Landscape fires annually generate large quantities of black carbon. The water-soluble fraction of black carbon (i.e., dissolved black carbon/DBC) is an important constituent of the dissolved organic carbon (DOC) pool, playing a crucial role in the global budget of refractory carbon and climate change. A key challenge in constraining the flux and fate of riverine DBC is to develop targeted and accurate quantification methods. Herein, we report that benzenepentacarboxylic acid (B5CA) intrinsically present in DBC can be used as an exclusive and holistic marker (representing both condensed aromatics and less-/nonaromatic fractions) for DBC quantification. B5CA was universally detected in water extractions of biochar and fire-affected soils with relatively large abundance but not produced by nonthermogenic processes. It has good mobility in the environment as it is not readily precipitated by cations or adsorbed by common geosorbents. B5CA also represents the recalcitrant components of DBC with excellent stability against photodegradation and biodegradation. Applying B5CA as the DBC marker in surface waters of the Changjiang River (i.e., the third largest river in the world), we calculate the DBC concentration in the downstream Changjiang River to be 4.8 ± 5.5% of the DOC flux. Our work provides a simple and reliable approach for the accurate quantification and source tracking of DBC in the soil and aquatic carbon pools.

中文翻译：

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苯聚（羧酸）作为唯一的内在标记来评估溶解黑碳的河流出口


景观火灾每年都会产生大量黑碳。黑碳的水溶性部分（即溶解黑碳/DBC）是溶解有机碳（DOC）库的重要组成部分，在全球难熔碳预算和气候变化中发挥着至关重要的作用。限制河流 DBC 的通量和归宿的一个关键挑战是开发有针对性的、准确的量化方法。在此，我们报告说，DBC 中固有存在的苯五甲酸 (B5CA) 可用作 DBC 定量的唯一整体标记物（代表稠合芳烃和较少/非芳烃馏分）。 B5CA 在生物炭和受火灾影响的土壤的水提取物中普遍检测到，丰度相对较高，但非产热过程不会产生。它在环境中具有良好的流动性，因为它不易被阳离子沉淀或被常见的地质吸附剂吸附。 B5CA 还代表了 DBC 的顽固成分，具有出色的光降解和生物降解稳定性。采用B5CA作为长江（世界第三大河）地表水体的DBC标记，计算出长江下游的DBC浓度为DOC通量的4.8±5.5%。我们的工作为土壤和水生碳库中 DBC 的准确定量和来源跟踪提供了一种简单可靠的方法。