A Slow-Release Substrate Stimulates Groundwater Microbial Communities for Long-Term in Situ Cr(VI) Reduction

Coupled processes involving ammonium inputs, microbial nitrification, and calcite dissolution control riverine nitrate pollution in the piedmont zone (Qingshui River, China)

Rivers in agricultural countries widely suffer from diffuse nitrate (NO3-) pollution. Although pollution sources and fates of riverine NO3- have been reported worldwide, the driving mechanisms of riverine NO3- pollution associated with mineral dissolution in piedmont zones remain unclear. This study combined hydrogeochemical compositions, stable isotopes (δ18O-NO3-, δ15N-NO3-, δ18O-H2O, and δ2H-H2O), and molecular bioinformation to determine the pollution sources, biogeochemical evolution, and natural attenuation of riverine NO3- in a typical piedmont zone (Qingshui River). High NO3- concentration (37.5 ± 9.44 mg/L) was mainly observed in the agricultural reaches of the river, with ~15.38 % of the samples exceeding the acceptable limit for drinking purpose (44 mg/L as NO3-) set by the World Health Organization. Ammonium inputs, microbial nitrification, and HNO3-induced calcite dissolution were the dominant driving factors that control riverine NO3- contamination in the piedmont zone. Approximately 99.4 % of riverine NO3- contents were derived from NH4+-containing pollutants, consisted of manure & domestic sewage (74.0 % ± 13.0 %), NH4+-synthetic fertilizer (16.1 % ± 8.99 %), and soil organic nitrogen (9.35 % ± 4.49 %). These NH4+-containing pollutants were converted to HNO3 (37.2 ± 9.38 mg/L) by nitrifying bacteria, and then the produced HNO3 preferentially participated in the carbonate (mainly calcite) dissolution, which accounted for 40.0 % ± 12.1 % of the total riverine Ca2+ + Mg2+, also resulting in the rapid release of NO3- into the river water. Thus, microbial nitrification could be a new and non-negligible contributor of riverine NO3- pollution, whereas the involvement of HNO3 in calcite dissolution acted as an accelerator of riverine NO3- pollution. However, denitrification had lesser contribution to natural attenuation for high NO3- pollution. The obtained results indicated that the mitigation of riverine NO3- pollution should focus on the management of ammonium discharges, and the HNO3-induced carbonate dissolution needs to be considered in comprehensively understanding riverine NO3- pollution in piedmont zones.

Cr(VI) Reduction and Sequestration by FeS Nanoparticles Formed in situ as Aquifer Material Coating to Create a Regenerable Reactive Zone

Remediation of large and dilute plumes of groundwater contaminated by oxidized pollutants such as chromate is a common and difficult challenge. Herein, we show that in situ formation of FeS nanoparticles (using dissolved Fe(II), S(-II), and natural organic matter as a nucleating template) results in uniform coating of aquifer material to create a regenerable reactive zone that mitigates Cr(VI) migration. Flow-through columns packed with quartz sand are amended first with an Fe2+ solution and then with a HS- solution to form a nano-FeS coating on the sand, which does not hinder permeability. This nano-FeS coating effectively reduces and immobilizes Cr(VI), forming Fe(III)-Cr(III) coprecipitates with negligible detachment from the sand grains. Preconditioning the sand with humic or fulvic acid (used as model natural organic matter (NOM)) further enhances Cr(VI) sequestration, as NOM provides additional binding sites of Fe2+ and mediates both nucleation and growth of FeS nanoparticles, as verified with spectroscopic and microscopic evidence. Reactivity can be easily replenished by repeating the procedures used to form the reactive coating. These findings demonstrate that such enhancement of attenuation capacity can be an effective option to mitigate Cr(VI) plume migration and exposure, particularly when tackling contaminant rebound post source remediation.

