scholarly journals Transport of biodeposits and benthic footprint around an oyster farm, Damariscotta Estuary, Maine

PeerJ ◽  
2021 ◽  
Vol 9 ◽  
pp. e11862
Author(s):  
Kara Gadeken ◽  
William C. Clemo ◽  
Will Ballentine ◽  
Steven L. Dykstra ◽  
Mai Fung ◽  
...  
Keyword(s):  
Sediment Cores ◽  
Shear Velocity ◽  
Sediment Surface ◽  
Major Influence ◽  
Shear Stresses ◽  
Flow Measurements ◽  
Geochemical Properties ◽  
Oyster Farm ◽  
Initial Deposition ◽  
A Site

The benthic impact of aquaculture waste depends on the area and extent of waste accumulation on the sediment surface below and around the farm. In this study we investigated the effect of flow on biodeposit transport and initial deposition by calculating a rough aquaculture “footprint” around an oyster aquaculture farm in the Damariscotta River, ME. We also compared a site under the farm to a downstream “away” site calculated to be within the footprint of the farm. We found similar sediment biogeochemical fluxes, geochemical properties and macrofaunal communities at the site under the farm and the away site, as well as low organic enrichment at both sites, indicating that biodeposition in this environment likely does not have a major influence on the benthos. To predict accumulation of biodeposits, we measured sediment erodibility under a range of shear stresses and found slightly higher erosion rates at the farm than at the away site. A microalgal mat was observed at the sediment surface in many sediment cores. Partial failure of the microalgal mat was observed at high shear velocity, suggesting that the mat may fail and surface sediment erode at shear velocities comparable to or greater than those calculated fromin situ flow measurements. However, this study took place during neap tide, and it is likely that peak bottom velocities during spring tides are high enough to periodically “clear” under-farm sediment of recent deposits.

scholarly journals Investigation the stability of reservoir sediments in the lab and field

2018 ◽  
Vol 246 ◽  
pp. 01002
Author(s):  
Markus Noack ◽  
Felix Beckers ◽  
Stefan Haun ◽  
Silke Wieprecht
Keyword(s):  
Sediment Cores ◽  
Sediment Surface ◽  
Shear Stresses ◽  
Reservoir Sediments ◽  
Fine Sediments ◽  
Erosion Stability ◽  
Order Of Magnitude ◽  
Sediment Layers ◽  
Bed Shear Stresses

To investigate the erosion stability of reservoir sediments, two measuring strategies were applied. Next to in situ measurements, sediment cores were extracted and analysed in the laboratory. At several sampling points at a reservoir in Germany, the in situ device was used to determine the critical bed shear stresses at the sediment surface. At the same time, sediment cores were withdrawn at each site to perform depth-orientated investigations in the hydraulic laboratory. The objective of this study is to investigate the remobilisation potential of the deposited fine sediments and to compare different methods to determine the erosion threshold. Next to critical shear stresses and erosion rates, additional sedimentary and biological parameters were examined such as bulk densities, particle size distributions, TOC-contents and chlorophylla concentrations. The results show generally a very low erosion stability, especially at the sediment surface and in the upper sediment layers. Deeper sediment layers are characterised by consolidation effects and show a higher erosion resistance. High clay contents result in increased stability while high sand contents show a high remobilisation potential. No significant relation to the parameters TOC-content or chlorophylla concentration are identified. A comparison between the different applied techniques to determine the critical bed shear stresses reveals values in the same order of magnitude; however, some significant variations occur because of different hydromorphological conditions and the different limitations for each device.

Pigment Preservation in Lake Sediments: A Comparison of Sedimentary Environments in Trout Lake, Wisconsin

1991 ◽  
Vol 48 (3) ◽  
pp. 472-486 ◽  
Author(s):  
James P. Hurley ◽  
David E. Armstrong
Keyword(s):  
Accumulation Rate ◽  
Sediment Cores ◽  
Sediment Accumulation ◽  
Sediment Surface ◽  
Water Interface ◽  
Sedimentary Pigments ◽  
Sedimentary Environments ◽  
Trout Lake ◽  
Secondary Carotenoids ◽  
Β Carotene

