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As a strategic mineral and energy resource, the enrichment and metallogenic mechanism of sandstone-hosted uranium deposits are highly dependent on hydrogeological conditions. However, the relationship between sandstone uranium mineralization and hydrogeological conditions has not received sufficient attention yet. The pumping test, hydrogeological parameters and hydrochemical characteristics were employed to analyze the change characteristics of hydrogeological conditions and evaluate the suitability of in situ leaching (ISL). The results showed that the study area in the Inner Mongolia Autonomous Region could be divided into two groundwater subsystems, namely Quanzha-Engeriyin and Luhai-Zhendai. The latter with relatively high water richness is confined and a main ore-bearing aquifer, which consists of four orebodies. The well discharge (Q) and hydraulic conductivity (K) of Orebody II ranged from 98.40 to 867.36 m3/d and 0.25 to 5.64 m/d, respectively, indicating the aquifer is suitable for the migration, enrichment and mineralization of uranium due to relatively high permeability and fast flow rate. The water storage of Orebodies III-IV gradually deteriorated from east to west in a stepped pattern. And the highest values of Q and K in Orebodies III-IV decreased from 1200 m3/d to 120 m3/d and 1.75 m/d to 0.035 m/d, respectively, suggesting these were conducive to a reduction in and accumulation of uranium under poor hydrodynamic conditions. Additionally, the study area would be defined as three grades, including favorable, relatively favorable and unfavorable areas of ISL according to a comprehensive evaluation. This study provided a scientific basis for evaluating the possibility of in situ leaching for sandstone-hosted uranium deposit. [ABSTRACT FROM AUTHOR]

Biogeochemical redox cycling of iron (Fe) essentially governs various geochemical processes in nature. However, the mechanistic underpinnings of Fe-redox cycling in deep-sea sediments remain poorly understood, due to the limited access to the deep-sea environment. Here, abyssal sediment collected from a depth of 5800 m in the Pacific Ocean was characterized for its elemental, mineralogical, and biological properties. The sedimentary environment was determined to be oligotrophic with limited nutrition, yet contained a considerable amount of trace elements. Fe-redox reactions in sediment progressed through an initial lag phase, followed by a fast Fe(II) reduction and an extended period of Fe(III) oxidation before achieving equilibrium after 58 days. The presence of an external H2 electron donor significantly increased the extent of Fe(III) bio-reduction by 7.73% relative to an amendment-free control under high pressure of 58 MPa. A similar enhancement of 11.20% was observed following lactate amendment under atmospheric pressure. Fe(II) bio-oxidation occurred after 16 days' anaerobic culturing, coupled with nitrate reduction. During Fe bio-redox reactions, microbial community composition was significantly shaped by the presence/absence of an electron donor, while the hydrostatic pressure levels were the controlling factor. Shewanella spp. emerged as the primary Fe(III)-reducing microorganisms, and were stimulated by supplemented lactate. Marinobacter hydrocarbonoclasticus was the predominant Fe(II)-oxidizing microorganism across all conditions. Our findings illustrate continuous Fe-redox reactions occurring in the deep-sea environment, with coexisting Fe-redox microorganisms determining the oscillation of Fe valence states within the abyssal sediment. [ABSTRACT FROM AUTHOR]