Biostimulation effect of different amendments on Cr(VI) recovering microbial community

The present study used Cr(VI)-polluted microcosms amended with lactate or yeast extract, and nonamended microcosms as control, to investigate how a native bacterial community varied in response to the treatment and during the pollutant removal. Results suggested that providing electron donors resulted in a proliferation of a few bacterial species, with the consequent decrease in observed species richness and evenness, and was a driving force for the bacterial compositional shift. Lactate promoted, in the first instance, the enrichment of fermentative bacteria belonging to Chromobacteriaceae, including Paludibacterium, and Micrococcaceae as observed after 4 days. When the rate of Cr(VI) removal was maximum in microcosms amended with lactate, the most represented taxa were Pseudarcicella and Azospirillum. Using yeast extract as a carbon source and electron donor led instead to the significant enrichment of Shewanella, followed by Vogesella and Acinetobacter on the 4th day, corresponding to 90% of Cr(VI) removed from the system. After the complete Cr(VI) removal, achieved in 7 days in the presence of yeast extract, α-diversity was notably increased. The amendment-specific turnover of the enriched bacterial taxa resulted in a different kinetic of pollutant removal. In particular, yeast extract promoted the quickest Cr(VI) reduction, while lactate supported a slower, but also considerable, pollutant removal from water. Since it is reasonable to assume that a macroscopic effect, such as the observed Cr(VI) removal, involved the overrepresented taxa, deepening the knowledge of the native bacterial community and its changes were used to hypothesize the possible microbial pathways involved.

Simultaneous bio-reduction of nitrate and Cr(VI) by mechanical milling activated corn straw

Abundant lignocellulose waste is an ideal energy source for environmental bioremediation, but its recalcitrance to bioavailability makes this a challenging prospect. We hypothesized that the disruption of straw's recalcitrant structure by mechanochemical ball milling would enhance its availability for the simultaneous bioreduction of nitrate and Cr(VI). The results showed that the ball-milling process increased the quantity of water-soluble organic matter released from corn straw and changed the composition of organic matter by strongly disrupting its lignocellulose structure. The increase in ball-milling time increased the specific surface area of the straw and favored the adhesion of microorganisms on the straw surface, which enhanced the bioavailability of the energy in the straw. Substantially increased removal of NO₃^--N (206.47 ± 0.67 mg/g) and Cr(VI) (37.62 ± 0.09 mg/g) was achieved by using straw that was ball milled for 240 min, which validated that ball milling can improve the utilization efficiency of straw by microorganisms. Cellular and molecular biological analyses showed that ball-milled straw increased microbial energy metabolism and cellular activity related to the electron transport chain. This work offers a potential way to achieve the win-win goal of utilizing agricultural wastes and remediating environmental pollution.

Field-scale studies on the change of soil microbial community structure and functions after stabilization at a chromium-contaminated site

Various remediation strategies have been developed to eliminate soil chromium (Cr) contamination which challenges the ecosystem and human health, and chemical stabilization is the most popular one. Limited work focuses on the change of soil microbial community and functions after chemical stabilization. The present study examined the diversity and structure of bacterial, fungal and archaeal communities in 20 soils from a Cr-contaminated site in China after chemical stabilization and ageing. Cr contamination significantly reduced microbial diversity and shaped microbial community structure. After chemical stabilization, bacterial and fungal communities had higher richness and evenness, whereas archaea behaved oppositely. Microbial community structure after stabilization were more similar to uncontaminated soils. Among all environmental variables, pH and Al explained 25.2% and 9.4% of the total variance of bacterial diversity, whereas the major variable affecting fungal community was pH (29.3%). Cr, organic matters, extractable-Al and moisture explained 25.8%, 22.4%, 9.9% and 9.9% of the total variance in archaeal community, respectively. This work for the first time unraveled the change of the whole soil microbial community structures and functions at Cr-contaminated sites after chemical stabilization on field scale and proved chemical stabilization as an effective approach to detoxicate Cr(VI) and recover microbial communities in soils.

Mechanism Across Scales: A Holistic Modeling Framework Integrating Laboratory and Field Studies for Microbial Ecology

Over the last century, leaps in technology for imaging, sampling, detection, high-throughput sequencing, and -omics analyses have revolutionized microbial ecology to enable rapid acquisition of extensive datasets for microbial communities across the ever-increasing temporal and spatial scales. The present challenge is capitalizing on our enhanced abilities of observation and integrating diverse data types from different scales, resolutions, and disciplines to reach a causal and mechanistic understanding of how microbial communities transform and respond to perturbations in the environment. This type of causal and mechanistic understanding will make predictions of microbial community behavior more robust and actionable in addressing microbially mediated global problems. To discern drivers of microbial community assembly and function, we recognize the need for a conceptual, quantitative framework that connects measurements of genomic potential, the environment, and ecological and physical forces to rates of microbial growth at specific locations. We describe the Framework for Integrated, Conceptual, and Systematic Microbial Ecology (FICSME), an experimental design framework for conducting process-focused microbial ecology studies that incorporates biological, chemical, and physical drivers of a microbial system into a conceptual model. Through iterative cycles that advance our understanding of the coupling across scales and processes, we can reliably predict how perturbations to microbial systems impact ecosystem-scale processes or vice versa. We describe an approach and potential applications for using the FICSME to elucidate the mechanisms of globally important ecological and physical processes, toward attaining the goal of predicting the structure and function of microbial communities in chemically complex natural environments.

