Inferences about solute transport in macroporous forest soils from time series models

Abstract

Solutes can move along macropores and other preferred flow channels in forest soils when input rates at the surface are high enough. In natural systems, the actual flow paths are, to all intents and purposes, indeterminate. The use of transfer function models to represent solute transport has been proposed under these circumstances. We estimated parameters in a discrete-time version of a transfer function model for a sequence of experiments performed by sprinkling an isolated soil block in a forested catchment near Orono, Maine. All experiments were performed at steady flow by adding a quantity of water labeled with potassium bromide. The travel time of solute in the soil block was computed for each of three application rates and the effective mixing volume of the solute within the block was inferred from the time series parameters. Results show that significant macropore flow occurs in the soil block. Despite the importance of macropore flow, the fractional volume of the total pore water that participates in solute transport decreases only slightly with increasing flow rate.