Nicholas Kettridge

Moderate drop in water table increases peatland vulnerability to post-fire regime shift

Northern and tropical peatlands represent a globally significant carbon reserve accumulated over thousands of years of waterlogged conditions. It is unclear whether moderate drying predicted for northern peatlands will stimulate burning and carbon losses as has occurred in their smaller tropical counterparts where the carbon legacy has been destabilized due to severe drainage and deep peat fires. Capitalizing on a unique long-term experiment, we quantify the post-wildfire recovery of a northern peatland subjected to decadal drainage. We show that the moderate drop in water table position predicted for most northern regions triggers a shift in vegetation composition previously observed within only severely disturbed tropical peatlands. The combined impact of moderate drainage followed by wildfire converted the low productivity, moss-dominated peatland to a non-carbon accumulating shrub-grass ecosystem. This new ecosystem is likely to experience a low intensity, high frequency wildfire regime, which will further deplete the legacy of stored peat carbon.

The role of fire in UK peatland and moorland management: the need for informed, unbiased debate

Fire has been used for centuries to generate and manage some of the UKs cultural landscapes. Despite its complex role in the ecology of UK peatlands and moorlands, there has been a trend of simplifying the narrative around burning to present it as an only ecologically damaging practice. That fire modifies peatland characteristics at a range of scales is clearly understood. Whether these changes are perceived as positive or negative depends upon how trade-offs are made between ecosystem services and the spatial and temporal scales of concern. Here we explore the complex interactions and trade-offs in peatland fire management, evaluating the benefits and costs of managed fire as they are currently understood. We highlight the need for (i) distinguishing between the impacts of fires occurring with differing severity and frequency, and (ii) improved characterization of ecosystem health that incorporates the response and recovery of peatlands to fire. We also explore how recent research has been contextualized within both scientific publications and the wider media and how this can influence non-specialist perceptions. We emphasize the need for an informed, unbiased debate on fire as an ecological management tool that is separated from other aspects of moorland management and from political and economic opinions. This article is part of the themed issue ‘The interaction of fire and mankind’.

Exploiting the temperature effects on low frequency electrical spectra of sandstone: A comparison of effective diffusion path lengths

A number of recent investigations have highlighted the potential value of using relaxation times derived from electrical spectra to infer key physical properties of permeable rocks. To date, most studies have assumed a grain size or pore throat as a measure of the length scale of the ionic diffusive process, although this has been challenged in recent experimental investigations. We compare the electrical spectra of three sandstones, adopting a new approach in which the temperature of the rock samples is perturbed and the relaxation time measured as a function of temperature. Our results suggest that, for the sandstones tested here, the effective diffusion coefficient should be considered as a function of the electrical tortuosity. These findings may help explain the apparent long relaxation times observed in low-permeability rocks in recent experimental studies. We also highlight the need to account for temperature in related studies of electrical spectra.

Do peatland microforms move through time? Examining the developmental history of a patterned peatland using ground‐penetrating radar

Using ground-penetrating radar (GPR) to map subsurface patterns in peat physical properties, we investigated the developmental history of meso-scale surface patterning of microforms within a raised bog. Common offset GPR measurements were obtained along a 45-m transect, at frequencies ranging from 100 to 900 MHz. We found that low-frequency (central frequency = 240 MHz) showed a striking pattern of subsurface reflections that dip consistently in a northerly direction. The angle of these dipping reflectors is calculated using a semblance algorithm and was shown to average 3.9 degrees between a depth of 1.0 and 2.5 m. These dipping reflectors may indicate downslope migration of surface microforms during the development of the peatland. Based on the estimated angle and the rate of peat accumulation, the average rate of downslope propagation of these surface microforms is calculated at 9.8 mm per year. Further survey work is required to establish whether the downslope migration is common across the peatland.

Low Evapotranspiration Enhances the Resilience of Peatland Carbon Stocks to Fire

Boreal peatlands may be vulnerable to projected changes in the wildfire regime under future climates. Extreme drying during the sensitive post-fire period may exceed peatland ecohydrological resilience, triggering long-term degradation of these globally significant carbon stocks. Despite these concerns, we show low peatland evapotranspiration at both the plot and landscape scale post-fire, in water-limited peatlands dominated by feather moss that are ubiquitous across continental western Canada. Low post-fire evapotranspiration enhance the resilience of carbon stocks in such peatlands to wildfire disturbance and reinforces their function as a regional source or water. Near-surface water repellency may provide an important, previously unexplored, regulator of peatland evapotranspiration that can induce low evapotranspiration in the initial post-fire years by restricting the supply of water to the peat surface.

The peatland vegetation burning debate: keep scientific critique in perspective. A response to Brown et al. and Douglas et al.

We are glad that Brown et al. [1] and Douglas et al. [2] agree that there is a need to move forward in the debate regarding the use of fire as a management tool in the UK uplands and appreciate their robust responses to some of the issues we identified. We may not agree, but discussing these problems and balancing the current debate from an ecological viewpoint is important. Our recent paper [3] contained a critique of certain aspects of two recent papers they published [4] and [5]. We believe this critique was important, because we believe the interpretations they provided sometimes lacked adequate engagement with existing research on peatland fire ecology, had the potential for damaging misinterpretation, and occasionally appeared to have an unintentional lack of balance. In the case of Brown et al. [4], this concern was exacerbated by the fact it was a review paper and such publications aim to provide an authoritative overview of knowledge in a certain area. We believe there were several respects in which that standard was not met. We also critiqued media outreach and coverage associated with their papers and, in the case of Brown et al. [3], the publication protocol associated with a research report they issued [6]. Here, we briefly address Brown et al. and Douglas et al.s main concerns regarding our recent paper.