Miyun Reservoir plays a vital role as a source of drinking water for Beijing, however it grapples with nitrogen contamination issues that have been poorly understood in terms of their distribution, source, and associated health risks. This study addresses this knowledge gap by employing data on nitrate nitrogen (NO3−–N), chloride (Cl−), dual isotopic compositions of NO3− (δ15N–NO3− and δ18O–NO3−) data in water ecosystems, systematically exploring the distribution, source and health risk of nitrogen contaminants in Miyun reservoir watersheds. The results showed that over the past 30 years, surface water runoff has exhibited a notable decrease and periodic fluctuations due to the combined influence of climate and anthropogenic activities, while the total nitrogen (TN) concentration in aquatic ecosystems presented an annual fluctuating upward trend. The TN concentration in the wet season was predominantly elevated because a large amount of nitrogen contaminants migrated into water ecosystems through heavy rainfall or river erosion. The concentration of NO3−–N, the main contaminant of the water ecosystems, showed distinct variations across different watersheds, followed as rivers over the Miyun reservoir. Moreover, NO3−–N levels gradually increased from upstream to downstream in different basins. NO3−–N in surface water was mainly derived from the mixture of agricultural ammonia fertilizer and sewage and manure, with a minority of samples potentially undergoing denitrification. Comparatively, the main sources of NO3−–N in groundwater were soil N and sewage and manure, while the denitrification process was inactive. The carcinogenic risks caused by NO3−–N in groundwater were deemed either nonexistent or minimal, while the focus should predominantly be on potential non-carcinogenic risks, particularly for infants and children. Therefore, it is crucial to perform proactive measures aimed at safeguarding water ecosystems, guided by an understanding of the distribution, sources, and associated risks of nitrogen contamination. [ABSTRACT FROM AUTHOR]

The mobilization, speciation, and transformation of these pollutants in the soil and groundwater ecosystem vary greatly depending on the specific hydro-biogeochemical processes and environments. To effectively address soil pollution sources and manage the risks of groundwater pollution, it is essential to comprehend how complex geological and hydrogeological factors in soil-groundwater systems interplay with climate change and human activities. The common types of organic pollutants in soil and groundwater environments include polycyclic aromatic hydrocarbons (PAHs), volatile organic compounds (VOCs), chlorinated solvents, polychlorinated biphenyls (PCBs), pesticides, and other emerging contaminants [[5], [7]]. The delicate balance of our ecosystems is under threat from the unrelenting release of contaminants into the environment. [Extracted from the article]

Over the past decade, heavy metal (HMs) contamination in soil environments has become severe worldwide. However, their resulting ecological and health risks remained elusive across a variety of soil ecosystems due to the complicated distributions and sources. This study investigated the HMs (Cr, As, Cu, Pb, Zn, Ni, Cd, and Hg) in areas with multi-mineral resources and intensive agricultural activities to study their distribution and source apportionment using a positive matrix factorization (PMF) model coupled with self-organizing map (SOM). The potential ecological and health risks were assessed in terms of distinct sources of HMs. The results disclosed that the spatial distribution of HM contaminations in the topsoil was region-dependent, primarily located in areas with high population intensity. The geo‑accumulation index (Igeo) and enrichment factor (EF) values collectively displayed that the topsoils were severely contaminated by Hg, Cu, and Pb, particularly in residential farmland areas. The comprehensive analysis combined with PMF and SOM identified both geogenic and anthropogenic sources of HMs including natural, agricultural, mining, and mixed sources (caused by multi-anthropogenic factors), accounting for 24.9%, 22.6%, 45.9%, and 6.6% contribution rates, respectively. The potential ecological risk was predominantly due to the enrichment of Hg, followed by Cd. The non-carcinogenic risks were mostly below the acceptable risk level, while the potential carcinogenic health risks caused by As and Cr should be paid prime attention to, particularly for children. In addition to the 40% geogenic sources, agricultural activities contributed to 30% of the non-carcinogenic risk, whereas mining activities contributed to nearly half of the carcinogenic health risks. [ABSTRACT FROM AUTHOR]

Life on Earth depends on N2‐fixing microbes to make ammonia from atmospheric N2 gas by the nitrogenase enzyme. Most nitrogenases use Mo as a cofactor; however, V and Fe are also possible. N2 fixation was once believed to have evolved during the Archean‐Proterozoic times using Fe as a cofactor. However, δ15N values of paleo‐ocean sediments suggest Mo and V cofactors despite their low concentrations in the paleo‐oceans. This apparent paradox is based on an untested assumption that only soluble metals are bioavailable. In this study, laboratory experiments were performed to test the bioavailability of mineral‐associated trace metals to a model N2‐fixing bacterium Azotobacter vinelandii. N2 fixation was observed when Mo in molybdenite, V in cavansite, and Fe in ferrihydrite were used as the sole sources of cofactors, but the rate of N2 fixation was greatly reduced. A physical separation between minerals and cells further reduced the rate of N2 fixation. Biochemical assays detected five siderophores, including aminochelin, azotochelin, azotobactin, protochelin, and vibrioferrin, as possible chelators to extract metals from minerals. The results of this study demonstrate that mineral‐associated trace metals are bioavailable as cofactors of nitrogenases to support N2 fixation in those environments that lack soluble trace metals and may offer a partial answer to the paradox. [ABSTRACT FROM AUTHOR]

