Using stable isotopes to estimate travel times in a data‐sparse Arctic catchment: Challenges and possible solutions

Abstract

Use of isotopes to quantify the temporal dynamics of the transformation of precipitation into run‐off has revealed fundamental new insights into catchment flow paths and mixing processes that influence biogeochemical transport. However, catchments underlain by permafrost have received little attention in isotope‐based studies, despite their global importance in terms of rapid environmental change. These high‐latitude regions offer limited access for data collection during critical periods (e.g., early phases of snowmelt). Additionally, spatio‐temporal variable freeze–thaw cycles, together with the development of an active layer, have a time variant influence on catchment hydrology. All of these characteristics make the application of traditional transit time estimation approaches challenging. We describe an isotope‐based study undertaken to provide a preliminary assessment of travel times at Siksik Creek in the western Canadian Arctic. We adopted a model–data fusion approach to estimate the volumes and isotopic characteristics of snowpack and meltwater. Using samples collected in the spring/summer, we characterize the isotopic composition of summer rainfall, melt from snow, soil water, and stream water. In addition, soil moisture dynamics and the temporal evolution of the active layer profile were monitored. First approximations of transit times were estimated for soil and streamwater compositions using lumped convolution integral models and temporally variable inputs including snowmelt, ice thaw, and summer rainfall. Comparing transit time estimates using a variety of inputs revealed that transit time was best estimated using all available inflows (i.e., snowmelt, soil ice thaw, and rainfall). Early spring transit times were short, dominated by snowmelt and soil ice thaw and limited catchment storage when soils are predominantly frozen. However, significant and increasing mixing with water in the active layer during the summer resulted in more damped steam water variation and longer mean travel times (~1.5 years). The study has also highlighted key data needs to better constrain travel time estimates in permafrost catchments.

Global Isotope Hydrogeology―Review

“…Relative to their areas, tropical and high‐latitude lands are underrepresented in the primary literature, whereas northern mid‐latitude catchments are overrepresented. Recent works are ameliorating this by studying tropical (Jacobs et al, ), high‐elevation, and high‐latitude systems (e.g., Ala‐aho et al, , ; Ren et al, ; Tetzlaff et al, ; Yi et al, ). Continuing streamflow, groundwater, and precipitation isotopic data set development in these regions may help to monitor consequences of atmospheric warming on hydrologic processes (Lyon et al, ; Wilusz et al, ).…”

Spatial variability in the isotopic composition of water in small catchments and its effect on hydrograph separation

“…These advancements include studies on flow pathways and runoff generation processes, as well as the identification of the sources of plant transpiration (Dawson, Mambelli, Plamboeck, Templer, & Tu, ; Werner et al, ; Penna et al, ) and the effects of vegetation on water fluxes at the catchment scale (e.g., Geris et al, ; McCutcheon, McNamara, Kohn, & Evans, ; Sprenger, Tetzlaff, & Soulsby, ). Long‐term time series of stream isotope data have been used to determine subsurface mixing and to assess the distribution of the times that it took for the water to become streamflow (i.e., transit time) (e.g., McGuire & McDonnell, ; Hrachowitz et al, ; Rigon, Bancheri, & Green, ; Benettin et al, , b; Tetzlaff et al, ; Sprenger et al, ,b; Sprenger et al, ), to determine the fraction of stream water that is younger than a certain age (young water fraction; Kirchner, ; von Freyberg, Allen, Seeger, Weiler, & Kirchner, ; Stockinger et al, ; Lutz et al, ), and to aid the calibration of hydrological models (e.g., Birkel & Soulsby, ; Smith, Welch, & Stadnyk, ).…”

Spatially-distributed tracer-aided runoff modelling and dynamics of storage and water ages in a permafrost-influenced catchment

“…In discontinuous permafrost environments, storage dynamics and water distribution are strongly affected by the seasonal variability of frozen ground, the heterogeneity in snow accumulation and melt, and (particularly in alpine areas) the strong variability in energy receipt due to low sun angles Woo, 2012). There has been limited 10 application of isotopes to investigate water sources and pathways in permafrost regions (McNamara et al, 1997;Metcalfe and Buttle, 2001;Hayashi et al, 2004;Carey et al, 2013b;Tetzlaff et al, 2018), and there have been fewer studies that have used hydrological models that explicitly incorporate tracers in permafrost and snow-dominated regions (e.g. Lessels et al, 2015).…”

“…(TTs), defined as the elapsed time between water entry to, and exit from, a catchment as stream discharge at the outlet. Very few studies have employed isotope methods in permafrost influenced catchments to determine source waters (McNamara et al, 1997;Metcalfe and Buttle, 2001;Hayashi et al, 2004;Carey et al, 2013b;Tetzlaff et al, 2018). Often, isotopic data were employed to explore runoff processes based on hydrograph separation techniques or conceptual models for individual events (Quinton et al, 2005;Boucher and Carey, 2010;Lessels et al, 2015), but to our knowledge no spatially distributed 5 tracer-aided models have been applied to snowmelt-dominated permafrost catchments.…”