Resuspension Of Bottom Sediments Research Articles

Marine geology of the Gulf of Trieste (northern Adriatic): Sedimentological aspects

The Gulf of Trieste, the northernmost part of the Mediterranean Sea, is a ∼ 20 m deep marine basin influenced by freshwater inflow, bottom sediment resuspension and increasing pollution. The surficial sediments can be subdivided into seven zones on the basis of grain-size and mineral composition. The western part of the gulf consists of up to 70% carbonate shells of various organisms (molluscs, foraminifera and echinoderms). In the inner part of the small bays of Koper, Piran, Muggia and Panzano the surficial sediments consist of clayey silt with approximately 30% carbonate. A part of the carbonate fraction and all the non-carbonate minerals are derived from flysch in the hinterland, while the River Isonzo is the main contributor of these minerals in the northern part of the Gulf of Trieste. The distribution of suspended sediments shows the highest values in the northern part of the gulf, intermediate values in the southeastern part, and lowest values in the southwestern sector in the gulf entrance under the influence of the inflow of western Istrian waters. About one third of the suspended sediment is in the form of organic matter. Sedimentation rates decrease from about 3–5 mm yr −1 within the small bays, to about 1 mm yr −1 in the central part of the gulf, gradually increasing to approximately 2.5 mm yr −1 towards the mouth of the River Isonzo. Depth profiles of Holocene sediments in the inner part of the bays of Koper and Piran reveal a change from fluvial to brackish and marine environments.

The effect of resuspension on algal production in a shallow lake

Waves cause erosion and resuspension of bottom sediments. In shallow lakes resuspension can take place over most of the lake area and the resuspended matter can stay in suspension for such a long time that the mean light intensity in the lake is reduced, causing reduced algal growth. The increase of suspended matter and light attenuation in the water of lake Tamnaren, Sweden, was found to be proportional to wind velocity to the third power. After each storm increased attenuation of light lasted for a week. The algal production was estimated to be reduced to only 15 % of what it would have been without increased turbidity due to resuspension.

Variability and transport of suspended sediment, particulate and dissolved organic carbon in the tidal freshwater Hudson River

Measurements of suspended matter, particulate organic carbon and dissolved organic carbon were made over a three year period at stations spanning 150 km of the tidal freshwater Hudson River. Suspended matter concentrations varied from year-to-year and were not related to freshwater discharge. The increase in suspended matter with depth in vertical profiles suggests that, during medium to low flow conditions, resuspension of bottom sediments was as important a source of sediment as loadings from tributaries. Particulate organic carbon showed significant variability among stations, and both autochthonous primary production and detrital organic matter are contributing to POC standing stocks. Dissolved organic carbon represented over half of the total organic carbon in the water column and showed little variation among stations.

The Importance of Emergent Vegetation in Reducing Sediment Resuspension in Wetlands

ABSTRACT Wind-induced resuspension of bottom sediment was measured with sediment traps in Sand Lake National Wildlife Refuge, South Dakota. Resuspension was significantly greater in open water areas than in areas protected from wind by emergent vegetation. Resuspended sediment was apparently uniformly distributed through the water column.

Seasonality and composition of particulate fluxes during ECOMARGE—I, western Gulf of Lions

