Across the United States, the impacts of stormwater runoff are being managed through the National Pollutant Discharge Elimination System (NPDES) in an effort to restore and/or maintain the quality of surface waters. State transportation authorities fall within this regulatory framework, being tasked with managing runoff leaving their impervious surfaces. Opportunely, the highway environment also has substantial amounts of green space that may be leveraged for this purpose. However, there are questions as to how much runoff reduction is provided by these spaces, a question that may have a dramatic impact on stormwater management strategies across the country. A highway median swale, located on Asheville Highway, Knoxville, Tennessee, was monitored for hydrology over an 11-month period. The total catchment was 0.64 ha, with 0.26 ha of roadway draining to 0.38 ha of a vegetated median. The results of this study indicated that 87.2% of runoff volume was sequestered by the swale. The Source Loading and Management Model for Windows (WinSLAMM) was used to model the swale runoff reduction performance to determine how well this model may perform in such an application. To calibrate the model, adjustments were made to measured on-site infiltration rates, which was identified as a sensitive parameter in the model that also had substantial measurement uncertainty in the field. The calibrated model performed reasonably with a Nash Sutcliffe Efficiency of 0.46. WinSLAMM proved to be a beneficial resource to assess green space performance; however, the sensitivity of the infiltration parameter suggests that field measurements of this characteristic may be needed to achieve accurate results.
Many bioretention models still incorporate simplifications and lumped parameters that do not fully account for fundamental physical processes. This review summarizes the representation of hydrologic pathways, notable features, and applications of bioretention models with the goals of recommending models well suited to bioretention modeling and identifying key research needs. As a result, HYDRUS and GIFMod were identified as the only models that use Richards' equation for determining infiltration under variably saturated conditions. Secondly, this study identified limited drainage configurations by most models except DRAINMOD-Urban. Thirdly, most models were inadequate for considering vegetation and plant water use, an area for improvement in future research. Finally, more calibration and validation studies are needed to build confidence in model results. This review intends to educate modelers of the processing equations for each water balance component, the input requirements in each model, and other model characteristics that should be considered in model selection.
Most of the nutrients in food supply chains are lost as waste and pollution at great environmental and economic cost. A more circular agricultural system can be developed through recycling of organic waste streams such as manure and food waste into organic fertilizers. This study assessed the agricultural system's circularity potential in the Susquehanna River Basin (SRB), the largest tributary to the Chesapeake Bay, by recycling organic waste streams such as manure and food waste into fertilizers. Using the Soil Water Assessment Tool (SWAT), we developed and deployed three different scenarios beyond the baseline of current practices. First, we created the Manure Transport scenario to study improved manure transport beyond the sub-watershed where it is produced. Second, we developed the High Nitrogen Recovery Manure scenario to evaluate an increase of available nitrogen (N) in manure assuming developing technologies could reduce N losses from storage and transportation, leaving more N to apply to cropland. The final Compost scenario used food-waste as a source for compost fertilizer applied to areas without manure available. We evaluated the level of circularity from each scenario through the spatial distribution and the proportion of cropland using organic fertilizers sourced from manure and compost generated in the SRB. Additionally, we considered water quality at the outlet of the SRB to determine the impact a circular agricultural system could have on the water quality goals set forth for Chesapeake Bay. The Manure Transport scenario showed circularity and water quality results similar to the baseline conditions. The High Nitrogen Recovery Manure scenario demonstrated the highest circularity, with 46% of cropland using organic fertilizers, resulting in the smallest phosphorus (P) loading per watershed area (3.26 kg/ha/yr) at the SRB outlet. However, it also had the highest N loading (9.97 kg/ha/yr) at the outlet. The Compost scenario doubled the area treated with organic fertilizers, with 16% of cropland utilizing compost application, and led to increased N (8.48 kg/ha/yr) and P (4.17 kg/ha/yr) loading at the SRB outlet. The study highlighted that cropland area in this region is sufficient to expand the use of manure and food waste compost as fertilizers, thereby enhancing circularity and reducing commercial fertilizer inputs. However, it emphasized the importance of integrating field management strategies to address agricultural runoff concerns and achieve both waste reduction and improved water quality.
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.
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