Shrubland is a pivotal terrestrial ecosystem in China. Soil nitrogen transformations play a crucial role in maintaining the productivity of this ecosystem, yet the driving forces underlying it have not been sufficiently addressed, particularly under ongoing climate changes. Herein, by incorporating 15N isotope pool dilution method in laboratory incubation, the rates of gross N ammonification, nitrification, and inorganic N consumption in soils in response to varying temperature and humidity conditions were determined at different depths (SL10: 0–10 cm, and SL20: 10–20 cm) in a typical shrub ecosystem in the Yanshan mountain and hilly region, North China. The gross rates of ammonification and nitrification of soils in SL10 were higher than those in SL20, which was likely affected by the higher soil organic matter and total N contents at a shallower depth. Both temperature and humidity significantly affected the N transformations. The gross ammonification and nitrification were significantly stimulated as the incubation temperature increased from 5 to 35 °C. The gross ammonification increased exponentially, while the gross nitrification increased differently in different temperature ranges. The increment of soil water contents (from 30% WHC to 60% and 100% WHC) promoted the gross nitrification rate more significantly than the gross ammonification rate. The gross nitrification ceased until soil water content reached 60%WHC, indicating that soil water availability between 60% and 100% WHC was not a limiting factor in the nitrification process for the shrubland soils in this study. The ammonium (NH4+) immobilization was significantly lower than nitrification irrespective of varying environmental conditions, even though the NH4+ consumption rate might be overestimated, uncovering two putative processes: (1) heterotrophic nitrification process; (2) and more competitive nitrifying bacteria than NH4+-immobilizing microorganisms. Our study is indispensable for assessing the stability and sustainability of soil N cycling in the shrub ecosystem under climate changes. [ABSTRACT FROM AUTHOR]

An increasing number of studies have demonstrated that natural source zone depletion (NSZD) in the vadose zone accounts for the majority (90%~99%) of the natural attenuation of light non-aqueous phase liquid (LNAPL). Until now, 0.05 to 12 kg/a.m2 NSZD rates at tens of petroleum LNAPL source zones have been determined in the middle or late evolution stage of LNAPL release, in which limited volatile organic compounds (VOCs) and methane (CH4) were detected. NSZD rates are normally estimated by the gradient method, yet the associated functional microbial activity remains poorly investigated. Herein, the NSZD at an LNAPL-releasing site was studied using both soil gas gradient methods quantifying the O2, CO2, CH4, and VOCs concentrations and molecular biology methods quantifying the abundance of the pmoA and mcrA genes. The results showed that the methanogenesis rates were around 4 to 40 kg/a.m2. The values were greater than the rates calculated by the sum of CH4 escaping (0.3~1.2 kg/a.m2) and O2 consuming (3~13 kg/a.m2) or CO2 generating rates (2~4 kg/a.m2), suggesting that the generated CH4 was oxidized but not thoroughly to CO2. The functional gene quantification also supported the indication of this process. Therefore, the NSZD rates at the site roughly equaled the methanogenesis rates (4~40 kg/a.m2), which were greater than most of the previously studied sites with a 90th percentile value of 4 kg/a.m2. The study extended the current knowledge of the NSZD and has significant implications for LNAPL remediation management. [ABSTRACT FROM AUTHOR]

