Crops are not efficient at removing fertilizer and manure nitrogen from the soil during a growing season. The presence of nutrients in surface water and ground water can limit the usefulness of these resources. Elevated nitrate nitrogen present in ground water used to supply drinking to humans and animals can cause health problems. Phosphate reaching streams, lakes and the Chesapeake Bay can lead to eutrophication. Elevated levels of phosphorus in water can be due to the use of commercial fertilizers, manures and sewage sludges in crop production.
Ground water is the water that fills the pores in sands or gravel or the cracks in fractured rocks.
Nutrients can reach ground water if they are leached out of the soil or if they are present in streams. Ground water can flow into streams when the water level in the ground water is higher than the level of water in the stream, carrying any nutrients present along with it. Ground water is not stationary. As ground water moves, dissolved pollutants will move with it, often great distances from where they were introduced. On the Eastern Shore of Maryland, for example, ground water may travel for several miles before discharging.