Enhanced Microbial Chromate Reduction Using Hydrogen and Methane as Joint Electron Donors

Hydrogen and methane commonly co-exist in aquifer. Either hydrogen or methane has been individually utilized as electron donor for bio-reducing chromate. However, little is known whether microbial chromate reduction would be suppressed or promoted when both hydrogen and methane are simultaneously supplied as joint electron donors. This study for the first time demonstrated microbial chromate reduction rate could be accelerated by both hydrogen and methane donating electrons. The maximum chromate reduction rate (4.70 ± 0.03 mg/L·d) with a volume ratio of hydrogen to methane at 1:1 was significantly higher than that with pure hydrogen (2.53 ± 0.02 mg/L·d) or pure methane (2.01 ± 0.02 mg/L·d) as the sole electron donor (p < 0.01). High-throughput 16S rRNA gene amplicon sequencing detected potential chromate reducers (e.g., Spirochaetaceae, Delftia and Azonexus) and hydrogenotrophic bacteria (e.g., Acetoanaerobium) and methane-metabolizing microorganisms (e.g., Methanobacterium), indicating that these microorganisms might play important roles on microbial chromate reduction using both hydrogen and methane as electron donors. Abundant hupL and mcrA genes responsible for hydrogen oxidation and methane conversion were harbored, together with chrA gene for chromate reduction. More abundant extracellular cytochrome c and intracellular NADH were detected with joint electron donors, suggesting more active electron transfers.

Honeycomb-like magnetic cornstalk for Cr(VI) removal and ammonium release

In this work, cornstalk (CS) was irradiated by high energy electron beam to obtain honeycomb-like porous CS (PCS). The PCS was loaded with ammonium sulfite (AS) and then coated by polyvinyl alcohol (PVA)-Fe₃O₄ to obtain PCS-AS@PVA-Fe₃O₄. The PCS-AS@PVA-Fe₃O₄ could reduce hexavalent chromium (Cr(VI)) to trivalent chromium (Cr(III)) by SO₃^2-, then the Cr(III) combined with PCS-AS@PVA-Fe₃O₄ through hydrogen bonds. The resulting PCS-AS@PVA-Fe₃O₄/Cr with a high magnetism could be conveniently separated from water via a magnet. PCS-AS@PVA-Fe₃O₄/Cr showed a high performance on controlling Cr(VI) migration in soil and uptake by plant. Meanwhile, ammonium could be released from PCS-AS@PVA-Fe₃O₄, favoring plant growth. Therefore, this work not only provides a promising and low-cost approach to remove Cr(VI) and promote plant growth simultaneously, but also provides a new route for CS recycling, which might have a potential application value.

Simulated reactive zone with emulsified vegetable oil for the long-term remediation of Cr(VI)-contaminated aquifer: dynamic evolution of geological parameters and groundwater microbial community

Cr(VI), which is highly toxic and soluble, is one of the most challenging groundwater contaminants. Previous work has indicated that emulsified vegetable oil (EVO) is an effective in situ amendment for removing Cr(VI) from groundwater. However, the spatial and temporal changes in geological parameters and microbial community structures throughout the remediation period are poorly understood. In this study, a large laboratory-scale sand-packed chamber (reactive zone of 100 × 50 × 30 cm) was used to simulate the bioremediation of Cr(VI)-contaminated aquifer by EVO over a 512-day period. Various geological parameters and microbial communities were monitored during both the establishment and remediation stages. The results indicate that several biogeochemical reactions occurred in a specific sequence following the injection of EVO, creating an acidic and reducing environment. A shift in the community structure and a decrease in the community diversity were observed. The abundance of microbes involved in the degradation of EVO and reduction of electron acceptors significantly increased. Then, the EVO reactive zone was flushed with Cr(VI)-contaminated groundwater. Biogeochemical reactions were inhibited after the inflow of Cr(VI) and subsequently recovered a month later. The pH of the aquifer returned to the initial neutral condition (approximately 7.2). The EVO reactive zone could remediate Cr(VI)-contaminated groundwater at an efficiency exceeding 97% over 480 days. Biogeochemistry played a major role in the early period (0~75 days). In the later period (240~480 days), the remediation of Cr(VI) in the reactive zone depended mostly on bio-reduction by Cr(VI)-reducing bacteria.

