Burke Molly, Marín-Spiotta Erika, Ponette-González Alexandra G
Department of Geography and the Environment, University of North Texas, 1155 Union Circle #305279, Denton, TX, 76203, USA.
Department of Geography, University of Utah, Salt Lake City, UT, 84112, USA.
Carbon Balance Manag. 2024 Mar 2;19(1):9. doi: 10.1186/s13021-024-00255-3.
Black carbon (BC) encompasses a range of carbonaceous materials--including soot, char, and charcoal--derived from the incomplete combustion of fossil fuels and biomass. Urban soils can become enriched in BC due to proximity to these combustion sources. We conducted a literature review of BC in urban soils globally and found 26 studies reporting BC and total organic carbon (TOC) content collected to a maximum of 578 cm depth in urban soils across 35 cities and 10 countries. We recorded data on city, climate, and land use/land cover characteristics to examine drivers of BC content and contribution to TOC in soil.
All studies were conducted in the northern hemisphere, with 68% of the data points collected in China and the United States. Surface samples (0-20 cm) accounted for 62% of samples in the dataset. Therefore, we focused our analysis on 0-10 cm and 10-20 cm depths. Urban soil BC content ranged from 0-124 mg/g (median = 3 mg/g) at 0-10 cm and from 0-53 mg/g (median = 2.8 mg/g) at 10-20 cm depth. The median proportional contribution of BC to TOC was 23% and 15% at 0-10 cm and 10-20 cm, respectively. Surface soils sampled in industrial land use and near roads had the highest BC contents and proportions, whereas samples from residential sites had among the lowest. Soil BC content decreased with mean annual soil temperature.
Our review indicates that BC comprises a major fraction (nearly one quarter) of the TOC in urban surface soils, yet sampling bias towards the surface could hide the potential for BC storage at depth. Land use emerged as an importer driver of soil BC contents and proportions, whereas land cover effects remain uncertain. Warmer and wetter soils were found to have lower soil BC than cooler and drier soils, differences that likely reflect soil BC loss mechanisms. Additional research on urban soil BC at depth and from diverse climates is critical to better understand the role of cities in the global carbon cycle.
黑碳（BC）包含一系列碳质材料，包括煤烟、焦炭和木炭，它们源自化石燃料和生物质的不完全燃烧。由于靠近这些燃烧源，城市土壤中的黑碳含量可能会增加。我们对全球城市土壤中的黑碳进行了文献综述，发现有26项研究报告了在10个国家的35个城市的城市土壤中，采集深度最大为578厘米的黑碳和总有机碳（TOC）含量。我们记录了有关城市、气候以及土地利用/土地覆盖特征的数据，以研究黑碳含量的驱动因素及其对土壤中总有机碳的贡献。
所有研究均在北半球进行，68%的数据点来自中国和美国。表层样本（0 - 20厘米）占数据集中样本的62%。因此，我们将分析重点放在0 - 10厘米和10 - 20厘米深度。城市土壤中黑碳含量在0 - 10厘米深度范围为0 - 124毫克/克（中位数 = 3毫克/克），在10 - 20厘米深度范围为0 - 53毫克/克（中位数 = 2.8毫克/克）。黑碳对总有机碳的中位数比例贡献在0 - 10厘米和10 - 20厘米深度分别为23%和15%。在工业用地和道路附近采集的表层土壤黑碳含量和比例最高，而来自居民区的样本含量和比例最低。土壤黑碳含量随年平均土壤温度降低。
我们的综述表明，黑碳在城市表层土壤的总有机碳中占很大比例（近四分之一），然而对表层的采样偏差可能掩盖了深层黑碳储存的潜力。土地利用是土壤黑碳含量和比例的一个重要驱动因素，而土地覆盖的影响仍不确定。研究发现，温暖湿润的土壤比寒冷干燥的土壤黑碳含量低，这种差异可能反映了土壤黑碳损失机制。对不同气候条件下城市土壤深层黑碳进行更多研究，对于更好地理解城市在全球碳循环中的作用至关重要。
