Preprints
https://doi.org/10.5194/egusphere-2024-2645
https://doi.org/10.5194/egusphere-2024-2645
18 Sep 2024
 | 18 Sep 2024
Status: this preprint is open for discussion.

The role of catchment characteristics, discharge, and active layer thaw on seasonal stream chemistry across ten permafrost catchments

Arsh Grewal, Erin M. Nicholls, and Sean K. Carey

Abstract. High latitude catchments are rapidly warming, leading to altered precipitation regimes, widespread permafrost degradation and observed shifts in stream chemistry for major arctic rivers. At headwater scales, stream discharge and chemistry are seasonally variable, and the relative influence of catchment characteristics, climate and active layer thaw on this seasonality has been poorly addressed. To provide new insight into mechanisms driving changes in streamflow chemistry within permafrost watersheds, we measured discharge and sampled major ion and dissolved organic carbon (DOC) concentrations across ten permafrost catchments in Yukon Territory, Canada. We incorporated concentration-discharge relationships within generalized additive models to resolve the distinct influence of discharge and seasonal active layer thaw on stream chemistry and identify the role of watershed characteristics on the magnitude and seasonality of solute concentrations. After accounting for seasonal variations in discharge, results indicate both major ions and DOC were highly seasonal across all catchments, with DOC declining and major ion concentration increasing post freshet. Seasonal variability in major ion concentrations were primarily driven by active layer thaw, whereas DOC seasonality was strongly controlled by flushing of soil organic carbon during freshet. While major ion concentrations were geologically mediated, greater permafrost extent led to enhanced seasonality in major ion concentrations. Catchments with strong topographical gradients and thinner organic soils had higher specific discharge, lower DOC concentrations but greater relative seasonality. Our results highlight the important role catchment characteristics play on shaping both the seasonal variations and magnitude of solute concentrations in permafrost underlain watersheds.

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Arsh Grewal, Erin M. Nicholls, and Sean K. Carey

Status: open (until 31 Dec 2024)

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  • RC1: 'Comment on egusphere-2024-2645', Anonymous Referee #1, 16 Oct 2024 reply
Arsh Grewal, Erin M. Nicholls, and Sean K. Carey
Arsh Grewal, Erin M. Nicholls, and Sean K. Carey

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Short summary
Stream chemistry in permafrost watersheds is highly seasonal. This variability can be driven by the seasonal thawing of the active layer (the layer of soil above the permafrost that thaws each year) or by streamflow (streamflow is typically highest during snowmelt). In this paper, we disentangle the influence of active layer thaw and streamflow on the seasonality of stream chemistry. We found that topography and the extent of permafrost are key factors controlling the degree of this seasonality.