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United States Department of Agriculture

Agricultural Research Service

Title: Combining Cesium-137 and Topographic Surveys for Measuring Soil Erosion/deposition Patterns in a Rapidly Accreting Area

Author
item Ritchie, Jerry

Submitted to: Environmental Geology and Water Sciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 1, 2000
Publication Date: N/A

Interpretive Summary: Erosion is a major concern in agricultural areas around the world leading to soil loss, reduced soil productivity, and downstream offsite pollution. Grass hedges are used widely used in the tropic to reduce soil loss, however, little quantitative data are available on such conservation practices. In studies at Beltsville, Maryland grass hedges were established don the contour across ephemeral gully areas. Quantitative data from these studies show that these narrow, stiff grass hedges act as filters to slow and broaden the water flow area, resulting in ponding that increases settling times for entrained material to be deposited. Deposition rates measured using field surveys (1991, 1995, 1998) found deposition rates of 1-2 cm per year up slope from these hedges. Erosion rates and patterns determined using Cesium-137 measured medium-term erosion near the hedge do not reflect the recent deposition patterns near the grass hedge measured by ytopographic surveys. Using the combination of topographic and 137Cs survey allows a better understanding of the role of grass hedges as barriers for capturing eroding soils and suggest that the recent deposition is associated with the grass hedge but there is still a net loss of soil near the hedge position over the past 45 years. Grass hedges can be an alternative conservation practice for reducing soil loss and dispersing runoff from areas of erosion in agricultural fields. However, grass hedges should not be seen as a panacea, but as another tool in the arsenal to control soil loss and runoff. Continued efforts to control soil loss at the point of detachment are critical. The NRCS has developed a Conservation Practice Standard for using grass hedges for runoff and sediment control.

Technical Abstract: Narrow, stiff grass hedges are biological barriers designed to slow runoff and capture soils carried in runoff water. This study was designed to measure quantitatively the deposition of soil up slope of a narrow, stiff grass hedge using topographic and Cesium-137 surveys. Topographic surveys made in 1991, 1995, and 1998 measured 1 to 2 cm per year of recent sediment tdeposited up slope of the grass hedge. Cesium-137 analyses of soil samples were used to determine the medium-term (45 years) soil redistribution patterns. Erosion rates and patterns determined using Cesium-137 measured medium-term erosion near the hedge do not reflect the recent deposition patterns near the grass hedge measured by topographic surveys. Using the combination of topographic and Cesium-137 surveys allows a better understanding of the role of grass hedges as barriers for capturing eroding soils and suggest that the recent deposition is associated with the grass hedge but that there is still a net loss of soil near the hedge position over the past 45 years.

Last Modified: 10/25/2014
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