Depth and areal extent of sheet and rill erosion based on radionuclides in soils and suspended sediment

Sheetwash and rilling are two important mechanisms of soil erosion by runoff. The relative contribution of each mechanism has been a vexing question because measuring thin sheet erosion is difficult. Fortuitously, various fallout radionuclides have distinct distributions in the soil column; thus, di...

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Bibliographic Details
Published in:Geology (Boulder) 2001-12, Vol.29 (12), p.1131-1134
Main Authors: Whiting, Peter J, Bonniwell, E. Chris, Matisoff, Gerald
Format: Article
Language:English
Subjects:
Agriculture
alkali metals
alkaline earth metals
Be-7
beryllium
case studies
cesium
Cs-137
data processing
depth
digital simulation
Environmental geology
erosion
field studies
Freshwater
hydrology
Iowa
isotopes
land use
mass balance
metals
numerical models
Pottawattamie County Iowa
radioactive fallout
radioactive isotopes
rills
runoff
sediment yield
Sediments
sheet erosion
SIRSEM
Soil erosion
soils
spatial distribution
suspended materials
Treynor Iowa
United States
water erosion
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Summary:Sheetwash and rilling are two important mechanisms of soil erosion by runoff. The relative contribution of each mechanism has been a vexing question because measuring thin sheet erosion is difficult. Fortuitously, various fallout radionuclides have distinct distributions in the soil column; thus, different depths of erosion produce suspended sediment with unique radionuclide signatures. Those signatures can be used to estimate the depth and areal extent of sheet and rill erosion. We developed a model to execute multiple mass balances on soil and radionuclides to quantify these erosion mechanisms. Radionuclide activities (7Be, 137Cs, 210Pb) in the soil of a 6.03 ha agricultural field near Treynor, Iowa, and in suspended sediment washed off the field during thunderstorm runoff were determined by gamma spectroscopy. Using the model, we examined 15.5 million possible combinations of the depth and areal extent of rill and sheet erosion. The best solution to the mass balances corresponded to rills eroding 0.38% of the basin to a depth of 35 mm and sheetwash eroding 37% of the basin to a depth of 0.012 mm. Rill erosion produced 29 times more sediment than sheet erosion.
ISSN:0091-7613
1943-2682
DOI:10.1130/0091-7613(2001)029<1131:DAAEOS>2.0.CO;2