PS 28-132 - Dissolved organic matter fluorescence as indicators of wildfire impacts in aquatic systems

Abstract: Wildfires are a major ecosystem disturbance that can accelerate surface runoff, sediment erosion, and the transport of pollutants to aquatic systems. The burning of terrestrial materials leads to an alteration of carbon signatures that may be delivered to the aquatic realm through the export of dissolved organic matter (DOM), a heterogenous collection of organic compounds of varying sources that underpin many biogeochemical processes. There remains a need to better disentangle wildfire-related signatures from bulk DOM to maximize our understanding and predictability of wildfire impacts on aquatic biogeochemistry and the implications for downstream water quality. However, DOM signatures are complex and representative of varying ecosystem dynamics, posing a notable challenge particularly for systems with diverse land cover sources and varying burn impacts. To overcome this challenge, we performed open-air burn simulations with major vegetation representative of the land cover classifications within the Pacific Northwest, a region of regular concern for increasing wildfire activity. The charred vegetation was categorized visually for burn severity consistent with post-hoc field-based assessments of wildfire impacts within the landscape. Leachates were generated with synthetic rainwater to simulate the mobilization of DOM from raw and burnt vegetation, which was characterized by excitation-emission fluorescence with parallel factor analysis (PARAFAC). Preliminary results highlight distinct fluorescence characteristics by land cover type, with forested land covers dominated by low wavelength proteinaceous-like signatures compared to shrub vegetation leachates that were enriched by long wavelength aromatic and humic-like signatures. With increasing burn severity, fluorescence for forested vegetation became increasingly red-shifted with increasing signals at high emission wavelengths whereas fluorescence from shrub vegetation became increasingly blue-shifted with increasing signals at shorter emission wavelengths. These shifts led to an ultimate convergence of signatures across all land cover types at high severities, which suggests that burning collectively leads to an enrichment in highly degraded DOM signatures with increasing severity. The results from this study highlight the potential applicability of using fluorescence for monitoring post-wildfire impacts in aquatic systems. By increasing our ability to link wildfire impacts to DOM fluorescence signatures, we become better positioned for future studies to obtain higher resolution information across spatial and temporal scales through the pairing of information with field-based applications (e.g. in-situ optical sensors), which will enhance our predictive understanding of wildfire impacts on terrestrial and aquatic biogeochemical cycles.