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Long-term monitoring reveals muted, seasonally distinct water quality responses to wildfire across a stream network in the Pacific Northwest, USA

Wampler, Basso, Barton, Donahue, Erkert, Cole, McCredie, Wondzell & Bladon
Water Resources Research

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The occurrence of large, high severity wildfires has increased across the Pacific Northwest, with potential effects on watershed processes and water quality. However, quantifying the magnitude and persistence of wildfire impacts remains challenging due to the unpredictable nature of wildfires and limited long-term and pre-fire reference data. In our study we used a unique dataset of 19 years of water quality data spanning 14 years pre-fire and 5 years post-fire across eight sites in the Cascade Mountains of western Oregon to evaluate wildfire effects on carbon, nitrogen, phosphorus, and sediment concentrations. Bayesian generalized linear mixed models were used to quantify wildfire effects on concentration differences across time (pre-/post-fire) and burn status (burned/unburned). Counter to much of the literature from wildfires in other regions, we found muted and uncertain wildfire effects. However, seasonal impacts were observed. During the dry summer period, dissolved organic carbon increased (174 \%) while orthophosphate (-53 \%) and nitrate (-113 \%) decreased, suggesting increased productivity following wildfire. The fall wetting-up period showed small increases in total suspended solids (140 \%) and total organic carbon (35 \%), which may reflect short-term increases in available sediment from dry ravel, enhanced bank erosion, or entrainment of channel sediment due to enhanced streamflow. We also found that site-level climate and landscape characteristics were critical for accurately assessing wildfire impacts, with daily precipitation strongly influencing constituent concentrations. Our findings underscore the value of long-term monitoring of reference sites for disentangling water quality responses to wildfire relative to natural climatic variability.

@article{wamplerLongtermMonitoringReveals2026, title = {Long-term monitoring reveals muted, seasonally distinct water quality responses to wildfire across a stream network in the {Pacific} {Northwest}, {USA}}, journal = {Water Resources Research}, author = {Katie A. Wampler and Marta Basso and Riley Barton and David Donahue and Lisa Erkert and Ryan P. Cole and Katherine E. McCredie and Steven M. Wondzell and Kevin D. Bladon}, year = {2026} }

Modeling recovery of hydrology and dissolved organic carbon dynamics after wildfire in the Pacific Northwest

Kang, Wampler, Bladon & Adam
Journal of Hydrology

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2026

Post-wildfire water quality and aquatic ecosystem response in the U.S. Pacific Northwest: science and monitoring gaps

Wall, Compton, Coble, Haley, Lin, Myers-Pigg, Reale, Wampler, Swartz, Moffett, Bladon, Carpenter, Chang, Chen, Donahue, Eckley, Hohner, Kiffney, Miralha, Regier, Seeds & River
Environmental Research: Water

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An increase in the occurrence of large, high severity wildfires in the western Pacific Northwest (PNW), USA, has created an urgent need for science to better inform forest management and policy decisions to maintain source water quality in the region. The western PNW faces similar challenges to other regions with shifting wildfire regimes and large population centers reliant on surface water from forested catchments. However, the uniquely wet and highly seasonal climate of the western PNW suggests that findings from other, more frequently burned regions may not be directly applicable. To identify science, monitoring, and management gaps and opportunities in the western PNW, this review was collaboratively undertaken by academics, non-government and industry representatives, and local, state, and federal government entities who have been working together since the 2020 Labor Day fires in Oregon. Focusing on Oregon and Washington, we found that monitoring networks for continuous water quantity and quality cover much of the state with greater representation in western U.S. ecoregions, but few studies have analyzed and published these data to capture and communicate the post-wildfire response. Approximately half of the streamgages in Oregon and Washington record major water quality parameters, and hundreds of sites in the area have discrete sampling for a wide range of water quality constituents. Still, numerous gaps exist in understanding the short- and long-term impacts of wildfire on hydrology, water chemistry, including pH and dissolved oxygen, mobilization of metals, aquatic ecosystems, and downstream drinking water treatment. Collective action to further collect, analyze, interpret, and publish the key data could help improve our understanding of post-wildfire water quality impacts in this and other increasingly wildfire-affected regions.