As part of the ECOMARGE program (ECOsystèmes de MARGE continentale), sequential sediment traps were deployed on the continental margin of the Gulf of Lions, in the northwestern Mediterranean Sea. Two sites located in the southwestern part of this region were selected for the first phase of the experiment: inner shelf (bottom depth: 27 m) and continental slope (Lacaze-Duthiers Canyon, bottom depth: 650 m). The canyon was selected as representative of the continental slope, because canyons comprise more than 50% of the slope area. Total mass, organic matter, opal, carbonate and siliciclastic residue fluxes were measured biweekly at 50, 100, 300 and 600 m in the upper part of the Lacaze-Duthiers Canyon (from July 1985 to April 1986) and for longer periods (2 weeks to 2 months) at 10 and 25 m on the shelf (from May 1985 to June 1986). Mass fluxes increased generally with depth, reaching values as high as 20,000 mg m −2 d −1 in the 600 m slope (canyon) trap; this indicated lateral transport of biogenic and abiogenic particulate matter, from local (adjacent shelf and upper slope waters) and distant origin (Rhoˆne River). Shelf-slope particulate transfer attested by the paracontemporaneity of high flux events on the shelf and the slope and by the continuity of the shelf benthic nepheloid layer and intermediate nepheloid layers over the canyon: this rapid and took generally less than 16 days (trap sample resolution time). Particle fluxes and compositions defined a layered system, in which the surface layers< 100m) were essentially characterized by biogenic material (organic matter and opal), and deep layers chiefly characterized by the collection of elastic material (carbonate and siliciclastic material). Significant temporal increases in total mass and constituent fluxes showed two frequencies: a low seasonal frequency, which was related to seasonal variations of the Liguro-Provençal Current and to the winter increase of the Rhoˆne River and other coastal river discharges; variations at higher frequencies, which were related to various impulse events such as summer internal waves, autumn and winter storms and spring nutrient enrichment. The role of the Lacaze-Duthiers Canyon in the particulate transfer across the continental margin is discussed within the particular context of this advective system. Although the importance of local, intra-canyon resuspension of bottom sediments could not be estimated, it seems that the high suspended particulate matter concentrations and particle fluxes observed are essentially related to the fact that this canyon acts as a natural trap which collects particles from the entire Gulf of Lions. Comparison of the flux necessary to sustain the unsupported 210Pb inventory in the canyon sediments, with the mean 210Pb flux measured by traps and of 210Pb-determined mass accumulation rates with total mass fluxes indicate that the canyon partly acts as a modern sediment depocenter of the particles swept into it from the shelf and the slope; also partly as a modern conduit of particles to the deep basin. Several biological mechanisms are probably responsible for the rapid settling of particles onto the slope (within the canyon); these may, thereby, reduce lateral transfer from the shelf to the open ocean and constitute a kind of “biological barrier”.

Flux of transuranium nuclides and chlorinated hydrocarbons in the northwestern Mediterranean

The transuranium nuclides, plutonium and americium, and selected chlorinated hydrocarbon compounds have been measured in sediment trap samples, bottom sediments and waters. These measurements have been used to quantify vertical fluxes and elucidate particulate biogeochemical cycles, of these man-made contaminants in the northwestern Mediterranean. Sediment trap experiments in the Gulf of Lions (Lacaze-Duthiers Canyon) have shown that transuranic fluxes are considerably higher in the Gulf of Lions, than those which have been reported for the northeast Pacific; principally this is due to the relatively high mass fluxes in this region of the Mediterranean. Water, surface sediment and sediment trap data indicate that 241Am is being transported downward (via particle settling) more rapidly than 239+240 Pu. From direct flux measurement, residence times for 239+240 Pu and 241Am in the upper 300 m were computed to be 2.5 and 0.14 years, respectively. Comparison of 239+240 Pu concentrations in the water column, in 1986, with similar measurements made 5–11 years earlier suggests that fallout input to the Mediterranean has decreased by nearly a factor of 2 during the period 1975–1986. Fluxes of PCB, HCB, γ-HCH and DDT residues varied by as much as an order of magnitude, or more, both temporally and with depth. The average fluxes of most of the compounds in the Lacaze-Duthiers Canyon, during 1985–1986, were quite similar to those measured off the coast of Monaco several years earlier. Generally, the increased chlorinated hydrocarbon fluxes observed with depth were a direct result of the much higher mass fluxes which occurred at depth. Demonstrated differences in PCB concentrations in the settling particles, deposited surface sediments and overlying sediment floc indicate that simple bottom sediment resuspension is not a major contributor to the enhanced PCB flux noted at depth. The PCB concentration in sedimenting particulate material collected from deeper waters, is similar to previously analysed benthic flocs; it is likely to have been advected into the canyon with the nepheloid layer, which is a common oceanographic feature in this region.

Dynamic behavior of suspended sediment concentrations in a shallow lake perturbed by episodic wind events

Field experiments were conducted in Lake Balaton, a large (surface area, 600 km2) but shallow (mean depth, 3.2 m) lake in Hungary, to quantify the resuspension and deposition of bottom sediment due to episodic storm events. Measurements were made of windspeed and direction, surface waves, mean water velocity, and suspended sediment concentration. During significant wind events, the computed bottom stress due to surface waves dominated that due to the mean current, and therefore surface waves were assumed to be the major cause of sediment resuspension. A simple model for the depth‐averaged suspended sediment concentration based on surface wave height was calibrated with about 10 h of data collected during one storm event and verified against 15 d of data collected at the same site. The success of the suspended sediment model, which assumes that the bottom sediment was noncohesive, is surprising since the bottom material was composed predominantly of sediment in the clay and fine‐silt size ranges. This fit may indicate the presence of a thin surface layer of loosely bound sediment that is continuously involved in resuspension. The suspended sediment model could easily be integrated into a water quality model (e.g. to predict light attenuation), provided that lateral transport is negligible, or it could be used to provide the bottom boundary condition for a more general suspended sediment transport model in which advective transport is included.

