Watershed-scale numerical modelling of nitrate transport using spatially uniform averaged N inputs

Groundwater nitrate concentration evolution under climate change and agricultural adaptation scenarios: Prince Edward Island, Canada

“…The fractured sandstone is characterized by relatively high hydraulic conductivity, between 1 × 10 −6 and 3 × 10 −4 m s −1 (Fig. 2b), but it has a low storage capacity (1-3%), as obtained from modeling of baseflow recession curves (Paradis et al, 2006(Paradis et al, , 2007 and seasonal nitrate sources in groundwater from isotopes (Ballard et al, 2009). In contrast, the matrix has a high porosity of about 17 %, but a much lower hydraulic conductivity as measured from laboratory core permeameter tests: mostly between 1 × 10 −8 and 5 × 10 −7 m s −1 but as low as 5 × 10 −10 m s −1 for mudstone (Francis, 1989).…”

“…With few exceptions, the surficial sediments over PEI do not represent significant aquifers as they are not water saturated, so the sandstone constitutes the main aquifer. Because the geology of the Island is relatively homogeneous, the hydrogeological conceptual model for all PEI is assumed to be similar to the one defined for the Winter River and Wilmot River watersheds where Francis (1989) and Paradis et al (2006Paradis et al ( , 2007 carried out extensive hydrogeological characterization. Based on these studies several observations relative to the hydrogeological framework of PEI can be made:…”

“…-Comparison between field (Paradis et al, 2006(Paradis et al, , 2007Francis, 1989) and laboratory (Francis, 1989) hydraulic conductivity measurements suggests that fractures play an important role in the rock aquifer permeability, and the general decrease in hydraulic conductivity with depth is the result of decreasing fracture aperture and frequency. Horizontal bedding of the sandstone forms the main fracture network above 35 m depth (82 % of all fractures; Francis, 1989).…”

“…-Tritium analyses on groundwater samples in the highflow system indicate the presence of "modern groundwater" younger than 50 years. In the low-flow system, no tritium is observed but carbon-14 analyses provide groundwater ages between 5000 and 7000 years at depths ranging between 50 and 85 m below the water table (Paradis et al, 2006(Paradis et al, , 2007).…”

“…In this study, the evolution of groundwater [NO 3 ] under a changing climate was modeled using the physically based groundwater flow and solute transport numerical simulator FEFLOW (Finite Element subsurface FLOW system; Diersch, 2010) considering the effect of the dual porosity of the fractured porous medium (sandstone), identified by Jackson et al (1990) as being responsible for the persistence of pesticides in the aquifer system of PEI. In particular, the hydrogeological model developed for the entire province was based on knowledge gained from the Wilmot watershed (Jiang and Somers, 2009;Paradis et al, 2006Paradis et al, , 2007, which is representative of most other regions of PEI regarding land use, soils, physiography, geology and hy- Table S1), with identification of the major rivers (names in blue), along with land use (see legend) and location of the weather stations (names in black).…”