Evaluation of a model framework to estimate soil and soil organic carbon redistribution by water and tillage using 137 Cs in two U.S. Midwest agricultural fields Claudia J. Young a,b, ⁎, Shuguang Liu b , Joseph A. Schumacher c , Thomas E. Schumacher c , Thomas C. Kaspar d , Gregory W. McCarty e , Darrell Napton c , Dan B. Jaynes d a ERT Inc., contractor to the U.S. Geological Survey (USGS) Earth Resources Observation and Science (EROS) Center, Sioux Falls, SD 57198, USA b USGS EROS Center, Sioux Falls, SD 57198, USA c South Dakota State University, Brookings, SD 57007, USA d USDA-ARS National Laboratory for Agriculture and the Environment, Ames, IA 50011, USA e USDA-ARS Hydrology and Remote Sensing Laboratory, Beltsville, MD 20705, USA abstract article info Article history: Received 21 October 2013 Received in revised form 21 May 2014 Accepted 24 May 2014 Available online xxxx Keywords: Erosion Deposition Water erosion Tillage Cs-137 Organic carbon Cultivated lands in the U.S. Midwest have been affected by soil erosion, causing soil organic carbon (SOC) redistri- bution in the landscape and other environmental and agricultural problems. The importance of SOC redistribution on soil productivity and crop yield, however, is still uncertain. In this study, we used a model framework, which includes the Unit Stream Power-based Erosion Deposition (USPED) and the Tillage Erosion Prediction (TEP) models, to understand the soil and SOC redistribution caused by water and tillage erosion in two agricultural fields in the U.S. Midwest. This model framework was evaluated for different digital elevation model (DEM) spatial res- olutions (10-m, 24-m, 30-m, and 56-m) and topographic exponents (m = 1.0–1.6 and n = 1.0–1.3) using soil redistribution rates from 137 Cs measurements. The results showed that the aggregated 24-m DEM, m = 1.4 and n = 1.0 for rill erosion, and m = 1.0 and n = 1.0 for sheet erosion, provided the best fit with the observation data at both sites. Moreover, estimated average SOC redistributions were 1.3 ± 9.8 g C m -2 yr -1 in field site 1 and 3.6 ± 14.3 g C m -2 yr -1 in field site 2. Spatial distribution patterns showed SOC loss (negative values) in the eroded areas and SOC gain (positive value) in the deposition areas. This study demonstrated the importance of the spatial resolution and the topographic exponents to estimate and map soil redistribution and the SOC dy- namics throughout the landscape, helping to identify places where erosion and deposition from water and tillage are occurring at high rates. Additional research is needed to improve the application of the model framework for use in local and regional studies where rainfall erosivity and cover management factors vary. Therefore, using this model framework can help to improve the information about the spatial distribution of soil erosion across agricul- tural landscapes and to gain a better understanding of SOC dynamics within eroding and previously eroded fields. © 2014 Elsevier B.V. All rights reserved. 1. Introduction Projected global warming and degradation of land resources by ero- sion are critical environmental challenges (Jacinthe and Lal, 2007). Soil erosion is a natural process; however, it can be accelerated by human ac- tivities, such as intensive and conventional agricultural practices. Furthermore, soil erosion can become a major environmental and agricul- tural problem and cause reductions in soil productivity and deterioration of water and air quality (Pimentel et al., 1995; USDA NRCS, 1997). Erosion is defined as the detachment or movement of soil caused by water, wind, or human activities (e.g., tillage operations). The magnitude of erosion, however, is mostly determined by rainfall intensity, soil type, ground cover, and landscape characteristics (Arriaga and Lowery, 2007; Flanagan, 2007; Römkens et al., 2002). Soil erosion can have several ef- fects on crop yield and soil productivity, including reductions in effective rooting depth, available nutrients and water for plants, and loss of surface soil structure and infiltration due to exposure of subsoil (Schumacher, 2007). Water erosion consists of three recognized types: sheet, rill, and gully (Brady and Weil, 2008). Sheet erosion occurs when raindrops im- pact the soil surface, uniformly dislodging soil particles in the top soil layer (Brady and Weil, 2008; Nelson, 2002; Pimentel, 2006). Rill erosion, which is especially common on bare land, happens as the sheet flow is concentrated into small channels (Brady and Weil, 2008). Gully erosion occurs when runoff is further concentrated, cutting deeper into the soil and creating larger channels that can become an obstacle for machinery operations (Brady and Weil, 2008). Tillage erosion can be defined as the Geoderma 232–234 (2014) 437–448 ⁎ Corresponding author at: ERT, Inc. at USGS EROS Center, 47914 252nd Street, Sioux Falls, SD 57198, USA. E-mail address: cyoung@usgs.gov (C.J. Young). http://dx.doi.org/10.1016/j.geoderma.2014.05.019 0016-7061/© 2014 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Geoderma journal homepage: www.elsevier.com/locate/geoderma