Microbial Interactions With Dissolved Organic Matter Drive Carbon Dynamics and Community Succession

Knowledge of dynamic interactions between natural organic matter (NOM) and microbial communities is critical not only to delineate the routes of NOM degradation/transformation and carbon (C) fluxes, but also to understand microbial community evolution and succession in ecosystems. Yet, these processes in subsurface environments are usually studied independently, and a comprehensive view has been elusive thus far. In this study, we fed sediment-derived dissolved organic matter (DOM) to groundwater microbes and continually analyzed microbial transformation of DOM over a 50-day incubation. To document fine-scale changes in DOM chemistry, we applied high-resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) and soft X-ray absorption spectroscopy (sXAS). We also monitored the trajectory of microbial biomass, community structure and activity over this time period. Together, these analyses provided an unprecedented comprehensive view of interactions between sediment-derived DOM and indigenous subsurface groundwater microbes. Microbial decomposition of labile C in DOM was immediately evident from biomass increase and total organic carbon (TOC) decrease. The change of microbial composition was closely related to DOM turnover: microbial community in early stages of incubation was influenced by relatively labile tannin- and protein-like compounds; while in later stages the community composition evolved to be most correlated with less labile lipid- and lignin-like compounds. These changes in microbial community structure and function, coupled with the contribution of microbial products to DOM pool affected the further transformation of DOM, culminating in stark changes to DOM composition over time. Our study demonstrates a distinct response of microbial communities to biotransformation of DOM, which improves our understanding of coupled interactions between sediment-derived DOM, microbial processes, and community structure in subsurface groundwater.

Enhanced bioelectroremediation of a complexly contaminated river sediment through stimulating electroactive degraders with methanol supply

Bioelectroremediation is an efficient, sustainable, and environment-friendly remediation technology for the complexly contaminated sediments. Although various recalcitrant pollutants could be degraded in the electrode district, the degradation efficiency was generally confined by the low total organic carbon (TOC) content in the sediment. How to enhance the electroactive degraders' activity and efficiency remain poorly understood. Here we investigated the bioeletroremediation of a complexly contaminated river sediment with low TOC in a cylindric sediment microbial fuel cell stimulated by methanol. After 200 days treatment, the degradation efficiencies of total petroleum hydrocarbons (TPH), polycyclic aromatic hydrocarbons (PAH), and cycloalkenes (CYE) in the electrode district with methanol stimulation were 1.45-4.38 times higher compared with those in the non-electrode district without methanol stimulation. The overall electrode district communities were significantly positively correlated with the variables of the enhanced TPH, PAH, CYE and TOC degradation efficiencies (p < .01). The joint electrical and exogenous methanol stimulation selectively enriched electroactive degraders (Geobacter and Desulfobulbus) in the anode biofilms, and their proportion was markedly positively correlated with the characteristic and total pollutants degradation efficiencies (p < .001). This study offers a new insight into the response of key electroactive degraders to the joint stimulation process.

Microbial Functional Gene Diversity Predicts Groundwater Contamination and Ecosystem Functioning

Contamination from anthropogenic activities has significantly impacted Earth’s biosphere. However, knowledge about how environmental contamination affects the biodiversity of groundwater microbiomes and ecosystem functioning remains very limited. Here, we used a comprehensive functional gene array to analyze groundwater microbiomes from 69 wells at the Oak Ridge Field Research Center (Oak Ridge, TN), representing a wide pH range and uranium, nitrate, and other contaminants. We hypothesized that the functional diversity of groundwater microbiomes would decrease as environmental contamination (e.g., uranium or nitrate) increased or at low or high pH, while some specific populations capable of utilizing or resistant to those contaminants would increase, and thus, such key microbial functional genes and/or populations could be used to predict groundwater contamination and ecosystem functioning. Our results indicated that functional richness/diversity decreased as uranium (but not nitrate) increased in groundwater. In addition, about 5.9% of specific key functional populations targeted by a comprehensive functional gene array (GeoChip 5) increased significantly (P < 0.05) as uranium or nitrate increased, and their changes could be used to successfully predict uranium and nitrate contamination and ecosystem functioning. This study indicates great potential for using microbial functional genes to predict environmental contamination and ecosystem functioning.

