Do nutrients vary regionally in groundwater?
Variations in the distribution of nitrate concentrations in groundwater are due to differences in types of nutrient inputs, physical factors that either favor or inhibit transport of nitrate to groundwater, and chemical factors that result in persistence or removal of nitrate in groundwater over time. (See question “How do factors such as the groundwater flow system, geochemical condition, groundwater age, and depth of the aquifer affect the concentrations of nitrate in groundwater?”) High concentrations of nitrate (greater than 2.6 milligrams per liter, mg/L) in shallow groundwater in agricultural areas are broadly distributed across the nation. Nitrate concentrations are highest in shallow, oxic groundwater that receives high inputs of nitrogen from fertilizer, manure, and atmospheric deposition. For example, median concentrations of nitrate in shallow groundwater were higher (greater than 2.6 mg/L) in many studies in the Northeast, the Midwest, and the Northwest, and in a few studie
