Nitrate sources and factors controlling its distribution in agricultural lands and groundwater in two small catchments in southern Quebec, Canada

R. Thériault, C. Rivard, M.M. Savard, R. Lefebvre

In the proceedings of: GeoMontréal 2013: 66th Canadian Geotechnical Conference; 11th joint with IAH-CNC

Session: Groundwater Quality

ABSTRACT: Agriculture is one of the main economical activities in the Montérégie Est region (southern Quebec, Canada) and the main rivers are heavily impacted by nitrate. However, groundwater in this area does not appear to be contaminated, except in a few places. A study on the nitrogen cycle was carried out as part of a regional aquifer assessment and it focused on two small catchments having intensive agricultural activities. This study investigated nitrogen exchanges between the vadose zone and the bedrock aquifer in order to better understand processes contributing to low nitrate concentrations in groundwater of this region. The presence of both agricultural drains and low-permeability soils have been found to be the main causes for these low concentrations. Poor drainage was identified to be mainly responsible for the occurrence of various biochemical reactions in the unsaturated zone that modify nitrogen and oxygen isotopic ratios and, therefore, preclude the identification of the nitrate sources.

RÉSUMÉ: L™agriculture est l™un des secteurs économiques les plus importants de la Montérégie (sud du Québec, Canada) et les principaux cours d™eau sont fortement affectés par les nitrates. Cependant, l™eau souterraine ne semble ne pas être contaminée, excepté à quelques endroits. Une étude sur le cycle de l™azote a été réalisée dans le cadre d™un projet régional de caractérisation hydrogéologique dans deux petits bassins versants à vocation agricole. Cette étude portait sur les échanges d™azote entre la zone vadose et l™aquifère rocheux afin de mieux comprendre les processus contribuant aux faibles concentrations de nitrate dans l™eau souterraine de cette région. La présence de drains agricoles et de sols peu perméables semble en être en grande partie responsable. Le mauvais drainage des sols a été identifié comme étant une des causes principales de la présence de multiples réactions biochimiques dans la zone non saturée, qui modifient les rapports isotopiques de l™azote et de l™oxygène et, donc, empêchent l™identification des sources de nitrate.

Access this article:
Canadian Geotechnical Society members can access to this article, along with all other Canadian Geotechnical Conference proceedings, in the Member Area. Conference proceedings are also available in many libraries.

Cite this article:
R. Thériault; C. Rivard; M.M. Savard; R. Lefebvre (2013) Nitrate sources and factors controlling its distribution in agricultural lands and groundwater in two small catchments in southern Quebec, Canada in GEO2013. Ottawa, Ontario: Canadian Geotechnical Society.

@article{GeoMon2013Paper609,author = R. Thériault; C. Rivard; M.M. Savard; R. Lefebvre,title = Nitrate sources and factors controlling its distribution in agricultural lands and groundwater in two small catchments in southern Quebec, Canada,year = 2013}