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Dynamics of Soil Surface Bulk Density: Role of Water Table Elevation and Rainfall Duration

^a UR Cemagref, Hydrosystèmes et Bioprocédés, BP 44, 92163 Antony cedex, France
^b UMR INRA/INAPG, Environnement et Grandes Cultures, 78850 Thiverval-Grignon, France
^c Institute of Soil, Water and Environ. Sciences, Volcani Center, ARO, P.O.B. 6, Bet-Dagan 50250, Israel
^d LTHE, UMR 5564 (CNRS, INPG, IRD, UJF), BP 53, 38041 Grenoble Cedex 9, France

View larger version (30K): [in this window] [in a new window]   Fig. 1. Schematic representation of the experimental setup.

View larger version (13K): [in this window] [in a new window]   Fig. 2. Example of a bulk density profile and the corresponding fitted model (Eq. [2]) accounting for sealing and slumping processes. Sample treatment: 40 min of the 30.5 mm h–1 rainfall and low initial water table depth, 0.7 m below the soil surface. The parameters of the model (i, 0, m, dc, ) are schematically reported.

View larger version (14K): [in this window] [in a new window]   Fig. 3. Mean measured values and standard deviation of bulk density profile and the corresponding fitted model for low (LWT, 0.7 m below the soil surface) and high (HWT, 0.3 m below the soil surface) initial water table conditions after 15 (1), 30 (2), and 40 min (3) of the 30.5 mm h–1 rainfall event.

View larger version (10K): [in this window] [in a new window]   Fig. 4. Evolution of (a) the exponential curvature, , and (b) the change in bulk density at the soil surface, 0, as a function of the 30.5 mm h–1 rainfall duration for the low (LWT) and high (HWT) initial water table conditions. Vertical bars correspond to the standard error of the fit. Equation [3] is fitted on 0 to model its change in time.

View larger version (8K): [in this window] [in a new window]   Fig. 5. Evolution of the slope of the slumping model (m) as a function of the 30.5 mm h–1 rainfall duration for the low (LWT) and high (HWT) initial water table conditions. Vertical bars correspond to the standard error of the fit except for the values of m before rainfall, which were obtained from core bulk density measurements and whose vertical bars correspond to the standard deviation.

View larger version (168K): [in this window] [in a new window]   Fig. 6. Thin-section images of structural surface seal under low (LWT) and high (HWT) initial water table conditions obtained by ultraviolet light after (a and c) 15, (b) 30, and (d) 40 min of the 30.5 mm h–1 rainfall event. Vertical bar gives the scale (0.8 mm). Initial aggregates are surrounded by bold solid lines.

View larger version (138K): [in this window] [in a new window]   Fig. 7. Thin-section image obtained by ultraviolet light showing the coalescence and welding of aggregates below the surface seal for high initial water table conditions (HWT) after 15 min of the 30.5 mm h–1 rainfall event. Vertical bar gives the scale (0.8 mm). Initial aggregates are surrounded by bold solid lines.

View larger version (12K): [in this window] [in a new window]   Fig. 8. Differences between (a) 0- and 2-mm-depth and (b) 10- and 20-mm-depth micro- and macrovoid indices as a function of the 30.5 mm h–1 rainfall duration for low (LWT) and high (HWT) initial water table elevations. Vertical bars correspond to the standard deviation between six subsample slices.

View larger version (12K): [in this window] [in a new window]   Fig. 9. Time course of (a) water table depth and (b) surface runoff measured during the 30.5 mm h–1 rainfall experiment for the low (LWT) and high (HWT) initial water table elevations.