Nitrate-nitrogen and total phosphorus river loads

Nitrate-nitrogen and total phosphorus loads from the major rivers draining Illinois were updated through the 2021 water year (Figure 3.1). Beginning with the 2023 biennial update to the Illinois NLRS, nutrient loads were estimated using data from the U.S. Geological Survey continuous monitoring stations rather than the original Illinois EPA monitoring stations. To maintain consistency with previous biennial report updates, the loads from the new sites were rescaled to match the original drainage areas (Table 3.1). As before, the statewide nutrient load was estimated by summing the loads of the eight major rivers adjusting for out-of-state contributions and unmonitored areas.