ASABE Technical Library - Abstract

Abstract. Juniper trees, primarily Eastern Redcedar (Juniperus virginiana), have encroached approximately 5 million ha of grasslands in Oklahoma alone as of 2008. Transition from grassland to Eastern Redcedar dominated woodland is associated with loss of several important ecosystem services the grasslands provide. Therefore, harvesting encroaching juniper species as a biofuel feedstock has been suggested because it could potentially improve both water quantity and quality while providing a sustainable fuel source. However, water quantity and quality impacts during Eastern Redcedar harvesting and biofuel feedstocks conversion process must be considered. The harvesting and conversion process will likely disturb soil leading to increased sediment runoff which is a common water quality pollutant. The Water Erosion Prediction Project (WEPP) was used to determine the predicted changes in water runoff and sediment transport and to evaluate the effects of biofuel feedstocks. The model was initially set up using the default parameter values that best represented the experimental watersheds, and then adjusted based on site-specific data. Model simulations were performed under 20-year forested conditions with encroached Eastern Redcedar, and then under fallow conditions assuming the Eastern Redcedar was harvested. Then, WEPP was examined with respect to default rill erodibility and critical shear stress inputs in the WEPP database under land conditions of 20-year forested and fallow and the same parameters determined from jet erosion tests (JETs) at field sites. Conversion from forested to fallow conditions resulted in an approximate three-fold increase in average annual runoff and a one to two order of magnitude increase in average sediment yield. Conducting in situ JETs to quantify erodibility only influenced the predicted sediment yield in the lower slope (3 to 5%) watershed under fallow conditions. Future research will collect actual runoff and sediment yield to verify the model simulations.