| A hydrologic and water quality model was developed for high water-table environments such as the flatwoods of Florida. The model was developed within the object-oriented framework of the ACRU2000 model. The model uses physical approximations suitable for highly conductive, poorly drained soils. The water quality component of the model uses nitrogen and phosphorus algorithms patterned after the GLEAMS model, with appropriate modifications for sandy, poorly drained, acid soils.;The hydrologic model operates on a daily time-step and assumes a hydrostatic distribution of soil moisture. Reference potential evapotranspiration can be estimated using the Penman-Monteith equation and the resulting atmospheric demand is applied in a top-down approach to intercepted water, ponded water on the ground surface, and to soil evaporation and plant transpiration. Vertical upward flow of soil moisture in response to evapotranspiration is approximated using a steady-state solution of Darcy's Law. Groundwater flow can occur to or from a deep aquifer or an adjacent water body. Runoff from the land surface is assumed to occur via saturation-excess only.;The hydrologic component of the model was validated using observed data from three field sites. The validation established the model's ability to predict water-table depths, soil moisture contents, evapotranspiration, and runoff volumes.;The water quality component of the model employs modifications for poorly drained, flatwoods soils that include the specification of optimal ranges of water contents affecting the rate of nutrient transformations, the effect of soil moisture on transformation rates under saturated or near-saturated conditions, the instantaneous, reversible sorption of phosphorus, and the extraction of nutrients into runoff water.;The water quality component of the model was validated for six experimental pastures. Model validation, while providing improved predictions of runoff nutrient loads compared to the model without modifications for shallow water-table environments, indicated several shortcomings of the model. These include the need for explicit representation of plant biomass and organic soil accretion and the need for more site- or region-specific information on nitrogen contents and the factors that control N and P cycling and retention in these soils. |
