Department of Earth Science, Rice University, 6100 Main St., Houston, TX 77005, USA.
Cinco Ranch High School, Katy Independent School District, Katy, TX 77494, USA.
Sci Total Environ. 2017 Aug 15;592:316-325. doi: 10.1016/j.scitotenv.2017.03.073. Epub 2017 Mar 17.
Although charcoal's density and porosity shape its environmental roles (e.g. controlling its landscape movement and determining the internal pore space available as microbial habitat), the rate of change of these properties in the environment remains largely unknown. With time, charcoal pores may fill or charcoal particles may shatter, altering the ecosystem services delivered. In this study we examined the effects of environmental exposure on the density and porosity of charcoals pyrolyzed at two different temperatures (350 and 520°C). Fresh charcoal made from the dominant local tree (Pinus sylvestris) was returned in litter incubations to Norwegian boreal forest soils for 20months in three different placements: (i) aboveground, (ii) in the humus layer, and (iii) under the humus layer in contact with the mineral subsoil. By varying soil horizon placement we were able to separate the effects of infill from the effects of environmental disturbance on charcoal density and porosity. Environmental exposure changed charcoal density and porosity, and the response varied with environmental placement. Charcoal placed in soil layers increased in porosity by 1-2% after 20months' incubation. This is likely because open indentations on the charcoal surface became partially occluded, creating more detectable pore space. In contrast, the porosity of charcoal incubated aboveground decreased slightly (1-2% over 20months). Because there were no minerals or humic substances to infill the aboveground charcoal samples, this porosity reduction was likely caused by breakage of particles induced by weathering. When charcoal particles cleave through pores, internal pore space is destroyed. The small changes observed here indicate that environmental exposure did not trigger rapid shifts in charcoal density and porosity. In addition, these physical properties appear not to have reached equilibrium after 20months incubation, suggesting that the effect of environmental exposure on charcoal's physical properties occurs on the timescale of years to decades.
虽然木炭的密度和孔隙度决定了其环境作用（例如控制其景观运动和确定微生物栖息地的内部孔隙空间），但其在环境中的这些特性的变化率在很大程度上仍然未知。随着时间的推移，木炭的孔隙可能会填满，或者木炭颗粒可能会破碎，从而改变提供的生态系统服务。在这项研究中，我们研究了环境暴露对在两种不同温度（350 和 520°C）下热解的木炭的密度和孔隙度的影响。从当地优势树种（欧洲赤松）中提取的新鲜木炭在 litter 孵育中返回挪威北方森林土壤中 20 个月，有三种不同的放置方式：（i）在地上，（ii）在腐殖质层中，以及（iii）在与矿物底土接触的腐殖质层下。通过改变土壤层次的放置位置，我们能够将木炭密度和孔隙度的填充效应与环境干扰效应分开。环境暴露改变了木炭的密度和孔隙度，且响应随环境位置而变化。在土壤层中放置的木炭在孵育 20 个月后，孔隙度增加了约 1-2%。这可能是因为木炭表面的开口凹陷部分被堵塞，从而创造了更多可检测的孔隙空间。相比之下，在地上孵育的木炭的孔隙度略有下降（20 个月内约减少 1-2%）。由于没有矿物质或腐殖质物质填充地上的木炭样本，这种孔隙度的降低可能是由于风化引起的颗粒破裂所致。当木炭颗粒穿过孔隙时，内部孔隙空间被破坏。这里观察到的微小变化表明，环境暴露没有引发木炭密度和孔隙度的快速变化。此外，这些物理性质在孵育 20 个月后似乎没有达到平衡，这表明环境暴露对木炭物理性质的影响发生在数年至数十年的时间尺度上。
