Modeling phosphorus in the Lake Allatoona watershed using SWAT: I. Developing phosphorus parameter values.
Lake Allatoona is a large reservoir north of Atlanta, GA, that drains an area of about 2870 km2 scheduled for a phosphorus (P) total maximum daily load (TMDL). The Soil and Water Assessment Tool (SWAT) model has been widely used for watershed-scale modeling of P, but there is little guidance on how to estimate P-related parameters, especially those related to in-stream P processes. In this paper, methods are demonstrated to individually estimate SWAT soil-related P parameters and to collectively estimate P parameters related to stream processes. Stream related parameters were obtained using the nutrient uptake length concept. In a manner similar to experiments conducted by stream ecologists, a small point source is simulated in a headwater sub-basin of the SWAT models, then the in-stream parameter values are adjusted collectively to get an uptake length of P similar to the values measured in the streams in the region. After adjusting the in-stream parameters, the P uptake length estimated in the simulations ranged from 53 to 149 km compared to uptake lengths measured by ecologists in the region of 11 to 85 km. Once the a priori P-related parameter set was developed, the SWAT models of main tributaries to Lake Allatoona were calibrated for daily transport. Models using SWAT P parameters derived from the methods in this paper outperformed models using default parameter values when predicting total P (TP) concentrations in streams during storm events and TP annual loads to Lake Allatoona.
Radcliffe
D E
DE
Dep. of Crop and Soil Sciences, Univ. of Georgia, Athens, GA 30602.
Lin
Z
Z
Risse
L M
LM
Romeis
J J
JJ
Jackson
C R
CR
D005618:Fresh Water / Q000032:analysis*; D005845:Georgia; D008956:Models, Chemical; D010758:Phosphorus / Q000032:analysis*; D012987:Soil / Q000032:analysis*; D014877:Water Pollution, Chemical / Q000032:analysis*
D012987:Soil; D010758:Phosphorus