Department of Chemical Engineering, McMaster University, Hamilton, Ontario, Canada.
School of Geography & Earth Sciences, McMaster University, Hamilton, Ontario, Canada.
Sci Total Environ. 2020 Apr 20;714:136444. doi: 10.1016/j.scitotenv.2019.136444. Epub 2020 Jan 16.
Boreal peatlands provide critical global and regional ecosystem functions including climate regulation and nutrient and water retention. Wildfire represents the largest disturbance to these ecosystems. Peatland resilience depends greatly on the extent of post-fire peat soil hydrophobicity. Climate change is altering wildfire intensity and severity and consequently impacting post-fire peat soil chemistry and structure. However, research on fire-impacted peatlands has rarely considered the influence of peat soil chemistry and structure on peatland resilience. Here we characterized the geochemical and physical properties of natural peat soils under laboratory heating conditions. The general trend observed is that hydrophilic peat soils become hydrophobic under moderate heating and then become hydrophilic again after heating for longer, or at higher, temperatures. The loss of peat soil hydrophilicity initially occurs due to evaporative water loss (250 °C and 300 °C for <5 min). Gently but thoroughly dried peat soils (105 °C for 24 h) also show mass losses after heating, indicating the loss of organic compounds through thermal degradation. Gas chromatography-mass spectrometry (GC-MS) and Fourier transform infrared (FTIR) spectroscopy were used to characterize the chemistry of unburned and 300 °C burned peat soils, and various fatty acids, polycyclic compounds, saccharides, aromatic acids, short-chain molecules, lignin and carbohydrates were identified. We determined that the heat-induced degradation of polycyclic compounds and aliphatic hydrocarbons, especially fatty acids, caused dried, hydrophobic peat soils to become hydrophilic after only 20 min of heating at 300 °C. Furthermore, peat soils became hydrophilic more quickly (20 min vs 6 h) with an increase in heat from 250 °C to 300 °C. Minimal structural changes occurred, as characterized by BET and SEM analyses, confirming that surface chemistry, in particular fatty acid content, rather than structure govern changes in peat soil hydrophobicity.
北方泥炭地提供了关键的全球和区域生态系统功能，包括气候调节、养分和水分保持。野火是对这些生态系统的最大干扰。泥炭地的恢复能力在很大程度上取决于火灾后泥炭土壤疏水性的程度。气候变化正在改变野火的强度和严重程度，从而影响火灾后泥炭土壤的化学性质和结构。然而，关于受火灾影响的泥炭地的研究很少考虑泥炭土壤化学性质和结构对泥炭地恢复能力的影响。在这里，我们在实验室加热条件下对天然泥炭土壤的地球化学和物理性质进行了表征。观察到的总体趋势是，亲水性泥炭土壤在适度加热下变得疏水性，然后在更长时间或更高温度加热后再次变得亲水性。泥炭土壤疏水性的丧失最初是由于蒸发失水（250°C 和 300°C 下<5 分钟）。即使是轻微但彻底干燥的泥炭土壤（105°C 下 24 小时）在加热后也会出现质量损失，这表明有机化合物通过热降解而损失。气相色谱-质谱联用（GC-MS）和傅里叶变换红外（FTIR）光谱用于表征未燃烧和 300°C 燃烧泥炭土壤的化学性质，鉴定出各种脂肪酸、多环化合物、糖、芳香酸、短链分子、木质素和碳水化合物。我们确定，热诱导的多环化合物和脂肪族碳氢化合物的降解，特别是脂肪酸的降解，导致在 300°C 加热仅 20 分钟后，干燥的疏水性泥炭土壤变得亲水。此外，随着加热温度从 250°C 增加到 300°C，泥炭土壤的亲水性增加得更快（20 分钟对 6 小时）。BET 和 SEM 分析表明，结构变化最小，这证实了表面化学性质，特别是脂肪酸含量，而不是结构，控制着泥炭土壤疏水性的变化。
