even absent oxygen. Microbial degradation of organic matter is expected to be reduced in OMZs, although quantitative evidence is low. Here, we present heterotrophic bacterial production (3H leucine-incorporation), extracellular enzyme rates (leucine aminopeptidase/ß-glucosidase) and bacterial cell abundance for various in situ oxygen concentrations in the water column of the Eastern Tropical South Pacific off Peru. Bacterial heterotrophic activity in the suboxic core of the OMZ (at in situ ≤ 5 µmol O2 kg−1) ranged from 0.6 to 160 µmol C m−3 d−1 and was not significantly lower than in waters of 5–60 µmol O2 kg−1. Moreover, bacterial abundance in the OMZ was slightly and leucine aminopeptidase activity even significantly higher in suboxic waters compared to the upper oxycline suggesting no impairment of bacterial organic matter degradation in the core of the OMZ. Nevertheless, high cell-specific bacterial production and extracellular enzyme rates were observed in samples from the upper or lower oxyclines corroborating earlier findings of highly active and distinct micro-aerobic bacterial communities. To assess the impact of bacterial degradation of dissolved organic matter for oxygen loss in the Peruvian OMZ, we compared diapycnal fluxes of oxygen and dissolved organic carbon (DOC) and their microbial uptake within the upper 60 m of the water column. Our data indicate bacterial growth efficiencies of 0.5–8.6 % at the upper oxycline, resulting in a high bacterial oxygen demand that can explain up to 33 % of the observed average oxygen loss over depth. Our study therewith shows that microbial degradation of DOM has a considerable share in sustaining the OMZ off Peru.

Preparation of integrated circuits for TEM electromigration in situ studies

1986 ◽  
Vol 44 ◽  
pp. 882-883
Author(s):  
J. V. Maskowitz ◽  
W. E. Rhoden ◽  
D. R. Kitchen ◽  
R. E. Omlor ◽  
P. F. Lloyd
Keyword(s):  
Integrated Circuits ◽  
Crystallographic Orientation ◽  
Silicon Wafers ◽  
Minimum Size ◽  
Test Vehicle ◽  
In Situ Studies ◽  
Boron Doped ◽  
Doped Silicon ◽  
Drill Holes

The fabrication of the aluminum bridge test vehicle for use in the crystallographic studies of electromigration involves several photolithographic processes, some common, while others quite unique. It is most important to start with a clean wafer of known orientation. The wafers used are 7 mil thick boron doped silicon. The diameter of the wafer is 1.5 inches with a resistivity of 10-20 ohm-cm. The crystallographic orientation is (111).Initial attempts were made to both drill and laser holes in the silicon wafers then back fill with photoresist or mounting wax. A diamond tipped dentist burr was used to successfully drill holes in the wafer. This proved unacceptable in that the perimeter of the hole was cracked and chipped. Additionally, the minimum size hole realizable was > 300 μm. The drilled holes could not be arrayed on the wafer to any extent because the wafer would not stand up to the stress of multiple drilling.

Wątek składania ofiar w dekoracji budowli sakralnych Dura Europos

Vox Patrum ◽  
2015 ◽  
Vol 64 ◽  
pp. 393-402
Author(s):  
Ilona Skupińska-Løvset
Keyword(s):  
Roman Empire ◽  
Late Antiquity ◽  
Archaeological Research ◽  
Dominant Form ◽  
Xxth Century ◽  
Desert Sand ◽  
Military Camp ◽  
The Military

Dura Europos, or as proposed today Europos Dura, was a fortified settlement on the border between the Roman Empire and the East. The archeological dis­coveries reflected the character of the settlement – the fortified agglomeration grouped at the military camp. After its fall Europos Dura was covered by desert sand only to be discovered in the XXth century. Archaeological research has dis­closed documentation of its multicultural character. This paper points to the fact of coexistence of various religions in late antiquity Europos Dura. Paintings and sculptures discovered in situ indicate that scene of offering was a favorite subject in the sacral art of Europos Dura, independent of religion. The ceremony of in­cense burning constitutes the dominant form of offering regarding visualizations of this important ceremony.

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