Quantifying Watershed Export in the Arctic: Challenges and Rewards of Capturing Highly Variable River Water Chemistry over Time and Space

Accurate estimates of watershed export via arctic rivers are important for global biogeochemical budgets as well as improved understanding of local processes in the Arctic Ocean. Furthermore, constraining these estimates is an important prerequisite for detecting changes in export that provide watershed-integrated information about land processes such as permafrost thaw. While quantification of export via rivers can be difficult anywhere, extreme seasonality and remoteness of field sites present unique challenges to scientists working in the Arctic. This presentation will address insight gained while implementing and maintaining a pan-arctic sampling program for river water chemistry, started as the PARTNERS project in 2002 and continuing as the Arctic–Great Rivers Observatory (Arctic–GRO). The sampling program focuses on export of dissolved and particulate material from the six largest rivers draining the pan-arctic watershed (Yenisey, Ob', Lena, Kolyma, Mackenzie, Yukon). Seasonally-explicit sampling has captured wide variations in constituent concentrations and resulted in significant changes in export estimates relative to historical estimates. For example, estimates of dissolved organic carbon (DOC) export have been revised upward to account for major increases in DOC concentrations during the spring freshet. Nonetheless, capturing the spring freshet has been a challenge. Peak flow occurs over a relatively short timeframe, and having a field crew on site at the right time requires either rapid mobilization or an extended stay that brackets the potential freshet period. Furthermore, ice break-up limits access during onset of the freshet and water chemistry changes rapidly with increasing discharge. High resolution sampling during this dynamic period has the potential to improve export estimates significantly beyond our current estimates. We will explore novel approaches for achieving major advances in our ability to accurately measure and model constituent fluxes in major arctic rivers.