4 years ago

Linking physiography and evaporation using the isotopic composition of river water in 16 Canadian boreal catchments

C. Welch, A.A. Smith, T.A. Stadnyk
Highly seasonal boreal catchments are hydrologically complex and generally data poor, and, hence, are ripe for investigation using tracer-aided hydrologic models. The influence of physiography on isotopic metrics was assessed to identify the catchment characteristics dominating evaporative enrichment. A multi-year stable isotope of water dataset was collected at the outlets of 16 boreal catchments in central Canada ranging in area from 12 km2 to 15,282 km2. Physiographic characteristics were obtained through raster analysis of freely available land cover images, stream networks, and digital elevation models. Correlation analysis indicated that as the percent coverage of open water increased, so too did the evaporative effects observed at the catchment outlet. Correlation to wetland metrics indicated that increasing the percent coverage of wetlands can reduce or increase evaporative effects observed, depending on the isotopic metric used, and the corresponding drainage density, catchment slope, and presence of headwater lakes. The slopes of river evaporative-mixing lines appear to reflect multi-faceted relationships, strongest between catchment slope, headwater lakes, and connected wetlands, while mean line-conditioned (lc-) excess is more directly linked to physiographic variables. Hence, the slopes of river evaporative-mixing lines and mean lc-excess are not interchangeable metrics of evaporative enrichment in a catchment. Relationships identified appear to be independent of catchment scale. These results suggest that adequate inclusion of the distribution of open water throughout a catchment, adequate representation of wetland processes, catchment slope, and drainage density, are critical characteristics to include in tracer-aided hydrologic models in boreal environments in order to minimise structural uncertainty.

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1002/hyp.11396

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