STRUCTURAL EQUATION MODELING OF DYNAMICS OF NITRATE CONTAMINATION IN-GROUND WATER

Most research on the temporal aspect of nitrate pollution in water res ources has focused on surface water. Comprehensive studies on the dyna mics of nitrate in ground water are lacking, especially on a drainage basin scale and for relatively long periods of time. In this study, st ructural equation modeling is applied in investigating the influences of climate, hydrology, and nitrogen management in agricultural product ion on nitrate concentration in the Big Spring Basin, Iowa, over a 10- year period. The study shows that for given hydrogeological settings, nitrogen management practices and climate are the two most important f actors that affect nitrate dynamics. The long-term trend of nitrate is closely related to the nitrogen input primarily determined by managem ent practices. The potential effects of nitrogen management, however, are contingent on the variations of climate. The improvements in water quality (reduced nitrate concentration and loads) in relation to impr oved nitrogen management are often overshadowed by the impact of clima te, especially in extremely dry or wet years. The variations of climat e and hydrology have much greater impacts on the nitrate dynamics than the changes in nitrogen input. This study reveals significant seasona l variation in the relations between nitrate concentration and influen cing factors, which is also closely related to the seasonal variation in climate. Assessment of management practices and resultant water qua lity should consider the impact of short- and long-term climate dynami cs.