| Lake Okeechobee, located at the center of the Kissimmee-Okeechobee-Everglades aquatic ecosystem in south Florida, is experiencing water quality degradation. Non-point agricultural runoff from dairies and cow-calf operations in the northern watershed of the lake is considered to be the primary source of excess phosphorus (P) loading discharged into the lake. In order to evaluate alternative land management practices that result in reduced P loading from the watershed to the lake, a coupled modeling system integrating hydrology, nutrient and vegetation dynamics simulation was developed.;The coupled modeling system was developed within the Java-based, object-oriented framework of the ACRU2000 modeling system by adding new hydrologic and nutrient components and a vegetation model to enable multi-directional spatial simulation of hydrological, chemical, and biological processes simultaneously in a daily time step. The coupled model was tested for accuracy by comparing performance with well-accepted models including MIKE SHE and MODFLOW. Results indicate that the coupled model is capable of simulating, with reasonable accuracy, hydrological and solute transport processes for the hypothetical scenarios. Additionally, the model was tested in the Kissimmee River Basin and Lake Okeechobee Basin by comparing with the FHANTM model and against measured data. These applications demonstrated that the coupled model is statistically close to the performance of FHANTM with respect to hydrologic response in the Kissimmee River Basin, but much better than FHANTM with regard to hydrologic and nutrient responses in the Lake Okeechobee Basin. From the testing, it was concluded that the model is able to continuously simulate the surface runoff and groundwater tables with adequate accuracy. However the model's capacity to simulate nutrient loading needs further testing after sufficient reliable nutrient data becomes available. The vegetation model, coupled with the hydrologic and nutrient models, was tested for a hypothetical scenario based on the conditions in the Lake Okeechobee Basin. The test results show that the temporal and spatial vegetation composition pattern can be an indicator of the ecohydrological impacts of alternative land management practices. However, for actual application of this model, further testing is required when more vegetation data are available.;Recommended future research includes further development of the coupled model to enable a user-friendly pre- and post-processing graphical interface, an option for subdaily time steps, beef-cattle roaming simulation, and plant competition. Further testing of the coupled model should be conducted at larger watershed scales and for the nutrient and vegetation simulations when additional data are available. |