Rapid growth of the brine shrimp, Artemia franciscana Kellogg, in xenic cultures of Chlorella sp. (Chlorophyceae)

A simple, quick, low-maintenance means to culture brine shrimp to adults is described. Continuously illuminated, organically enriched 1.5-l bacterialized (xenic) cultures dominated by a small Chlorella sp. MWB at a density of > 1 × 10 7 cells/ml were inoculated with brine shrimp cysts and aerated for 24 h. Cyst hatching was followed by rapid growth of nauplii to preadults. Copulating adults appeared as early as 8 days. In cultures aerated for only about 1 min/day, final mixtures of preadults and adults had a mean size range of 6–8 mm, in densities of 0.26–2.18/ml ( x = 1.3 ml ) in 11–16 days. With continuous aeration, a mixture of preadults and adults with a mean size of 7.0 mm (with riders) was obtained in 9 days at a density of 0.34/ml, and a mean size of 10.4 mm in 13 days at a density of 0.55/ml. The final Chlorella densities of cultures aerated for only about 1 min/day, or continuously, were similar to or greater than initial densities and reached as high as 5 × 10 8 cells/ml. Experiments suggest that resuspension of bottom fertilizer and sediments of cultures, by aeration or by mechanical stirring, are ways in which dissolved oxygen can be rapidly lowered and the brine shrimp fatally stressed. The strategy of growing food for brine shrimp with the brine shrimp, the community culture concept, is thus demonstrated. Advantages include: no food addition during growth; no separate biological filtration; no removal of brine shrimp feces or exuviae; no additions to cultures during growth except water to make up for evaporation.

Sedimentation of particulate nitrogen and amino acids in shallow coastal waters (Gulf of Trieste, Northern Adriatic)

Fluxes of particulate organic carbon, nitrogen and particulate amino acids were determined in samples collected by a moored sediment trap deployed at a depth of 15 m in the Gulf of Trieste, Northern Adriatic, during Summer 1982, Winter 1983, and during all seasons in 1985–1986. The differences in the absolute fluxes were related to the sources and composition of sedimenting particulate matter. It was found that the sedimentation rates of particulate organic carbon and nitrogen are little affected by the input of allochthonous particulate matter and the contribution of benthic macrophytes. The resuspension of bottom sediments has a great influence on the gross sedimentation rates of particulate organic carbon and nitrogen, averaging about 80–90%. 50–70% of particulate organic carbon and nitrogen produced in the water column is decomposed there or transported away by horizontal currents. About 88% of particulate amino acids are decomposed or transferred to the dissolved amino acid pool during sedimentation. From amino acid analyses in different classes of suspended and sedimentary organic matter the generalized order of amino acid stability during sedimentation was found to be: sulphur amino acids< hydroxy amino acids < aromatic, neutral amino acids with branched C-chain < basic < acidic, neutral amino acids with straight C-chain, proline.

The Eutrophication of Lake Okeechobee

ABSTRACT Average annual total phosphorus concentrations in Lake Okeechobee increased from 0.049 mg/L in 1973 to 0.098 mg/L in 1984. The increases in total phosphorus concentrations were not correlated to external phosphorus inputs, but to changes in lake water levels. It is proposed that the flooding of marshes and exposed lake bottom primarily caused increased total phosphorus concentrations, but that the resuspension of bottom sediments by wind action may also be a major factor influencing in-lake total phosphorus concentrations. Reducing phosphorus inputs by 40 percent as proposed by the Lake Okeechobee Technical Advisory Committee (LOTAC) will not significantly improve water quality in Lake Okeechobee. Average total phosphorus concentrations will not decline significantly. Chlorophyll a concentrations and Secchi transparencies are not correlated to total phosphorus concentrations so massive expenditures of public funds to reduce nutrient inputs will not protect long-term water quality at Lake Okeechobee.

Hydrodynamics and sedimentation in a back-barrier lagoon-salt marsh system, Great Sound, New Jersey — A summary

