HR: 0800h
AN: H51I-0888    [Abstracts]
TI: Mobilisation, Transport and Reactivity of Contaminated Sediments in a High Capacity Estuarine Flume
AU: * Millward, G E
EM: gmillward@plymouth.ac.uk
AF: University of Plymouth, Marine Institute Portland Square Drake Circus, Plymouth, PL4 8AA, United Kingdom
AU: Rauen, W
EM: rauenw@cardiff.ac.uk
AF: Cardiff University, Hydroenvironmental Research Centre School of Engineering Queen's Building The Parade, Cardiff, CF24 3AA, United Kingdom
AU: Couceiro, F
EM: fcouceiro@plymouth.ac.uk
AF: University of Plymouth, Marine Institute Portland Square Drake Circus, Plymouth, PL4 8AA, United Kingdom
AU: Turner, A
EM: aturner@plymouth.ac.uk
AF: University of Plymouth, Marine Institute Portland Square Drake Circus, Plymouth, PL4 8AA, United Kingdom
AU: Falconer, R
EM: falconerra@cardiff.ac.uk
AF: Cardiff University, Hydroenvironmental Research Centre School of Engineering Queen's Building The Parade, Cardiff, CF24 3AA, United Kingdom
AU: Lin, B
EM: linbl@cardiff.ac.uk
AF: Cardiff University, Hydroenvironmental Research Centre School of Engineering Queen's Building The Parade, Cardiff, CF24 3AA, United Kingdom
AB: Experiments have been carried out in a high capacity flume to quantify the transport and reactivity of contaminated estuarine sediments. The study focuses on the parameterisation of the axial re-distribution of metal contaminants within the bed sediment, including the mixing depth, as a function of local bed shear stresses and the sediment-water partitioning of exchangeable metals. The results are directed towards the improvement of coupled hydrodynamic-geochemical models. A high capacity flume, 17 m in length and 1.2 m in width, was modified to accommodate a model funnel-shaped estuary. The flume was filled with contaminant-free sand having particle diameters in the range >63 to <180 µm. A plug of contaminated sediment, from either the Plym or Mersey estuaries, with similar texture was tagged with Rhodium (Rh) and Platinum (Pt) and the chemically labile metals, Ni and Zn and inserted 4.5 m downstream. The vertical velocity profiles of the water were monitored using acoustic Doppler velocimeter. The axial bed level change due to sediment erosion or deposition was recorded regularly during the experiments using an acoustic bed profiler and, simultaneously, water samples were taken near the bed and at 40% of the water column height. Water samples were filtered and the water and suspended particulate matter (SPM) retained for analysis. Sediment cores obtained along the flume, using a liquid nitrogen-cooled corer, were sectioned. Particulate Rh and Pt, and dissolved and particulate Ni and Zn, were determined by inductively coupled plasma-mass spectrometry. The concentrations of SPM near-bed were greater than concentrations near the surface. After 0.5 h, near-bed SPM concentrations had a maximum of 1000 mg L-1, whereas after 8 h they were about 50 mg L-1. The highest concentrations were in the vicinity of the plug, where erosion occurred and they declined within the region of deposition. The concentrations of Rh/Pt in the near-bed SPM varied as function of distance from the plug allowing the mobilisation of contaminated plug sediment to be tracked. Dilution of the Rh/Pt in solids resuspended from the plug by the "background" SPM allowed the formulation of a particle mixing model based on the proportional mixing of the two particle types. Typically, the mixing ratio in the near-bed SPM was <0.2 and in surface SPM <0.1 which may be related to varying bed shear stresses. Determinations of Rh/Pt in the sediment cores showed the migration Rh/Pt downstream of the plug and, importantly, they appeared below the surface layer in the cores suggesting the sediments are vertically mixed, as a consequence of a combination of bed and suspended load transport. Partition coefficients for Ni and Zn, KDs, were quantified and linked to the sediment transport processes. The sediment transport, mixing and partitioning parameters were incorporated into a three-dimensional numerical model comprising sediment and chemical dynamics. The bed shear stresses predicted by the model were used to analyse the transport and mixing of contaminated sediments in the flume.
DE: 1847 Modeling
DE: 1861 Sedimentation (4863)
DE: 1862 Sediment transport (4558)
SC: Hydrology [H]
MN: 2007 Fall Meeting