Date of Award

5-17-2024

Document Type

Thesis

Abstract

Wildfires are becoming more severe, frequent, and intense in the boreal forest, which has large repercussions for ecosystem processes, such as carbon and nutrient cycling. Combustion of terrestrial soils and biomass can propagate to influence streams, including increased nutrient inputs, flashier discharge, and changes to the light regime. Due to a warming climate, fire regimes are changing in concert with precipitation regimes, including more frequent and larger storms, which can scour primary producers and remove poorly attached detritus. Changing physicochemical attributes of streams resulting from fire and precipitation could influence metabolic processes that in turn influence carbon (C) storage and flux to the atmosphere. I modeled rates of gross primary production (GPP) and ecosystem respiration (ER) during the ice-free period in nine boreal streams of Interior Alaska that drained watersheds varying in fire history and across up to four years that varied in timing and magnitude of precipitation. Gross primary production and ER increased with watershed size. Average rates of GPP and ER were greater in streams of unburned compared to burned watersheds while controlling for watershed size. Streams were typically heterotrophic and net ecosystem production (NEP, GPP - ∎ER∎) was greater in burned than in unburned watersheds. GPP was correlated with physicochemical attributes including water temperature, whereas ER was unrelated to measured attributes of streams. Temporal patterns in GPP were explained by precipitation at seasonal and daily timescales, with reduced cumulative GPP in the year of greatest cumulative precipitation. Gross primary production declined and remained low following storms that occurred in late summer, but returned to pre-storm rates when storms occurred earlier in the open-water season. Increases in frequency of wildfire are expected to decrease the contribution of aquatic metabolism to CO₂ emissions from streams of the boreal forest due to higher rates of NEP, whereas increased precipitation will likely increase C emissions by suppressing GPP.

Handle

http://hdl.handle.net/11122/15125

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