Vertical mixing of lake sediments by tubificid oligochaetes was studied in laboratory experiments by using a radioactive (cesium 137 labeled sediment) marker horizon. Results from these experiments were used to develop and test a mathematical model describing tubificid sediment mixing as a dominantly advective process. Tubificids were found to mix sediments to a depth of 6-9 cm. The rate of tubificid sediment processing observed in the experiments agrees well with those reported by other workers. Extrapolation of laboratory results to Lake Erie shows that the feeding activity of tubificids alone may result in significant sediment mixing throughout the lake. terials such as microfossils and sediment associated radionuclides [Berger and Heath, 1969; $tockner and Lund, 1970; Arniard-Triquet, 1974; Davis, 1974a; Guianasso and $chink, 1975; Robbins and Edgington, 1975; Krezoski et al., 1978; Aller and Cochran, 1976; Schink and Guianasso, 1978]. It has also been shown that biogenic particle mixing affects the chemical diagenesis of sediments [Lee, 1970; Jernelb'v, 1970; Davis, 1974b; Davis et al., 1975; Aller, 1977, 1978]. Because of these important effects, numerous authors have conducted field and laboratory experiments to quantify bioturbation phenomena [Darwineddy diffusion equations [Goldberg and Koide, 1962; Guianasso and Schink, 1975; Aller and Cochran, 1976; Noyaki et al., 1977; Robbins et al., 1977, 1979]. Models using transport analogies other than diffusion have been proposed, but such models are neither numerous nor widely applied [Berger and Heath, 1969; Davis, 1974a; Aller, 1977; Goreau, 1977].In this paper, detailed information on the rate and depth distribution of tubificid feeding and resultant sediment mixing is presented. This information, obtained from a radioactive (cesium 137 labeled illitic clay) marker horizon experiment, is used to develop and test a mathematical description of tubificid sediment mixing. In addition, results from this and other studies are used to evaluate the significance of tubificid sediment mixing in Lake Erie. [Britt et al., 1977], it could be readily obtained in large numbers from Cleveland Harbor, and it was easily differentiated from other tubificid species found in Cleveland Harbor. T. tubilex individuals were obtained by sieving sediment collected from the western portion of Cleveland Harbor (41 ø30.05'N, 81 ø43.35'W) through a 250-/.tm mesh screen. The sieve residue was placed in shallow plastic trays and kept in an aquarium at 15øC. When required for experimentation, T. tubilex individuals were collected from the residue by hand picking with a Pasteur pipette under a stereo microscope. Sediment used as the experimental substratum was collected from a silt clay deposit in the central basin of Lake Erie approximately 4 km offshore of Ashtabula, Ohio. Macrofauna were removed from this sediment by sieving through a 250-pm mesh screen. The sediment used as the recipieni of the cesium 137 label was clay-rich material obtained by soaking partially decomposed material from ...

No abstract

No abstract

IIlite clay particles with adsorbed 137Cs were added as a submillimeter layer to the surface of stir-clay sediments contained in rectangular Plexiglas ceils stored in a temperature-regulated aquarium, in order to tmee the effect of the ollgochaete, Tubifex tubifex, and the amphipod, Pontoporeia hoyi, on mass redistribution near the sedimentwater 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 ceil with tubificids (~5 X 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 era/day (20°C). When labeled particles entered the feeding zone, 137Cs reappeared in surface sediments creating a bimodal activity prof'de. 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-defned 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 molecuhr diffusion coefficient of 0.02 cm2/yr.

No abstract