@article{wallPostwildfireWaterQuality2026, title = {Post-wildfire water quality and aquatic ecosystem response in the {U}.{S}. {Pacific} {Northwest}: science and monitoring gaps}, volume = {2}, url = {https://doi.org/10.1088/3033-4942/ae36cb}, doi = {10.1088/3033-4942/ae36cb}, number = {1}, journal = {Environmental Research: Water}, publisher = {IOP Publishing}, author = {Sara Wall and Jana E Compton and Ashley A Coble and Beth M Haley and Jiajia Lin and Allison Myers-Pigg and Justin Reale and Katie Wampler and Allison Swartz and Kevan Moffett and Kevin D Bladon and Kurt Carpenter and Heejun Chang and Junjie Chen and David Donahue and Chris S Eckley and Amanda K Hohner and Peter M Kiffney and Lorrayne Miralha and Peter Regier and Joshua Seeds and Mark River}, month = {feb}, year = {2026}, pages = {015004}, note = {Last visited on 09/16/2026} }

When Do Riverine Systems “Feel the Burn”? Simulating How Burn Extent and Severity Modulate Hydrologic Controls on Biogeochemical Export

Wampler, Myers-Pigg, Kang, Regier, Scheibe & Bladon
Water Resources Research

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Wildfires impact terrestrial landscapes and downstream river corridors through shifts in vegetation and soil properties leading to downstream hydrologic and water quality impacts. The magnitude of these impacts depend on a complex and interconnected set of wildfire, landscape, and aquatic processes. Here, we isolate the impact of post-fire hydrologic changes on streamflow, nitrate, and dissolved organic carbon using the Soil and Water Assessment Tool (SWAT) model. We explore how responses differ across burn severity and area burned in two test basins: a humid forested basin and a semi-arid mixed land use basin. We ran 1830 wildfire simulations testing impacts of area burned, burn severity, and post-fire precipitation on streamflow, nitrate, and dissolved organic carbon. Our work suggests that area burned thresholds differ with burn severity and analyte. Additionally, post-fire transport of dissolved organic carbon was sensitive to both area burned and severity, while nitrate was primarily sensitive to area burned. Despite a muted (−9.5 to 5.7 mm yr−1 change) hydrologic response in the semi-arid basin, the model predicted large (7\%–288\% increase) shifts in dissolved organic carbon, suggesting that post-fire shifts in flow pathways and soil properties are key in its response. The limited shifts in nitrate responses in the simulations highlight that terrestrial post-fire transformations, rather than hydrologic changes, may control the increases in stream nitrate often observed post-fire. As wildfire regimes are shifting, improving understanding of post-fire nutrient export responses is critical to protect freshwater resources and aquatic ecosystems.

@article{wamplerWhenRiverineSystems2026, title = {When {Do} {Riverine} {Systems} “{Feel} the {Burn}”? {Simulating} {How} {Burn} {Extent} and {Severity} {Modulate} {Hydrologic} {Controls} on {Biogeochemical} {Export}}, volume = {62}, url = {https://onlinelibrary.wiley.com/doi/abs/10.1029/2025WR040678}, doi = {10.1029/2025WR040678}, number = {2}, journal = {Water Resources Research}, author = {K. A. Wampler and A. N. Myers-Pigg and H. Kang and P. Regier and T. D. Scheibe and K. D. Bladon}, year = {2026}, pages = {e2025WR040678}, annote = {e2025WR040678 2025WR040678}, note = {Last visited on 09/16/2026} }

2025

Spatial and Temporal Shifts in Dissolved Organic Matter Character Across a Burned Stream Network

Wampler, Bladon, Myers-Pigg & Roebuck Jr.
Journal of Geophysical Research: Biogeosciences

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Increasing wildfire activity can impact the global carbon cycle, aquatic ecosystem health, and drinking water treatment through alterations in aquatic dissolved organic matter (DOM) composition. However, uncertainty remains about the spatial and temporal variability in wildfire effects on DOM composition. We sought to improve understanding of how burn severity affects stream DOM and how weather, hydrology, and landscape factors contribute to variability in post-fire DOM responses across space and time. Following a large 2020 wildfire in Oregon, USA, we collected water samples to quantify dissolved organic carbon and DOM optical properties at 129 stream sites across the fire-affected stream network. Sampling was repeated across seasonal hydrologic conditions to capture variation in hydrologic pathways and organic matter sources. We developed a PARAFAC model using excitation-emission matrices (EEMs) and used spatial stream network (SSN) models to determine how DOM composition changed across the stream network with burn severity. The greatest shifts in DOM composition were observed during the dry and wetting seasons, with an increase in aromatic DOM at higher burn severities. In contrast, an increase in protein-like DOM was observed during the wet season at higher burn severities. Drainage area, 31-day and 1-day antecedent precipitation, and baseflow index impacted the relationship between DOM composition and burn severity, which could partially explain the variability in post-fire DOM responses. Our study contributes a mechanistic understanding of how wildfire impacts DOM sources and composition, which is critical to predicting wildfire effects on aquatic biogeochemical cycling and preserving ecosystem health and source water quality.

