Citation

Shuang Wang, Karl Butler, Serban Danielescu, Brent Petersen and Mark Grimmett, "Dynamics of solute transport through the deep vadose zone under a potato field as assessed by a year-long tracer test and cross-hole resistivity imaging," 2016 Joint Scientific Meeting of the Canadian Meteorological and Oceanographic Society (CMOS) and Canadian Geophysical Union (CGU), (Fredericton, NB, Canada), Rick Fleetwood and Erick Ouellette, eds, May 29-June 2, 2016, ISBN 978-9880587-4-3.

Abstract

Nitrate is a necessary nutrient for crops, but high nitrate concentrations in water can negatively affect aquatic ecosystem and human health. At AAFC-AAC Harrington Research Farm (PEI), 3D cross-hole electrical resistivity imaging (ERI) is being used to investigate the transport of conductive tracer through a vadose zone as a proxy for the transport of nitrate under natural recharge conditions. The objectives are to investigate the effect of heterogeneity on transport pathways and infer how long it would take changes in farming practices at the surface to affect nitrate loading to the underlying aquifer. Borehole geological logs, and pre-tracer resistivity surveys indicate the 17 m deep vadose zone can be divided into five layers including ~ 6 m of soil and glacial till overlying interbedded sandstone and shaley sandstone. On March 27th, 2015, 1.1 m of snow was removed from a 15.2 m2 area positioned symmetrically inside the triangular cross-hole resistivity array and 100 kg of granular KCl was evenly distributed on the ground surface. The removed snow was replaced to await the spring thaw. Post-tracer surveys indicate tracer had percolated to depths of 1 m, 1.2 m, 3.0 m and 3.5 m by the 4th, 26th, 30th, and 46th days after tracer application. Its movement slowed significantly by early May with the end of snow melt. The most recent data from February 4th, 2016 yielded a resistivity model very similar to that obtained in mid-May, 2015. The stalling of tracer is thought to be caused by a low permeability layer. Preferential percolation of tracer towards west was observed, indicating heterogeneity within overburden. Tracer movement will be monitored through the spring thaw of 2016, and results will be used to improve infiltration and percolation models. Forward modelling and volume of investigation studies are ongoing to determine the sensitivity and resolution of this ERI array.

Abstract book

See also, page 110 of the Abstract Book: http://cmos.in1touch.org/uploaded/web/congress/Files/2016%20Files/Abstract%20Book%20CMOS-CGU%202016%20final.pdf

Acknowledgements

This work was supported by Agriculture and Agri-Food Canada (AAFC) at both Fredericton, NB, and Harrington, PE. The work was also supported by the University of New Brunswick (UNB).


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