Arctic concentration–discharge relationships for dissolved organic carbon and nitrate vary with landscape and season

Abstract

Climate change is intensifying the Arctic hydrologic cycle, potentially accelerating the release of carbon and nutrients from permafrost landscapes to rivers. However, there are limited riverine flow and solute data of adequate frequency and duration to test how seasonality and catchment landscape characteristics influence production and transport of carbon and nutrients in Arctic river networks. We measured high frequency hydrochemical dynamics at the outlets of three headwater catchments in Arctic Alaska over 3 years. The catchments represent common Arctic landscapes: low‐gradient tundra, low‐gradient and lake‐influenced tundra, and high‐gradient alpine tundra. Using in‐situ spectrophotometers, we measured dissolved organic carbon (DOC) and nitrate (NO3−) concentrations at 15‐min intervals through the flow seasons of 2017, 2018, and 2019. These high‐frequency data allowed us to quantify concentration–discharge (C‐Q) responses during individual storm events across the flow season. Differences in C‐Q responses among catchments indicated strong landscape and seasonal controls on lateral DOC and NO3− flux. For the two low‐gradient tundra catchments, we observed consistent DOC enrichment (transport‐limitation) and NO3− dilution (source‐limitation) during flow events. Conversely, we found consistent NO3− enrichment and DOC dilution in the high‐gradient alpine catchment. Our analysis revealed how high flow events may contribute disproportionately to downstream export in these Arctic streams. Because the duration of the flow season is expected to lengthen and the intensity of Arctic storms are expected to increase, understanding how discharge and solute concentration are coupled is crucial to understanding carbon and nutrient dynamics in rapidly changing permafrost ecosystems.

Multi-year, spatially extensive, watershed scale synoptic stream chemistry and water quality conditions for six permafrost-underlain Arctic watersheds

“…Generally high concentration variability in smaller headwaters, which converges to mean watershed behaviour towards the catchment outlet holds with the conceptualizations of large rivers as "chemostats" (Creed et al, 2015 watershed Trevor Creek, has relatively low DOC and high NO3concentrations, likely due to shorter and faster hydrologic flowpaths and lower terrestrial biomass (Shogren et al, 2019). Overall, these findings are consistent with studies that indicate that slower, longer flowpaths and productive terrestrial vegetation control carbon and nutrient transfer and mobilization in lower-gradient tundra watersheds (Shogren et al, 2019(Shogren et al, , 2021). If we assume that spatial variability in stream network water chemistry depends primarily on the extent and connectivity of upstream sources/sinks, then the patches sizes that control solute fluxes can be assessed by the spatial scale of the variance collapse (Abbott et al, 2018;Shogren et al, 2019).…”

“…behaviour, the watershed and season-dependent directionality of net leverage patterns are congruent with emerging evidence that landscape template exerts strong control on biogeochemical signals in Arctic rivers (Vonk et al, 2019;Tank et al, 2020;Shogren et al, 2021).…”

“…Indeed, using sampling and monitoring approaches that capture the watershed outlet response over time has logistic and safety advantages for site access. Further, the recent application of novel sensor technology has enabled high-frequency watershed-scale studies (Shogren et al, 2021). For example, the paired high-frequency flow and a limited set of chemical properties for the watersheds in this data paper are available at the Arctic Data Center (Zarnetske et al, 2020b, c, a).…”

“…For example, the paired high-frequency flow and a limited set of chemical properties for the watersheds in this data paper are available at the Arctic Data Center (Zarnetske et al, 2020b, c, a). While these riverine measurements are inherently valuable from remote regions (Laudon et al, 2017;Shogren et al, 2021), there are still challenges related to using watershed-scale measurements to diagnose primary drivers of solute export (Burns et al, 2019).…”

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).…”