Permafrost and wildlife influences on stream nutrient dynamics and metabolism in boreal forest watersheds of Interior Alaska

Abstract

In the boreal forest of interior Alaska, both permafrost and wildfire impact stream solute concentrations, but their effect on stream function is unknown. This research focused on the effects of wildfire and permafrost on stream nutrient dynamics and metabolism in the Caribou Poker Creeks Research Watershed (CPCRW) in interior Alaska. Wildfire impact on chemistry was determined through comparison of pre- and post-fire stream chemistry in a control and a burned watershed. We predicted that increased nutrient and decreased dissolved organic carbon (DOC) delivery to streams after fire would stimulate gross primary productivity (GPP) and reduce ecosystem respiration in burned watersheds. Fire resulted in higher stream nitrate, sulfate, and cation concentrations, and lower DOC concentration, at the burned site than at the control site. Streams draining burned watersheds had higher summer GPP (2.4 gO₂ m⁻² day⁻¹) than the unburned sites (1.2 gO₂ m⁻² day⁻¹). Respiration was also higher in burned than unburned watersheds (3.9 and 3.0 gO₂ m⁻² day⁻¹, respectively). Metabolism was not correlated with the increased nutrient concentrations observed after fire. Instead, we suggest GPP was stimulated through increased soluble reactive phosphorus availability after fire, whereas respiration was likely controlled by pre-existing differences in stream physical or chemical characteristics.