Sediment–water interface

The flux of oxygenated water into and out of the sediments is mediated by bioturbation or mixing of the sediments, for example, via the construction of worm tubes.

In oceanography and limnology, the sediment–water interface is the boundary between bed sediment and the overlying water column. The term usually refers to a thin layer (approximately 1 cm deep, though variable) of water at the very surface of sediments on the seafloor. In the ocean, estuaries, and lakes, this layer interacts with the water above it through physical flow and chemical reactions mediated by the micro-organisms, animals, and plants living at the bottom of the water body.[1] The topography of this interface is often dynamic, as it is affected by physical processes (e.g. currents causing rippling or resuspension) and biological processes (e.g. bioturbation generating mounds or trenches).

Definition

The location of the top of the sediment-water interface in the water column is defined as the break in the vertical gradient of some dissolved component, such as oxygen, where the concentration transitions from higher concentration in the well-mixed water above to a lower concentration at the sediment surface. This can include less than 1 mm to several mm of the water column. [2][3]

Physical processes

Waves and tidal currents can alter the topography of the sediment-water interface by forming sand ripples, like the ones shown here that are exposed at low tide.

Physical movement of water and sediments alter the thickness and topography of the sediment-water interface. Sediment resuspension by waves, tides, or other disturbing forces (e.g. human feet at a beach) allows sediment pore water and other dissolved components to diffuse out of the sediments and mix with the water above. For resuspension to occur the movement of water has to be powerful enough to have a strong critical shear stress that is greater than the bed shear stress. For example, a very consolidated bed would only be resuspended under a high critical shear stress, while a "fluff layer" of very loose particles could be resuspended under a low critical shear stress.[4]

Physical processes that affect the sediment-water interface include, but are not limited to:

Biological processes

Interactions between sediments and organisms living within sediments can also alter the fluxes of oxygen and other dissolved components in and out of the sediment-water interface. Animals like worms, mollusks and echinoderms can enhance resuspension and mixing through movement and construction of burrows.[5] Microorganisms such as benthic algae can stabilize sediments and keep the sediment-water interface in a more stable condition by building mats. These microalgal mats' stabilizing effect is in part due to the stickiness of the exopolymeric substances (EPS) or biochemical "glue" that they secrete.[6]

Biological processes that affect the sediment-water interface include, but are not limited to:

See also

References

  1. ↑ Santschi, Peter; Höhener, Patrick; Benoit, Gaboury; Brink, Marilyn Buchholtz-ten. "Chemical processes at the sediment-water interface". Marine Chemistry. 30: 269–315. doi:10.1016/0304-4203(90)90076-o.
  2. ↑ 1946-, Sarmiento, Jorge Louis, (2006). Ocean biogeochemical dynamics. Gruber, Nicolas, 1968-. Princeton: Princeton University Press. ISBN 9780691017075. OCLC 60651167.
  3. ↑ Gundersen, Jens K.; Jorgensen, Bo Barker (June 1990). "Microstructure of diffusive boundary layers and the oxygen uptake of the sea floor". Nature. 345 (6276): 604–607. doi:10.1038/345604a0. ISSN 1476-4687.
  4. ↑ Mehta, Ashish J.; Partheniades, Emmanuel. "Resuspension of Deposited Cohesive Sediment Beds". Coastal Engineering 1982. doi:10.1061/9780872623736.095.
  5. ↑ Gingras, Murray K.; Pemberton, S. George; Smith, Michael (2015). "Bioturbation: Reworking Sediments for Better or Worse" (PDF). Schlumberger. Oilfield Review. pp. 46–58.
  6. ↑ Tolhurst, T.J.; Gust, G.; Paterson, D.M. The influence of an extracellular polymeric substance (EPS) on cohesive sediment stability. pp. 409–425. doi:10.1016/s1568-2692(02)80030-4.
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