How Arctic rivers respond to hydrological disturbances

To further our understanding of how climate change is altering hydrological processes and the functioning of Arctic ecosystems, we measure carbon and nitrogen concentrations to assess changes after seasonal disturbance events.

The Arctic is one of the first regions to experience the impacts of climate change and is already experiencing rapid changes to the water cycle, seasonality, and permafrost state. These changes can be expressed in the chemistry observed in a river network, and ecosystem-scale responses to change are integrated at a watershed outlet. With this study, we leveraged 5 years of high-frequency data collected from two Arctic headwaters to observe how these watersheds respond to hydrologic disturbance. Overall, we found that at the event-scale, Arctic rivers are responsive to precipitation events, where carbon (C) increases and reactive nitrogen (N) as nitrate (NO₃−), is diluted in tandem when a storm event occurs. We also found that after the peak of the storm event, there is a difference in recovery rates for C and N that indicate storm events represent a hydrologic and biogeochemical disturbance. Overall, our findings are important for documenting hydrologic responses to a changing Arctic.

Hydrology Controls Dissolved Organic Carbon and Nitrogen Export and Post-Storm Recovery in Two Arctic Headwaters

Abstract

Climate change is rapidly altering hydrological processes and consequently the structure and functioning of Arctic ecosystems. Predicting how these alterations will shape biogeochemical responses in rivers remains a major challenge. We measured [C]arbon and [N]itrogen concentrations continuously from two Arctic watersheds capturing a wide range of flow conditions to assess understudied event-scale C and N concentration-discharge (C-Q) behavior and post-event recovery of stoichiometric conditions. The watersheds represent low-gradient, tundra landscapes typical of the eastern Brooks Range on the North Slope of Alaska and are part of the Arctic Long-Term Ecological Research sites: the Kuparuk River and Oksrukuyik Creek. In both watersheds, we deployed high-frequency optical sensors to measure dissolved organic carbon (DOC), nitrate (NO₃−), and total dissolved nitrogen (TDN) for five consecutive thaw seasons (2017–2021). Our analyses revealed a lag in DOC:NO3− stoichiometric recovery after a hydrologic perturbation: while DOC was consistently elevated after high flows, NO₃− diluted during rainfall events and consequently, recovery in post-event concentration was delayed. Conversely, the co-enrichment of TDN at high flows, even in watersheds with relatively high N-demand, represents a potential “leak” of hydrologically available organic N to downstream ecosystems. Our use of high-frequency, long-term optical sensors provides an improved method to estimate carbon and nutrient budgets and stoichiometric recovery behavior across event and seasonal timescales, enabling new insights and conceptualizations of a changing Arctic, such as assessing ecosystem disturbance and recovery across multiple timescales.

Shogren, A. J., J. P. Zarnetske, B. W. Abbott, A. L. Grose, A. F. Rec, J. Nipko, C. Song, J. A. O'Donnell, and W. B. Bowden. 2024. Hydrology controls dissolved organic carbon and nitrogen export and post-storm recovery in two Arctic headwaters. HGR Biogenosciences 129(2): e2023JG007583.