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TitleMulti-scale nitrate transport in a sandstone aquifer system under intensive agriculture
AuthorParadis, D; Ballard, J -M; Lefebvre, R; Savard, M M
SourceHydrogeology Journal vol. 26, issue 2, 2017 p. 511-531, (Open Access)
Alt SeriesEarth Sciences Sector, Contribution Series 20100143
PublisherSpringer Nature
Mediapaper; on-line; digital
File formatpdf
ProvincePrince Edward Island
NTS11E/03; 11E/04; 11E/05; 11E/06
AreaWilmot River; Summerside; Bedeque Bay
Lat/Long WENS -64.0000 -63.0000 46.5000 46.1667
Subjectshydrogeology; geochemistry; environmental geology; Agriculture; geochronology; groundwater resources; aquifers; surface waters; rivers; watersheds; groundwater geochemistry; groundwater pollution; nitrate; transport mechanisms; stream water geochemistry; bedrock geology; lithology; sedimentary rocks; sandstones; structural features; fractures; modelling; computer simulations; hydraulic analyses; hydraulic conductivity; leaching; porosity; water quality; flow regimes; water wells; land use; meteorology; isotopic studies; oxygen isotopes; nitrogen; radiometric dating; Wilmot watershed; contamination; fertilizers; manure; groundwater-surface water interaction; resource management; groundwater recharge; calibrations
Illustrationslocation maps; tables; profiles; time series; models; geoscientific sketch maps; diagrams
ProgramAquifer Assessment & support to mapping, Groundwater Geoscience
ProgramSources, Environmental Geoscience
Released2017 09 26
AbstractNitrate 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 model - reproducing multiple hydraulic and chemical targets - was 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 20 years 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.