Suspended Sediments In Estuaries Research Articles

Estuarine Suspended Sediment Dynamics: Observations Derived from over a Decade of Satellite Data

Suspended sediment dynamics of Corpus Christi Bay, Texas, USA, a shallow-water wind-driven estuary, were investigated by combining field and satellite measurements of total suspended solids (TSS). An algorithm was developed to transform 500-meter Moderate Resolution Imaging Spectroradiometer (MODIS) Aqua satellite reflectance data into estimated TSS values. The algorithm was developed using a reflectance ratio regression of MODIS Band 1 (red) and Band 3 (green) with TSS measurements (n=54) collected by the Texas Commission on Environmental Quality for Corpus Christi Bay and other Texas estuaries. The algorithm was validated by independently collected TSS measurements during the period of 2011-2014 with an uncertainty estimate of 13%. The algorithm was applied to the period of 2002-2014 to create a synoptic time series of TSS for Corpus Christi Bay. Potential drivers of long-term variability in suspended sediment were investigated. Median and IQR composites of suspended sediments were generated for seasonal wind regimes. From this analysis it was determined that long-term, spatial patterns of suspended sediment in the estuary are related to wind-wave resuspension during the predominant northerly and prevalent southeasterly seasonal wind regimes. The impact of dredging is also apparent in long-term patterns of Corpus Christi Bay as concentrations of suspended sediments over dredge spoil disposal sites are higher and more variable than surrounding areas, which is most likely due to their less consolidated sediments and shallower depths requiring less wave energy for sediment resuspension. This study highlights the advantage of how long-synoptic time series of TSS can be used to elucidate the major drivers of suspended sediments in estuaries.

Tidal impact on suspended sediments in the Macuse estuary in Mozambique

Many studies around the world have found that tidal dynamics control the transport of suspended sediments in estuaries, as well as their relationship with runoff discharges and bathymetry morphology. This manuscript examines tidal impact on suspended sediments in the Macuse estuary in Mozambique, southern Africa. Data was collected at 42 stations, including tidal current measurements with an Acoustic Doppler Current Profiler (ADCP), tide elevation with a tidal gauge and suspended sediments with a Niskin bottle. A 14-month model simulation was implemented beginning in November 2013, forced by tides, wind regime and runoff discharges. The results indicated a tidal elevation of 4 m that generated tidal currents of 120 cm s−1. These currents combined with the runoff of 500 m3 s−1 and bathymetry configuration, drove the suspended sediments during the ebb and flood tides. Suspended sediment concentrations suggested the occurrence of sedimentation where water flow was less than 0.10 cm s−1for silt and less than 10 cm s−1 for fine sand. Results of silt concentrations was about ∼ 300 mg l−1 while fine sand was found to be 0.2 mg l−1in both tidal periods in ebb and flood tides during the rainy and dry seasons. The model accuracy of about R2 = 0.88 between the observed and simulated results demonstrated the ability to predict the impact of tides and runoff discharges in the Macuse estuary and may be extended to other estuaries. The model matches in reproducing the sediment transport mechanism will help making political decisions about the estuary sustainability and local coastal management.

The 7Be/210Pbxs ratio as an indicator of suspended sediment age or fraction new sediment in suspension

AbstractReported here is a technique to use the 7Be/210Pbxs ratio as a measure of suspended sediment age or as an indicator of the fraction of the suspended sediment that is recently eroded from the landscape. Although both 7Be and 210Pbxs are delivered seasonally and stochastically to the landscape by precipitation, the ratio of the two radionuclides varies substantially less. The 7Be/210Pbxs ratios measured in three different catchments decrease in the following manner: precipitation (c. 16) > suspended sediments in rivers (6–7) > suspended sediments in estuaries (4–6) > sediment collected in sediment traps in the estuary (c. 1) > surface sediment of the estuary (c. 0·5). Decreases in the 7Be/210Pbxs ratio in suspended sediments can be interpreted to be the result of increased age of the sediment, since 7Be decays faster than 210Pb. Alternatively, a decrease in the 7Be/210Pbxs ratio in suspended sediments can be interpreted to be the result of dilution of newly tagged 7Be‐rich sediment by 7Be‐dead sediment, for example, by erosion of soil below the 7Be‐enriched surface layer or by resuspension of 7Be‐dead bottom sediment. Presented here is a model which uses the 7Be/210Pbxs ratio in suspended sediments to determine the time since the particles were tagged by precipitation‐derived radionuclides (i.e. the age of the suspended sediment). In addition, an alternative model is presented to determine the fraction of the sediment that is ‘newly tagged’. These two models are applied to three catchments – Old Woman Creek, Ohio; Weeks Bay, Alabama; and South Slough, Oregon – and yield similar findings at all three sites. Sediment ages increase from 0 in newly tagged material, to 50–80 days in rivers, to about 80–100 days in the estuaries, to about 200 days in the sediment traps, to about 300 days on surface bottom sediments. Alternatively, the percentage new sediment decreases from 100 per cent in newly tagged material, to about 35–50 per cent in rivers, to 25–35 per cent in the estuary, to less than 10 per cent in the sediment traps, to 1–4 per cent on the surface of the bottom sediments.