Disentangling the relationships between biodiversity and ecosystem functioning is an important but poorly understood topic in ecology. Predicting ecosystem functioning on the basis of biodiversity is even more difficult, particularly with microbial biomarkers. As an exploratory effort, this study used key microbial functional genes as biomarkers to provide predictive understanding of environmental contamination and ecosystem functioning. The results indicated that the overall functional gene richness/diversity decreased as uranium increased in groundwater, while specific key microbial guilds increased significantly as uranium or nitrate increased. These key microbial functional genes could be used to successfully predict environmental contamination and ecosystem functioning. This study represents a significant advance in using functional gene markers to predict the spatial distribution of environmental contaminants and ecosystem functioning toward predictive microbial ecology, which is an ultimate goal of microbial ecology.

Cr(VI) reduction and physiological toxicity are impacted by resource ratio in Desulfovibrio vulgaris

Desulfovibrio spp. are capable of heavy metal reduction and are well-studied systems for understanding metal fate and transport in anaerobic environments. Desulfovibrio vulgaris Hildenborough was grown under environmentally relevant conditions (i.e., temperature, nutrient limitation) to elucidate the impacts on Cr(VI) reduction on cellular physiology. Growth at 20 °C was slower than 30 °C and the presence of 50 μM Cr(VI) caused extended lag times for all conditions, but once growth resumed the growth rate was similar to that without Cr(VI). Cr(VI) reduction rates were greatly diminished at 20 °C for both 50 and 100 μM Cr(VI), particularly for the electron acceptor limited (EAL) condition in which Cr(VI) reduction was much slower, the growth lag much longer (200 h), and viability decreased compared to balanced (BAL) and electron donor limited (EDL) conditions. When sulfate levels were increased in the presence of Cr(VI), cellular responses improved via a shorter lag time to growth. Similar results were observed between the different resource (donor/acceptor) ratio conditions when the sulfate levels were normalized (10 mM), and these results indicated that resource ratio (donor/acceptor) impacted D. vulgaris response to Cr(VI) and not merely sulfate limitation. The results suggest that temperature and resource ratios greatly impacted the extent of Cr(VI) toxicity, Cr(VI) reduction, and the subsequent cellular health via Cr(VI) influx and overall metabolic rate. The results also emphasized the need to perform experiments at lower temperatures with nutrient limitation to make accurate predictions of heavy metal reduction rates as well as physiological states in the environment.

Development of phosphate rock integrated with iron amendment for simultaneous immobilization of Zn and Cr(VI) in an electroplating contaminated soil

This study aims to develop an amendment for simultaneous immobilization of Zn and Cr(VI) in an abandoned electroplating contaminated soil. Nature phosphate rock was first activated with oxalic acid (O-PR) and then combined with FeSO₄ or zero-valent iron (ZVI) for immobilization of Zn and Cr(VI) from aqueous solutions. Finally, the optimized approach showing the highest immobilization ability in solution was applied in an electroplating contaminated soil. The O-PR combined with FeSO₄ was more effective in simultaneously removing Zn and Cr(VI) than the O-PR integrated with ZVI within the tested solution pH range of 5.5-8.5. Both O-PR with FeSO₄ and with ZVI removed over 95% of Zn from the solution; however, only 42-46% of Cr(VI) was immobilized by O-PR with ZVI, while O-PR with FeSO₄ almost precipitated all Cr(VI). Moreover, there were 75-95% Zn and 95-100% Cr(VI) remaining in the exhausted O-PR with FeSO₄ solid after toxicity characteristic leaching test (TCLP) while the exhausted O-PR with ZVI solid only retained 44-83% Zn and 32-72% Cr(VI). Zinc was immobilized mainly via formation of insoluble Fe-Zn phosphate co-precipitates, while iron-induced reduction of Cr(VI) into stable Cr(OH)₃ or Cr_xFe_(1-x)(OH)₃ was responsible for Cr(VI) immobilization. Application of the O-PR integrated with FeSO₄ in the electroplating contaminated soil rapidly reduced the TCLP extractable Zn and Cr(VI) to below the standard limits, with decrease by 50% and 94%, respectively. This study revealed that combination of oxalic acid activated phosphate rock with FeSO₄ could be an effective amendment for remediation of Zn and Cr(VI) contaminated soil.

