Stream Chemistry Indicates Catchment Response to Disturbance and Regional Warming in the Boreal Forest
Abstract
Fire can alter exports of carbon (C) and nutrients from catchments by reducing capacity for nutrient retention by vegetation and combusting soil organic layers. In regions underlain by permafrost, fire additionally thaws permafrost, potentially increasing the depths of flowpaths draining catchments, and concomitantly the contributions of ions derived from mineral soils. Thus, stream chemistry might serve as an indicator of catchments' ability to recover from fire. As fire frequency and intensity are increasing in high latitude ecosystems, quantifying catchments' ability to recover from fire is critical to understand long-term consequences for carbon storage, nutrient exports, and permafrost stability. A spatially extensive survey of more than 50 streams draining boreal forest in Interior Alaska revealed that dissolved organic C concentration declined 200 μM, on average, in extensively burned compared to unburned catchments. Though previous research in the boreal forest and other regions has highlighted increased concentration of nitrate in individual streams following fire, we found that catchment attributes such as slope superseded the influence of fire on stream nitrogen export at a broad spatial extent. Repeated observations of a subset of the sampled streams over 17 years indicated a significant increase in specific conductivity of stream water (~75 μS cm -1 ). We attribute this effect to increased contribution of ions derived from mineral soils and hypothesize that regional permafrost thaw is rerouting catchment flowpaths through deeper soils. Thus, co-occurring changes in the fire and thermal regimes of the boreal forest are expected to result in changes to stream chemistry, including declining dissolved organic C concentration and increasing conductivity, providing spatially integrative indicators of ecosystem response to disturbance.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.B23H2518C
- Keywords:
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- 0414 Biogeochemical cycles;
- processes;
- and modeling;
- BIOGEOSCIENCES;
- 0428 Carbon cycling;
- BIOGEOSCIENCES;
- 0439 Ecosystems;
- structure and dynamics;
- BIOGEOSCIENCES;
- 0475 Permafrost;
- cryosphere;
- and high-latitude processes;
- BIOGEOSCIENCES