Southern New Jersey is a barrier island coast, characterized by a tide-dominated hydrographic regime. Great Sound, a shallow, open lagoon which is fed by tidal channels within the back-barrier salt marsh complex, is a sediment sink, apparently for detritus imported from the inner continental shelf through two tidal inlets. Study of the system tidal hydrodynamics and sediment accumulation patterns provides the basis for a numerical sedimentation model. This model predicts rapid accumulation of coarse-grained (> 20 μm) sediment near the Intracoastal Waterway which cuts through Great Sound, and dominance of storm-related sedimentation events. Observations generally confirm the model predictions. Sands are deposited rapidly on flood tidal deltas associated with the two major channels, Great Channel and Ingram Thorofare, and along the Intracoastal Waterway. Finer detritus is transported predominantly as organic-mineral aggregates, and accumulates slowly (< 2.7 mm/yr) in the southwestern and eastern parts of the sound. Resuspension of bottom sediments is common in the shallow (0.6 m) sound due to wave action and flood tidal currents on the deltas ( U 0.4 d max ≲ 42 cm/s). Low tidal flow velocities ( U 0.4 d max < 18 cm/s) over much of Great Sound and the presence of macroalgae in some locations, however, promote net accumulation. Although sediment deposition and accumulation data are variable, the range of accumulation rates suggests that recent accretion in Great Sound is approximately equivalent to the local sea-level rise of 4 mm/yr.

Assessment of Phosphorus Sources to Black Lake, New York

Studies are undertaken to assess the nature and extent of phosphorus (P) sources affecting eutrophic Black Lake, located in northern New York State. The analysis requires both field and laboratory activities. The results indicate that the shallow, well‐mixed body of water has a greater than average potential for resuspension of bottom sediments and associated internal P loading. P levels in the lake often exceed those of fluvial sources, indicating the significance of direct diffuse loading, including sediment P release. Experimental batch studies show that resuspension of sediments in aerobic systems result in P release to water of the same order of magnitude as that caused by anaerobic incubation. The extent of P release from internal sources exceeds the inputs from all other sources over relatively short periods during the growing season.

Measuring contaminant transport rates between water and sediments using limnocorrals

Radiotracers injected as soluble salts into ≈1.2 m3 limnocorrals in a shallow dystrophic lake were transported rapidly (2 to 12% d−1) from the water to the bottom sediments. Removal rates of most contaminants declined after ≈14 days. Tracers were removed from the water much more rapidly than stable element analogs present naturally. After 3 weeks Am, Co, Ra, Hg, Sn and Fe activities on the enclosure walls were greater than 15% of the activity in the water. However, activity on the walls was a small fraction (< 6%) of the total amount of tracer injected. Particle fluxes inside the corrals were lower and much less variable than those measured outside. This difference appears to result from greater resuspension of bottom sediments in the lake than in the enclosures. Both particle-bound and soluble tracers were measured in cores of bottom sediments. Tracer sorption onto particles, diffusion into the bottom sediments, and uptake on the plastic enclosure walls were rapid and reversible. Tracer kinetics were very reproducible in replicate enclosures, providing a simple, experimental system in which limnological conditions can be manipulated. Loss rates and distributions of stable isotopes and radioisotopes can be used to develop and test a general model of element transport applicable to both short and long term analyses.

Aliphatic hydrocarbons in surface sediments from the North Queensland coast and Great Barrier Reef: Effects of tropical cyclone Winifred

Aliphatic hydrocarbons were determined in inner shelf and reef lagoon surface sediments off the North Queensland coast near Innisfail in February 1986, immediately after tropical cyclone Winifred passed through the region causing severe rainfall, runoff, and disturbance of bottom sediments. Lagoon sediments from Feather, Gilbey, and Potter reefs 25–50 km offshore were characterized by a suite of C 15–C 25 n-alkanes and alkenes derived predominantly from algal sources; terrestrial hydrocarbons were not present. In contrast, inner shelf sediments contained relatively large amounts of terrestrial derived C 25–C 33 n-alkanes which decreased in concentration with distance from the coast. Inner shelf sediments collected after the cyclone also contained a suite of petroleum-derived hydrocarbons. The concentrations of terrestrial-derived hydrocarbons increased in samples collected from the inner shelf after the cyclone. However, the distribution of terrestrial hydrocarbons was largely confined to the inner shelf after the cyclone, and only occurred in trace concentrations in midshelf sediments. These results indicate that cyclone-related outwelling of suspended sediments (and presumably nutrients) from rivers was confined to the inner shelf and did not reach the reef zone. The post-cyclone phytoplankton bloom was probably caused by resuspension of bottom sediments and release of porewater nutrients rather than advection of river plumes to the offshore reefs.

Predictive model for resuspension and deposition of bottom sediment in a lake.

To estimate the time change of resuspended sediment concentration in a lake, a field observation was carried out at the platform in the Northern Basin of Lake Biwa, and a predictive model, containing effects of both wind waves and currents induced by wind, was constructed. In this model, two layers were considered : one, the lower layer, referred to the bottom turbid layer, and the other, the upper layer, above the lower layer. The bottom turbid layer was defined as the region where an acceleration term is balanced with a stress term. The prediction was applied to the field data, and the predicted values were compared with the observed ones. It was found that the unsteady solution yields better agreement with the field data than the steady solution. The depth of erosion was also estimated to be less than 0.2 cm. With the optimization method, the drag coefficient (Cd) and the parameter (γ) concerned with suspended sediment concentration in the bottom turbid layer were estimated, and the values of 0.71.2×10-3 for Cd and 0.33.9×10-3 for γ were obtained. The correlation coefficient between the predicted values and the observed values was 0.83.

