Evaluating the hydrological and hydrochemical responses of a High Arctic catchment during an exceptionally warm summer

Abstract

The Arctic has experienced substantial warming during the past century with models projecting continued warming accompanied by increases in summer precipitation for most regions. A key impact of increasing air surface temperatures is the deepening of the active layer, which is expected to alter hydrological processes and pathways. The aim of this study was to determine how one of the warmest and wettest summers in the past decade at a High Arctic watershed impacted water infiltration and storage in deeply thawed soil and solute concentrations in stream runoff during the thaw period. In June and July 2012 at the Cape Bounty Watershed Observatory, we combined active layer measurements with major ion concentrations and stable isotopes in surface waters to characterize the movement of different runoff sources: snowmelt, rainfall, and soil water. Results indicate that deep ground thaw enhanced the storage of infiltrated water following rainfall. Soil water from infiltrated rainfall flowed through the thawed transient layer and upper permafrost, which likely solubilized ions previously stored at depth. Subsequent rainfall events acted as a hydrological flushing mechanism, mobilizing solutes from the subsurface to the surface. This solute flushing substantially increased ion concentrations in stream runoff throughout mid to late July. Results further suggest the importance of rainfall and soil water as sources of runoff in a High Arctic catchment during mid to late summer as infiltrated snowmelt is drained from soil following baseflow. Although there was some evaporation of surface water, our study indicates that flushing from solute stores in the transient layer was the primary driver of increased ion concentrations in stream runoff and not evaporative concentration of surface water. With warmer and wetter summers projected for the Arctic, ion concentrations in runoff (especially in the late thaw season), will likely increase due to the deep storage and subsurface flow of infiltrated water and subsequent flushing of previously frozen solutes to the surface.

Li and U Isotopes as a Potential Tool for Monitoring Active Layer Deepening in Permafrost Dominated Catchments

“…The lower relative proportion of the "long-residence time" end-member (Figure 4), lower ionic strength, lower ( 234 U/ 238 U) ratios and negligible seasonal variation observed in the glaciated catchment ( Figures 2B, 3A) can be explained by the layer of dead ice underneath the sandur (glacial outwash plain, Figure 1, Ziaja and Pipała, 2007), which restricts water to the surface and limits water residence time (Figure 5). A similar "blocking" effect was observed in a Canadian high Arctic catchment where ground ice and ice-rich soil prevented active layer deepening and resulted in lower than expected solute fluxes (Lamhonwah et al, 2017).…”

“…At this point further increases in residence time have only a minor impact on chemical concentrations (Maher, 2011). Freezing will also concentrate solutes and thereby increase ionic strength, but as these pockets of water are unlikely to contribute to the stream chemistry until they are flushed out during spring thaw (Kokelj and Burn, 2005;Lamhonwah et al, 2017;Lehn et al, 2017), they can also be considered to have a long residence time. Consistent with the reactive transport model predictions for dilute waters (Maher, 2011), we observe a positive correlation between ionic strength and ( 234 U/ 238 U) ( Figure 3A).…”

“…Similarly, a decrease in the radiogenic strontium isotopic composition of a stream in Alaska was attributed to an increase in the weathering of carbonate minerals exposed as a result of active-layer deepening (Keller et al, 2010). Other studies have pointed to the role of flushing during spring melt, which removes previously frozen solutes that became concentrated due to solute exclusion during freezing, contributing to seasonal variations (Kokelj and Burn, 2005;Lamhonwah et al, 2017;Lehn et al, 2017). Trace metal concentrations (Barker et al, 2014) and several metal isotope systems (Sr, U, Ca, Mg, Si, Keller et al, 2010;Bagard et al, 2011Bagard et al, , 2013Pokrovsky et al, 2013;Mavromatis et al, 2016;Lehn et al, 2017) have also been used as tracers of chemical weathering during the seasonal cycle of active-layer thaw and re-freeze.…”

Hillslope water tracks in the High Arctic: Seasonal flow dynamics with changing water sources in preferential flow paths

“…Ground ice is usually not identified as an important contributor to streamflow in polar desert (Woo & Steer, ). However, late‐season ionic enrichment of streamflow has been measured and attributed to ground ice melt in at least one other High Arctic locations (Lamhonwah, Lafrenière, Lamoureux, & Wolfe, ). In addition, similar late‐season seeps in the McMurdo Dry Valleys, Antarctica, had also been attributed to the melt of ground ice, which was initially formed during snowmelt periods in colder years (Harris, Carey, Lyons, Welch, & Fountain, ).…”

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

“…This makes environmental tracers, particularly stable isotopes, potentially useful tools for hydrological monitoring. Tracers provide integrated insight into the hydrological functioning of catchments and have been used previously to assess water sources and flow paths in Arctic and permafrost settings (Ala‐aho, Soulsby, et al, ; Blaen, Hannah, Brown, & Milner, ; Lamhonwah, Lafrenière, Lamoureux, & Wolfe, ; Obradovic & Sklash, ; Song et al, ; Yi et al, ). In addition to their capacity to quantify water provenance, flow paths, and transit times, tracer studies provide insights for calibration and testing more detailed conceptual and numerical models at different spatial scales (Ala‐aho, Tetzlaff, McNamara, Laudon, & Soulsby, ; Birkel, Soulsby, & Tetzlaff, ; Soulsby et al, ; Stadnyk, Delavau, Kouwen, & Edwards, ; van Huijgevoort, Tetzlaff, Sutanudjaja, & Soulsby, ).…”