Streams in agricultural areas are vulnerable to nutrient contamination where subsurface tile drains and ditches quickly transport excess precipitation from field to stream such as in the Eastern Iowa Basins. Some of the streams in this region are the direct or indirect source for drinking water supplies. Nitrate-nitrogen (NO3-N) in these streams can exceed the EPA Maximum Contaminant Level (MCL) of 10 mg L-1. Nitrogen is also a major pollutant of estuarine and marine ecosystems. Oxygen depletion in these ecosystems, known as hypoxia, occurs when dissolved oxygen concentrations in shallow waters decrease below the level required for aquatic organisms to survive (≤ 2 mg L-1).