Nitrate concentrations were generally higher in ground water than in streams. The primary exception was in the Midwest, where poorly drained soils restrict downward water movement and artificial drainage provides a quick path for nutrient-rich runoff to reach streams. Nitrate concentrations generally are low in both ground water and streams in agricultural areas throughout the Southeast. Poor soil drainage, an abundance of soil organic carbon, warm temperatures, and high rainfall combine to produce conditions that restrict nitrate formation in soils and shallow ground water of this region. Forested buffer strips between and within agricultural fields also are common and might retain nutrients.
Concentrations also are low in ground water and streams of the arid Southwest.
The sources of nitrate are limited in this region.