Assessing inter-annual and seasonal patterns of DOC and DOM quality across a complex alpine watershed underlain by discontinuous permafrost in Yukon, Canada

Abstract

Abstract. High-latitude environments store approximately half of the global organic carbon pool in peatlands, organic soils and permafrost, while large Arctic rivers convey an estimated 18–50 Tg C a−1 to the Arctic Ocean. Warming trends associated with climate change affect dissolved organic carbon (DOC) export from terrestrial to riverine environments. However, there is limited consensus as to whether exports will increase or decrease due to complex interactions between climate, soils, vegetation, and associated production, mobilization and transport processes. A large body of research has focused on large river system DOC and dissolved organic matter (DOM) lability and observed trends conserved across years, whereas investigation at smaller watershed scales show that thermokarst and fire have a transient impact on hydrologically mediated solute transport. This study, located in the Wolf Creek Research Basin situated ∼20 km south of Whitehorse, YT, Canada, utilizes a nested design to assess seasonal and annual patterns of DOC and DOM composition across diverse landscape types (headwater, wetland and lake) and watershed scales. Peak DOC concentration and export occurred during freshet, as is the case in most northern watersheds; however, peaks were lower than a decade ago at the headwater site Granger Creek. DOM composition was most variable during freshet with high A254 and SUVA254 and low FI and BIX. DOM composition was relatively insensitive to flow variation during summer and fall. The influence of increasing watershed scale and downstream mixing of landscape contributions was an overall dampening of DOC concentrations and optical indices with increasing groundwater contribution. Forecasted vegetation shifts, enhanced permafrost and seasonal thaw, earlier snowmelt, increased rainfall and other projected climate-driven changes will alter DOM sources and transport pathways. The results from this study support a projected shift from predominantly organic soils (high aromaticity and less fresh) to decomposing vegetation (more fresh and lower aromaticity). These changes may also facilitate flow and transport via deeper flow pathways and enhance groundwater contributions to runoff.

Storm‐Scale and Seasonal Dynamics of Carbon Export From a Nested Subarctic Watershed Underlain by Permafrost

“…10.1029/2021JG006268 10 of 15 ( Godsey et al, 2009;Shogren et al, 2021). Clockwise hysteresis was observed in all events and is common in boreal environments especially during the spring freshet, where mobile pools of DOM exist near the stream and can be flushed at the onset of melt or storms (Ågren et al, 2007;Carey, 2003;Prokushkin et al, 2007;Shatilla & Carey, 2019). WTC shows a significant decrease in the fDOM-Q slope over the course of the summer (Figure 6), approaching chemostasis by autumn.…”

Structural Characterization of Dissolved Organic Matter in Permafrost Peatland Lakes

“…BIX and β:α displayed a similar trend in all samples since both indices are related to the proportion of recently produced DOM (β:α)/autotrophic productivity (BIX) [32,35] to older and more terrestrial DOM [36]. The values obtained suggest SAS 1A samples and SAS 2A B had more recently produced DOM (likely resulting from microbial activity) than SAS 2A S and SAS 1B M. The BIX and β:α values of SAS 1A were greater at the surface than at the bottom, possibly arising from the surface leaching of labile organic matter from emergent macrophytes that proliferate in the surrounding environments during the warm season, as revealed in automated camera images from this site throughout the year [16,37].…”

Characterization of contrasting flow and thermal regimes in two adjacent subarctic alpine headwaters in Northwest Canada

“…Seasonal response was typical of alpine catchments dominated by permafrost at high latitudes, with the wettest period in late-spring/early-summer when most snowmelt occurs (Yang, Marsh, & Ge, 2014;Ye, Yang, Zhang, & Kane, 2009). Note that these observations occurred post-freshet when the streams were ice-free and full seasonal flows are reported in Shatilla and Carey (2019).…”

“…However, predictions at a local scale are highly variable (both in space and time), and thus difficult to quantify with confidence (Bates, Kundzewicz, Wu, & Palutikof, 2008;Debeer et al, 2016). Furthermore, in alpine permafrost catchments, the increase in precipitation can hardly compensate the effect of an early snowmelt (Huntington & Niswonger, 2012), although in some recent years the importance of rainfall events to sustain late summer flow both in GC and BB has increased (Shatilla & Carey, 2019).…”