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Nitrate-nitrogen Loading Rates in a Glacial Till Aquitard

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan

Citation:  Paper number  022215,  2002 ASAE Annual Meeting . (doi: 10.13031/2013.9528) @2002
Authors:   Victor B. Ella, Stewart W. Melvin, Rameshwar S. Kanwar
Keywords:   Nitrate-nitrogen loading, geostatistical analysis, variogram modeling, kriging, groundwater modeling, USGS-MODFLOW, glacial till aquitard

Estimates of NO3-N loading rates in a glacial till aquitard could serve as a gage not only of the extent of nitrate loss from applied nitrogen fertilizer and other nitrogen sources but also of potential nitrate contamination of groundwater resources in this type of formation. This study was carried out to develop a methodology for estimating NO3-N loading rates in a glacial till aquitard based on a three-dimensional finite difference groundwater recharge model and geostatistical models of NO3-N concentration observed in shallow groundwater. Annual NO3-N loading rates at the glacial till aquitard were estimated by coupling the two models and employing advective transport principles. The strength of the method developed lies in its ability to account for the spatial variability of NO3-N concentrations and hydraulic conductivity. The NO3-N loading rates estimated by the method developed in this study proved to be significantly different from simplified approaches of using the average of point observations of NO3-N concentrations. Results also indicated that NO3-N loading rates were positively correlated with groundwater recharge rates (r = 0.67), precipitation (r = 0.51) and NO3-N concentrations (r = 0.50). The annual NO3-N loading rates at the glacial till aquitard during the five-year period considered estimated using the method developed averaged 0.43 kg/ha, constituting approximately 0.4 % of the average annual nitrogen fertilizer application rate. This study provided additional evidence of the general effectiveness of the glacial till aquitard in minimizing nitrate leaching to groundwater..

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