Evaluating the role of large-scale fires on nutrient uptake in Arctic streams underlain with permafrost

Abstract:

In the Siberian Arctic thawing permafrost soils can mobilize solutes as they are transported from soils to streams, and nutrients such as N and P may be rapidly transformed or stored within streams before they are exported to the Arctic Ocean. With climate change an increased frequency of wildfire is also expected, and these extreme events will further impact solute concentrations and the composition of dissolved organic matter entering streams. Our research objective was to determine how fire affects in-stream nutrient uptake in the central Siberian Arctic. We used two approaches to address this question 1) a before after control impact (BACI) design and 2) a fire gradient. We measured in-stream uptake of ammonium (NH₄⁺-N) and phosphate (PO₄^3-) twice in the summer of 2016 across three boreal headwater streams including sites that burned 3, 23, and more than 100 years ago. To determine in-stream uptake we used the Tracer Additions for Spiraling Curve Characterization (TASCC) method with combined additions of NH₄⁺ and PO₄^3-. Previous measurements were taken prior to the 2013 fire at the 3 (previously > 100 year since burn) and 23 years since burn sites. Preliminary data suggest that among N, P, and C species the primary changes in background chemistry were a decrease in dissolved organic carbon and dissolved organic nitrogen at the most recently burned site. By using a robust BACI study design combined with a fire gradient the results from this study will aid in our understanding of nutrient export from Arctic soils as extreme events (fires) become more frequent and permafrost soils thaw.

Site name	Year(s) Burned	2013 NH4 and PO4 uptake measured?	2016 NH4 and PO4 uptake measured?
N9	1993	Yes (control across years)	Yes (control across years)
N11	2013, previously >100 y	Yes (BEFORE; >100 y since burn)	Yes (AFTER; 3 years since burn)
N20	>100 y	No	Yes (>100 y control)