Fluxes and concentrations of a phorbins and major algal carotenoids were quantified in sediment trap material and sediment cores from two basins of Trout Lake, Wisconsin (TrDH and TrAB). The basins were chosen to contrast the influence of oxygen content at the sediment–water interface (TrDH, oxic and TrAB, reducing), sediment accumulation rate, and focusing. Pigment diagenesis occurred in both basins, but transformations and destruction were more extensive in TrDH. Although untransformed chlorophyll a was the major phorbin deposited at the sediment surface of both basins (51–64 mol%), pigment destruction, coupled with transition to pheophytin, accounted for substantial losses, especially in oxic TrDH sediments. Fucoxanthin, peridinin, and diadinoxanthin, despite representing > 70% of the deposited carotenoid flux, were substantially degraded or transformed in both basins. However, preservation was relatively high for secondary carotenoids, such as diatoxanthin and β-carotene, and for a major cryptomonad pigment, alloxanthin. Residual profiles in sediments show that pigment sedimentation from the epilimnion and accumulation in the permanent sediments are not directly related and that diagenesis must be considered in interpreting sedimentary pigments.

Ribbed bedforms, markers of palaeo-ice stream margins, basal meltwater drainage and ice flow dynamic

2021 ◽  
Author(s):  
Jean Vérité ◽  
Édouard Ravier ◽  
Olivier Bourgeois ◽  
Stéphane Pochat ◽  
Thomas Lelandais ◽  
...  
Keyword(s):  
Flow Direction ◽  
Local Stress ◽  
Sediment Surface ◽  
Shear Stresses ◽  
Ice Streams ◽  
Ice Flow ◽  
Ice Stream ◽  
Physical Experiments ◽  
Stream Beds ◽  
Ice Water

<p>Over the three last decades, great efforts have been undertaken by the glaciological community to characterize the behaviour of ice streams and better constrain the dynamics of ice sheets. Studies of modern ice stream beds reveal crucial information on ice-meltwater-till-bedrock interactions, but are restricted to punctual observations limiting the understanding of ice stream dynamics as a whole. Consequently, theoretical ice stream landsystems derived from geomorphological and sedimentological observations were developed to provide wider constraints on those interactions on palaeo-ice stream beds. Within these landsystems, the spatial distribution and formation processes of subglacial periodic bedforms transverse to the ice flow direction – ribbed bedforms – remain unclear. The purpose of this study is (i) to explore the conditions under which these ribbed bedforms develop and (ii) to constrain their spatial organisation along ice stream beds.  </p><p>We performed physical experiments with silicon putty (to simulate the ice), water (to simulate the meltwater) and sand (to simulate a soft sedimentary bed) to model the dynamics of ice streams and produce analog subglacial landsystems. We compare the results of these experiments with the distribution of ribbed bedforms on selected examples of palaeo-ice stream beds of the Laurentide Ice Sheet. Based on this comparison, we can draw several conclusions regarding the significance of ribbed bedforms in ice stream contexts:</p><ul><li>Ribbed bedforms tend to form where the ice flow undergoes high velocity gradients and the ice-bed interface is unlubricated. Where the ribs initiate, we hypothesize that high driving stresses generate high basal shear stresses, accommodated through bed deformation of the active uppermost part of the bed.</li> <li>Ribbed bedforms can develop subglacially from a flat sediment surface beneath shear margins (i.e., lateral ribbed bedforms) and stagnant lobes (i.e., submarginal ribbed bedforms) of ice streams, while they do not develop beneath surging lobes.</li> <li>The orientation of ribbed bedforms reflects the local stress state along the ice-bed interface, with transverse bedforms formed by compression beneath ice lobes and oblique bedforms formed by transgression below lateral shear margins.</li> <li>The development of ribbed bedforms where the ice-bed interface is unlubricated reveals distinctive types of discontinuous basal drainage systems below shear and lobe margins: linked-cavities and efficient meltwater channels respectively.</li> </ul><p>Ribbed bedforms could thus constitute convenient geomorphic markers for the reconstruction of palaeo-ice stream margins, palaeo-ice flow dynamics and palaeo-meltwater drainage characteristics.</p>

An Experimental Study of Mist/Air Film Cooling With Fan-Shaped Holes on an Extended Flat Plate—Part II: Two-Phase Flow Measurements and Droplet Dynamics

2017 ◽  
Vol 140 (4) ◽  
Author(s):  
Reda Ragab ◽  
Ting Wang
Keyword(s):  
Flow Behavior ◽  
Data Rate ◽  
Main Flow ◽  
Shear Stresses ◽  
Two Phase ◽  
Flow Measurements ◽  
Droplet Dynamics ◽  
Mist Flow ◽  
Film Layer ◽  
Upper Boundary

