Carbon isotope discrimination and water stress in trembling aspen following variable retention harvesting

Variable retention harvesting (VRH) has been proposed as a silvicultural practice to maintain biodiversity and ecosystem integrity. No previous study has examined tree carbon isotope discrimination to provide insights into water stress that could lead to dieback and mortality of trees following VRH. We measured and compared the carbon isotope ratios (δ13C) in stem wood of trembling aspen (Populus tremuloides Michx.) before and after VRH. Eight trees were sampled from isolated residual, edge and control (interior of unharvested stand) positions from each of seven plots in three regions (Calling Lake and Drayton Valley, Alberta and Lac Duparquet, Qu

Potential bioavailability of representative pyrogenic organic matter compounds in comparison to natural dissolved organic matter pools

Pyrogenic organic matter (PyOM) from wildfires impacts river corridors globally and is widely regarded as resistant to biological degradation. Though recent work suggests PyOM may be more bioavailable than historically perceived, estimating bioavailability across its chemical spectrum remains elusive. To address this knowledge gap, we assessed potential bioavailability of representative PyOM compounds relative to ubiquitous dissolved organic matter (DOM) with a substrate-explicit model. The range of potential bioavailability of PyOM was greater than natural DOM; however, the predicted thermodynamics, metabolic rates, and carbon use efficiencies (CUEs) overlapped significantly between all OM pools. Compound type (e.g., natural versus PyOM) had approximately 6-fold less impact on predicted respiration rates than simulated carbon and oxygen limitations. Within PyOM, the metabolism of specific chemistries differed strongly between unlimited and oxygenlimited conditions – degradations of anhydrosugars, phenols, and polycyclic aromatic hydrocarbons (PAHs) were more favorable under oxygen limitation than other molecules. Notably, amino sugar-like, protein-like, and lignin-like PyOM had lower carbon use efficiencies relative to natural DOM of the same classes, indicating potential impacts in process-based model representations. Overall, our work illustrates how similar PyOM bioavailability may be to that of natural DOM in the river corridor, furthering our understanding of how PyOM may influence riverine biogeochemical cycling

A Global Index for Mapping the Exposure of Water Resources to Wildfire

Wildfires are keystone components of natural disturbance regimes that maintain ecosystem structure and functions, such as the hydrological cycle, in many parts of the world. Consequently, critical surface freshwater resources can be exposed to post-fire effects disrupting their quantity, quality and regularity. Although well studied at the local scale, the potential extent of these effects has not been examined at the global scale. We take the first step toward a global assessment of the wildfire water risk (WWR) by presenting a spatially explicit index of exposure. Several variables related to fire activity and water availability were identified and normalized for use as exposure indicators. Additive aggregation of those indicators was then carried out according to their individual weight. The resulting index shows the greatest exposure risk in the tropical wet and dry forests. Intermediate exposure is indicated in mountain ranges and dry shrublands, whereas the lowest index scores are mostly associated with high latitudes. We believe that such an approach can provide important insights for water security by guiding global freshwater resource preservation.Keywords: wildfire hazard, global index, water security, water resources exposure, wildfire water ris

Scientists' warning on extreme wildfire risks to water supply

2020 is the year of wildfire records. California experienced its three largest fires early in its fire season. The Pantanal, the largest wetland on the planet, burned over 20% of its surface. More than 18 million hectares of forest and bushland burned during the 2019–2020 fire season in Australia, killing 33 people, destroying nearly 2500 homes, and endangering many endemic species. The direct cost of damages is being counted in dozens of billion dollars, but the indirect costs on water‐related ecosystem services and benefits could be equally expensive, with impacts lasting for decades. In Australia, the extreme precipitation (“200 mm day −1 in several location”) that interrupted the catastrophic wildfire season triggered a series of watershed effects from headwaters to areas downstream. The increased runoff and erosion from burned areas disrupted water supplies in several locations. These post‐fire watershed hazards via source water contamination, flash floods, and mudslides can represent substantial, systemic long‐term risks to drinking water production, aquatic life, and socio‐economic activity. Scenarios similar to the recent event in Australia are now predicted to unfold in the Western USA. This is a new reality that societies will have to live with as uncharted fire activity, water crises, and widespread human footprint collide all‐around of the world. Therefore, we advocate for a more proactive approach to wildfire‐watershed risk governance in an effort to advance and protect water security. We also argue that there is no easy solution to reducing this risk and that investments in both green (i.e., natural) and grey (i.e., built) infrastructure will be necessary. Further, we propose strategies to combine modern data analytics with existing tools for use by water and land managers worldwide to leverage several decades worth of data and knowledge on post‐fire hydrology