Mineral–microbe interactions play important roles in environmental change, biogeochemical cycling of elements and formation of ore deposits. Minerals provide both beneficial (physical and chemical protection, nutrients, and energy) and detrimental (toxic substances and oxidative pressure) effects to microbes, resulting in mineral-specific microbial colonization. Microbes impact dissolution, transformation and precipitation of minerals through their activity, resulting in either genetically controlled or metabolism-induced biomineralization. Through these interactions, minerals and microbes co-evolve through Earth history. Mineral–microbe interactions typically occur at microscopic scale but the effect is often manifested at global scale. Despite advances achieved through decades of research, major questions remain. Four areas are identified for future research: integrating mineral and microbial ecology, establishing mineral biosignatures, linking laboratory mechanistic investigation to field observation, and manipulating mineral–microbe interactions for the benefit of humankind. [ABSTRACT FROM AUTHOR]

Deep groundwater characteristics provide valuable information on oil and gas extraction and evolution of hydrosphere, and nonmetallic and metallic elements in deep groundwater are raising industrial interest. There is therefore a need for a better understanding of the origin and evolution of deep groundwater in large sedimentary basins, e.g., by using non-traditional isotopes. Here, we review the constraints of isotopes of chloride (Cl), bromine (Br), boron (B), lithium (Li), helium (He), neon (Ne), and argon (Ar) on the origin and evolution of deep groundwater in large sedimentary basins. In deep groundwater, δ37Cl ranges from −1.96 to + 2.07‰, δ81Br from −1.50 to + 3.35‰, δ11B from + 1.10 to + 39.99‰, and δ7Li from −1.00 to + 31.80‰. These values either overlap or are different compared to those in freshwater, e.g., meteoric water, river water and shallow groundwater, hydrothermal fluid, seawater, subsurface brine, lake sediment, or mineral. Noble gas isotopes such as 3He/4He, 4He/20Ne, and 36Ar/40Ar are also effective tracers for deep groundwater evolution. Integrating multiple non-traditional isotopes allows to study dissolution, sedimentation, evaporation, and mixing of different waters in deep aquifers. [ABSTRACT FROM AUTHOR]

Mineral surfaces are known for their ability to adsorb enzymes, but their effects on enzyme activity are not well studied. This study explores the extent to which interaction with primary silicates and secondary minerals affects the activity and longevity of a model soil enzyme β‐glucosidase (BG). The BG activity was correlated with the capacity‐related properties of minerals (controlling space for adsorption), including specific surface area (SSA) and the SSA‐normalized amount of BG adsorption, but not with the functional properties (controlling the mechanisms of adsorption) such as surface charge. BG conformational change is a function of SSA‐normalized amount of adsorption, suggesting that spatially more distributed enzyme molecules would have a higher probability of encounter with the substrate than the congested molecules. The highest decay rate of BG activity was observed in the presence of Mn‐oxide. Our results shed new light on the effect of mineral surface on enzyme activity. Plain Language Summary: Extracellular enzymes catalyze the rate‐limiting steps of biogeochemical carbon and nutrient cycling. Although the enzyme activities have been incorporated into predictive biogeochemical models, they exhibit a range of catalytic, kinetic, and stability properties across different environments. Furthermore, association of substrate with minerals protects the substrate from enzymatic degradation, but the mineral effect on enzyme activity has not been well‐constrained. Our results disclose the previously underappreciated effects of soil minerals on inhibition of enzyme activity, and thus offer additional protection to the substrate. However, minerals can also increase the longevity of enzyme activity and thus increase the interaction time with the substrate, which is unfavorable for ultimate substrate preservation. The inhibition effect of minerals on enzyme activity can be predicted by the enzyme‐adsorbing capacity of the minerals. Understanding the capacity‐related properties of minerals is important for assessing the active extracellular enzyme pool in soils and sediments and should be further incorporated into the prediction of enzyme activity in the global carbon biogeochemical models. Key Points: Enzyme activity can be predicted by the capacity of a mineral to adsorb enzymesThe conformational change of enzyme is determined by the enzyme‐adsorbing capacity of mineral surfaceFunctional lifespan of enzyme decays fastest in the presence of Mn‐oxide surface [ABSTRACT FROM AUTHOR]

