Nitrate, a component of total nitrogen, showed an upward trend at Lewisburg and no change at any other sites. Constant or increasing nitrate concentrations may be related to flow from ground water and nonpoint sources. The trend shown is for total nitrate plus nitrite nitrogen, which is a close approximation to the trend in nitrate-nitrogen. The trend for Marietta is based on data from 1987 to 1996. The maximum and minimum results illustrate the range of possible trends.
Negative numbers indicate downward trends.