河套平原不同深度高砷地下水硫酸盐还原菌群落分布特征及环境意义

Distribution characteristics and environmental significance of sulfate-reducing bacterial community in high arsenic groundwater from different depth of Hetao Plain, China

摘要:

【目的】探究不同深度的高砷含水层中硫酸盐还原菌的丰度、群落组成和多样性的差异，并结合硫酸盐硫同位素等多种水化参数，揭示不同深度高砷地下水中硫酸盐还原菌群落分布特征及其环境意义。【方法】以我国典型高砷地下水分布区河套平原为研究区，采集不同深度含水层中的高砷地下水样品，测定水化参数，采用qPCR对样品16S rRNA基因和dsrB基因进行定量；通过dsrB基因高通量测序对硫酸盐还原菌群落进行分析，并将dsrB基因相对丰度、群落组成及多样性与水化因子结合，进行统计学分析。【结果】基于dsrB基因的定量结果表明，浅层地下水中dsrB基因相对丰度高于深层地下水。浅层地下水中，dsrB基因相对丰度与CH₄浓度呈显著正相关，且δ³⁴S-SO₄^2–与CH₄浓度显著正相关。而深层高砷地下水中，dsrB基因相对丰度与SO₄^2–浓度、DOC浓度存在显著正相关性。高通量测序结果表明，深层地下水中硫酸盐还原菌的α多样性显著高于浅层地下水。研究区内硫酸盐还原菌可分为264个OTUs，以Desulfobacterales、Nitrospirales、Rhodospirillales、Syntrophobacterales等10个目为主。不同种属硫酸盐还原菌在深、浅层地下水的丰度及影响丰度的环境因子存在一定差异，其中浅层地下水中Nitrospirales的相对丰度与As_T浓度和δ³⁴S-SO₄^2–呈正相关，指示出硫酸盐还原菌中Nitrospirales类群在浅层地下水砷的迁移转化中的重要作用。RDA结果表明，As_T浓度、CH₄浓度和Fe²⁺浓度是控制研究区地下水中硫酸盐还原菌群落分布的关键环境因子。【结论】深、浅层高砷地下水中，硫酸盐还原菌多样性、种属构成与多样性存在显著差异，且受到了不同水化参数影响。

Abstract:

[Objective] To investigate the relative abundance, community composition and diversity of sulfate-reducing bacteria in high arsenic groundwater of different depths, and to reveal the main geochemical factors (e.g., δ³⁴S-SO₄^2–) affecting the distribution characteristics of sulfate-reducing bacterial community in high arsenic groundwater and the environmental significance. [Methods] High arsenic groundwater samples from both shallow and deep aquifers were collected from Hetao Plain, a typical high arsenic groundwater-distributed area in China. Various geochemical parameters were measured and the relative abundance of 16S rRNA gene and dsrB gene of the samples was quantified by qPCR. High-throughput sequencing of dsrB gene was conducted to reveal the community composition of sulfate-reducing bacteria. Statistical analysis was further performed to analyze the correlations between geochemical variables and sulfate-reducing bacterial community characteristics. [Results] The relative abundance of dsrB gene in shallow samples was higher than that in deep samples. In shallow high arsenic groundwater, the relative abundance of dsrB gene and the δ³⁴S-SO₄^2– were both significantly positively correlated with the concentration of CH₄. In contrast, the relative abundance of dsrB gene showed positive correlations with the concentrations of SO₄^2– and DOC in deep high arsenic groundwater. The high-throughput sequencing of dsrB gene displayed that the α-diversity of sulfate-reducing bacteria in deep groundwater was remarkably higher than that in shallow groundwater. Sulfate-reducing bacteria in the study area were divided into 264 operational taxonomic units (OTUs), including ten predominant orders such as Desulfobacterales, Nitrospirales, Rhodospirillales and Syntrophobacterales. The relative abundance of each order and the environmental factors affecting their abundance were different in shallow or deep groundwater. Specifically, the relative abundance of Nitrospirales in shallow groundwater was positively correlated with the concentrations of As_T and δ³⁴S-SO₄^2–, indicating the key role of Nitrospirales in arsenic migration and transformation in shallow groundwater. The redundancy analysis (RDA) found that As_T, CH₄ and Fe²⁺ were the key environmental factors controlling the distribution of sulfate-reducing bacterial community in groundwater of the study area. [Conclusion] The relative abundance, community composition and diversity of sulfate-reducing bacteria in deep and shallow high arsenic groundwater varied, and were affected by geochemical parameters.