Understanding ecohydrological pathways in an Arctic Finland watershed: Continuous in-situ stream water, vapor, and precipitation isotope (δ18O, δ2H) measurements.

Understanding the changing Arctic water cycle has new urgency as sea ice, moisturesources, and precipitation patterns are rapidly shifting due to climate change. InJuly 2018, we installed a Picarro Continuous Water Sampler and isotopic analyzerto a second-order stream in Pallas-Yllästunturi National Park, Finland. This newintegrated system enables us to continuously measure the stable isotope geochemistry(δ18O and δ2H) of stream water in-situ with exceptionally high-frequency (10/min)allowing us to reveal patterns and processes previously out of reach with standardcampaign sampling. Coupling these data with standard measurements of streamwater discharge, temperature, DOC and pH, as well as event-based precipitation andcontinuous real-time water vapor isotope measurements places watershed and regionalisotope hydrology into a new realm of understanding. Initial results indicate thatduring the prolonged mid-summer 2018 drought, mean stream water δ18O andδ2H values were -14 ± 1 ‰ and -99 ± 2 ‰ respectively. These values reflectthe fundamental recharge of the basin being mostly driven by snow melt water(typical snow δ18O ∼ -17 ‰). Our baseline drought measurements allow us topartition and quantify hydrologic threshold for enrichment of stream water isotopes asprecipitation was detected in the system later in fall 2018, and further for depletion asisotope values decreased when moving towards winter. Continuous high-frequencymeasurements of stream isotope geochemistry will provide insight into how water ismobilized in the catchment on different seasons and an assessment of how futurechanges in precipitation patterns and seasonality of flow regimes will affect Arcticwatersheds. These data will further allow more accurate hydrograph separation andprovide the basis to investigate changing watershed scale ecohydrological pathwaysthrough seasons, including in-stream biogeochemical and biological processes. [ABSTRACT FROM AUTHOR]