It is of significance to elucidate the groundwater quality and hydrogeochemical processes for sustainable utilization of groundwater resources in water shortage regions. A total of 256 groundwater samples were collected in typical watersheds in Zhangjiakou, northern China. The hydrochemical parameters, conventional ions, and trace elements were measured, and δD and δ18O data were collected to delineate the groundwater quality and hydrogeochemical processes. The results showed that 32.91% of the groundwater could be directly used for drinking water sources in the Bashang Plateau, north of the study area. The F− and NO3−-N were the main parameters above the standard threshold for drinking water. In contrast, the groundwater quality in the Baxia River Basins, south of the study area, was of a better scenario. Nonetheless, high concentrations of F−, total hardness, and SO42− were still observed. Most samples in the Bashang Plateau had relatively higher salinity than the Baxia River Basins. Both surface water and groundwater in the study area originated from local meteoric water with considerable hydraulic connections. The high-fluoride groundwater was primarily formed by dissolution of fluoride-rich minerals under conditions of high pH and Na+, low Ca2+, and rich in HCO3−. The dissolution of carbonate and silicate minerals accompanied by strong cation exchange and weak evaporation was the dominant water-rock interaction affecting the hydrochemical composition of groundwater, and anthropogenic NO3− input had an extra influence on hydrochemical process. This study provides a scientific guideline for the protection and allocation of local groundwater resources. [ABSTRACT FROM AUTHOR]

Knowledge of the behavior of microbial communities in ecosystems is limited, yet microbes control partly all element cycles and, in turn, processes influencing pollution and climate change. In particular, heterotrophic denitrification is major process controlling the transformation of nitrogen oxides pollutants, e.g. nitrates (NO4-) and nitrous oxide (N2O), a greenhouse gas. Iron acts as either nutrient or stress in denitrifying microbial communities, yet underlying mechanisms are unclear. We hypothesized that iron plays a vital role in the assembly process of heterotrophic denitrifying microbial communities. To test this hypothesis we cultivated 17 microcosms under carbon- and iron-rich conditions. Geochemical analysis, 16S rRNA gene high-throughput sequencing, and multivariate statistical analysis were implemented to unravel the driving forces that shape the assembly process of microbial communities. Results reveal that iron was the most dominant factor influencing the diversity and composition of heterotrophic denitrifying communities, versus pH, C/N, temperature, nitrate reduction, and iron oxidation rates. Higher Fe concentration induced more clustered microbial interactions. Heterotrophic microbial community assembly is shaped by 90% stochastic processes, whereas deterministic processes rose with Fe(II) concentration. Overall our findings demonstrate that iron controls the balance between the deterministic and stochastic processes of heterotrophic denitrifying microbial communities. These mechanisms may have implications for bioremediation strategies. [ABSTRACT FROM AUTHOR]

Environmental factors (e.g., temperature and pH) shaping the distribution of microbial communities in hot springs have been extensively studied, whereas how hydrochemical formation mechanisms and hydrological circulation processes affect microbial community composition is not comprehensively elucidated. In the present study, hydrochemical, isotopic, and high‐throughput sequencing methods were employed to investigate hydrochemical characteristics and evolution of springwater as well as their underlying roles in shaping the microbial community in multiple acidic and alkaline hot springs in southwestern Yunnan, China. Distinct hydrochemical (e.g., pH, temperature, sulfate, SiO2, and trace metals) and isotopic (δ2H and δ18O) characteristics revealed the recharge sources and circulation processes of springwater were different in alkaline, high‐temperature and acidic, moderate‐temperature hot springs. Two acidic, moderate‐temperature springs (43°C–55°C), characterized by high sulfate, showed shallow circulation depths and were potentially heated by upwelling hot, high H2S abundance gases, and sulfur oxidation might be one of the main underlying hydrochemical processes. Seven alkaline, high‐temperature springs (>70°C), in contrast, which originated from a different recharge source as indicated by the lighter isotopic compositions (δ2H and δ18O), showed characteristics of deeper circulation. Hydrogenobacter sp. is the most abundant microorganism in alkaline, high‐temperature springs, whereas acidic, moderate‐temperature springs are mainly composed of Chlorobiaceae, Thiomonas sp., Halothiobacillus sp., Sulfurihydrogenibium sp., and Hydrogenobaculum sp. which have been reported to possess the potentials to cycle sulfur. The hydrochemical constraints on shaping microbial communities may help us better understand biogeochemical cycles across a range of temperatures in acidic and alkaline springs. Key Points: Hydrochemical characteristics of alkaline, high‐temperature and acidic, moderate‐temperature springs reflect distinct circulation pathsMicrobial communities respond to hydrochemical constraints on alkaline, high‐temperature and acidic, moderate‐temperature springsHydrogenobacter sp. dominates in alkaline springs and Chlorobiaceae and Sulfurihydrogenibium sp. dominate in acidic springs [ABSTRACT FROM AUTHOR]

