Abstract
ABSTRACTBoth the rate and the vertical distribution of soil disturbance modify soil properties such as porosity, particle size, chemical composition and age structure; all of which play an important role in a soil's biogeochemical functioning. Whereas rates of mixing have been previously quantified, the nature of bioturbation's depth dependence remains poorly constrained. Here we constrain, for the first time, the relationship between mixing rate and depth in a bioturbated soil in northeast Queensland, Australia using a novel method combining OSL (optically‐stimulated luminescence) ages and meteoric beryllium‐10 (10Be) inventories. We find that the best fit mixing rate decreases non‐linearly with increasing soil depth in this soil and the characteristic length scale of 0.28 m over which the mixing coefficient decays is comparable to reported rooting depth coefficients. In addition we show that estimates of surface mixing rates from OSL data are highly dependent on erosion rate and that erosion rate must be constrained if accurate mixing rates are to be quantified. We calculate surface diffusion‐like mixing coefficients of 1.8 × 10−4 and 2.1 × 10−4 m2 yr−1 for the studied soil for two different estimates of soil erosion. © 2014 The Authors. Earth Surface Processes and Landforms Published by John Wiley & Sons Ltd.
Highlights
Soil is the living biogeochemical reactor that supports the majority of terrestrial life
We have made the assumption that the mean is representative of the data
The luminescence ages of the quartz mated from the optically-stimulated luminescence (OSL) ages and Equation (2)
Summary
Soil is the living biogeochemical reactor that supports the majority of terrestrial life. In recent years there has been renewed interest in modelling of soil processes and functioning due to concern about the soil resource in the face of uncertain future climate and land use (Minasny et al, 2008). Models of pedogenesis are only as good as the mathematical descriptions of soil processes they contain, and the functional form of many soil processes remains poorly constrained. The rate and depth dependence of mixing can fundamentally alter soil functioning, both by modifying the pore and particle size structure of the soil (Wilkinson et al, 2009) and by modifying the age structure of particles contained within the soil, which influences soil geochemistry (Mudd and Yoo, 2010). Recent studies have incorporated depth dependent mixing into modelling attempts (Vanwalleghem et al, 2013) and it has been employed to analyse observations (Yoo et al, 2011). No study has yet attempted to discriminate between these two end member scenarios using field data
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