@article{wamplerSpatialTemporalShifts2025, title = {Spatial and {Temporal} {Shifts} in {Dissolved} {Organic} {Matter} {Character} {Across} a {Burned} {Stream} {Network}}, volume = {130}, url = {https://onlinelibrary.wiley.com/doi/abs/10.1029/2024JG008687}, doi = {10.1029/2024JG008687}, number = {7}, journal = {Journal of Geophysical Research: Biogeosciences}, author = {K. A. Wampler and K. D. Bladon and A. N. Myers-Pigg and J. A. {Roebuck Jr.}}, year = {2025}, pages = {e2024JG008687}, annote = {e2024JG008687 2024JG008687}, note = {Last visited on 09/16/2026} }

2024

The influence of burn severity on dissolved organic carbon concentrations across a stream network differs based on seasonal wetness conditions

Wampler, Bladon & Myers-Pigg
Biogeosciences

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Large, high-severity wildfires in many regions across the globe have increased concerns about their impacts on carbon cycling in watersheds. Altered sources of carbon and changes in catchment hydrology after wildfire can lead to shifts in dissolved organic carbon (DOC) concentrations in streams, which can have negative impacts on aquatic ecosystem health and downstream drinking-water treatment. Despite its importance, post-fire DOC responses remain relatively unconstrained in the literature, and we lack critical knowledge of how burn severity, landscape elements, and climate interact to affect DOC concentrations. To improve our understanding of the impact of burn severity on DOC concentrations, we measured DOC at 129 sites across a stream network extending upstream, within, and downstream of a large, high-severity wildfire in Oregon, USA. We collected samples across the study sub-basin during four distinct seasonal wetness conditions. We used our high-spatial-resolution data to develop spatial stream network (SSN) models to predict DOC across the stream network and to improve our understanding of the controls on DOC concentrations. Spatially, we found no obvious wildfire signal – instead, we observed a pattern of increasing DOC concentrations from the high-elevation headwaters to the sub-basin outlet, while the mainstem maintained consistently low DOC concentrations. This suggests that effects from large wildfires may be “averaged” out at higher stream orders and larger spatial scales. When we grouped DOC concentrations by burn severity group, we observed a significant decrease in the variability of DOC concentrations in the moderate and high burn severity sub-catchments. However, our SSN models were able to predict decreases in DOC concentrations with increases in burn severity across the stream network. Decreases in DOC concentrations were also highly variable across seasonal wetness conditions, with the greatest (−1.40 to −1.64 mg L−1) decrease occurring in the high-severity group during the wetting season. Additionally, our models indicated that in all seasons, baseflow index was more influential in predicting DOC concentrations than burn severity was, indicating that groundwater discharge can obscure the impacts of wildfire in a stream network. Overall, our results suggested that landscape characteristics can regulate the DOC response to wildfire. Moreover, our results also indicated that the seasonal timing of sampling can influence the observed response of DOC concentrations to wildfire.

@article{wamplerInfluenceBurnSeverity2024, title = {The influence of burn severity on dissolved organic carbon concentrations across a stream network differs based on seasonal wetness conditions}, volume = {21}, url = {https://bg.copernicus.org/articles/21/3093/2024/}, doi = {10.5194/bg-21-3093-2024}, number = {13}, journal = {Biogeosciences}, publisher = {Copernicus GmbH}, author = {Katie A. Wampler and Kevin D. Bladon and Allison N. Myers-Pigg}, month = {jul}, year = {2024}, pages = {3093--3120}, note = {Last visited on 09/16/2026} }

2023

Modeling wildfire effects on streamflow in the Cascade Mountains, Oregon, USA

Wampler, Bladon & Faramarzi
Journal of Hydrology

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Increasing occurrence of large and severe wildfires represents a growing threat to forested watersheds and the many ecosystem services they provide. Past research has shown that wildfires can cause substantial increases in peak flows and annual water yields, leading to potential water quality concerns and land and water management challenges. However, responses have been variable, and there have been few studies at large basin scales, leading to uncertainties about post-fire hydrologic responses. To address these uncertainties, we projected the effect of three large wildfires ({\textgreater}70,000 ha) on streamflow in two important forested watersheds in the Cascade Range of Oregon, US. We modeled the streamflow response using the Soil and Water Assessment Tool (SWAT) model, calibrated on data from prior to the wildfires. We modified model parameters to represent the impacts of the wildfires based on burn severity maps. Burned and unburned scenarios were compared using random forest models to identify drivers of increased annual water yields and peak flows. Post-fire annual water yield changes were controlled by burn severity, annual precipitation, area burned, aridity, and vegetation type, while post-fire peak flow changes were controlled by burn severity, area burned, aridity, soil type, and geologic province. We also found that post-fire increases in annual water yields, peak flows, and low flows were greatest at the headwater scale but were more muted at the downstream basin scale. Our work provides valuable insights into the range of potential post-fire streamflow changes at the headwater and larger basin scale, which is becoming increasingly critical for effective forest and water management decisions.

