SWAT Model of Phosphorus Transport to Lake Allatoona.
David E. Radcliffe and Zhulu Lin. Univ of Georgia, Dept of Crop and Soil Science, 3111 Miller Plant Science Building, Athens, GA 30602
The 2800 square km Etowah River Basin forms the watershed of Lake Allatoona in North Georgia. Lake Allatoona is classified as in transition to eutrophic and the state has placed a cap on annual phosphorus (P) loads to the lake. Our objective was to develop a watershed-scale model of P transport to Lake Allatoona using the Soil Water Assessment Tool (SWAT). We used the Parameter Estimator (PEST) software for auto-calibration of daily water flow and manual calibration for monthly Suspended Sediment (SS) and P concentrations. PEST did an excellent job of calibrating flow, although peak flows during storms were slightly under-predicted. There was a tendency to under-predict base-flow concentrations of SS and P and it was difficult to judge how well the model was calibrated for storm SS and P predictions due to the sparse observed data set. SWAT predictions of annual load of Total P (TP) to Lake Allatoona agreed well with observed data. Point sources accounted for only 10.4% of the TP load. Export coefficients for TP were highest from pasture landuse in the Etowah River basin (7 kg TP/ha/yr) where poultry operations are common. These results indicate that non-point sources of TP loading to Lake Allatoona are significant and there is a potential for trading P credits between point and nonpoint sources.