Impact of Wildfire on Stream Nutrient Chemistry and Ecosystem Metabolism in Boreal Forest Catchments of Interior Alaska

Abstract

With climatic warming, wildfire occurrence is increasing in the boreal forest of interior Alaska. Loss of catchment vegetation during fire can impact streams directly through altered solute and debris inputs and changed light and temperature regimes. Over longer time scales, fire can accelerate permafrost degradation, altering catchment hydrology and stream nutrient dynamics. In 2004, the 217,000 ha Boundary Fire burned 65% of an established study site in the Caribou-Poker Creeks Research Watershed. We used this opportunity to investigate the impact of wildfire on stream chemistry and metabolism in boreal forest catchments. Wildfire impacts on chemistry were evaluated by examining solute chemistry in four catchments from 2002 to 2007. Ecosystem metabolism was measured over the summer of 2005 in one burned and two unburned catchments. Wildfire led to stream nitrate concentration increasing up to threefold, whereas dissolved organic carbon (DOC) and dissolved organic nitrogen concentrations decreased post-fire. Average stream gross primary production in the burned catchment was double that of the unburned sites (2.4 and 1.2 g 02 m-2 day-1, respectively). Respiration rate was also elevated in the burned stream (6.6 g 02 m~2 day-1) compared with the control streams (1.2 and 4.5 g 02 m-2 day-1). Climatic warming has the potential to impact boreal forest streams through permafrost thaw and increased fire frequency, leading to altered solute inputs and production and respiration rates.