Peat depth as a control on moss water availability under evaporative stress.

Northern peatlands are a vital component of the global carbon cycle, containing large stores of soil organic carbon and acting as a long-term carbon sink. Moss productivity is an important factor in determining whether these wetlands will retain this function under future climatic conditions. Research on unsaturated water flow in peatlands, which controls moss productivity during periods of evaporative stress, has focused on relatively deep bog systems. However, shallower peatlands and marginal connective wetlands can be essential components of many landscape mosaics. In order to better understand factors influencing moss productivity, water balance simulations using Hydrus 1-D were run for different soil profile depths, compositions and antecedent moisture conditions. Our results demonstrate a bimodal distribution of peatland realizations; either primarily conserving water by limiting evapotranspiration or, maximizing moss productivity. For sustained periods of evaporative stress, both deep water storage and a shallow initial water table delay the onset of high vegetative stress, thus maximizing moss productivity. A total depth of sand and peat of 0.8 m is identified as the threshold above which increasing peat depth has no effect on changing vegetative stress response. In contrast, wetlands with shallow peat deposits (less than 0.5 m thick) are least able to buffer prolonged periods of evaporation due to limited labile water storage, and will thus quickly experience vegetative stress and so limit evaporation and conserve water. With a predicted increase in the frequency and size of rain events in continental North America the moss productivity of shallow wetland systems may increase, but also greater moisture availability will increase the likelihood they remain as wetlands in a changing climate.

Thermal sensitivity of CO 2 and CH 4 emissions varies with streambed sediment properties

Globally, rivers and streams are important sources of carbon dioxide and methane, with small rivers contributing disproportionately relative to their size. Previous research on greenhouse gas (GHG) emissions from surface water lacks mechanistic understanding of contributions from streambed sediments. We hypothesise that streambeds, as known biogeochemical hotspots, significantly contribute to the production of GHGs. With global climate change, there is a pressing need to understand how increasing streambed temperatures will affect current and future GHG production. Current global estimates assume linear relationships between temperature and GHG emissions from surface water. Here we show non-linearity and threshold responses of streambed GHG production to warming. We reveal that temperature sensitivity varies with substrate (of variable grain size), organic matter (OM) content and geological origin. Our results confirm that streambeds, with their non-linear response to projected warming, are integral to estimating freshwater ecosystem contributions to current and future global GHG emissions.Rivers and streams are important sources of carbon dioxide and methane; however, the drivers of these streambed gas fluxes are poorly understood. Here, the authors show that temperature sensitivity of streambed greenhouse gas emissions varies with substrate, organic matter content and geological origin.

Thermodynamic control of the carbon budget of a peatland.

The transformations and transitions of organic matter into, through, and out of an ecosystem must obey the second law of thermodynamics. This study considered the transition in the solid components of the organic matter flux through an entire ecosystem. Organic matter samples were taken from each organic matter reservoir and fluvial transfer pathway in a 100% peat‐covered catchment (Moor House National Nature Reserve, North Pennines, UK) and were analyzed by elemental analysis and bomb calorimetry. The samples analyzed were as follows: bulk aboveground and belowground biomass; individual plant functional types (heather, mosses, and sedges); plant litter layer; peat soil; and samples of particulate and dissolved organic matter (POM and DOM). Samples were compared to standards of lignin, cellulose, and plant protein. It was possible to calculate: enthalpy of formation ( urn:x-wiley:21698953:media:jgrg21153:jgrg21153-math-0001); entropy of formation ( urn:x-wiley:21698953:media:jgrg21153:jgrg21153-math-0002); and Gibbs free energy of formation ( urn:x-wiley:21698953:media:jgrg21153:jgrg21153-math-0003) for each of the samples and standards. The increase (decreasing negative values) in urn:x-wiley:21698953:media:jgrg21153:jgrg21153-math-0004 through the ecosystem mean that for all but litter production, the transformations through the system must be balanced by production of low (large negative values) urn:x-wiley:21698953:media:jgrg21153:jgrg21153-math-0005 products, not only CO2 or CH4 but also DOM. The change in urn:x-wiley:21698953:media:jgrg21153:jgrg21153-math-0006 down the peat profile shows that reaction of the soil organic matter decreases or even ceases at depth and the majority of the reaction has occurred above 40 cm below the surface. This approach represents a new objective way to test and trace organic matter transformations in and through an ecosystem.

Birmingham Bog outdoor laboratory: potentials and possibilities for embedding field-based teaching within the undergraduate classroom

ABSTRACT Providing cost-effective, hands-on field-based experiences to large cohorts of undergraduate students provides a core challenge for effective teaching and learning. This grand challenge is tackled through the construction of an exemplar outdoor learning environment within the Environmental Change Outdoor Laboratory (ECOLAB): Birmingham Bog (BB). Adjacent to the Geography building, the facility aims to produce a seamless, interconnected learning environment (in both space and time) that brings inaccessible fieldwork activities direct to the classroom at the time and frequency appropriate to the learning objectives. With the integration of this facility within a 3rd year undergraduate module, we explore through group interviews the ways in which BB adapted and influenced students’ engagement with lecture material, and the extent to which the approach can complement or replace current field based teaching activities. The group interviews identified how BB was considered an example of “effective learning” within the context of the wider degree programme. However, if confirmed, the value placed on residential field courses cannot be met by such campus experiences. Despite this, BB represents an increasingly fertile space for deeper stimulation and innovative ways of learning; diversifying pedagogical techniques and enabling students to re-engage with lecture content.