Carl Mendoza


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Severe wildfire exposes remnant peat carbon stocks to increased post-fire drying
Nicholas Kettridge, Max Lukenbach, Kelly Hokanson, K. J. Devito, Richard M. Petrone, Carl Mendoza, J. M. Waddington
Scientific Reports, Volume 9, Issue 1

The potential of high severity wildfires to increase global terrestrial carbon emissions and exacerbate future climatic warming is of international concern. Nowhere is this more prevalent than within high latitude regions where peatlands have, over millennia, accumulated legacy carbon stocks comparable to all human CO2 emissions since the beginning of the industrial revolution. Drying increases rates of peat decomposition and associated atmospheric and aquatic carbon emissions. The degree to which severe wildfires enhance drying under future climates and induce instability in peatland ecological communities and carbon stocks is unknown. Here we show that high burn severities increased post-fire evapotranspiration by 410% within a feather moss peatland by burning through the protective capping layer that restricts evaporative drying in response to low severity burns. High burn severities projected under future climates will therefore leave peatlands that dominate dry sub-humid regions across the boreal, on the edge of their climatic envelopes, more vulnerable to intense post-fire drying, inducing high rates of carbon loss to the atmosphere that amplify the direct combustion emissions.


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Potential influence of nutrient availability along a hillslope: Peatland gradient on aspen recovery following fire
Midori Depante, Richard M. Petrone, K. J. Devito, Nicholas Kettridge, Merrin L. Macrae, Carl Mendoza, J. M. Waddington
Ecohydrology, Volume 11, Issue 5

The Boreal Plains (BP) of Western Canada have been exposed to increasing disturbance by wildfire and host a mixture of upland‐wetland‐pond complexes with substantial quantities of trembling aspen (Populus tremuloides Michx.) throughout the terrestrial areas. The ability of these tree species to regenerate within both upland and wetland areas of the BP following wildfire is unclear. The purpose of this study was to investigate the influence of fire on nutrient dynamics in soil and water in peatlands and forested landscapes in the BP and relate this to aspen regeneration. Nutrient concentrations, nutrient supply rates, and net nutrient mineralization rates were determined in burned and unburned sections of a peatland and forest and compared with the regeneration of aspen. NO3−, NH4+, and P varied spatially throughout the landscape, and differences were observed between peatland and upland areas. In general, differences in nutrient dynamics were not observed between burned and unburned areas, with the exception of P. Nutrient and growth data suggest that aspen do not require nutrient‐rich conditions for regeneration and instead relied on forest litter to satisfy nutrient demands. Although the peatlands contained high nutrients, aspen did not flourish in the combination of anoxic and aerobic organic‐rich soils present in this area. Although aspen may use peat water and nutrients through their rooting zones, peatlands are unsuitable for aspen re‐establishment in the long‐term. However, the combination of abundant nutrients in surface mineral soils in peat margins may indicate the vulnerability of margins to upland transformations in later successional stages.

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A hydrogeological landscape framework to identify peatland wildfire smouldering hot spots
Kelly Hokanson, Paul A. Moore, Max Lukenbach, K. J. Devito, Nicholas Kettridge, R. M. Petrone, Carl Mendoza, J. M. Waddington
Ecohydrology, Volume 11, Issue 4

Northern peatlands are important global carbon stores, but there is concern that these boreal peat reserves are at risk due to increased fire frequency and severity as predicted by climate change models. In a subhumid climate, hydrogeological position is an important control on peatland hydrology and wildfire vulnerability. Consequently, we hypothesized that in a coarse‐textured glaciofluvial outwash, isolated peatlands lacking the moderating effect of large‐scale groundwater flow would have greater water table (WT) variability and would also be more vulnerable to deep WT drawdown and wildfire during dry climate cycles. A holistic approach was taken to evaluate 3 well‐accepted factors that are associated with smouldering in boreal peatlands: hollow microform coverage, peatland margin morphometry, and gravimetric water content. Using a combination of field measurements (bulk density, humification, WT position, hummock–hollow distribution, and margin width) and modelling (1‐D vertical unsaturated flow coupled with a simple peat–fuel energy balance equation), we assessed the vulnerability of peat to smouldering. We found that a peatland in the regionally intermediate topographic position is the most vulnerable to smouldering due to the interaction of variable connectivity to large‐scale groundwater flow and the absence of mineral stratigraphy for limiting WT declines during dry conditions. Our findings represent a novel assessment framework and tool for fire managers by providing a priori knowledge of potential peat smouldering hot spot locations in the landscape to efficiently allocate resources and reduce emergency response time to smouldering events.

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Disturbance Impacts on Thermal Hot Spots and Hot Moments at the Peatland-Atmosphere Interface
Rhoswen Leonard, Nicholas Kettridge, K. J. Devito, Richard M. Petrone, Carl Mendoza, J. M. Waddington, Stefan Krause
Geophysical Research Letters, Volume 45, Issue 1

Soil‐surface temperature acts as a master variable driving nonlinear terrestrial ecohydrological, biogeochemical, and micrometeorological processes, inducing short‐lived or spatially isolated extremes across heterogeneous landscape surfaces. However, subcanopy soil‐surface temperatures have been, to date, characterized through isolated, spatially discrete measurements. Using spatially complex forested northern peatlands as an exemplar ecosystem, we explore the high‐resolution spatiotemporal thermal behavior of this critical interface and its response to disturbances by using Fiber‐Optic Distributed Temperature Sensing. Soil‐surface thermal patterning was identified from 1.9 million temperature measurements under undisturbed, trees removed and vascular subcanopy removed conditions. Removing layers of the structurally diverse vegetation canopy not only increased mean temperatures but it shifted the spatial and temporal distribution, range, and longevity of thermal hot spots and hot moments. We argue that linking hot spots and/or hot moments with spatially variable ecosystem processes and feedbacks is key for predicting ecosystem function and resilience.

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Water table dynamics in a constructed wetland, Fort McMurray, Alberta
Haley M. Spennato, Scott J. Ketcheson, Carl Mendoza, Sean K. Carey
Hydrological Processes, Volume 32, Issue 26

Surface mining in northern Alberta transforms wetlands and forests into open pits, tailings ponds, and overburden. As part of their license to operate, mine operators are required to reclaim this altered landscape to a predisturbance capacity. In 2012, Syncrude Canada Limited constructed one of the first of two reclaimed wetlands, the Sandhill Fen Watershed (SFW), to evaluate wetland reclamation strategies. SFW is a 52-ha system atop soft-tailings that includes an inflow/outflow pump system, underdrains, upland hummocks, and a fen lowland. In this study, water table dynamics of the fen lowland were evaluated in the 2 years following commissioning (2014–2015) to assess whether this newly constructed watershed has hydrological conditions that facilitate hydric soils with water table regimes similar to reference systems. Results indicate that the location and hydrophysical properties of placed materials control water table responses to both water management and precipitation. This differential water table response in the SFW lowland drove lateral fluxes between adjacent landforms, suggesting periods of intermittent water supply from uplands to wetlands along hummock margins. As in natural systems, the lowland fen exhibited several lateral flow reversals over the 2 years depending upon water level. Water tables on-average were greater than those observed in natural analogues. Comparison during these first 2 years following commissioning contribute to the increasing insight as to how construction and management practices support reclamation postmining.