Nitrogen Content of Shallow Ground Water in the North Carolina Coastal Plain

Abstract

Abstract The NO 3 ‐N and NH 4 ‐N concentrations in shallow (< 3 m) ground water under a range of soil types, drainage conditions, and type of crop grown were monitored. The NO 3 ‐N levels were always low (1 ppm or less) in ground water under wooded areas. The concentrations were somewhat higher under cultivated fields with the levels usually being 1 to 5 ppm although several values in the range of 10 to 20 ppm were recorded. The concentrations in all wells were always higher during the winter months. There seemed to be no relationship between cultivated crop and NO 3 ‐N in the ground water. The NO 3 ‐N concentration was almost always higher in the middle of the field than on the edge of the field even though the direction of water flow was toward the edge of the field. It is suggested that denitrification is responsible for this decrease. There was little difference in NH 4 ‐N concentration in water under cultivated fields and under unfertilized woods or pasture. The NH 4 ‐N concentrations were normally in the range of 0.1 to 1 ppm with the higher levels being found under poorly‐drained soils. Based upon the characteristics of the surface sediments, it is concluded that very little of the NO 3 ‐N present in the shallow ground water moves into deep aquifers in any area of the North Carolina Coastal Plain. However, the amount of NO 3 ‐N that moves through the surficial sediments to the streams probably varies with location and characteristics of the confining beds.