Showing papers by "Peter A. Jumars published in 1996"

Nutrient fluxes to planktonic osmotrophs in the presence of fluid motion

Abstract: We present solutions for nutrient transfer to osmotrophs in the full range of flow regimes for which solutions have been published, and we extend some of those solutions to new parameter domains and flow environments. These regimes include stagnant water; steady, unitorm flow arising from swimming or sinking; steady shear flows; and fluctuating shear from dissipation of turbulence, as well as the combined effects of turbulence-induced shear and swimming or sinking. Solutions for nutrient fluxes cannot be carried over from one flow regime to another. In all cases, however, mass transfer increases with cell size and with flow velocity. Cell shape becomes particularly important at high flow velocities. For steady, uniform flow arising from sinking or swimming, we find asymptotic analytic and numerical solutions from the engineering literature superior to those in more common use within oceanography. These engineering solutions suggest flow effects an order of magnitude smaller than commonly supposed. A cell radius near 20 Ilm is needed before swimming or sinking can be expected to increase the flux of nutrients, such as nitrate or phosphate, substantially (by ~50%) over the stagnant-water case. We find sound asymptotic solutions for the case oflinear shear and supplement them with numerical solutions of our own to cover the range of cell sizes and shear rates of interest for phytoplankton. We extend them further to cover viscous shears from dissipating turbulence for cells smaller than the Kolmogorov scale (order of 1-6mm in the ocean). Our analysis suggests turbulence effects an order of magnitude greater than previously postulated, with a cell size of 60~lm needed to experience substantial gain. Cell rotation, whether induced by the propulsion mechanism in swimming or passively by shear across the cell perimeter, will reduce the rate of nutrient transfer relative to a non-rotating cell unless the axis of rotation parallels the direction of flow. Although in calm water dinoflagellates by swimming are able to increase nutrient uptake, in strong turbulence they may not be able to maintain a rotational axis parallel to the direction of swimming or the direction of shear, resulting in a relative reduction in flux. Conversely, large chains of diatoms and filamentous cyanobacteria that span the radius of the smallest vortices are best able to take advantage of turbulence. Despite these deductions from a diversity of analytic and numerical solutions, unequivocal data to test the contribution of advection to nutrient acquisition by phytoplankton are scarce owing, in large part, to the inability to visualize, record and thus mimic fluid motions in the vicinities of cells in natural flows.

Bioavailability of Sedimentary Contaminants Subject to Deposit-Feeder Digestion

Abstract: Contaminants in sediments are less available than their concentrations might imply, but measures of this availability have been generally lacking. Sediments ingested by benthic animals can be expected to undergo a unique chemical environment controlled by the digestive chemistry of the organism. We measured solubilization of sedimentary contaminantsCu, Pb, and polycyclic aromatic hydrocarbons (PAH)by digestive fluids extracted from marine invertebrates. Bioavailability of these contaminants, thus measured, is a small fraction of total contaminant loadingtypically 1−10%. The amounts of metals solubilized by digestive fluids were orders of magnitude greater than would be predicted from water−solid partitioning with clean seawater, although they correlated well with solubilization by seawater. Digestive fluids from two different animal species solubilized different amounts of metals, indicating that bioavailability varies among species even under constant mode of uptake. High concentrations of solubilizing a...

The effects of bacteria on the flow behavior of clay-seawater suspensions

Abstract: The presence of glue-like exopolymer produced by the marine benthic bacterium Alteromonas atlantica present in concentrations comparable with typical marine muds can enhance the yield stress of dilute clay-seawater suspensions typical of the sediment-water interface by 60%. This effect is inferred to be due mainly to bacterial attachment to and exopolymeric bridging between clay domains under nutrient-poor conditions. The relative change in the yield stress of a clay-seawater suspension, and by inference its erosion resistance, is dependent on the availability of nutrients and the history of microbial attachment. This conclusion applies regardless of the constitutive model used to describe the behavior of the suspension under shear. Our results are relevant to rheological studi s of fine-particle suspensions in general because inevitable contamination of "abiotic" slurries often occurs under the very conditions (nutrient poor) that can result in maximal binding effects.

Acoustic remote sensing of benthic activity: A statistical approach

Abstract: Acoustic backscatter at 40 kHz was recorded from a circular area of silt 75 m in radius every 0.1 d at a water depth of 91 m off the coast of northern California for 49 d in winter 1988-1989. Data were resolved into pixels that extended 7.5 m radially and 5° azimuthally. We analyzed the relatively small change in backscatter intensity and phase from a given pixel. In a time-series analysis, this change in backscatter was decomposed into three components putatively due to large, rare, transient nekton and epibenthos; more abundant benthopelagic organisms that caused volume reverberation; and more sedentary benthos. Benthic change in backscatter was presumed due to movement of animals and other biogenic modifications of sound speed in the sediment-water medium. Patterns of benthic activity and volume backscatter near the seabed changed abruptly twice, with the middle interval showing highest levels. During this middle interval, winter storms disturbed surficial sediments, offshore transport occurred near the seabed, and the benthic component was dominated by activity perfectly in phase with and linearly proportional to median, local, downwelling irradiance. We suspect that this circadian pattern was due to the burrowing urchin Brisaster latifrons that is known from previous studies at this site to emerge on the sediment surface at night when food resources are available there and to reburrow during the lighted part of the day. Extensive correlative physical data collected at the site as part of interdisciplinary studies (CODE and STRESS) allowed us to exclude other physical forcings as likely explanations for diurnal change in backscatter. In a spatial analysis, the transient component was removed explicitly pixel by pixel, and volume reverberation was removed implicitly to leave a benthic remainder that could be analyzed for spatial variation. Benthic activity showed distinct patchiness with coherence scales of roughly 5-10 m and negative spatial autocorrelation in activity levels near the largest spatial lag available (∼ 140 m). Patches did not move appreciably during the study.