Why use a 7 Parameter Regression Model?
The 7 parameter model is the simplest model that captures the main sources of variability for most nutrient species. The first coefficient is a constant; the next two address variability connected with discharge; the next two deal with time trends; the final two capture annual seasonality. Simpler models are appropriate in some circumstances; the 7 parameter model seems to work for almost all nutrient species for large (greater than 100 square miles) watersheds.
