Using water stable isotopes for tracing surface and groundwater flow systems in the Barlow-Ojibway Clay Belt, Quebec, Canada

Abstract

This study aims to improve the understanding of surface and groundwater flow systems based on water stable isotopes data in a 19,549 km 2 region of the Barlow-Ojibway Clay Belt, in western Quebec, Canada. The available geochemical database contains 645 samples including precipitation, snow cores, surface waters, groundwater and springs. All samples were analyzed for water stable isotopes (δ 2 H-δ 18 O) and complementary tritium analyses were conducted on 98 groundwater and spring samples.Precipitations depict a clear temperature-dependent seasonal pattern and define a local meteoric water line (LMWL) without a latitudinal trend in δ 2 H-δ 18 O. Samples collected from the snowpack plot on the LMWL, suggesting that the bulk snowpack preserves the isotopic composition of precipitation throughout the frozen period, prior to the spring snowmelt. Surface water samples define a local evaporation line (LEL) and evaporation over inflow (E/I) ratios range between 0% and 36%. Groundwater and springs samples are evenly distributed around the LMWL, suggesting that evaporation processes are limited prior to infiltration and that surface waters do not significantly contribute to groundwater recharge. Shallow unconfined aquifers present a greater variability in δ 2 Hδ 18 O compared to confined aquifers located further down gradient, suggesting the mixing of varied recharge waters along the regional groundwater flow system. A threecomponent mixing model based on isotopic and specific electrical conductivity data allows the quantification of such mixing processes. The interpretation of isotopic data constrains a regional-scale conceptual model of groundwater flow systems and describes processes related to the timing of recharge, evaporation, mixing and discharge.

Global Isotope Hydrogeology―Review

“…In many cases, however, groundwater δ 18 O and δ 2 H values are not altered substantially by evaporation or water‐rock isotope exchanges (e.g., Gill, ; Rey et al, ). For example, among the compiled well and spring water deuterium excess values (Table ; Figure ), over 90% have deuterium excess values of greater than 0‰, and 73% have deuterium excess values exceeding 5‰.…”

A graphical approach for documenting peatland hydrodiversity and orienting land management strategies

“…In RHU-F, it is assumed that water preferentially circulates within the acrotelm, macropores, and piping networks. The hydrological framework of the study area is further described in Nadeau et al (2017) and Rey, Rosa, Cloutier, and Lefebvre (2017).…”

“…Peatland complexes that are likely to be in contact with surrounding fractured bedrock and/or granular unconfined aquifers. The peatland complexes associated with the "SG" vertex are generally located on the flanks of eskers and moraines, which host major unconfined aquifers in the region (Nadeau et al, 2017;Rey et al, 2017). The hydrological exchanges between peatlands and the bedrock aquifer will strongly depend on the hydraulic properties of the bedrock.…”

“…Peatland complexes that are unlikely to be in direct contact with surrounding aquifers, mainly because the regional "SC" unit is considered as an aquitard (Nadeau et al, 2017;Rey et al, 2017).…”

Results from the Quebec Groundwater Knowledge Acquisition Program

“…The papers focus on three main components of aquifer characterization, i.e. aquifer geometry (Légaré-Couture et al 2018;Nadeau et al 2018;Walter et al 2018), hydrogeochemistry and isotope tracers (Chaillou et al 2018;Rey et al 2018;Beaudry et al 2018), and groundwater flow modeling and particle tracking (Gagné et al 2018;Janos et al 2018;Montcoudiol et al 2018;Turgeon et al 2018). The paper by Walter et al (2018) combines the topics of geometry and hydrogeochemistry.…”