SOURCES AND FLUX OF NITRATE-NITROGEN IN THE CEDAR RIVER, IOWA, 2001-2004

The Federal Clean Water Act requires each state to complete a Total Maximum Daily Load (TMDL) for each impaired waterbody. The Cedar River in eastern Iowa has been listed as impaired by nitrate. Nitrate-N in the Cedar River has consistently measured above the 10 mg/L drinking water standard near the City of Cedar Rapids. Due to the impairment, a nitrate TMDL was completed on the watershed. This TMDL details all potential sources and loadings of total nitrogen directly to the stream and the watershed.

The U.S. Geological Survey modeled discharge and nitrate flux from six of the major tributaries of the Cedar River during the 2001-2004 calendar years. Models used were the Diffusion Analogy Surface Water Flow (DAFLOW) model and the chemical transport model WASP (Water Quality Simulation Program). Results from these models were paired with empirical methods to determine quantity of loads per source. The results of this report indicate that nonpoint source pollution is the significant contributor (>90%) of nitrate discharged from the Cedar River, with fertilizer and legume fixation the principal sources. Dams and wetlands have had significant impact on decreasing nitrate levels in the tributaries.