Does the study assess loads and yields in streams, in addition to concentrations?
Statistical models that relate nutrient concentrations to streamflow and time were used to compute flow-weighted mean annual concentrations, loads (expressed as pounds per year), and yields (pounds of nutrients entering a stream per square mile of watershed) of ammonia, nitrate, total nitrogen, orthophosphate, and total phosphorus. In general, nutrient loads get larger as the drainage area of stream sites gets larger, even if nothing else changes. Normalizing loads by drainage area to calculate yields allows comparison of other factors (besides drainage area) that influence nutrient loads at different stream sites. Use of flow-weighted values facilitates comparisons among sites and avoids the potential bias to assessment results caused by differences in the number of samples collected at a site, sampling frequency, and varying flow conditions during the period of sampling. Natural factors such as climate (that is, wet and dry years) can affect loads in streams.
