Black (pyrogenic) carbon in boreal forests: a synthesis of current knowledge and uncertainties
Black (pyrogenic) carbon in boreal forests: a synthesis of current knowledge and uncertainties
复制标题
北方森林中的黑（热成）碳：当前知识和不确定性的综合
DOI：
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发表时间：
2006
期刊：
影响因子：
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通讯作者：
M. Schmidt
中科院分区：
文献类型：
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作者：
C. Preston;M. Schmidt
北方地区的碳（C）循环受到火灾的强烈影响，火灾将生物质和碎屑碳主要转化为气态形式（CO2和较小比例的CO和CH4），约1-7%的质量转化为热解碳（PyC）。 PyC 主要以固体烧焦残留物的形式产生，包括视觉上定义的木炭和化学上因其耐实验室氧化性而定义的黑碳 (BC) 部分，以及比例低得多的挥发性烟灰和多环芳烃 (PAH)。所有 PyC 的特征都是稠合芳环，但簇大小各不相同，并且存在其他元素（N、O）和官能团。当前有兴趣更精确地定义 PyC 在北方地区 C 循环中的作用，有几个原因。首先，PyC 不易分解，因此有助于在土壤和沉积物中形成非常稳定的碳库。其次，它主要通过其吸附特性和阳离子交换能力影响土壤过程，第三，烟灰气溶胶吸收太阳辐射，可能导致全球变暖。然而，解决这些主题所需的基本信息存在很大差距。虽然木炭通常通过视觉标准来定义，但BC的分析方法主要基于各种抗氧化性测量或苯多羧酸的产率。这些方法仍在开发中，并捕获 PyC“连续体”的不同部分。关于北方森林 PyC 产量和库存的定量报告很少（北方泥炭地基本上没有），并且由于实验目标和方法不同以及术语不一致，结果难以比较。几乎没有对北方野火产生的碳化碳气溶胶产生的直接现场测量，并且关于 PyC 损失的速率和机制的直接信息也很少。野火烧焦的生物质和森林地面的结构特征通常表明热蚀变程度较低，大部分材料的 H/C 比仍大于 0.2，芳香族簇尺寸较小。对于化学上更难降解的BC部分，各种主要间接证据表明分解非常缓慢，周转时间为千年时间尺度（5000？10 000年），具体取决于环境条件和PyC特性，但土壤中PyC储存的主要限制可能是随后的火灾消耗。降解的功能化 PyC 也被纳入腐殖化土壤有机质中，并以溶解和颗粒形式输送到沉积物中。北部地区的固体残留物产量估计为 7?17 Tg BC y?1，气溶胶产量为 2?2.5 Tg BC y?1。主要研究需求包括北方森林和泥炭地的 PyC 生产和库存的基本现场数据，适合支持碳预算模型，以及开发标准化分析方法和改进的方法来评估北方野火典型炭的化学顽抗性。为了有效地实现这些目标，需要更加重视跨学科合作。
The carbon (C) cycle in boreal regions is strongly influenced by fire, which converts biomass and detrital C mainly to gaseous forms (CO2 and smaller proportions of CO and CH4), and some 1?7% of mass to pyrogenic C (PyC). PyC is mainly produced as solid charred residues, including visually-defined charcoal, and a black carbon (BC) fraction chemically defined by its resistance to laboratory oxidation, plus much lower proportions of volatile soot and polycyclic aromatic hydrocarbons (PAHs). All PyC is characterized by fused aromatic rings, but varying in cluster sizes, and presence of other elements (N, O) and functional groups. There are several reasons for current interest in defining more precisely the role of PyC in the C cycle of boreal regions. First, PyC is resistant to decomposition, and therefore contributes to very stable C pools in soils and sediments. Second, it influences soil processes, mainly through its sorption properties and cation exchange capacity, and third, soot aerosols absorb solar radiation and may contribute to global warming. However, there are large gaps in the basic information needed to address these topics. While charcoal is commonly defined by visual criteria, analytical methods for BC are mainly based on various measures of oxidation resistance, or on yield of benzenepolycarboxylic acids. These methods are still being developed, and capture different fractions of the PyC "continuum". There are few quantitative reports of PyC production and stocks in boreal forests (essentially none for boreal peatlands), and results are difficult to compare due to varying experimental goals and methods, as well as inconsistent terminology. There are almost no direct field measurements of BC aerosol production from boreal wildfires, and little direct information on rates and mechanisms for PyC loss. Structural characterization of charred biomass and forest floor from wildfires generally indicates a low level of thermal alteration, with the bulk of the material having H/C ratios still >0.2, and small aromatic cluster sizes. For the more chemically-recalcitrant BC fraction, a variety of mainly circumstantial evidence suggests very slow decomposition, with turnover on a millennium timescale (5000?10 000 y), depending on environmental conditions and PyC properties, but the main limitation to PyC storage in soil is likely consumption by subsequent fires. Degraded, functionalized PyC is also incorporated into humified soil organic matter, and is transported to sediments in dissolved and particulate form. Boreal production is estimated as 7?17 Tg BC y?1 of solid residues and 2?2.5 Tg BC y?1 as aerosols. Primary research needs include basic field data on PyC production and stocks in boreal forests and peatlands, suitable to support C budget modeling, and development of standardized analytical methods and of improved approaches to assess the chemical recalcitrance of typical chars from boreal wildfires. To accomplish these goals effectively will require much greater emphasis on interdisciplinary cooperation.