Modeling phosphorus in the Lake Allatoona watershed using SWAT: I. Developing phosphorus parameter values

Area of Science:

• Environmental Science
• Hydrology
• Water Quality Modeling

Background:

• Lake Allatoona requires a phosphorus (P) total maximum daily load (TMDL) due to its large drainage area.
• Estimating P parameters, particularly for in-stream processes within the Soil and Water Assessment Tool (SWAT) model, lacks clear guidance.

Purpose of the Study:

• To demonstrate methods for estimating SWAT P parameters, focusing on both soil-related and in-stream processes.
• To improve the accuracy of watershed-scale P modeling for TMDL development.

Main Methods:

• Individually estimated SWAT soil-related P parameters.
• Collectively estimated in-stream P parameters using the nutrient uptake length concept and simulated point sources.
• Calibrated SWAT models for daily transport using developed P parameters.

Main Results:

• Simulated P uptake lengths ranged from 53 to 149 km, compared to measured values of 11 to 85 km.
• SWAT models using the derived P parameters outperformed those with default values in predicting total P concentrations and annual loads.
• Improved prediction of total phosphorus (TP) concentrations during storm events and TP annual loads to Lake Allatoona.

Conclusions:

• The developed methods provide a robust approach for estimating P-related parameters in SWAT models.
• Accurate P parameterization is crucial for effective watershed management and TMDL implementation.
• This approach enhances the reliability of SWAT for predicting phosphorus dynamics in reservoirs and their tributaries.