Peatlands are among the many ecosystems affected by annual fire occurrence, in the form of both wildfires and prescribed burns. These fires create a range of charred vegetation products; ranging from slightly charred matter to ash and soot, these materials are referred to as ‘black carbon’ (BC).
BC constitutes a potentially refractory, high density store of carbon, with demonstrated global carbon cycle importance. Whilst BC has some demonstrated resilience to physical and elemental change over time, ecosystem processes lead to degradation at varying rates. Such degradation can result in aqueous and particulate losses of carbon from BC. An improved understanding of the characteristics of BC is required in order to more fully quantify its role in the carbon cycle spatially and temporally, with both feedstocks of BC and field conditions leading to significantly different degradation rates.
Lab-based experiments were enacted to characterise the kinds of BC that would form in a UK peatland fire, using observed fire temperature and duration values, as well as common peatland vegetation species, to produce BC samples. These samples were grouped by mass loss (e.g. ~60% relating to a ‘low severity’ burn), with short/hot burns (e.g. 2 minutes/600°C) being compared to longer/cooler burns (e.g. 10 minutes/350°C), in order to assess any variance between samples. Using elemental, physical and molecular analyses, it was demonstrated that mass loss can act as a good indicator of BC composition.
C values displayed a relatively low range of values across all severity groups (59-69% for Vaccinium myrtillus, 54-66% for Calluna vulgaris and 46-65% for Polytrichum juniperinum), though the C concentration in relation to mass loss varies between species. Surface area values show a good deal of agreement between grouped mass loss samples, though at high burn severities a greater degree of variance is observable (e.g. ~13-50m2/g-1 for very high burn severity Polytrichum samples). Broad trends in molecular composition are were also evident as burn severity increases, with minimal variance between samples within severity groups.
These findings provide good insight into the potential range of BC characteristics that would be observable in a peatland fire; such information will help quantify the role of BC within the global carbon cycle, as well as improving understanding of fire impacts on affected plots.