Graduate Thesis Or Dissertation
 

Interstitial fluid mixing in estuarine benthic sediments

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/9593tz882

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  • A method of measuring interstitial fluid mixing rates for evaluation of exchange between pore water of estuarine benthic sediments and the overlying water in a bay is presented. Pore water movement is monitored by reducing conductivity of the interstitial fluid within a zone of the benthic sediment to a depth of 26 cm, then monitoring the movement of the natural saline pore water back into the sediment. The equipment, designed for the investigation, reduces the conductivity of the interstitial water with little disturbance of the sediment structure. Newly designed conductivity probes, placed at four depths in the sediment, monitor the flux of the interstitial water. The probe developed measures interstitial fluid motion in the field at rates as low as 10⁻⁵ cm/sec, well below the range of previous instruments. The probe yields easily evaluated, accurate results over the wide range of conductances (salinities) in a bay with no corrosion or stability problems. Interstitial fluid mixing rates are measured at five sites in South Slough, Coos Bay, on the Southern Oregon coast. The rate of aqueous molecular diffusion of the natural saline pore water, the "static's condition, is compared to the "dynamic" mixing rates observed in the field. Bioturbation and hydrodynamic mixing mechanisms are identified and evaluated (within the limits of present theories) to clarify observed mixing rates. Graphical Modified Schmidt plot and unsteady-state chart methods are presented for calculation of the interstitial fluid mixing coefficients from field data. The graphical solutions are also used to verify the form of the analytic solutions. The interstitial fluid mixing rate is presented in the form of an "apparent" diffusivity coefficient (analogous to an eddy mixing coefficient) and also as a vertical rate of penetration (migration) of concentrations of saline pore water. Field test sites are established on tide flats, a beach exposed to wave activity and in the middle of a water channel. Interstitial fluid mixing coefficients for different field test sites vary from 1. 0 x 10 ⁻⁴ cm²/sec to 2.5 x 10⁻³ cm²/sec while the respective penetration rates vary from 2. 1 x 10⁻⁵ cm/sec to 1. 1 x 10⁻³ cm/sec. These values are in agreement with similar previous investigations and are within the range of predicted results.
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