Spatial analysis of NO3-N concentration in glacial till

Abstract

Analysis of the spatial variability of groundwater NO3-N concentration is a logical step for a meaningful groundwater quality assessment, for mapping out areas of environmental concern, and for developing appropriate management schemes in a glacial till aquitard. This study was conducted to characterize the spatial variability of NO3-N concentration in shallow (<6.0 m) and deep (>6.0 m) groundwater in a 12-ha. glacial till aquitard and to estimate NO3-N concentration in unsampled locations. Omnidirectional and directional semivariogram analysis, statistical anisotropy analysis, and model fitting were performed for average and extreme monthly groundwater NO3-N data. Results indicated a weak spatial structure of NO3-N concentration for both shallow and deep well data. However, the best-fitted variogram models generally performed satisfactorily during cross validation, yielding a mean reduced error of -0.01 to -0.074 and reduced variance of 0.6 to 2.18. Untransformed shallow-well NO3-N exhibited a lower range of correlation than deep-well data. Statistical anisotropy was found to coincide with the general groundwater flow directions for the average and maximum observed NO3-N concentrations in shallow wells. Geostatistical estimation using ordinary kriging indicated relatively higher NO3-N concentrations at the down-gradient areas for shallow wells and at regions close to nitrogen fertilizer application sites for the deep wells. With satisfactory cross-validation performance of the variogram models, the geostatistical results of this study may be used as basis for estimating spatially variable NO3-N loading rates in the glacial till aquitard.

Source or Periodical Title

Transactions of the American Society of Agricultural Engineers

ISSN

12351

Page

317-327

Document Type

Article

Subject

Geostatistical analysis, Glacial till, Groundwater nitrate-nitrogen, Kriging, Spatial variability

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