A phase Doppler particle analyzer (PDPA) system is employed to measure the two-phase mist flow behavior including flow velocity field, droplet size distribution, droplet dynamics, and turbulence characteristics. Based on the droplet measurements made through PDPA, a projected profile describing how the air–mist coolant jet flow spreads and eventually blends into the hot main flow is prescribed for both cylindrical and fan-shaped holes. The mist film layer consists of two layers: a typical coolant film layer (cooling air containing the majority of the droplets) and a wider droplet layer containing droplets outside the film layer. Thanks to the higher inertia possessed by larger droplets (>20 μm in diameter) at the injection hole, the larger droplets tend to shoot across the coolant film layer, resulting in a wider droplet layer than the coolant film layer. The wider droplet layer boundaries are detected by measuring the droplet data rate (droplet number per second) distribution, and it is identified by a wedge-shaped enclosure prescribed by the data rate distribution curve. The coolant film layer is prescribed by its core and its upper boundary. The apex of the data rate curve, depicted by the maximum data rate, roughly indicates the core region of the coolant film layer. The upper boundary of the coolant film layer, characterized by active mixing with the main flow, is found to be close to relatively high values of local Reynolds shear stresses. With the results of PDPA measurements and the prescribed coolant film and droplet layer profiles, the heat transfer results on the wall presented in Part I are re-examined, and the fundamental mist-flow physics are analyzed. The three-dimensional (3D) droplet measurements show that the droplets injected from the fan-shaped holes tend to spread wider in lateral direction than cylinder holes and accumulate at the location where the neighboring coolant film layers meet. This flow and droplet behavior explain the higher cooling performance as well as mist-enhancement occurs between the fan-shaped cooling holes, rather than along the hole's centerline as demonstrated in the case using the cylindrical holes.

Some new measurements of heat flow in the Superior Province of the Canadian Shield

1987 ◽  
Vol 24 (7) ◽  
pp. 1486-1489 ◽  
Author(s):  
Malcolm Drury ◽  
Alan Taylor
Keyword(s):  
Standard Deviation ◽  
Heat Flow ◽  
Canadian Shield ◽  
Superior Province ◽  
Flow Measurements ◽  
Radiogenic Heat ◽  
Radiogenic Heat Production ◽  
Climatic Variations ◽  
The Mean ◽  
A Site

Borehole heat-flow measurements are reported from six new sites in the Superior Province of the Canadian Shield. Values adjusted for glaciation effects, but not for Holocene climatic variations, range from 42 to 56 mW/m2. When these new values are combined with 21 previously published borehole values the mean is 42 mW/m2 with a standard deviation of 11 mW/m2. The data for a site on the Lac du Bonnet batholith suggest that the batholith has a thin veneer, less than 3 km, of rock of high radiogenic heat production at the surface.

M. J. Hartmann Memorial Session Paper: Turbulence Characteristics in a Supersonic Cascade Wake Flow

1994 ◽  
Vol 116 (4) ◽  
pp. 586-596 ◽  
Author(s):  
P. L. Andrew ◽  
Wing-fai Ng
Keyword(s):  
Boundary Layer ◽  
Incidence Angle ◽  
Reynolds Numbers ◽  
Wake Flow ◽  
Shear Stresses ◽  
State University ◽  
Mean Flow ◽  
Flow Measurements ◽  
The Mean ◽  
Supersonic Wake

The turbulent character of the supersonic wake of a linear cascade of fan airfoils has been studied using a two-component laser-doppler anemometer. The cascade was tested in the Virginia Polytechnic Institute and State University intermittent wind tunnel facility, where the Mach and Reynolds numbers were 2.36 and 4.8 × 106, respectively. In addition to mean flow measurements, Reynolds normal and shear stresses were measured as functions of cascade incidence angle and streamwise locations spanning the near-wake and the far-wake. The extremities of profiles of both the mean and turbulent wake properties´ were found to be strongly influenced by upstream shock-boundary -layer interactions, the strength of which varied with cascade incidence. In contrast, the peak levels of turbulence properties within the shear layer were found to be largely independent of incidence, and could be characterized in terms of the streamwise position only. The velocity defect turbulence level was found to be 23 percent, and the generally accepted value of the turbulence structural coefficient of 0.30 was found to be valid for this flow. The degree of similarity of the mean flow wake profiles was established, and those profiles demonstrating the most similarity were found to approach a state of equilibrium between the mean and turbulent properties. In general, this wake flow may be described as a classical free shear flow, upon which the influence of upstream shock-boundary-layer interactions has been superimposed.

