Environ. Sci. Technol. 1997, 31, 289-295
Physiological Considerations in Applying Laboratory-Determined Buoyant Densities to Predictions of Bacterial and Protozoan Transport in Groundwater: Results of In-Situ and Laboratory Tests R O N A L D W . H A R V E Y , * ,† DAVID W. METGE,† NANCY KINNER,‡ AND NALEEN MAYBERRY‡ U.S. Geological Survey, 3215 Marine Street, Boulder, Colorado 80303, and Environmental Research Group, 236 Kingsbury Hall, University of New Hampshire, Durham, New Hampshire 03824
Buoyant densities were determined for groundwater bacteria and microflagellates (protozoa) from a sandy aquifer (Cape Cod, MA) using two methods: (1) density-gradient centrifugation (DGC) and (2) Stoke’s law approximations using sedimentation rates observed during natural-gradient injection and recovery tests. The dwarf (average cell size, 0.3 µm), unattached bacteria inhabiting a pristine zone just beneath the water table and a majority (∼80%) of the morphologically diverse community of free-living bacteria inhabiting a 5-km-long plume of organically-contaminated groundwater had DGC-determined buoyant densities
