|Title||Multi-scale nitrate transport in a sandstone aquifer system under intensive agriculture|
|Author||Paradis, D; Ballard, J -M; Lefebvre, R; Savard, M M|
|Source||Hydrogeology Journal vol. 26, 2, 2018 p. 511-531, https://doi.org/10.1007/s10040-017-1668-z (Open Access)|
|Alt Series||Natural Resources Canada, Contribution Series 20182042|
|Media||paper; on-line; digital|
|Released||2017 09 26|
|Abstract||Nitrate transport in heterogeneous bedrock aquifers is influenced by mechanisms that operate at different spatial and temporal scales. To understand these mechanisms in a fractured sandstone aquifer
with high porosity, a groundwater-flow and nitrate transport modelÑreproducing multiple hydraulic and chemical targetsÑwas developed to explain the actual nitrate contamination observed in groundwater and surface water in a study area on Prince
Edward Island, Canada. Simulations show that nitrate is leached to the aquifer year-round, with 61% coming from untransformed and transformed organic sources originating from fertilizers and manure. This nitrate reaches the more permeable shallow
aquifer through fractures in weathered sandstone that represent only 1% of the total porosity (17%). Some of the nitrate reaches the underlying aquifer, which is less active in terms of groundwater flow, but most of it is drained to the main river.
The river-water quality is controlled by the nitrate input from the shallow aquifer. Groundwater in the underlying aquifer, which has long residence times, is also largely influenced by the diffusion of nitrate in the porous sandstone matrix.
Consequently, following a change of fertilizer application practices, water quality in domestic wells and the river would change rapidly due to the level of nitrate found in fractures, but a lag time of up to 20Êyears would be necessary to reach a
steady level due to diffusion. This demonstrates the importance of understanding nitrate transport mechanisms when designing effective agricultural and water management plans to improve water quality. © 2017, Her Majesty the Queen in Right of Canada
as represented by: Yves Michaud.|