Estimating Phosphorous Load from a Large Watershed in the Great Lakes Basin

Common ways to quantify watershed nutrient loads include estimating the annual or seasonal loads using simple relations between discharge and load, such as the ratio estimator, and fitting complex nutrient transport models to the observed concentrations. The former approach produces quite uncertain estimates even at low temporal resolution, when based on typically infrequent routine monitoring data. The second approach may produce more reliable estimates, even at high temporal resolution, but requires a lot of computing effort and auxiliary data. The approach explored in this paper uses linear combination of river discharge at the time of estimate and for antecedent periods to estimate daily Total Phosphorous (TP) concentration, yielding high resolution load estimates sufficiently reliable for a variety of applications.