State Key Laboratory of Pollution Control and Resource Reuse, School of the Environment, Nanjing University , Jiangsu 210023, China.
State Key Laboratory of Petroleum Pollution Control, CNPC Research Institute of Safety and Environmental Technology , Beijing 102206, China.
Environ Sci Technol. 2017 Dec 5;51(23):13723-13732. doi: 10.1021/acs.est.7b04232. Epub 2017 Nov 21.
The fluvial export of dissolved black carbon (DBC) is a major land-ocean flux in the global black carbon cycle, affecting the size of refractory carbon pool in the oceans. The aggregation behavior of DBC is a significant determinant of its transport and vertical mass flux. In this study, the aggregation kinetics and interaction energy of DBC leached from biochar were investigated. DBC was mainly stabilized by hydration force and underwent structural compacting in divalent cation solutions. Na and Mg had limited impact on the colloidal stability of DBC due to the strong hydration of these cations. Ca and Ba readily destabilized DBC by forming inner-sphere complexes, reducing its hydrophilicity. Consistently, charge reversal of DBC was observed with high concentrations of Ca and Ba. Simulated sunlight exposure led to photo-oxidation of DBC, increasing its colloidal stability. DBC behaved nonconservatively in laboratory mixing experiments using estuary water samples due to aggregation/sedimentation; while model aquatic humic acid behaved conservatively. Our results infer that there is a vertical mass flux of DBC and possible fractionation from the dissolved organic matter pool in the fluvial and estuarine systems, which have been overlooked in efforts to determine global carbon budgets and associated climate change implications.
河流向海洋输出溶解态黑碳（DBC）是全球黑碳循环中的一个主要陆海通量，影响着海洋中难降解碳库的规模。DBC 的聚集行为是决定其输运和垂直物质通量的重要因素。本研究考察了生物炭中溶出的 DBC 的聚集动力学和相互作用能。DBC 主要通过水合力稳定，在二价阳离子溶液中发生结构压实。由于这些阳离子的强水合作用，Na 和 Mg 对 DBC 的胶体稳定性影响有限。Ca 和 Ba 容易通过形成内球配合物而使 DBC 失稳，降低其亲水性。相应地，DBC 的电荷反转伴随着 Ca 和 Ba 的高浓度出现。模拟阳光照射导致 DBC 的光氧化，增加了其胶体稳定性。由于聚集/沉降，DBC 在使用河口水样进行的实验室混合实验中表现为非保守行为；而模型水生腐殖酸则表现为保守行为。我们的研究结果推断，在河流和河口系统中，DBC 存在垂直物质通量和可能的从溶解有机物质库中分离出来的情况，这在确定全球碳预算和相关气候变化影响方面被忽视了。
