Post-Wildfire Water Quality in the Kenai Lowlands: Six Years After the 2019 Swan Lake Fire

Author: Logan Wieland, University of Alaska Anchorage, Northern Hydroclimate Laboratory

Poster

Video Presentation

Abstract

The Kenai Peninsula is experiencing a warming and drying climate trend that is increasing the frequency and severity of boreal wildfires, threatening the quantity and quality of regional surface water resources and the communities they supply. As part of a broader investigation into wildfire- driven carbon mobilization across Kenai lowland wetland systems, we incorporated the first comprehensive post-burn aqueous geochemical assessment for the region, examining the aquatic legacy of the 2019 Swan Lake Fire (SLF) to evaluate mid- and long-term surface water quality following wildfire containment. Here we focus on the East Fork Moose River subwatershed (73% burned during the SLF), which feeds into the Kenai River above the communities of Sterling, Soldotna, and Kenai. In 2025, six years post-disturbance, we sampled five waterbodies across burned (Peterson Lake, Egumen Lake, Egumen Wetland, Watson Lake) and unburned (Lily Lake) catchments during three field campaigns (June, August, November), analyzing major ions, trace metals, and dissolved organic carbon (DOC). Egumen Wetland showed progressive geochemical deterioration through the 2025 season, with dissolved iron increasing 21-fold and arsenic 19-fold from June to November. These trends coincided with near-anoxic conditions consistent with reductive dissolution of metal-oxyhydroxide minerals driven by currently unknown local/regional mechanisms in this shallow, poorly flushed system. Egumen and Watson Lakes (positioned above and below the wetland complex, respectively) reflect their relative isolation from Egumen Wetland through nominal solute content, though whether this isolation persists during wetter seasons remains unclear. Peterson Lake exhibited the lowest DOC of all sites, suggesting either an advanced DOC flush stage or a buffered hydrological regime. Differences between Lily Lake and burned sites likely reflect pre-existing catchment geology and ecology rather than fire effects alone, complicating simple burned/unburned comparisons. Taken together, these results indicate that waterbody type, particularly the susceptibility of shallow wetlands to sustained anoxic metal and carbon mobilization is a stronger predictor of ongoing fire impact than burn history alone. As climate-driven fire regimes intensify across southcentral Alaska, understanding these divergent recovery trajectories will be essential for anticipating downstream water quality impacts.

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