Source: Case Western Reserve University submitted to NRP
QUANTIFYING SHEETWASH AND RILL EROSION WITH RADIONUCLIDE AND GEOCHEMICAL TRACERS
Sponsoring Institution
National Institute of Food and Agriculture
Project Status
COMPLETE
Funding Source
NRI COMPETITIVE GRANT
Reporting Frequency
Annual
Accession No.
0192878
Grant No.
2002-35102-12489
Cumulative Award Amt.
$250,000.00
Proposal No.
2002-01444
Multistate No.
(N/A)
Project Start Date
Sep 1, 2002
Project End Date
Jun 28, 2006
Grant Year
2002
Program Code
[26.0]- (N/A)
Recipient Organization
Case Western Reserve University
10900 Euclid Avenue
CLEVELAND,OH 44106
Performing Department
GEOLOGICAL SCIENCES
Non Technical Summary
Soil erosion by sheetwash and rilling degrades soil productivity and watershed health. Many soil nutrients and other constituents vary in their distribution in agricultural soils and under different tillage conditions. Consequently the proportion of these constituents lost by erosion varies depending on whether erosion is by thin sheetwash or by deep rills. The proposed work will refine and extend a quantitative method to determine the ?recipe? for erosion ? how deep over how much of the field did the rills erode and how deep over how much of the field did sheetwash erode? We will conduct detailed experiments at the Deep Loess Research Station near Treynor, Iowa. We will measure the distribution of fallout radionuclides (7Be, 137Cs, 210Pb, and 239+240Pu), nutrients and other constituents in the soil column. We will measure the loss of sediment, radionuclides, nutrients and other soil constituents in runoff from fields. By mass balancing radionuclides, soil constituents and sediment, we will calculate the area of the plot and basin that was uneroded, the areas rill and sheet eroded, and the depth of rills and sheet erosion. Detailed surveying will be used to monitor the evolution of rills, and to provide independent estimates of erosion. The study will also provide estimates of particle transit distances and delivery ratios of particles eroded from the landscape, and information on the relationship between the type of erosion and nutrient loss. Such insight contributes to the development of strategies for agricultural sustainability and ecosystem protection.
Animal Health Component
30%
Research Effort Categories
Basic
70%
Applied
30%
Developmental
(N/A)
Classification

Knowledge Area (KA)Subject of Investigation (SOI)Field of Science (FOS)Percent
1010110201050%
1120210203050%
Knowledge Area
112 - Watershed Protection and Management; 101 - Appraisal of Soil Resources;

Subject Of Investigation
0110 - Soil; 0210 - Water resources;

Field Of Science
2010 - Physics; 2030 - Geology;
Goals / Objectives
We will conduct detailed studies of soil erosion at the Deep Loess Research Station (DLRS), an Agricultural Research Service facility near Treynor, Iowa. We will use complementary techniques to understand the depth and areal extent of sheet and rill erosion, the nature of eroded material, and the consequences of that erosion on agricultural sustainability. A first objective is the characterization of the distribution of radionuclides (7Be, 137Cs, 210Pb, 239Pu, 240Pu), soil nutrients and constituents, and particle sizes in the soil column. Soil bulk density will be measured using a new gamma-attenuation method. During runoff we will characterize the fluxes of soil constituents and radionuclides and deployed tracers from nested basins at the DLRS. We will quantify the evolution of topography in the nested basins in response to runoff. The distribution of radionuclides and soil constituents and the outflow will be the basis for using multiple mass balances to quantify the depth and areal extent of sheetwash and rill erosion. The topographic information will provide independent estimates of erosion during runoff. Deployed surface tracers will be used to monitor very shallow erosion and to allow recognition of particle transport distances. The fluxes of soil constituents will be used to examine the consequences of erosion on soil productivity. The final objectives of the study are to use the data to estimate delivery ratios and to explore the implication of the results for management strategies to reduce loss of soil and loss of soil fertility.
Project Methods
The radionuclide and geochemical constituents in the soil column will be measured at a minimum of 5 locations adjacent to the test plot immediately prior to the first expected rain and at 5 sites within the plot after the runoff. We will sample at 4 mm intervals near the surface and at larger intervals deeper in the profile. Radionuclide activities will be determined by gamma spectroscopy and the rare earth analyses will be determined by ICPMS. Gamma spectroscopy will be done at Case Western Reserve University while the rare earth analyses will be done at North Arizona University. Soil nutrients will be measured in the lab by standard methods. Major and minor elements will be established by ICP or ICPOES. Most of this work will be done by Ohio State University. Bulk density will be determined using a novel technique that establishes a relationship between bulk density and the attenuation of gamma particles. Sediment in runoff will be collected at the outlet of the test plot and at the outlet of the field. The various constituents in the runoff will be analyzed by the same methods as those used for determining concentrations in the soil. We will estimate the depth and areal extent of erosion mechanisms with a computer model (SIRSEM) that executes multiple mass balances of three radionuclides (7Be, 137Cs and 210Pb) and soil to examine the large variety of possible erosion conditions. We will modify the model to allow the use of additional tracers. We will improve the algorithm to more efficiently search for reasonable solutions of the mass balances. We will employ a laser scanning device in the plot and repeated transects in the field to characterize evolution of topography in response to runoff events. The scanner may be able to recognize areas of sheet erosion if the cumulative erosion exceeds the 1 mm vertical resolution. We will estimate particle transit distances of soil based upon the downslope redistribution of deployed tracers. We will describe the longitudinal concentration distribution with exponential and advection-diffusion models. Short-term delivery ratios will be estimated in several ways: from the redistribution of REEs in the test plot, from the local erosion and the fluxes out of the plot, and from long term erosion of the landscape and basin yields. We will explore the implications of the results for management by considering the relative yield of various mechanisms of erosion and the relative costs and benefits associated with strategies to address the particular erosion mechanism. Furthermore we will consider the effect the vertical distribution soil constituents has on the loss of important nutrients and the implications for sustainable agriculture.

