高砷含水层参与腐殖酸-铁矿物转化的关键微生物群落及其对砷迁移转化的影响

Key microbial communities involved in humic acid-Fe mineral transformation in high arsenic aquifers and their effects on arsenic release

摘要:

【目的】探究不同腐殖酸浓度下参与含砷水铁矿转化的微生物类群组成和丰度变化及对砷释放的影响，预测原位高砷含水层中功能微生物群参与有机质—含砷铁矿物转化过程对砷转化释放的作用。【方法】对河套平原高砷地下水和同深度高砷沉积物中的铁还原功能群落进行富集培养，构建室内厌氧微宇宙体系，将富集菌群分别加入到实验室条件下合成的不同浓度腐殖酸(0、1.5、7、14 mg C/L)-含砷水铁矿体系中，通过体系中砷、铁形态及浓度的变化分析，结合高通量测序技术、X-射线衍射(X-ray diffractometer, XRD)，探究不同条件下砷的释放固定和群落的演替。【结果】高砷地下水组(G组)和沉积物组(S组)富集得到的铁还原功能群落具有明显差异，G组中以Aeromonadaceae为特殊优势菌群，而S组中以Shewanellaceae为特殊优势菌群。微宇宙实验结果显示，S组的铁还原量相对较高且速率较快；G组与S组中液相砷形态存在明显差异，整个培养期内G组均以As(V)为主，而S组中前期以As(V)为主，当反应到达20 d时液相As(III)高达3.4 μmol/L，推测此时具有砷还原功能的群落占优势地位。当反应达到45 d时，G组和S组中液相砷在添加腐殖酸下均呈现不同程度的固定。不同腐殖酸浓度影响下砷的释放量不同，G组中砷释放量与腐殖酸浓度相一致，而S组中在腐殖酸浓度为7 mg C/L条件下砷释放量最低。X-射线衍射结果显示，S组铁矿物整体转化程度较高，但S组和G组均以针铁矿为主。冗余分析(redundancy analysis, RDA)结果显示，反应前后群落组成和相对丰度发生较大变化，砷添加和腐殖酸添加对群落组成变化具有显著影响。G组向苜蓿科(Comamonadaceae)、脱硫杆菌科(Desulfobacteraceae)、伯克氏菌科(Burkholderiaceae)等菌群变化，而S组中向优势群落Comamonadaceae、假单胞菌科(Pseudomonadaceae)、Burkholderiaceae等转变。【结论】在不同浓度腐殖酸-含砷水铁矿体系中，高砷含水层关键微生物类群的组成和相对丰度会发生不同演替，从而对砷的迁移转化造成不同影响。

Abstract:

[Objective] To investigate the variation of composition and abundance of microbial communities involved in the transformation of arsenic-bearing ferrihydrites under different humic acid concentrations and their effects on arsenic release, and to predict the role of functional microbial communities in participating the transformation processes of organic matter-arsenic-bearing iron minerals on arsenic release from high arsenic aquifers. [Methods] Iron-reducing microbial populations were enriched from a high arsenic groundwater and a high sediment sample from the same depth from Hetao Plain, Inner Mongolia Autonomous Region. Anaerobic microcosms were constructed by amendments of bacterial enrichment and different concentrations of humic acid (0, 1.5, 7, and 14 mg C/L) into arsenic-bearing ferrihydrites. The variation of arsenic and iron species during the 50-day incubation was monitored. The composition succession of microbial communities was analyzed by high-throughput sequencing, and the transformation of iron minerals was visualized by X-ray diffractometer (XRD). [Results] The iron-reducing functional communities enriched in the high arsenic groundwater group (group G) and the sediment group (group S) were significantly different, with Aeromonadaceae as the specific dominant family in group G while Shewanellaceae as the specific dominant family in group S. Results of microcosm experiments showed that the iron reduction rates and amount in group S were relatively faster and higher than those in group G. The liquid phase arsenic speciation in group G and group S were different. As(V) was the dominant arsenic form in group G throughout the incubation period. In contrast, in group S, As(V) was the main arsenic species in the early stage, and As(III) became dominant and was up to 3.4 μmol/L in the incubation of 20 d. It was assumed that the microbial communities capable of arsenic reduction were dominated at this time. In the final stage of incubation, the released arsenic in both group G and group S showed different degrees of fixation under the addition of humic acid. Different concentrations of humic acid led to different amounts of arsenic release. XRD results showed that the transformation of arsenic-bearing ferrihydrites was relatively higher in group S, with goethite the dominant secondary mineral in both groups. Redundancy analysis (RDA) indicated that the addition of arsenic and humic acid influenced the overall succession of microbial community composition. Comamonadaceae, Desulfobacteraceae, and Burkholderiaceae became the predominant populations in group G, while populations of Pseudomonadaceae, Comamonadaceae, and Burkholderiaceae were dominated in group S. [Conclusion] The amendments of different concentrations of humic acid into arsenic-bearing ferrihydrites led to differentiated successions of microbial communities, which might play different effects on iron mineral transformation and arsenic release.