scholarly journals Experimental investigation of reservoir sediments

2018 ◽  
Vol 40 ◽  
pp. 03030 ◽  
Author(s):  
Felix Beckers ◽  
Stefan Haun ◽  
Markus Noack
Keyword(s):  
Sediment Cores ◽  
Critical Shear Stress ◽  
Objective Evaluation ◽  
Shear Stresses ◽  
Stability Parameters ◽  
Reservoir Sediments ◽  
Erosion Rates ◽  
Erosion Stability ◽  
Photogrammetric Method ◽  
Sediment Layers

This study presents an experimental approach to investigate cohesive reservoir sediments. It is shown, how adjacent sediment cores can be extracted from reservoir beds with a Frahm Sediment Sampler. The cores are subsequently used for detailed investigations in a hydraulic laboratory. In a first step, related cores are identified based on their bulk density profiles. One part of the related cores is used to analyze the sediment properties over depth by means of potential stability parameters. The other part is used to determine the depth-dependent erosion stability in an erosion flume (SETEG-system). In the SETEG-system, a photogrammetric method is applied to measure the erosion rates of pre-defined sediment layers at different exposed shear stresses. Subsequently, the critical shear stress can be derived, which leads to an objective evaluation and allows a systematic approach. Finally, both results are combined to investigate possible correlations between the evaluated depth-dependent stability parameters and the measured erosion stability. The approach is presented on sediment cores from the case study “Kleiner Brombachsee”, a reservoir that is located in Middle Franconia, Germany.

Surface Area and Radionuclide Sorption in Contaminated Aquifers

1987 ◽  
Vol 22 (1) ◽  
pp. 85-98 ◽  
Author(s):  
K.J. Inch ◽  
R.W.D. Killey
Keyword(s):  
Surface Area ◽  
Distribution Coefficients ◽  
Bet Surface Area ◽  
Sediment Surface ◽  
Major Influence ◽  
Minor Role ◽  
Aqueous Geochemistry ◽  
Ion Chemistry ◽  
Radionuclide Distribution ◽  
Contaminated Aquifers

Abstract Strong linear correlations between 90Sr and 60Co sorption and BET surface area have been found in samples of sands from three contaminated aquifers. The sands have a granitic mineralogy, and the sequence for both surface area and radionuclide retention is vermiculite >> sericite > amphibole > muscovite = biotite > feldspar > quartz. Where aqueous geochemistry of the aquifer is relatively constant, a strong linear correlation between whole-sediment surface area and in situ radionuclide distribution coefficients was found. Distribution coefficients cannot be reliably predicted from surface area measurements if substantial differences in major ion chemistry are known or suspected at the various soil sampling localities. From the results presented here, we conclude that surface coatings (predominantly iron oxyhydroxides) provide most of the surface area and sorption capacity. Particle mineralogy has a major influence on the development of coatings, but plays a minor role in the direct sorption of contaminants.

Recent Foraminifers and Stable Isotopes Records on a Bathymetric Transect off Portugal (Cruise JC089) and implications for the Palaeoxygenation proxy

2020 ◽  
Author(s):  
Maryline Mleneck-Vautravers ◽  
David Hodell
Keyword(s):  
Stable Isotopes ◽  
Pore Water ◽  
Bottom Water ◽  
Habitat Preferences ◽  
Sediment Cores ◽  
Geochemical Data ◽  
Major Influence ◽  
The One ◽  
Productive Systems ◽  
Iberian Margin

