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Effects of bioavailability on degradation of 14C-p-hydroxybenzoate were examined using sterile soil inoculated with Arthrobactersp. Physical accessibility of p-hydroxybenzoate was controlled by varying pore continuity with a range of moisture regimes (-33 to -420 kPa), whereas sorption was controlled via addition of an exchange resin. Arthrobactersp. accessed 94% of p-hydroxybenzoate in soil at -33 kPa, owing to continuity of soil pores and sufficient cells to exploit available space. A deviation in degradation kinetics at -420 kPa soil was attributed to inaccessible p-hydroxybenzoate in solution. Addition of resin decreased extent of degradation, though the effect diminished as pore continuity decreased. Subtle differences in effects of these processes on degradation kinetics may facilitate their separate treatment in environmental fate models.

The objectives of this study were to: (i) examine the efficacy of two sampling techniques for characterizing solute transport under steady‐state water flow, (ii) study the variation in transport model parameters with increasing depth of solute leaching, and (iii) perform model discrimination to examine the transport process operative within a field plot. Bromide, NO ‐3, and Cl‐were applied sequentially to a plot instrumented with two sets of 12 solution samplers located at depths of 0.25 and 0.65 m. At the conclusion of the experiment we destructively sampled the entire 2.0 by 2.0 m plot to a depth of 2.0 m. Mass recovery by the solution samplers ranged from 63 to 83% for the three tracers, and recovery by soil excavation ranged from 96 to 105%. The mean solute velocity estimated with the solution sampler data was significantly less than that determined by soil excavation. Mean solute velocity determined from soil excavation implied an effective transport volume equal to 0.829, (where 0, is volumetric water content) for the three tracers. Solution samplers and soil excavation provided similar measures of vertical dispersion. Both sampling methods revealed a scale‐dependent dispersion process in which the dispersivity increased linearly with mean residence time. The depth profiles for all three solutes were accurately described with a stochastic convective lognormal transfer function model (CLT) using the applied mass and two constant parameters (estimated from simultaneous fitting to the depth profiles).