Fire decreases near-surface hydraulic conductivity and macropore flow in blanket peat

Abstract

Many peatlands have been subjected to wildfire or prescribed burning but it is not 22 known how these fires influence near-surface hydrological processes. Macropores are 23 important flowpaths in the upper layers of blanket peat and were investigated through 24 the use of tension disk infiltrometers, which also provide data on saturated hydraulic 25 conductivity. Measurements were performed on unburnt peat (U), where prescribed 26 burning had taken place 2 years (B2), four years (B4) and >15 (B15+) years prior to 27 sampling, and where a wildfire (W) had taken place four months prior to sampling. 28Where there had been recent burning (B2, B4 and W), saturated hydraulic 29 conductivity was approximately three times lower than where there was no burning 30 (U) or where burning was last conducted > 15 years ago (B15+). Similarly, the 31 contribution of macropore flow to overall infiltration was significantly lower 32 (between 12 and 25 % less) in the recently burnt treatments compared to B15+ and U. 33There were no significant differences in saturated hydraulic conductivity or 34 macropore flow between peat which had been subject to recent wildfire (W) and those 35 which had undergone recent prescribed burning (B2 and B4). The results suggest fire 36 influences the near-surface hydrological functioning of peatlands but that recovery in 37 terms of saturated hydraulic conductivity and macropore flow may be possible within 38 two decades if there are no further fires.

Impacts of peat bulk density, ash deposition and rainwater chemistry on establishment of peatland mosses

“…On the other hand, the bulk densitywater retention plots presented by Thompson and Waddington (2013) for soil water pressures of -100mb flatten out considerably for bulk densities >0.17 g cm-3 and so the effects on water retention, at -100mb, of enhanced bulk density beyond the range we tested may not be substantially greater in the field for fire affected sites. The normal bulk density treatment was similar to bulk densities measured by Holden et al (2014) on unburned plots. As water was supplied from below throughout the experiment, water intercepted from precipitation was not accounted for, but past work has shown that dependence on precipitation can increase susceptibility to drought and reduce carbon uptake in Sphagnum (Nijp et al 2014).…”

“…The fact that C. introflexus was unaffected reflects the species' lower Ellenberg indicator value for moisture (Table 1) and could indicate a risk of a shift to species which can tolerate lower water availability at high bulk density. Holden et al (2014) found that peat bulk densities decreased with time since burning, so leaving sites unburned for longer may create more favourable conditions for Sphagnum establishment. However, the high bulk density treatment in this experiment was actually lower than many of the bulk densities measured on burned plots by Holden et al (2014), suggesting that greater limitations to Sphagnum establishment may occur in the field.…”

“…Holden et al (2014) found that peat bulk densities decreased with time since burning, so leaving sites unburned for longer may create more favourable conditions for Sphagnum establishment. However, the high bulk density treatment in this experiment was actually lower than many of the bulk densities measured on burned plots by Holden et al (2014), suggesting that greater limitations to Sphagnum establishment may occur in the field. On the other hand, the bulk densitywater retention plots presented by Thompson and Waddington (2013) for soil water pressures of -100mb flatten out considerably for bulk densities >0.17 g cm-3 and so the effects on water retention, at -100mb, of enhanced bulk density beyond the range we tested may not be substantially greater in the field for fire affected sites.…”

“…Increased bulk density can reduce water availability to mosses, which are nonvascular and rely on passive capillary transport, but species may differ in their responses depending on water requirements and desiccation tolerance (Sagot and Rochefort 1996). Holden et al (2014) measured a mean bulk density of 0.259 (±0.013) g cm −3 in peatland plots where the surface vegetation had been subjected to prescribed burning 2 years previously compared to 0.110 (±0.008) g cm −3 in unburned plots, potentially due to drying-induced compression and collapse of the peat mass after burning. Prescribed burns are normally controlled to burn vegetation without igniting the underlying peat.…”

Impacto da carga combustível nas propriedades hidráulicas de um solo pós-incêndio em condições laboratoriais

“…Segundo , em solos onde a matéria orgânica é responsável pela agregação, a combustão contribui para a perda de estabilidade dos agregados e à libertação de partículas finas provenientes quer dos agregados quer das cinzas (Zavala et al, 2009). Este efeito causa a colmatação dos poros, principalmente na superfície do solo, o que contribui para a diminuição da capacidade de infiltração da água (Holden et al, 2014 Dada a diversidade dos graus de severidade que podem ocorrer num incêndio florestal, os resultados sugerem que os parâmetros associados à condutividade hidráulica têm um padrão heterogéneo no pós-incêndio, ou seja, existem distintos mosaicos de zonas de infiltração e de formação ou transmissão da escorrência (cawson et al, 2013;Keesstra et al, 2014). Este facto é relevante na altura de projetar planos de atuação e recuperação de solos queimados (Williams et al, 2015), onde um estudo detalhado poderá permitir a identificação de áreas de maior risco de erosão e a aplicação de medidas corretivas à microescala.…”