Year of Award
2026
Document Type
Thesis
Degree Type
Master of Science (MS)
Degree Name
Systems Ecology
Department or School/College
W.A. Franke College of Forestry & Conservation
Committee Chair
Ashley Ballantyne
Commitee Members
Robert O. Hall, Jr., Benjamin Colman, Jessica Corman
Keywords
lakes, wildfire, nutrients, net ecosystem production, Rocky Mountains
Subject Categories
Terrestrial and Aquatic Ecology
Abstract
Wildfires are increasing in frequency and severity across the western United States, yet the effects of fire on oligotrophic mountain lakes remains poorly understood. We investigated whether recent wildfires altered the water chemistry and metabolism of subalpine lakes by comparing ecosystem processes and structure in watersheds that experienced recent burn to those without recent burns (reference watersheds). Across the Sawtooth region of Idaho and in the Seeley-Swan Valley of Montana, we compared water chemistry in ten lakes and net ecosystem production (NEP) in five lakes during the first ice-free season following one year after fire. To further understand nutrient dynamics following wildfire, we supplemented the regional comparisons with historical pre-fire nutrient concentrations in Bull Trout, Stanley, and Yellow Belly Lakes from previous studies and deeper chlorophyll-a (chl-a) and inflow stream sampling at Bull Trout Lake (Sawtooth region). Lakes within burned watersheds had elevated total phosphorus (TP, 82%), total nitrogen (TN, 46%), dissolved organic carbon (DOC, 55%), and total suspended solids (TSS, 80%) relative to reference lakes, with more phosphorus enrichment compared to nitrogen. Despite higher concentrations of TSS, water clarity as measured by Secchi disk depth within burned lakes did not decline and epilimnentic chl-a weakly increased. Net ecosystem production (NEP) was higher in the burned lakes early in the season but converged with reference lakes by midsummer, suggesting oligotrophic mountain lakes may buffer wildfire inputs in the epilimnion. Bull Trout Lake, however, exhibited intermittent subsurface chl-a maxima, elevated only in June and August, alongside pronounced oxygen depletion in the hypolimnion consistent with elevated decomposition at depth. These patterns suggest that fire effects may concentrate at depth and within episodic events, such as snowmelt and rainfall, that surface-based monitoring is likely to underestimate.
Recommended Citation
Fletcher, Sage Haviland, "Wildfire effects on the biogeochemistry and metabolism of lakes in the Northern Rockies, USA" (2026). Graduate Student Theses, Dissertations, & Professional Papers. 12759.
https://scholarworks.umt.edu/etd/12759
© Copyright 2026 Sage Haviland Fletcher