Progress 01/01/05 to 12/31/05

Outputs
A 4 x 9 m erosion plot with cement sill and collecting flume was installed at the Deep Loess Research Station. A 5 cm rain storm was monitored on June 12, 2004. Rainfall and runoff were collected. The storm generated 520 liters of runoff and 8 kg of sediment from the plot. The rill network was observed to deepen and extend during the event. Twelve soil depth profiles were collected and sampled at 4 mm intervals to a depth of 28 cm. Samples were analyzed by gamma spectrometry for Pb-210, Cs-137 and Be-7. The plot was laser scanned at 1.5 mm resolution prior to and after the rainstorm. Approximately 6.2 million data points were analyzed in ArcGIS to obtain the digital topography and the difference between the two scans. Areas of deposition, caused by soil eroded from uphill in the plot, were separated from areas of erosion. This data was then used to distinguish areas of rill development from areas of sheet wash. Results indicate a mean erosion rate of 0.0275 mm for the event. Less than 1% of the plot was eroded > 1.0 cm and less than 1% experienced > 1.3 cm of deposition. Soil tagged with rare earth elements (REE) was applied in three 25 cm wide strips. Sediment recovered in plot runoff and surface samples were analyzed by ICP-MS. REE tagging proved to be an effective measure of particle transport distance and travel time. The lowest band contributed the greatest volume of particles to plot runoff and had the shortest transit time. Higher bands showed less contribution of particles and later times of concentration. This reflects further travel distance, but also reduced contributing area resulting in smaller channels. Surface samples indicated an exponential decay in REE concentration with distance from the zone of application. Preliminary radionuclide mass balance solutions (with the SiRSEM computer model) confirm earlier work at Treynor demonstrating rill cutting to be the dominant process, contributing >99% of erosion. Rill depths were 10 mm and sheetwash depths 0.001 mm. The importance of rill erosion is supported by observed variation in the radionuclide signature of runoff sediment. During periods of high sediment yield, sediment had low Be-7 signatures characteristic of deep soil horizons. High resolution monitoring of the storm event gave the opportunity to directly relate rill incision to development of channel networks, soil saturation and rainfall intensity, giving insight into the hydrologic factors behind each process. Comparison between the SiRSEM model, field data, and laser scan results is underway. We are currently preparing manuscripts for publication. The following abstracts have been accepted: Stubblefield, A.P., P.J. Whiting, G. Matisoff, C. Fondran, and M. Ketterer. Fine-scale temporal resolution of sediment source by Be-7. Poster presentation at the American Geophysical Union Meeting. May 2005. New Orleans, Louisiana. Stubblefield, A.P., P.J. Whiting, G. Matisoff, C. Fondran, and M.E. Ketterer. Radionuclide and rare earth element tracers of erosional processes on the plot scale. In Press. Proceedings of the 8th Federal Interagency Sedimentation Conference. Reno, Nevada. April 3-6, 2006.

Impacts
Investigation of the processes by which sediment erodes off the landscape and is transported through watersheds to receiving water bodies is of importance in improved management practices in agricultural settings. Erosion results in reduced agricultural productivity and the degradation of aquatic resources. This study points to the importance of rill erosion, erosion resulting from concentrated water flow paths, in transporting the majority of sediment eroding from a field. The impact of the work will be to focus management practices on reducing rill erosion and ultimately, reduced erosion rates. The second impact of the study will be the development of tools for studying erosional processes that can be used in many settings to improve land management.

Publications

  • No publications reported this period