<p>The oceanographic cruise 89 (RRS James Cook) sailed in 2013 off the Iberian margin in support of an IODP proposal centred on IODP Site 1385. JC089 collected a range of hydrographic data and recovered a set of short sediment cores. We focus on 11 of the later, sampling the hydrography of the last c.400 years along a bathymetric gradient (600-4600 m). The stable isotopes (δ<sup>18</sup>O & δ<sup>13</sup>C) for: 8 common benthic foraminifer species with varied habitat preferences, the sediment pore-water and the bottom water above the sites were measured. The geochemical data is compared to various sedimentary and micropalaeontological data. The later comprises abundances of the main benthic foraminifera species >212μm, checking for living position of the endo-fauna in Rose-Bengal stained samples and for the abundances of phytodetritus-loving species <em>E.exigua</em> in the >90μm for all the 0-1cm samples. The study of the planktonic foraminifer assemblages along a gradient stretching 170 km offshore confirms the major influence of the upwelling to the East. Except for the epi-benthic species <em>C.wuellestorfi</em>, which records the bottom water δ<sup>13</sup>C at equilibrium, all other species failed to record the δ<sup>13</sup>C of the (pore) water at the depth of their living-position. We find that <em>G.affinis</em> could record the δ<sup>13</sup>C<sub>DIC</sub> near equilibrium with the pore-water at a depth of c.-1cm; therefore above its living population peak. This could be explained by vertical migrations through the sediment column at sites where the supply of organic matter is pulsed. The later assumption seems supported by a reverse correlation between high relative abundances of <em>E.exigua</em> and that of the planktonic upwelling indicator species <em>G.bulloides</em> under productivity pulses corresponding to higher Δδ<sup>13</sup>C(epi-<em>G.affinis</em>).</p><p>The Δδ<sup>13</sup>C varies from 1.7 to 4.9‰ (n=6) across a decreasing but increasingly pulsed surface productivity gradient further away from the coast. Across this range, <em>G.affinis</em> is observed living at increasing depths in the sediment but always peaks in oxic sediments. The absence of <em>G.affinis</em> from water deeper than 3100 meters prevents Δδ<sup>13</sup>C estimates at deeper water depths. For 6 of the 11 sites where <em>G.affinis</em> was present <em>C.wuellestorfi</em> occurred only twice. The δ<sup>13</sup>C for <em>H.elegans</em> and <em>C.mundulus</em> adjusted by -1.08 and +0.25‰ respectively (this study) were used instead for the shallower sites. Off the Iberian Margin the style of seasonally fluctuating food supply could be the main factor on Δδ<sup>13</sup>C. The implication on future and long-ranging IODP-based palaeoclimatic studies is that the Δδ<sup>13</sup>C could be used to estimate the type of productivity regime back in time. In the one hand the sites mostly influenced by the main upwelling cell exhibit Δδ<sup>13</sup>C < 3‰ & correspond to less than 10% of the time spent in an oligotrophic setting below 0.2mg (chla)/m<sup>3</sup>. In the other hand Δδ<sup>13</sup>C >3‰ trace offshore rare productive surface filaments in an environment otherwise corresponding to c.90% of the time under oligotrophic surface water. The absence <em>G.affinis</em> (for the range of depths studied) could indicate a record sitting outside either of these productive systems' influence.</p>

A Study of Metal Accumulation Trends in Sediment Cores from the Turkey Lakes (Algoma, Ontario)

1988 ◽  
Vol 45 (S1) ◽  
pp. s145-s154 ◽  
Author(s):  
J. R. Morris ◽  
W. Kwain
Keyword(s):  
Dry Matter ◽  
Metal Accumulation ◽  
Sediment Cores ◽  
Sediment Surface ◽  
Sedimentation Rates ◽  
Accumulation Rates ◽  
Spatial Trends ◽  
Pb Accumulation ◽  
Lead Zinc ◽  
Ni Accumulation

Temporal (vertical) and spatial trends in sediment accumulations of nonresidual aluminum, manganese, lead, zinc, copper, and nickel were investigated in 18 core samples collected from four of the Turkey Lakes in 1980–81. Accumulation rates of nonresidual Al differed among sampling sites, both within and among lakes, but was assumed to have been temporally constant at each location. Concentrations of dry matter and all other metals were expressed as mass per unit mass of Al. Cumulative Al was used as an index of time. Since Mn enrichments near the sediment surface may reflect an oxidation zone, they were not interpreted as increased Mn inputs. Other metal enrichments were considered anthropogenic. Little Pb occurred at the bottom of sediment cores, but Pb accumulation rates increased greatly towards the sediment surface. Major Pb enrichments were assumed to have begun at 1940. Zn accumulation rates had also progressively increased through most of the previous four decades. During the same period, there was a modest rise in Cu and Ni accumulation rates. Metal accumulation rates differed considerably among lakes, and among sites within lakes, but these differences primarily reflected variations in dry matter sedimentation rates.

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