Title:

Arctic stream resiliency and nutrient uptake dynamics across a wildfire chronosequence

Fire return intervals in Arctic Boreal forest are shortening causing an increase in the number of fires. These fires lead to changes in stream chemistry such as increases in NO3 and declines in DOC and DON for boreal forest on continuous permafrost. These increases in NO3 last for about 10 years while declines in DOM remain for over 50 years. Even though the resiliency of stream chemistry has been determined, the response to in nutrient processing and exports of these fluvial systems is unknown. We have conducted a series of NO3 and NH4 nutrient pulse additions across 4 streams ranging between 3 to >100 years since the last burn, in the Central Siberian Plateau, dominated by Larch forest on continuous permafrost. Uptake velocities were determined from these pulse additions and were observed across the burn gradient. Generally, NH4 uptake was greater than NO3 in intermediate burn sites but NO3 uptake/demand was greater in recent and older burn sites but uptake for both peaked in the intermediate burn sites. Uptake across the burn gradient suggest that recently burned sites can be net exporters of NO3, intermediate burn sites have a greater demand for inorganic N, but old burn sites demonstrate little uptake with a more mature forest.

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