Reactivity enhancement of iron sulfide nanoparticles stabilized by sodium alginate: Taking Cr (VI) removal as an example

The widespread distribution of chromium(VI) in the environment leads to groundwater contamination. The use of iron sulfide (FeS) to remove Cr(VI) has therefore been proposed. However, aggregation is one of the main problems associated with the use of FeS nanoparticles prepared by traditional methods In this study, we used sodium alginate (SA) to stabilize FeS nanoparticles (FeS-SA). SA could prevent aggregation of FeS by the concurrent electrostatic repulsion and steric hindrance. Homogeneously dispersed FeS-SA nanoparticles 100nm in diameter were observed. FeS-SA showed high efficiency in Cr(VI) removal, corresponding to an enhancement of efficiency from 65% (7.50mmol Cr(VI) per g FeS) to 100% (11.54mmol Cr per g FeS) relative to that achieved with naked FeS. Analysis of reaction products by X-ray diffraction and X-ray photoelectron spectroscopy revealed the co-existence of α-FeOOH, S₈, and Cr(OH)₃ that apparently were introduced by Fe(II), S(-II), and Cr(VI), respectively. In-depth analysis of the removal mechanism revealed that reduction and adsorption respectively account for 82% and 18% of the Cr removal. In addition, higher pH and CaCl₂ concentration resulted in lower removal efficiency. This study provides a promising application of SA in enhancing FeS reactivity for the remediation of groundwater pollution.

Long-Term Immobilization of Technetium via Bioremediation with Slow-Release Substrates

Radionuclides are present in groundwater at contaminated nuclear facilities with technetium-99, one of the most mobile radionuclides encountered. In situ bioremediation via the generation of microbially reducing conditions has the potential to remove aqueous and mobile Tc(VII) from groundwater as insoluble Tc(IV). However, questions remain regarding the optimal methods of biostimulation and the stability of reduced Tc(IV) phases under oxic conditions. Here, we selected a range of slow-release electron donor/chemical reduction based substrates available for contaminated land treatment, and assessed their potential to stimulate the formation of recalcitrant Tc(IV) biominerals under conditions relevant to radioactively contaminated land. These included a slow-release polylactate substrate (HRC), a similar substrate with an additional organosulfur ester (MRC) and a substrate containing zerovalent iron and plant matter (EHC). Results showed that Tc was removed from solution in the form of poorly soluble hydrous Tc(IV)-oxides or Tc(IV)-sulfides during the development of reducing conditions. Reoxidation experiments showed that these phases were largely resistant to oxidative remobilization and were more resistant than Tc(IV) produced via biostimulation with an acetate/lactate electron donor mix in the sediments tested. The implications of the targeted formation of recalcitrant Tc(IV) phases using these proprietorial substrates in situ is discussed in the context of the long-term management of technetium at legacy nuclear sites.

Bacterial Diversity in Submarine Groundwater along the Coasts of the Yellow Sea

Submarine groundwater (SGD) is one of the most significant pathways for the exchange of groundwater and/or source of nutrients, metals and carbon to the ocean, subsequently cause deleterious impacts on the coastal ecosystems. Microorganisms have been recognized as the important participators in the biogeochemical processes in the SGD. In this study, by utilizing 16S rRNA-based Illumina Miseq sequencing technology, we investigated bacterial diversity and distribution in both fresh well water and brackish recirculated porewater along the coasts in the Yellow Sea. The results showed that Actinobacteria and Betaproteobacteria, especially Comamonas spp. and Limnohabitans spp. were dominated in fresh well samples. Distinct patterns of bacterial communities were found among the porewater samples due to different locations, for examples, Cyanbacteria was the most abundant in the porewater samples far from the algal bloomed areas. The analysis of correlation between representative bacterial taxonomic groups and the contexture environmental parameters showed that fresh well water and brackish porewater might provide different nutrients to the coastal waters. Potential key bacterial groups such as Comamonas spp. may be excellent candidates for the bioremediation of the natural pollutants in the SGD. Our comprehensive understanding of bacterial diversity in the SGD along the coasts of the Yellow Sea will create a basis for designing the effective clean-up approach in-situ, and provide valuable information for the coastal management.