Manganese Distribution and Patterns of Soil Wetting and Depletion in a Piedmont Hillslope
2002
Cassel, D. K. | Afyuni, M. M. | Robarge, W. P.
The distribution of Mn in soils across the landscape is a function of mineralogy, topography, vegetation, and soil properties that control soil water movement and solute transport. We hypothesized (i) that current landscape properties and processes would explain the observed distribution of acid-extractable soil Mn in a cropped hillslope in the Carolina Slate Belt of the southern Piedmont, and (ii) that the current spatial patterns of soil water movement would be related to the observed Mn distribution. Soil samples were collected in 10-cm increments to the 1-m depth at 5-m intervals along 110-m-long Transect AB and at 10-m intervals along 80-m-long Transect CD. The air-dried samples were analyzed for acid-extractable (1 M HCl) Mn. Soil water content (θ) along the transects was periodically monitored by neutron attenuation to the 120-cm depth. Duplicate banks of tensiometers were installed at depths of 30, 45, and 60 cm at these locations. The concentration of acid-extractable soil Mn was greatest in the footslope (FS), exceeding values >500 and 600 mg kg⁻¹ soil for Transects AB and CD, respectively. For a wet period in July 1989, θ along Transect AB varied from 0.40 m³ m⁻³ for the FS to 0.50 m³ m⁻³ at the summit and was significantly correlated with clay content. Increases in water content of a dry soil after rainfall of 80 mm in July 1989 were similar at all landscape positions, but further increases following additional rainfall were less for the FS, indicating that soil at the FS was already near saturation. The slightly coarser-textured FS consistently had the lowest water contents. Tensiometric and lateral Br transport data for this site, coupled with the water content measurements, indicate that subsurface flow of water and dissolved Mn from higher to lower elevations on the hillslopes is occurring.
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