FIELD OBSERVATION AND SIMULATION OF DEPOSITION AND RESUSPENSION OF COHESIVE SEDIMENT IN A SHALLOW LAKE

The main purpose of this study is to present and discuss the results of field observation and numerical simulation of deposition and resuspension of cohesive bottom sediment in a shallow lake. Field data taken in Lake Kasumigaura, such as lake current, wind over the lake, water wave, and turbidity of the lake, are shown. Based on these results, we discuss how sediments were suspended in this lake. We show the model to estimate the bottom shear stress causing sediment resuspension and the equations expressing the behavior of resuspended sediment in current which are used in the above simulation. The calculated turbidity showed a good agreement with that obtained by the field observation.

Mass encystment of a planktonic oligotrich ciliate

Sediment traps were deployed in a 60 m water column near the Eddystone Lighthouse on the south west coast of England for one year from March 1984. In April, the traps collected the cysts of a planktonic ciliate with a flux of almost 35 000 m-2 d-1. The cysts were attributed to a planktonic oligotrich [provisionally identified as Strombidium crassulum (Leegard) Kahl], which was common in the water at the time. Identification was achieved through the discovery of the incipient formation of the cysts in preserved water samples and by the similarity of the morphology of the cysts with that of other oligotrichid ciliates. Attempts to prove the relationship by incubation have so far failed. The production of the cysts followed the main spring bloom of diatoms and coincided with a small bloom of autotrophic oligotrichs. In the traps, the total number and percentage of cysts with contents decreased rapidly after the encystment event. However, potentially viable cysts were still recorded in the plankton eleven months later, with minimum fluxes of 200 cysts m-2 d-1. Resuspension of bottom sediments by tides and storms ensured that a large population of cysts was always present in the water column during the winter, awaiting the right conditions to stimulate excystment and the initiation of a new motile population.

Application of CZCS data to productivity and water quality studies in the Northern Adriatic Sea

The Northern Adriatic Sea is a shallow ocean basin with considerable fresh water input and presents some unique wateroptical features related to suspended matter input caused by rivers and resuspension of bottom sediments, phytoplankton production because of nutrient input from rivers and bottom, and dissolved organic matter (yellow substance) production by decomposition processes of the organic material. All these features influence the spectral reflectance of the water and make the algorithms for CZCS data interpretation quite different from that used in open ocean (type I) water. Therefore, special test-site specific algorithms must be derived from in-situ measurements of wateroptical parameters and the water constituents. The results from such measurements are presented together with the algorithms and the evaluated CZCS data obtained from them. It is then discussed how the experimental and evaluated satellite data can be used to evaluate standing crop and productivity.

Internal waves of the second vertical mode in a stratified lake

A time series of measurements of thermal structure and near‐bottom currents in a stratified lake revealed both first and second vertical mode internal seiching. The transition into second‐mode seiching occurred after first‐mode waves, usually generated by pulses of strong winds, died down. We describe the major features of the second‐mode seiche and discuss its effects on mixing in the lake below the thermocline. On the basis of calculations of eddy diffusion coefficients, there is only weak mixing in the interior of the hypolimnion. Scaling arguments suggest that mixing at the lake’s edges due to motion of the isotherms is not significant despite the larger amplitudes of the second‐mode seiche. The most important mixing region appears to be a turbulent bottom boundary layer driven by seiche currents. However, resuspension of bottom sediments did not occur, probably due to a combination of sediment nature and low current speeds.

Application of CZCS data to productivity and water quality studies in the Northern Adriatic Sea

The Northern Adriatic Sea is a shallow ocean basin with considerable fresh water input and presents some unique water-optical features realted to: - suspended matter input caused by rivers and resuspension of bottom sediments; - phytoplankton production because of nutrient input from rivers and bottom; - dissolved organic matter (yellow substance) production by decomposition processes of the organic material. All these features influence the spectral reflectance of the water and make the algorithms for CZCS data interpretation quite different from those used in open ocean (type I) water. Therefore, special test-site specific algorithms must be derived from in-situ measurements of water-optical parameters and the water constituents. The results from such measurements are presented together with the algorithms and the evaluated CZCS data obtained from them. It is then discussed how the experimental and evaluated satellite data can be used to evaluate standing crop and productivity.