Flow-Induced Uptake of Particulate Matter in Permeable Sediments

We demonstrate the fast transfer of suspended particles from the boundary layer into the upper strata$(z < 4 cm)$of permeable sediments with topography-related interfacial water flows. The transport is driven by pressure gradients (Δ P ≤ 3 Pa) generated when bottom flows (u ≥ 10 cm s-1) are defle...

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Veröffentlicht in:Limnology and oceanography 1996-03, Vol.41 (2), p.309-322
Hauptverfasser: Huettel, M., Ziebis, W., Forster, S.
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Sprache:eng
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Zusammenfassung:We demonstrate the fast transfer of suspended particles from the boundary layer into the upper strata$(z < 4 cm)$of permeable sediments with topography-related interfacial water flows. The transport is driven by pressure gradients (Δ P ≤ 3 Pa) generated when bottom flows (u ≥ 10 cm s-1) are deflected by small surface structure$(z < 3 cm)$of hydrodynamical or biological origin. Acrylic pigments grains of 1-and$10-\mum$diameter tracer the intrusion of particulate matter into sandy sediment$(k > 2 \times 10^-11 m^2)$incubated in a laboratory flume. Increased pressure up- and downstream of small mounds (z = 2.5 cm) drove water 5.5 cm into the core, carrying suspended particles$(1 \mum)$to 2.2-cm sediment depth within 10 h. Simultaneously, decreased pressure at the downstream slope of the protrusions drew pore fluid from deeper layers (z ≤ 10 cm) to the surface. In the sediment, friction reduced the velocity of the particulate tracers, resulting in size fractionation and layers of increased particle concentration. Ripple topography (0.8-2.8 cm high) enhanced interfacial particle$(1 \mum)$flux by a factor 2.3 when compared to a level control core. The pathways of the particle and solute tracers below a sediments ripple are axplained with a source-sink model that describes the pore flow velocity field. Our results suggest that bedform-induced interfacial flows are important for the uptake of particulate organic matter into permeable shelf sediments.
ISSN:0024-3590
1939-5590
DOI:10.4319/lo.1996.41.2.0309