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\norganic carbon pool in peatlands, organic soils and permafrost, while large\nArctic rivers convey an estimated 18–50\u2009Tg\u2009C\u2009a −1 to the Arctic Ocean.\nWarming trends associated with climate change affect dissolved organic\ncarbon (DOC) export from terrestrial to riverine environments. However,\nthere is limited consensus as to whether exports will increase or decrease\ndue to complex interactions between climate, soils, vegetation, and\nassociated production, mobilization and transport processes. A large body of\nresearch has focused on large river system DOC and dissolved organic matter (DOM) lability and observed\ntrends conserved across years, whereas investigation at smaller watershed\nscales show that thermokarst and fire have a transient impact on\nhydrologically mediated solute transport. This study, located in the Wolf\nCreek Research Basin situated ∼20 \u2009km south of Whitehorse, YT,\nCanada, utilizes a nested design to assess seasonal and annual patterns of\nDOC and DOM composition across diverse landscape types (headwater, wetland and lake) and watershed scales. Peak DOC concentration and export occurred\nduring freshet, as is the case in most northern watersheds; however, peaks were lower than\na decade ago at the headwater site Granger Creek. DOM composition was most\nvariable during freshet with high A254 and SUVA 254 and low FI and BIX. DOM\ncomposition was relatively insensitive to flow variation during summer and\nfall. The influence of increasing watershed scale and downstream mixing of\nlandscape contributions was an overall dampening of DOC concentrations and\noptical indices with increasing groundwater contribution. Forecasted\nvegetation shifts, enhanced permafrost and seasonal thaw, earlier snowmelt,\nincreased rainfall and other projected climate-driven changes will alter DOM\nsources and transport pathways. The results from this study support a projected shift from\npredominantly organic soils (high aromaticity and less fresh) to decomposing\nvegetation (more fresh and lower aromaticity). These changes may also\nfacilitate flow and transport via deeper flow pathways and enhance\ngroundwater contributions to runoff.