@article{wamplerModelingWildfireEffects2023, title = {Modeling wildfire effects on streamflow in the {Cascade} {Mountains}, {Oregon}, {USA}}, volume = {621}, url = {https://www.sciencedirect.com/science/article/pii/S0022169423005279}, doi = {10.1016/j.jhydrol.2023.129585}, journal = {Journal of Hydrology}, author = {K. A. Wampler and K. D. Bladon and M. Faramarzi}, month = {jun}, year = {2023}, pages = {129585}, note = {Last visited on 09/16/2026} }

2022

Spatiotemporal Controls on the Delivery of Dissolved Organic Matter to Streams Following a Wildfire

Roebuck Jr., Bladon, Donahue, Graham, Grieger, Morgenstern, Norwood, Wampler, Erkert, Renteria, Danczak, Fricke & Myers-Pigg
Geophysical Research Letters

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Refereed Technical and Extension Publications

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References

Kang, H., Wampler, K. A., Bladon, K. D., & Adam, J. C. (2026). Modeling recovery of hydrology and dissolved organic carbon dynamics after wildfire in the Pacific Northwest. Journal of Hydrology.

Roebuck Jr., J. A., Bladon, K. D., Donahue, D., Graham, E. B., Grieger, S., Morgenstern, K., Norwood, M. J., Wampler, K. A., Erkert, L., Renteria, L., Danczak, R., Fricke, S., & Myers-Pigg, A. N. (2022). Spatiotemporal Controls on the Delivery of Dissolved Organic Matter to Streams Following a Wildfire. Geophysical Research Letters, 49(16), e2022GL099535. https://doi.org/10.1029/2022GL099535

Wall, S., Compton, J. E., Coble, A. A., Haley, B. M., Lin, J., Myers-Pigg, A., Reale, J., Wampler, K., Swartz, A., Moffett, K., Bladon, K. D., Carpenter, K., Chang, H., Chen, J., Donahue, D., Eckley, C. S., Hohner, A. K., Kiffney, P. M., Miralha, L., … River, M. (2026). Post-wildfire water quality and aquatic ecosystem response in the U.S. Pacific Northwest: Science and monitoring gaps. Environmental Research: Water, 2(1), 015004. https://doi.org/10.1088/3033-4942/ae36cb

Wampler, K. A., Basso, M., Barton, R., Donahue, D., Erkert, L., Cole, R. P., McCredie, K. E., Wondzell, S. M., & Bladon, K. D. (2026). Long-term monitoring reveals muted, seasonally distinct water quality responses to wildfire across a stream network in the Pacific Northwest, USA. Water Resources Research.

Wampler, K. A., Bladon, K. D., & Faramarzi, M. (2023). Modeling wildfire effects on streamflow in the Cascade Mountains, Oregon, USA. Journal of Hydrology, 621, 129585. https://doi.org/10.1016/j.jhydrol.2023.129585

Wampler, K. A., Bladon, K. D., & Myers-Pigg, A. N. (2024). The influence of burn severity on dissolved organic carbon concentrations across a stream network differs based on seasonal wetness conditions. Biogeosciences, 21(13), 3093–3120. https://doi.org/10.5194/bg-21-3093-2024

Wampler, K. A., Bladon, K. D., Myers-Pigg, A. N., & Roebuck Jr., J. A. (2025). Spatial and Temporal Shifts in Dissolved Organic Matter Character Across a Burned Stream Network. Journal of Geophysical Research: Biogeosciences, 130(7), e2024JG008687. https://doi.org/10.1029/2024JG008687

Wampler, K. A., Myers-Pigg, A. N., Kang, H., Regier, P., Scheibe, T. D., & Bladon, K. D. (2026). When Do Riverine Systems “Feel the Burn”? Simulating How Burn Extent and Severity Modulate Hydrologic Controls on Biogeochemical Export. Water Resources Research, 62(2), e2025WR040678. https://doi.org/10.1029/2025WR040678