Abstracts

Faced with increasing nitrate concentration in the Woodstock municipal supply wells (located
in Ontario, Canada), mandatory agricultural best management practices (BMPs) were
implemented in a farmland located within the capture zone in 2003 to reduce nitrate leaching.
Early field investigations suggest that the impact of the BMPs on nitrate leaching was
gradual and not consistent across the capture zone as a result of the different soil stratigraphy,
and current and historical agricultural management practices. In this study, the long-term
(i.e., over 10 years) reduction of nitrate load to the groundwater as a result of BMP implementation
was simulated for different locations within the capture zone. These locations
represent the most dominant cropping practices within the farmland, and each has distinctive
geologic characteristics. To adapt the model to the field conditions, selected soil hydraulic,
organic matter and crop growth parameters were calibrated using a heuristic optimization algorithm.
The simulation results indicated that the long-term impact of the BMPs on nitrate
leaching was different at various locations and ranged from a 54% reduction to a 9% increase
over the 10-year period. Post-BMP annual nitrate leaching, in some years, was shown to
be similar or even greater than the loading prior to the implementation of the BMPs. This
finding was consistent with field observations and implies that BMP effectiveness needs to
be averaged over a long period of time and single field measurements can be misleading. No
relationship was found between soil nitrate content and nitrate leaching, suggesting that soil
nitrate content should not be used as a BMP effectiveness index. The anticipated effects of
two alternative BMP scenarios on nitrogen balance (yield, loss and storage) from a farmland
under conventional agricultural practice will also be discussed.
Regional Groundwater Systems 2
Wednesday, October 28, 15:20 – 17:00
Chair: Tom Gleeson
Room: Wagner
176 - A Continental-Scale Groundwater Flow Model Calibrated to
Groundwater Age
Mark Ranjram
Department of Civil Engineering – McGill University, Montreal, QC, Canada
Tom Gleeson
Department of Civil Engineering – University of Victoria, Victoria, BC, Canada
Throughout its distinguished history, the science of hydrogeology has developed elegant
models of site- and local-scale groundwater flow. Although the work of Tóth and others
provide an elegant theoretical framework for regional-scale groundwater flow, more complex
methods are needed to account for regional heterogeneities and limited observational
data at regional scales. These problems are further exacerbated when considering groundwater
flow at continental scales. In this study, we develop a groundwater flow and transport
model beneath the continental United States and relate our current continental-scale
permeability, porosity, dispersion, and recharge estimates to observed values of water table
72 IAH-CNC 2015 WATERLOO CONFERENCE