Computer Science
Scientific paper
Feb 1979
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1979e%26psl..42..277r&link_type=abstract
Earth and Planetary Science Letters, Volume 42, Issue 2, p. 277-287.
Computer Science
5
Scientific paper
Illite clay particles with adsorbed 137Cs were added as a submillimeter layer to the surface of silt-clay sediments contained in rectangular Plexiglas cells stored in a temperature-regulated aquarium, in order to trace the effect of the oligochaete, Tubifex tubifex, and the amphipod, Pontoporeia hoyi, on mass redistribution near the sediment-water interface. A well-collimated NaI gamma detector scanned each sediment column (~10 cm deep) at daily or weekly intervals for six months, depicting the time evolution of radioactivity with and without added benthos. In a cell with tubificids (~5 × 104 m-2), which feed below 3 cm and defecate on surface sediments, the labeled layer was buried at a rate of 0.052 +/- 0.007 cm/day (20°C). When labeled particles entered the feeding zone, 137Cs reappeared in surface sediments creating a bimodal activity profile. In time, the activity tended toward a uniform distribution over the upper 6 cm, decreasing exponentially below to undetectable levels by 9 cm. In a cell with amphipods (~1.6 × 104 m-2) uniform activity developed rapidly (~17 days) down to a well-defined depth (1.5 cm). The mixing of sediments by Pontoporeia is described by a simple quantitative model of eddy diffusive mixing of sediment solids. The value of the diffusion coefficient, 4.4 cm2/yr (7°C) was computed from a least squares fit of theoretical to observed profile broadening over time. In a cell without benthos, small but measurable migration of 137Cs indicated an effective molecular diffusion coefficient of 0.02 cm2/yr.
Fisher Berton J.
Krezoski John R.
McCall Peter L.
Robbins John A.
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