How are long-term discharge and water-quality data integrated to calculate an annual stream load?
|Back to Top| The SPARROW model uses the mean annual load (mass per unit time, expressed, for example, as kilograms per year) at each stream monitoring station to calibrate the model. The mean annual load is computed using USGS load estimation methods; for details, see the SPARROW model documentation. In brief, these load estimation methods combine regularly collected nutrient measurements at the monitoring stations with daily streamflow values, typically from the previous 30-year period. This approach yields more accurate estimates of the long-term mean annual load than can be obtained by using the individual contaminant measurements alone. The mean annual contaminant load is also standardized to a single time referred to as the base year, which is the designated time period for comparing contemporaneously spatial variability in water-quality loads and contaminant sources in the SPARROW model. Standardizing provides an estimate of the mean contaminant load that would have occurred in
