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Non-diffusive transport processes

Non-diffusive transport processes. Transport driven by infauna Advection in permeable sediments. Schematic view of solute Profiles resulting from Organic matter oxidation: “layered” sediments Diffusive transport.

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Non-diffusive transport processes

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  1. Non-diffusive transport processes Transport driven by infauna Advection in permeable sediments

  2. Schematic view of solute Profiles resulting from Organic matter oxidation: “layered” sediments Diffusive transport

  3. Comparing fluxes:Diffusive fluxes from pore water profiesvsFluxes from in situ benthic flux chambersLocation: Massachusetts Bay, water depth 35m

  4. Bill Marti Comparisons in Offshore, Continental Slope Sediments 2x “Biological enhancement factor” vs. water depth ~50 µmol/cm2/y

  5. Organic C oxidation ratesContinental Margin, NW Atlantic

  6. Are sediments really “layered”?

  7. Example: Rn-222 deficits in Buzzards Bay:winter: alpha ~ 0spring / summer: alpha > 0

  8. Rn results:Continental slope Filled : Rn-222 production rate Open: Rn-222 measured in pore water Dashed line: Rn-222 model: diffusion only

  9. Problem…“reaction mosaic” around burrows

  10. Another Problem…Solute concentrations in burrows are not constant

  11. And: 1. Flushing can affect reaction rates e.g. : removal of products 2. Burrows are active environments on their own

  12. Viewing sediments as a 2-dimensional system:The “average microenvironment”

  13. …Applying the 2-D model to data… Parameters: r1 = 0.05 cm: est. based on numerically dominant poychaete L = 15 cm: est. from x-radiographs R = based on incubations for SO4 and NH4+; for SiO2, assume Ceq = 577µM; vary rate constant to fit r2 = 2.1 cm: varied to fit NH4+ profile; used for other 2 solutes

  14. Advective flow through sediments Permeability: Relates the velocity of fluid flow through a porous medium in response to a pressure gradient Unit = darcy Permeability is related to Grain size:

  15. Where are there sandy sediments?

  16. Relict sands -- e.g. on continental shelves --do contain fine-grained particlesand are sites of diagenetic cycling Excess Pb-210 Inventories -- Contintental shelf

  17. Advective flow through permeable sediments in response to bottom currents flowing over “rough” features : e.g., mounds or dunes High pressure Low pressure

  18. Flow+filtering of particles from flow … Measurements of dissolve Oxygen around a mound -- Results from experiment in a flume

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