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 km(2)) and was representative of 91 % of Canada's annual water yield. Study focus: Baseline data, including 4603 O-18 and H-2 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 delta O-18-delta H-2 space, streamflow characteristically plotted on or below the Canadian Meteoric Water Line (CMWL) (delta H-2 = 8.6(18)O+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 (delta H-2 = 7.89.delta O-18+0.45, r(2) = 0.962; n = 161).