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Non-diffusive transport processes

Explore transport mechanisms in sediment layers impacted by infauna activity, with a focus on advection and organic matter oxidation. Bill Marti's comparisons in Massachusetts Bay and Continental Margin sediments shed light on diffusion vs. benthic chamber fluxes. Investigate the impact of biological enhancements and layered sediments in the NW Atlantic’s continental margin. Overcome challenges related to reaction rates and solute concentrations in burrows for a comprehensive understanding of sediment dynamics.

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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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