Abstract: Spatial distribution (horizonal and vertical) of groundwater microbial communities and the hydrogeochemistry in confined aquifers were studied approximately along the groundwater flow path from coteau to plain in the Nomhon area, Qinghai‐Tibet plateau, China. The confined groundwater samples at different depths and locations were collected in three boreholes through a hydrogeological section in this arid and semi‐arid area. The phylogenetic analysis of 16S rRNA genes and multivariate statistical analysis were used to elucidate similarities and differences between groundwater microbial communities and hydrogeochemical properties. The integrated isotopic geochemical measurements were applied to estimate the source and recharge characteristics of groundwater. The results showed that groundwater varied from fresh to saline water, and modern water to ancient water following the flowpath. The recharge characteristics of the saline water was distinct with that of fresh water. Cell abundance did not vary greatly along the hydrogeochemical zonality; however, dissimilarities in habitat‐based microbial community structures were evident, changing from Betaproteobacteria in the apex of alluvial fan to Gammaproteobacteria and then to Epsilonproteobacteria in the core of the basin (alluvial‐lacustrine plain). Rhodoferax, Hydrogenophaga, Pseudomonas, and bacterium isolated from similar habitats unevenly thrived in the spatially distinct fresh water environments, while Sulfurimonas dominanted in the saline water environment. The microbial communities presented likely reflected to the hydrogeochemical similarities and zonalities along groundwater flowpath. [ABSTRACT FROM AUTHOR]

With depleted coal resources or deteriorating mining geological conditions, some coal mines have been abandoned in the Fengfeng mining district, China. Water that accumulates in an abandoned underground mine (goaf water) may be a hazard to neighboring mines and impact the groundwater environment. Groundwater samples at three abandoned mines (Yi, Er and Quantou mines) in the Fengfeng mining district and the underlying Ordovician limestone aquifer were collected to characterize their chemical and isotopic compositions and identify the sources of the mine water. The water was HCO3·SO4-Ca·Mg type in Er mine and the auxiliary shaft of Yi mine, and HCO3·SO4-Na type in the main shaft of Quantou mine. The isotopic compositions (δD and δ18O) of water in the three abandoned mines were close to that of Ordovician limestone groundwater. Faults in the abandoned mines were developmental, possibly facilitating inflows of groundwater from the underlying Ordovician limestone aquifers into the coal mines. Although the Sr2+ concentrations differed considerably, the ratios of Sr2+/Ca2+ and 87Sr/86Sr and the 34S content of SO42− were similar for all three mine waters and Ordovician limestone groundwater, indicating that a close hydraulic connection may exist. Geochemical and isotopic indicators suggest that (1) the mine waters may originate mainly from the Ordovician limestone groundwater inflows, and (2) the upward hydraulic gradient in the limestone aquifer may prevent its contamination by the overlying abandoned mine water. The results of this study could be useful for water resources management in this area and other similar mining areas. [ABSTRACT FROM AUTHOR]

