Single- and Dual-Porosity Calibration and Long-Term Modeling of Highly Conductive Floodplain Soils in the Ozark Ecoregion

Phosphorus (P) is a critical nutrient for agriculture, but is also responsible for surface water enrichment that leads to algal growth. While P loading to surface waters has traditionally been thought to occur from surface runoff, contributions from subsurface transport can also be significant. Subsurface transport through gravelly soils in the Ozark ecoregion can have a significant, yet poorly-documented effect on P movement to groundwater. Long-term P modeling was performed in HYDRUS-1D and 2D using data collected from short-term plot experiments featuring gravelly soils. Seven model levels were developed to illustrate a wide variety of laboratory and field conditions. Calibration was performed in HYDRUS-2D using single- and dual-porosity models with both homogeneous and heterogeneous gravel profiles as well as a mesh macropore profile. The dual-porosity model with heterogeneous hydraulic conductivity best matched experimental data, although the dual-porosity model with homogenous soil layers also performed well. Long-term P transport to a 3 m-deep water table was simulated in HYDRUS-1D and 2D using nine years of both daily and modified 5 minute rainfall data with a P flux consistent with annual poultry litter applications. HYDRUS-1D models produced a wide range of long-term results, while HYDRUS-2D models produced a much narrower range of results. There was little difference between analogous 1D and 2D models, suggesting that HYDRUS-1D may be sufficient to model long-term transport. The lack of distinction between the single- and dual-porosity long-term models could be explained by the large P concentration gradient between the poultry litter leachate and the soil water. Advisor: Derek M. Heere