Xiwei Guo (Penn State University, United States); Nynaeve Phillipson (Penn State University, United States); Ben Crosby (Idaho State University, United States)

Rising temperatures are drastically impacting Arctic river dynamics; yet for many of these rivers, we lack a good baseline to understand their current hydrology. Information about sediment fluxes is even more stark and almost entirely missing from most Arctic rivers. Understanding the timing and controls on river discharge, suspended sediment transport and changes in river turbidity is important both for impacts to marine ecosystems and locally to the people who depend on the river for food and water resources. This project aims to fill these knowledge gaps by quantifying variability in river discharge, suspended sediment transport, and turbidity on the ungauged Noatak River in Alaska. This project integrates field measurements with multiple satellite-based observations to achieve three goals: (1) provide measurements of river discharge timed with SWOT satellite overpasses to reduce uncertainty in SWOT discharge estimates on an ungauged river; (2) quantify monthly, seasonal, and annual variability in river discharge, suspended sediment flux, and turbidity and their interrelationships; and (3) estimate seasonal and annual suspended sediment fluxes and associated changes in turbidity for the Noatak River.

In the first two years of this project, we have been collecting field measurements of river discharge, suspended sediment concentrations (SSC), and turbidity over the open water season. River discharge has been collected coincident with multiple SWOT overpasses and shared on HydroShare for incorporation into Confluence to support discharge estimates from SWOT data. In addition to our field measurements, we have prioritized investigating seasonality of river turbidity from remotely sensed data, utilizing daily imagery from Planet to quantify turbidity for all available cloud-free days over the Planet record. We examined various metrics of remotely sensed turbidity so that we can determine which metric best characterizes actual turbidity and suspended sediment concentration in the Noatak. Preliminary results show that turbidity is consistently highest in May, coinciding with the spring melt season. Turbidity in summer and fall is temporally and spatially variable, with lowest values typically occurring in September-October, but short-term increases occurring sporadically, likely following rain events. Our first field season coincided with a summer rainstorm, allowing us to directly observe changes in discharge, turbidity, and suspended sediment transport over short timescales. These types of observations, combined with river discharge estimates from SWOT, will enable us to explore the variability of Arctic river fluxes over event-based, seasonal, and annual timescales. Understanding the variability in discharge, turbidity, and SSC, and in their interrelationships, will provide critical insights as to processes affecting Arctic river discharge, sediment supply, and sediment transport in these rapidly changing systems.