Partitioning of mercury onto suspended sediments in estuaries.

Radiochemical partitioning experiments using 203Hg have been undertaken with mixtures of river, seawater and sediment samples taken from three geochemically contrasting UK estuaries: the Plym, Beaulieu and Mersey. Species of dissolved Hg were determined using reversed-phase C18 chelating columns and particulate species were determined by sequential leaching with 1 M NH4OAc and 1 M HCl. Mercury had a high particle reactivity with partition coefficients, KDs, ranging from 10(4) to 5 x 10(5) ml g(-1), depending on salinity, the chemical composition of the end-member waters, and on the physico-chemical characteristics of the sediment. Dissolved organic matter present in the waters (humic substances and/or anthropogenic compounds) was found to be the main factor governing the forms of dissolved Hg and their reactivity. From the spiked 203Hg, up to 95% of the dissolved metal was retained on the C18 columns for the Mersey waters, whereas this fraction was < 60% in the Plym and Beaulieu waters. Quasi-irreversible adsorption of Hg onto particles from each estuary was observed over a time-scale of a few hours and < 20% of total particulate Hg was released by the sequential leach. In this paper, physico-chemical processes are proposed to explain the estuarine behaviour of Hg and the results are discussed in terms of Hg availability in estuarine systems.

Modelling coastal sediment transport on a parallel computer

The movement of suspended sediments in estuaries and coastal environments cause many problems, e.g. siltation of navigation waterways, harbours and coastal environments. The transport of sediment in a tidal environment is rather complex. This is due to the complexity of the coastal hydrodynamics and the interaction of the sediments with the flow. Numerical simulations of the tidal flow and sediment transport are useful tools for planning, design and management. Computations become expensive when the flow model and the sediment transport model are coupled, especially when the computations are done with small grid sizes. In this paper we describe a coupled model for the Belgian coast area, where a grid size of 75 m ∗ 75 m is needed to resolve the complicated bathymetry. In order to improve the performance of the coupled model, the codes have been modified to run on a parallel computer (IBM/SP2). The modification includes a transformation from FORTRAN 77 code into FORTRAN 90. The MPI communication library is used for exchanging information between the processors. The model results and the performance on the IBM/SP2 machine are presented and discussed.

ASPECTS OF BIODEPOSITION BY OYSTERS AND OTHER INVERTEBRATE FILTER FEEDERS1

Quantities of suspended matter removed by oysters (Crassostrea virginica) and deposited as feces or pseudofeces varied seasonally, reaching maxima in September. Below 2.8C, measurable quantities were not produced. At certain seasons, levels of suspended solids influenced quantities of biodeposits. Laboratory studies indicated that the oysters on 0.405 hectare of an estuarine bottom may produce up to 981 kg of feces and pseudofeces weekly. Of the particles, 95% were under 3 µ in diameter. all types of algal cells present in the surrounding water were represented. The deposits contained 77–91% inorganic matter, mostly illite, chlorite, and mixed‐layer clays, 4–12% organic carbon, and 1.0 g/kg phosphorus. biodeposits of filter feeders such as barnacles, tunicates, and other lamelli‐branchs were similar to those of oysters. Filter feeders may influence deposition, transport, and the composition of suspended sediments in estuaries. A possible relationship between the removal from suspension and the subsequent deposition of radionuclides associated with particles of clay, silt, or planktonic algae and feces or pseudofeces is suggested.