Turnover and Retention of Nitrogen in an Arctic Watershed: Links to Organic Matter Accumulation and Response to Climate

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Over the past quarter-century, many studies have shown that the characteristics of tundra nitrogen cycles play a major role in controlling the response of tundra carbon cycles to climate change and disturbance. This research will determine how the characteristics of nitrogen cycling influence carbon accumulation and loss at 1- to 10-year time scales in an arctic Alaska watershed. The PIs will (1) measure N inputs and outputs such as atmospheric deposition, fixation, and losses in streams, (2) perform a 15N -labeling experiment to identify major N sinks, quantify their turnover rates, and trace downslope N fluxes, and (3) model C-N interactions, focusing on N limitation as a constraint on change in the C cycle. The investigators intend to use the models that are developed to compare C-N interactions in arctic tundra with other ecosystem types. The research is important because nitrogen is a key regulator of carbon cycling in most terrestrial ecosystems, including arctic tundras, but relatively little work on C-N interactions has been done at the watershed scale. Understanding C-N interactions is key to understanding long-term responses of ecosystems to climate change. Turnover and retention of nitrogen in watersheds are also key ecosystem services in a world where the annual nitrogen turnover rate has doubled globally due to human activity.