Evaluation of the distributed simulation of critical source areas and targeted conservation applications

Ames Francis Fowler

Despite millions of conservation dollars spent, nonpoint source pollution associated with agricultural disturbance and fertilization continues to be a significant problem across the nation. For conservation efforts to be effective in abating agricultural soil erosion, the selection and placement of conservation practices must fit the landscape's critical areas of erosion generation and farmer decision making. This thesis evaluated the Revised Universal Soil Loss Equation (RUSLE), the Water Erosion Prediction Project (WEPP), and the Soil Moisture Routing (SMR) models' ability to locate critical areas at the watershed scale. Building on model results, an integrated system dynamics (SD) model explored non-physical drivers of conservation adoption using three disciplinary hypotheses: physical--using critical source areas, social--using the diffusion of innovation, and economic--using the opportunity cost. Three agricultural watersheds were modeled with RUSLE, WEPP and SMR: Thorn and Kamiache Creek watersheds in Washington State, and Paradise Creek watershed in Idaho. The SD model simulated areas of land under conventional and conservation treatments. The RUSLE erosion rates strongly correlated with slope, producing a nearly normal distribution of erosion with the highest values on steep back slopes. WEPP simulated a highly nonlinear distribution of erosion rates with the greatest average erosion on toe slopes. The hydrology of WEPP and SMR support the nonlinear distribution of erosion. Topography defined the location of critical areas for infiltration excess dominant cases, and soil characteristics exacerbated topographical effects where saturation excess controls runoff. The nonlinearity in runoff and erosion generation supports the need for targeted conservation efforts to maximize impacts by treating a small portion of the landscape. Based on the SD model, crop price effects and conservation funds, applied uniformly and targeting the critical areas, influenced rates of conservation. In the short term, targeting critical source areas produced greater reductions in erosion for the same cost as untargeted programs. In the long term, the diffusion of innovation behavior produced a positive trajectory towards effective conservation. Crop price effects slowed conservation adoption rates with strong impacts on funding dependent practices. For lasting conservation, critical areas should be targeted while favoring conservation practices that benefit farmers beyond conservation payments.

Evaluation of the distributed simulation of critical source areas and targeted conservation applications

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