LOADSS Update and Verification Project

SWET in association with Breedlove, Dennis & Assoc. and Hazen and Sawyer performed a major update of the Lake Okeechobee Agricultural Decision Support System (LOADSS).   LOADSS is a GIS-based tool for evaluating the environmental and economic impacts of different agricultural management practices on reducing phosphorus loads from the Lake Okeechobee watershed.  LOADSS stores and retrieves data; edits modeling scenarios; and generates reports and maps.  Within LOADSS, a land use and phosphorus management plan can be developed using a menu-driven user interface.  LOADSS was originally developed with data collected from 1973 to 1987 and was updated by SWET to take into account the substantial changes in dairy land use and phosphorus management practices that occurred since 1987.  The updated LOADSS model also provides a better estimate of in-stream phosphorus assimilation.  In the previous version of LOADSS, the in-stream phosphorus assimilation was estimated using an exponential decay function based on flow travel distance.  However, the assimilation of phosphorus is influenced by many other factors.  In this study, an improved phosphorus assimilation algorithm was developed.  The algorithm is based on a second-order exponential relationship among flow rate, concentration, travel distance, and background concentration.  The updated LOADSS model was re-calibrated using observed tributary phosphorus loads from 1991 to 1995.  The updated model was used by Dr. Joyce Zhang with the SFWMD to evaluate alternative land use and phosphorus management strategies for reducing phosphorus loads to Lake Okeechobee.