High contents of nitrogen in groundwater were found in the Turpan-Hami area, Xinjiang, China, whereas the enrichment characteristics and sources of nitrogen were poorly understood. In this study, totally 19 groups of groundwater samples were collected in the Turpan-Hami area for chemistry and isotope analysis. Combining with the hydrochemical, hydrogen, oxygen, and nitrogen stable isotopes data, the distribution and sources of nitrogen of groundwater in the Turpan-Hami area were analyzed. The results showed that the groundwater mainly originated from the atmospheric precipitation, and the evaporation was the dominant mode for groundwater discharge in Turpan-Hami area. The concentration of nitrate (NO-N) in groundwater varies from 23.29 to 1819.49 mg/L. Obvious enrichment trend of nitrogen was observed along the groundwater flow direction. The increase of nitrate, nitrite, and ammonia concentrations were consistent with that of TDS in the area. The concentrations of nitrogen species were dominated by the strong evaporation rather than human activity except for one sample. The δN-NO in groundwater ranges from −0.6 to +31 ‰, and mostly in a range of +4.1 to +19.3 ‰. The δO-NO ranges from +16.3 to +37.4 ‰. The result indicated that nitrate in groundwater was mainly derived from atmospheric precipitation, and the conversion of nitrate, nitrite, and ammonia in groundwater was not active in the area. [ABSTRACT FROM AUTHOR]

A total of 43 groundwater samples were collected from 9 multimonitoring wells at a petrochemical site, Baoding City, North China, from June 2008 to December 2009 to investigate the biogeochemical processes and/or bacterial conmmunity using both culture-dependent and -independent methods. The results showed that aromatic hydrocarbons and chlorinated hydrocarbons were the major pollutants in the groundwater. Denitrification and iron reduction might be the main biogeochemical processes in the aquifers at this site, which seemed to transform from denitrification-dominated to iron reduction-dominated in some sections. Denaturing gradient gel electrophoresis (DGGE) revealed that the dominant bacterial groups of the groundwater were related to some oil-degrading bacteria, which can grow under denitrifying, iron-reducing and sulfate-reducing anaerobic conditions. In some serious contaminated groundwater niches, there might be sulfur cycles, as sulfur oxidizer was also abundant, which was further confirmed by 16S rRNA gene cloning analysis. The operational taxonomic units (OTUs) that highly related toPseudomonassp.,Hydrogenophagasp.,Sphingomonassp.,Ferribacteriumsp. andSulfuricurvum Kujienseetc. were predominant in the groundwater contaminated by chlorinated hydrocarbons (CHCs), benzene, toluene, ethylbenzene, and xylenes (BTEX) and/or polycyclic aromatic hydrocarbons (PAHs), respectively. Biodiversity seemed to be undermined by oil contamination, and varied with seasons. The bacterial community in the contaminated groundwater was largely determined by the groundwater geochemistry. [ABSTRACT FROM AUTHOR]

Petroleum hydrocarbons consisting of complicated mixtures of non-aqueous and hydrophobic components have raised a widespread environmental problem and influenced the subsurface microbial ecology. Three subsurface soil samples were collected at an oil field (Hebei, China) to investigate the microbial diversity patterns and their responds to different petroleum hydrocarbon contaminations by using 16S rRNA gene cloning analysis combined with multivariate statistical analysis. The results showed that bacterial clone libraries fell into 16 phylogenetic divisions and 184 operational taxonomic units. Gammaproteobacteria ubiquitously dominated in all samples, while the relative abundance was lowest in the sample with the highest total petroleum hydrocarbon concentration. Known petroleum degrading bacterial genera Alcanivorax, Stenotrophomonas, Pseudomonas, Pseudoxanthomonas, Sphingomonas, and Acidobacterium were abundantly observed, whereas their relative abundances differed greatly under a selection pressure by the complex hydrocarbons. For example, Alcanivorax spp. were the most abundant genera in polycyclic aromatic hydrocarbons and chlorinated hydrocarbons contaminated soils, while both Alcanivorax spp. and Stenotrophomonas spp. dominated in benzene, toluene, ethylbenzene, and xylenes contaminated soils. Additionally, a large fraction of bacterial clones were expectedly affiliated to some uncultured bacteria originated from several similar polluted ecosystems, and bacteria without certain petroleum degrading capacities. These observations indicated that microbial diversity, abundance and community were highly influenced by the concentrations of petroleum constituents in the contaminated soil ecosystems. Understanding the underlying factors that control the abundance of these heterotrophic microorganisms may be advantageous in the bioremediation of petroleum contaminated environments. [ABSTRACT FROM AUTHOR]