As a result of global climate change, the Arctic region is warming at twice the rate of the rest of the planet, releasing terrestrially stored carbon and nutrients that were previously frozen in permafrost soils. As the Arctic continues to experience permafrost degradation, as well as shifts in the timing, magnitude, and duration of precipitation extremes and the restructuring of terrestrial vegetation communities, it is predicted that the transport of carbon and nutrients from land to water will increase. The enhanced release of nutrients and carbon from land to water is already evidenced by increasing fluxes of biogeochemical solutes at the outlets of most large Arctic rivers. To better understand the fate of hydrologically mediated carbon and nutrient mobilization and transformations in Arctic landscapes, attention has recently turned to monitoring spatial and temporal patterns of biogeochemistry in intermediate-scale watersheds (<200 km2). However, within these same watersheds, there is emerging indirect evidence that “stream-lake interactions”, the interruption of streamflow by lakes that are nested within a river network, can modify or confound the biogeochemical signals that are observed at river outlets. Here, I conducted two studies that directly explore how stream-lake interactions alter spatial and temporal biogeochemical signals in two permafrost-dominated headwater river networks located on the North Slope of Alaska. First, I analyzed water chemistry from repeated “synoptic” sampling campaigns that occurred in June and August over three years (2016-2018) in the Oksrukuyik Creek watershed. This data includes a suite of biologically reactive solutes (dissolved carbon, nitrogen, and phosphorus species), and numerous other geogenic solutes (SO42-, Si, Ca, Cl, Na, Ba, and Fe). To better understand the role of lake residence time in altering stream solute chemistry, I analyzed data from three distinct subcatchments within the Oksrukuyik watershed: those with no lake presence, intermediate lake presence, and a lake-dominated system. Second, I investigated the role of high-flow events on upstream to downstream biogeochemical signals in a single Arctic lake (Lake I8) during the 2019 thaw season. I used data from novel high-frequency, in-situ water quality sensors installed at the stream inflow and outflow of the lake. These two studies found evidence that stream-lake interactions do alter biogeochemical signals, and specifically that: 1) lake residence time will determine the capacity for a lake to process nutrients and carbon, where lakes with higher residence time will have greater effects and 2) that the ability for the lake to retain and process inputs from storm events will be greatest in the late thaw season. Together, these studies indicate that stream-lake interactions can modulate biogeochemical conditions, including solute fluxes, through Arctic river networks. Hence, incorporating steam-lake interactions into future landscape biogeochemical studies of Arctic regions with lakes presents an opportunity to advance Arctic system science.
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