Nocturnal increases in soil water potential (ψ) and soil water content (θ) in the upper soil profile have often been attributed to hydraulic redistribution (HR) by roots. We have previously reported HR values up to 0.29 mm day-1 in the upper soil for an old-growth ponderosa pine site. However, unsaturated liquid or vapor flux of water between soil layers independent of roots also contributes to the diel patterns in θ, confounding efforts to identify the actual magnitude of HR. In this study, we estimated liquid (Jl) and vapor (Jv) fluxes and their impacts on apparent HR at 20, 30, 40, 50 and 60 cm by applying existing data sets of ψ, θ, temperature (T) and soil physical properties to soil water transport equations. Diel surface T patterns propagating into the soil strongly controlled both the direction and magnitude of Jv, which was most apparent at the 20 and 30 cm depths where it could reduce or enhance hourly estimates of HR by up to 20% or more depending on thermal conditions. The thermal signal dampened with depth, and θ concurrently increased such that Jv diminished while Jl increased. Early in the season Jl between layers was likely larger than measured HR. However, unsaturated hydraulic conductivity declined rapidly as seasonal drought progressed, resulting in upper soil values <1E-07 mm hr-1 (<5% of HR) by early September. At deeper depths, estimates of HR were confounded by variance of calculated Jl - necessitating further refinement of soil transport parameters vertically through the soil profile. While the absolute magnitude of HR is not easily quantified, total diel fluctuations in upper soil water content can be quantified, and remain highly applicable for modeling dynamics of total ecosystem water flux.
