“城—郊—乡”样带土壤黑碳空间变异特征及来源解析

Black carbon (BC) is an important component of soil organic carbon (SOC). Being considered highly recalcitrant, it has made BC playing an important role in the global carbon and oxygen biogeochemical cycles and SOC pool. Thus the study of geochemical characteristics and environmental effects of BC in soil have received more and more attentions. As urban soil is an important carbon sink in the terrestrial ecosystems, its carbon cycle is impacted by the urbanization, industrialization as well as other human activities. In recent years, the level of urbanization in China is continually rising, however, to what extent the variation of BC in soil, carbon pool and carbon cycle are impacted by this process still remains unknown. Thus, in this research, a case study in Wuhan City and surrounding rural areas is conducted to contrast the BC quantities in soils along an urban-suburban-rural gradient, via multiple research methods such as thermo-optical reflectance method, soil physical and chemical properties identifying, carbon isotope and ratio source apportionment method. The major purposes of this study include to understand the alteration in spatial distribution of soil BC and its storage, to discuss the influence of gradient change in physical and chemical properties of soils on BC accumulation, and to reveal the main sources of BC and to estimate the relative contribution rate, therefore to understand the likely influence on soil carbon pool and carbon cycle accurately from the perspective of urbanization. This research will provide basic data and insight into the law of the carbon cycle and the soil carbon pool in urban ecosystem. It will also provide scientific evidence for regional BC study.

黑碳是土壤有机碳的重要组成部分，因其化学惰性及热稳定性，使得它对全球碳和氧的生物地球化学循环及土壤有机碳库有重要影响，受到国内外学者的广泛关注。城市土壤作为陆地生态系统中重要的碳汇，其碳循环直接受到城市化、工业化等人为活动的扰动。近年来我国城市化水平不断加剧，但是城市化过程对土壤黑碳含量变化、碳库和碳循环的影响究竟有多大，目前还不清楚。本研究拟以武汉及周边农村为例，通过热光反射法、土壤理化性质测定、碳同位素示踪、比值源解析法等方法手段，对“城—郊—乡”梯度土壤中的黑碳进行研究。主要目的是研究土壤黑碳含量空间变异特征及碳库储量大小，探讨土壤基本理化性质梯度变化对黑碳累积的影响，揭示土壤中黑碳的主要来源并对其贡献进行估算，从而更准确地理解城市化过程对土壤碳库及碳循环的潜在影响。本研究可为城市生态系统碳循环和土壤碳库提供基础数据与规律认识，也为区域黑碳研究提供科学依据。

近年来我国城市化水平不断加剧，但是城市化过程对土壤黑碳含量变化、碳库和碳循环的影响究竟有多大，目前还不清楚。本研究拟以武汉市及周边地区为例，通过热光反射法、土壤理化性质测定、碳同位素示踪、比值源解析法等方法手段，对“城—郊—乡”梯度土壤中的黑碳进行研究，研究土壤黑碳含量空间变异特征及碳库储量大小，探讨土壤基本理化性质对黑碳累积的影响，揭示土壤中黑碳的主要来源并对其贡献进行估算。主要结果如下：.（1）土壤黑碳、焦炭、烟炱含量水平及空间变异特征. 武汉市四个不同功能区中，公园绿地黑碳含量介于0.01-2.70g/kg之间，大学校园黑碳含量介于0.01-8.46g/kg之间，道路绿化带黑碳含量介于0.04-4.01g/kg之间，农田旱地黑碳含量在0.03-2.91g/kg之间。不同功能区黑碳含量平均值从高到低顺序为：大学校园>道路绿化带>公园绿地>农田旱地。土壤黑碳、焦炭、烟炱的变异系数均大于100%，属于强变异。. 黄石市表层土壤中黑碳含量的变化范围为0.01-5.79g/kg，平均值为1.06g/kg。.（2）土壤理化性质对有机碳、总氮及黑碳累积的影响. 在武汉市偏中性表层土壤中，pH值与黑碳含量之间相关性并不显著；土壤TOC、TP、碳酸盐含量与黑碳含量之间存在一定负相关。黑碳与TOC、焦炭和烟炱之间存在显著的正相关，说明黑碳是土壤有机碳的重要组成部分，对黑碳的积累有重要影响。.（3）土壤中黑碳的可能来源. 黄石市土壤焦炭/烟炱比值(char/soot)分析结果表明土壤中的黑碳受人为源的影响很大，主要来源于化石燃料燃烧（工业燃煤及机动车尾气排放）。武汉市表层土壤中char/soot比值均小于3.0，说明武汉市表层土壤中的黑碳主要来源于化石燃料的燃烧，如燃煤发电以及机动车尾气的排放等。char/soot比值大于2.5的样品出现频率只有1.69，除了化石燃料燃烧外，可能还和农田秸秆焚烧以及农村柴薪燃烧有关。. 以上结论对于对研究城市生态系统土壤有机碳循环和土壤碳库提供了基础数据。