College of Water Sciences, Beijing Normal University, Beijing 100875, China; Engineering Research Center of Groundwater Pollution Control and Remediation, Ministry of Education, Beijing 100875, China.
School of Civil Engineering, University of Leeds, Leeds LS2 9JT, UK.
J Contam Hydrol. 2022 Jun;248:104017. doi: 10.1016/j.jconhyd.2022.104017. Epub 2022 Apr 28.
n-Alkanes, the main component of diesel fuel, are common light non-aqueous phase liquids (LNAPLs) that threaten ecological security. The subsurface from vadose zone, through fluctuating zone, to saturated zone, is a critical multi-interface earth layer which significantly affects the biodegradation processes of n-alkanes. A pilot-scale diesel contaminated aquifer column experiment has been undertaken to investigate the variations of bacterial community and alkane monooxygenase (alkB) gene abundance in these zones due to water-table fluctuations. The n-alkanes formed a layer immediately above the water table, and when this was raised, they were carried upwards through the fluctuating zone into the vadose zone. Water content and n-alkanes component C10-C12 are main factors influencing bacterial community variation in the vadose zone, while C10-C12 is a key driving factor shaping bacterial community in the fluctuating zone. The most abundant bacterial phyla at all three zones were Proteobacteria, Firmicutes and Actinobacteria, but moisture-niche selection determined their relative abundance. The intermittent wetting cycle resulted in higher abundance of Proteobacteria, and lower abundance of Actinobacteria in the vadose and fluctuating zones in comparison to the control column with a static water-table. The abundances of the alkB gene variants were relatively uniform in different zones, probably because the bacterial populations harboring alkB gene are habituated to biogenic n-alkanes rather than responding to diesel fuel contamination. The variation in the bacterial populations with height due to moisture-niche selection had very little effect on the alkB gene abundance, possibly because numerous species in both phyla (Proteobacteria and Actinobacteria) carry an alkB gene variant. Nevertheless, the drop in the water table caused a short-term spike in alkB gene abundance in the saturated zone, which is most likely associated with transport of solutes or colloids from the fluctuating zone to bacteria species in the saturated zone, so a fluctuating water table could potentially increase n-alkane biodegradation function.
正构烷烃是柴油燃料的主要成分，也是常见的轻质非水相液体（LNAPLs），它们会对生态安全造成威胁。从包气带、变动带，到饱和带的地下环境是一个关键的多界面土层，它会显著影响正构烷烃的生物降解过程。本研究开展了一个中试规模的柴油污染含水层柱实验，以调查由于地下水位波动，这些带中正构烷烃的细菌群落和烷烃单加氧酶（alkB）基因丰度的变化。正构烷烃在地下水位之上形成一个层，当地下水位上升时，它们会通过变动带向上移动到包气带。含水量和正构烷烃的 C10-C12 组分是影响包气带细菌群落变化的主要因素，而 C10-C12 是塑造变动带细菌群落的关键驱动因素。所有三个带中最丰富的细菌门是变形菌门、厚壁菌门和放线菌门，但水分小生境的选择决定了它们的相对丰度。与具有静态地下水位的对照柱相比，间歇增湿循环导致包气带和变动带中变形菌门的丰度更高，而放线菌门的丰度更低。在不同带中，alkB 基因变体的丰度相对均匀，这可能是因为携带 alkB 基因的细菌种群已经适应了生物源正构烷烃，而不是对柴油燃料污染做出响应。由于水分小生境的选择，细菌种群随高度的变化对 alkB 基因丰度的影响很小，这可能是因为两个门（变形菌门和放线菌门）中的许多物种都携带 alkB 基因变体。然而，地下水位的下降导致了饱和带中 alkB 基因丰度的短期飙升，这很可能与从变动带向饱和带的溶质或胶体的运输有关，因此地下水位的波动可能会潜在地增加正构烷烃的生物降解功能。