Data and scripts describing dissolved organic carbon concentrations across a stream network in Oregon following the 2020 Holiday Farm Wildfire

In 2020, the Holiday Farm Wildfire burned ~18 % of the McKenzie sub-basin in Oregon, USA. To investigate the impact of the wildfire on in-stream dissolved organic carbon (DOC) concentrations, we collected water samples from 129 stream sites within the McKenzie sub-basin stream network over four distinct seasonal wetness conditions (wetting, wet, drying, dry) between November 2022 and September 2023. This data was used to create spatial network models to model DOC concentrations across the stream network. This data package consists of (1) a spreadsheet spreadsheet containing DOC concentrations, landscape characteristics, and site information for the stream sites within the McKenzie sub-basin, OR, USA. (2) A spatial stream network (SSN) object developed for the McKenzie sub-basin from the proceeding DOC and landscape data. (3) Scripts written in R used to process, analyze, and report our findings from this data. This data package is associated with the publication "The influence of burn severity on dissolved organic carbon concentrations across a stream network differs based on seasonal wetness conditions post-fire" submitted to Biogeosciences (Wampler et al. 2024)

Baseline geographic information on wildfire-watershed risk in Canada: Needs, gaps, and opportunities

As the pressures on water supply from shifting forest disturbance regimes continue to escalate, researchers are being asked to answer increasingly complex questions. However, many questions in wildfire-watershed risk (WWR) research remained unaddressed due to a paucity of relevant datasets. There are, indeed, many fundamental processes we do not understand that require additional data collection to develop risk management frameworks. As such, WWR researchers and managers face a paradox in their need to address critical questions important for the sustainability of socio-hydrological systems while dealing with incomplete information. In many cases, this leads to valuable research ideas being discarded on the account of limited data availability. However, imperfect, incomplete, or limited data should not deter researchers and managers from performing analyses to assess risk. In fact, such analyses improve the research benefit-to-cost ratio of existing data, help unravel gaps in data sources, enable generation of new hypotheses, and highlight where data availability and openness can be improved. If we do not use what we have, how can we know what we need? This issue is of particular interest in Canada, where baseline WWR information for the entire country is generally missing, despite growing concerns about water security in the face of a shifting wildfire regimes. In this commentary, we (a) identify several relevant open geospatial datasets, (b) illustrate how these datasets can be leveraged to produce simple yet relevant risk information, (c) identify some high priority data gaps that require immediate attention, and (d) discuss future avenues towards the creation of baseline Pan-Canadian WWR information

A spatial evaluation of global wildfire-water risks to human and natural systems

International audienceThe large mediatic coverage of recent massive wildfires across the world has emphasized the vulnerability of freshwater resources. The extensive hydrogeomorphic effects from a wildfire can impair the ability of watersheds to provide safe drinking water to downstream communities and high-quality water to maintain riverine ecosystem health. Safeguarding water use for human activities and ecosystems is required for sustainable development; however, no global assessment of wildfire impacts on water supply is currently available. Here, we provide the first global evaluation of wildfire risks to water security, in the form of a spatially explicit index. We adapted the Driving forces-Pressure-State-Impact-Response risk analysis framework to select a comprehensive set of indicators of fire activity and water availability, which we then aggregated to a single index of wildfire-water risk using a simple additive weighted model. Our results show that water security in many regions of the world is potentially vulnerable, regardless of socio-economic status. However, in developing countries, a critical component of the risk is the lack of socio-economic capability to respond to disasters. Our work highlights the importance of addressing wildfire-induced risks in the development of water security policies; the geographic differences in the components of the overall risk could help adapting those policies to different regional contexts. Crow

Hallema&al_ChallengesGlobalWildfireWaterSupplies_Figure1_Wildfire-Impacts-Water-Domains.jpg

Specific challenges for data and models in post-fire hydrology are best addressed by subdividing global hydrological functioning into water domains, shown in the figure as the ecohydrological domain, ecosystem services domain, socio-hydrologic domain, and water security domain.Water supply is impacted by wildfire via water domain interactions, but much remains unclear about the magnitude and direction of these interactions (background image credit: NASA’s Earth Observatory, 2002)