Abstract High arsenic (As) groundwaters are generally associated with high concentration of ammonium in Pleistocene-Holocene aquifers. Ammonia/ammonium-oxidizing microorganisms (AOM) play an important role in the nitrogen cycle. To investigate AOM distribution and their diversity in the high As aquifers, 12 samples from deep wells (80–120 m below surface level) and another 12 samples from shallow wells (15–30 m) in the Hetao Plain of Inner Mongolia were taken for this investigation. Anammox bacteria were mainly detected in deep wells while ammonia-oxidizing archaea (AOA) were detected only in shallow wells. Ammonia-oxidizing bacteria (AOB) were detected in both shallow wells and deep wells. Anammox bacteria were diverse, but primarily composed of Candidatus Brocadia, Ca. Kuenenia, Ca. Scalindua, Ca. Jettenia, and unidentified groups. Only two genera were detected in both AOA and AOB, which were dominated by Nitrosopumilus (79%–100%) and Nitrosomonas (83.3%–100%), respectively. The distribution of AOM in high arsenic groundwater was associated with hydrogeological conditions and geochemical factors including oxidation-reduction potential (ORP), dissolved oxygen (DO), total organic carbon (TOC), and concentrations of As, NH4+-N, NO2−-N, and Fe. The qPCR results showed ratios of hzo/hzsB and amoA genes to 16S rRNA genes in shallow and deep wells varied widely (0.12%–3.04%). Positive correlations were observed between hzo/Arch-amoA gene abundances and Fe(II) as well as Fe(II) and As, implying microbial ammonia/ammonium oxidizing might be linked to iron reduction and As release. This work improves our understanding of the nitrogen cycle in high As aquifer systems.

中文翻译：

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高砷全新世-更新世含水层中氨/铵氧化和厌氧氨氧化的微生物

摘要 高砷 (As) 地下水通常与更新世-全新世含水层中高浓度的铵有关。氨/氨氧化微生物 (AOM) 在氮循环中起着重要作用。为研究高砷含水层中 AOM 的分布及其多样性，采集了内蒙古河套平原深井（地表以下 80-120 m）的 12 个样品和浅井（15-30 m）的 12 个样品。本次调查。厌氧氨氧化细菌主要在深井中检测到，而氨氧化古菌（AOA）仅在浅井中检测到。在浅井和深井中均检测到氨氧化细菌（AOB）。厌氧氨氧化细菌多种多样，但主要由 Candidatus Brocadia、Ca 组成。库内尼亚，加利福尼亚州 加利福尼亚州斯卡林杜瓦 Jettenia 和身份不明的团体。在 AOA 和 AOB 中仅检测到两个属，分别以 Nitrosopumilus (79%–100%) 和 Nitrosomonas (83.3%–100%) 为主。AOM在高砷地下水中的分布与水文地质条件和地球化学因素有关，包括氧化还原电位（ORP）、溶解氧（DO）、总有机碳（TOC）以及As、NH4+-N、NO2--的浓度N 和 Fe。qPCR结果显示，浅井和深井中hzo/hzsB和amoA基因与16S rRNA基因的比例差异很大（0.12%~3.04%）。在 hzo/Arch-amoA 基因丰度和 Fe(II) 以及 Fe(II) 和 As 之间观察到正相关，这意味着微生物氨/铵氧化可能与铁还原和 As 释放有关。这项工作提高了我们对高砷含水层系统中氮循环的理解。