Components of the phosphorus budget
¥Watershed land use
ÐCoefficient
ÐLand area
¥  Septic systems
ÐSoil retention
ÐOccupancy rates
¥ Internal recycling and sediment release
ÐAnoxia
ÐWater quality
The external sources of phosphorus consist of the different land uses and other factors such as septic systems.  The model also includes internal sources such as sediment release.