A FRAMEWORK FOR PHOSPHORUS TRANSPORT MODELING IN THE LAKE OKEECHOBEE WATERSHED¹

Abstract

A modeling framework was developed to determine phosphorus loadings to Lake Okeechobee from watersheds located north of the lake. This framework consists of the land-based model CREAMS-WT, the in-stream transport model QUAL2E, and an interface procedure to format the land-based model output for use by the in-stream model. QUAL2E hydraulics and water quality routines were modified to account for flow routing and phosphorus retention in both wetlands and stream channels. Phosphorus loadings obtained from previous applications of CREAMS-WT were used by QUAL2E, and calibration and verification showed that QUAL2E accurately simulated seasonal and annual phosphorus loadings from a watershed. Sensitivity and uncertainty analyses indicated that the accuracy of monthly loadings can be improved by using better estimates of in-stream phosphorus decay rates, ground water phosphorus concentrations, and runoff phosphorus concentrations as input to QUAL2E. (KEY TERMS: hydraulics; modeling; nonpoint source pollution; phosphorus; surface water hydrology; water quality; wetlands; uncertainty analysis.) nonpoint pollution that ultimately reaches Lake Okeechobee has not been established. As phosphorus is transported to the lake, it may be retained temporarily or permanently in stream channels and wetlands via physical, chemical, and biological processes. Examples of these processes are the settling of organic phosphorus, the sorption of dissolved phosphorus to suspended particulate matter or sediment, and the uptake of phosphorus by aquatic macrophytes and algae. The ability to accurately assess phosphorus retention, or assimilation, is important, because assimilation can significantly reduce phosphorus loads ultimately reaching Lake Okeechobee.

Evaluating Effects of Poultry Waste Application on Phosphorus Loads to Lake Tenkiller

“…GIS elevation and watershed boundary data were used to subdivide HRUs to place them within the study watersheds. The combination of GLEAMS and a routing equation is similar to the approach by Ouyang [44] and Wagner et al [45] in modeling P loads from a watershed reaching Lake Okeechobee because GLEAMS does not simulate P routing in stream/rivers. Many other researchers have developed pollutant routing models to simulate transportation of pollutants from sources to receiving water and most of P routing equations are power functions with stream flow rate [46][47][48][49].…”

Diffuse Phosphorus Models in the United States and Europe: Their Usages, Scales, and Uncertainties

“…The Areal Nonpoint Source Watershed Environmental Response Simulation (ANSWERS‐2000; Beasley et al, 1980) is another fully distributed model. The Groundwater Loading Effects of Agricultural Management Systems (GLEAMS; Knisel, 1993), which is primarily a leaching model, has been modified for wetlands (GLEAMS‐WT; Wagner et al, 1996) for use in simulating P loading to a large sensitive reservoir (Lake Okeechobee) in Florida.…”

INTEGRATION OF WATER QUALITY MODELING, REMOTE SENSING, AND GIS1

“…QUAL2E, designed by the U.S. Environmental Protection Agency, simulates the spatial and temporal variations of water quality variables, including DO, BOD, water temperature, algae reported as chlorophyll a, organic phosphorus, and dissolved phosphorus (Brown and Barnwell, 1985). The QUAL2E model has been successfully applied in many water quality studies (see Lung, 1986;Cole, 1994;Wagner et al, 1996).…”