18O and 2H in streamflow across Canada

Study region Water samples for isotopic analysis were collected during 2013–2019 at 331 gauging stations across Canada in representative watersheds ranging from the Atlantic to the Pacific to the Arctic Oceans. Drainage area coverage of the network included 56 % of Canada’s landmass (9,984,670 km2) and was representative of 91 % of Canada’s annual water yield. Study focus Baseline data, including 4603 18O and 2H analyses, are described to assess potential for process studies and predictive model calibration. New hydrological insights for the region While similar patterns are noted between isotopes in streamflow and precipitation across Canada, systematic evaporative enrichment in streamflow occurs in lake- and wetland-rich areas, and systematic depletion occurs in some mountainous and/or cold-regions watersheds. The latter are attributed to uncertainty in precipitation isotope records, glacial melt and/or permafrost thaw. In δ18O-δ2H space, streamflow characteristically plotted on or below the Canadian Meteoric Water Line (CMWL) (δ2H = 8∙δ18O+8.5) along imbricated Regional River Lines (RRL) displaying a range of regression slopes (4.34–9.31) and intercepts (-54 to +24), reflecting regional variations in isotopic composition of input sources, evaporative enrichment, and tributary mixing. We define the Canadian Rivers Line (CRL) based on the linear regression of flow-weighted mean values of station data (δ2H = 7.89∙δ18O+0.45, r2 = 0.962; n = 161).