Assessment of vadose zone solute transport under a potato field by a 19 month time-lapse cross-hole resistivity imaging survey
University of New Brunswick
Nitrate is a necessary nutrient for crops, however high concentrations of nitrate in surface water and groundwater can negatively affect aquatic ecosystems and human health. 3D cross-hole Electrical Resistivity Imaging (ERI) has been used to investigate the percolation of a conductive tracer (KCl) through a 17 m thick vadose zone as a proxy for the transport of nitrate under natural recharge conditions. Post-tracer surveys indicate that tracer movement has slowed significantly by early May, 2015 (about one month after tracer application), at the end of snow melt. The shallow conductivity anomaly produced by the tracer diminished significantly over the winter and spring of 2016, but showed little evidence of bulk matrix flow below approximately 6 m depth (top of the bedrock). It is speculated that fractures in the bedrock, too thin to be resolved by the ERI survey, conveyed tracer downward. After 18.5 months, there is no ERI evidence of tracer migrating through the matrix below approximately 6 m.