Hypoxia in the Gulf of Mexico
The flux (sometimes referred to as the load) of a river-borne constituent such as nitrate is the amount (mass) that passes a given point on the river over a given period of time. The yield of a river-borne constituent is the flux per unit drainage area. Nutrient flux and yield are calculated as follows:
Nutrient flux = streamflow (discharge) MULTIPLIED BY nutrient concentration in streamwater.
Nutrient yield = nutrient flux DIVIDED BY watershed area.
Nutrient fluxes at a river station are estimated using statistical models with data from a continuous streamflow record at a gaging station and water-quality samples taken at or near the gaging station. The temporal resolution of flux estimates (annual, seasonal, or monthly flux estimates) are limited by the number of water-quality samples collected during the year and the changeability of flow and water-quality conditions at the station.