Co-migration behavior of toluene coupled with trichloroethylene and the response of the pristine groundwater ecosystems - A mesoscale indoor experiment.

Experimental scale and sampling precision are the main factors limiting the accuracy of migration and transformation assessments of complex petroleum-based contaminants in groundwater. In this study, a mesoscale indoor aquifer device with high environmental fidelity and monitoring accuracy was constructed, in which dissolved toluene and trichloroethylene were used as typical contaminants in a 1.5-year contaminant migration experiment. The process was divided into five stages, namely, pristine, injection, accumulation, decrease, and recovery, and characteristics such as differences in contaminant migration, the responsiveness of environmental factors, and changes in microbial communities were investigated. The results demonstrated that the mutual dissolution properties of the contaminants increased the spread of the plume and confirmed that toluene possessed greater mobility and natural attenuation than trichloroethylene. Attenuation of the contaminant plume proceeded through aerobic degradation, nitrate reduction, and sulfate reduction phases, accompanied by negative feedback from characteristic ion concentrations, dissolved oxygen content, the oxidation-reduction potential and microbial community structure of the groundwater. This research evaluated the migration and transformation characteristics of typical petroleum-based pollutants, revealed the response mechanism of the ecosystem to pollutant, provided a theoretical basis for predicting pollutant migration and formulating control strategies.

Evaluating groundwater ecosystem dynamics in response to post in-situ remediation of mixed chlorinated volatile organic compounds (CVOCs): An insight into microbial community resilience, adaptability, and metabolic functionality for sustainable remediation and ecosystem restoration.

The in-situ remediation of groundwater contaminated with mixed chlorinated volatile organic compounds (CVOCs) has become a significant global research interest. However, limited attention has been given in understanding the effects of these remediation efforts on the groundwater microbial communities, which are vital for maintaining ecosystem health through their involvement in biogeochemical cycles. Hence, this study aimed to provide valuable insights into the impacts of in-situ remediation methods on groundwater microbial communities and ecosystem functionality, employing high-throughput sequencing coupled with functional and physiological assays. The results showed that both bioremediation and chemical remediation methods adversely affected microbial diversity and abundance compared to non-polluted sites. Certain taxa such as Pseudomonas, Acinetobacter, and Vogesella were sensitive to these remediation methods, while Aquabacterium exhibited greater adaptability. Functional annotation unveiled the beneficial impact of bioremediation on the sulfur cycle and specific taxa such as Cellvibrio, Massilia, Algoriphagus, and Flavobacterium which showed a significant positive relationship with dark oxidation of sulfur compounds. In contrast, chemical remediation showed adverse impacts on the nitrogen cycle with a reduced abundance of nitrogen and nitrate respiration along with a reduced utilization of amines (nitrogen rich substrate). The findings of this study offer valuable insights into the potential impacts of in-situ remediation methods on groundwater microbial communities and ecosystem functionality, emphasizing the need for meticulous consideration to ensure the implementation of effective and sustainable remediation strategies that safeguard ecosystem health and function.

Response and recovery of a pristine groundwater ecosystem impacted by toluene contamination - A meso-scale indoor aquifer experiment.

Microbial communities are the driving force behind the degradation of contaminants like aromatic hydrocarbons in groundwater ecosystems. However, little is known about the response of native microbial communities to contamination in pristine environments as well as their potential to recover from a contamination event. Here, we used an indoor aquifer mesocosm filled with sandy quaternary calciferous sediment that was continuously fed with pristine groundwater to study the response, resistance and resilience of microbial communities to toluene contamination over a period of almost two years, comprising 132days of toluene exposure followed by nearly 600days of recovery. We observed an unexpectedly high intrinsic potential for toluene degradation, starting within the first two weeks after the first exposure. The contamination led to a shift from oxic to anoxic, primarily nitrate-reducing conditions as well as marked cell growth inside the contaminant plume. Depth-resolved community fingerprinting revealed a low resistance of the native microbial community to the perturbation induced by the exposure to toluene. Distinct populations that were dominated by a small number of operational taxonomic units (OTUs) rapidly emerged inside the plume and at the plume fringes, partially replacing the original community. During the recovery period physico-chemical conditions were restored to the pristine state within about 35days, whereas the recovery of the biological parameters was much slower and the community composition inside the former plume area had not recovered to the original state by the end of the experiment. These results demonstrate the low resilience of sediment-associated groundwater microbial communities to organic pollution and underline that recovery of groundwater ecosystems cannot be assessed solely by physico-chemical parameters.

Assessment of environmental risks to groundwater ecosystems related to use of veterinary medicinal products.

The current EU guidelines for the environmental risk assessment of veterinary pharmaceutical products (VMPs) in groundwater (GW) suggest an approach based on the comparison between the calculated concentration in GW (PECgw) and a threshold concentration of 0.1 µg/L. The latter is the upper limit of the concentration for pesticides in groundwater in the EU. If the calculated PECgw does not exceed the threshold, then the risk is considered acceptable. It is assumed that the concentration of 0.1 µg/L is by default safe for both humans and exposed GW organisms. On this basis, it is not clear whether the GW is recognized as an ecosystem or as a source of drinking water. Largely unrecognized biodiversity in GW is worthy of protection through the adoption of a more scientifically sound risk analysis, which should be based on the consideration of ecological criteria. Based on the evidence of their vulnerability, we propose that risk assessments of GW ecosystems should be a compulsory part of the overall risk assessment of VMPs (as well as pesticides, biocides and feed additives). Furthermore, we suggest the use of a risk quotient approach based on the PEC/PNEC ratio in which the PNEC is calculated including an additional safety factor of 10 to the calculated PNEC for surface water.

[Assessment of Ecosystem Health of Baogang Tailings Groundwater Based on Microbiome Index of Biotic Integrity (M-IBI)].

Index of Biological Integrity (IBI) is a scientific tool used to evaluate health of aquatic ecosystems. IBI associates anthropogenic influences with biological activity in the water body, and is formulated using data developed from biosurveys. Compared with other biotic assemblage indicators of water quality, little attention has been paid to the application of microbial community in ecosystem health assessment for groundwater bodies so far. An approach based on microbiome index of biotic integrity was developed to assess groundwater ecosystem health in this study. The method based on Illumina high-throughput DNA sequencing was applied to achieve the information of microbial community. The key environmental factors were selected based on CCA analysis and the optimized values were calculated for defining the taxonomic genera sensitive and resistant to these factors. The resulting candidate biotic factors were used to construct microbiome index of biotic integrity (M-IBI) evaluating system. The results showed among the studied sample sites from groundwater of Baogang rare earth tailings, 33.3% of samples were at "Great" level, 16.7% at "Good" level, most of samples (41.7%) at "moderate" level and 8.3% at "Bad" level. The ecosystem healthy status of the sample sites near the tailings was affected by human disturbances, while the samples far away the tailings were at healthy level. The results of the groundwater ecosystem healthy assessment based on M-IBI system had a good match with the groundwater quality standard based on chemical properties. It indicated that M-IBI could be a potential index to evaluate the health of groundwater ecosystem.

River-aquifer interactions and their relationship to stygofauna assemblages: a case study of the Gwydir River alluvial aquifer (New South Wales, Australia).

In contrast to surface water ecosystems, groundwater ecosystems are usually considered to have relatively stable conditions and physically inert environments. However, many groundwater ecosystems undergo substantial changes through space and time, related to fluxes in groundwater flow, exchange and nutrient imports. In this study we used hydrochemical data to: 1) determine the different hydrogeological conditions in an alluvial system, the shallow Gwydir River alluvial aquifer (located in Northern New South Wales, Australia); and 2) analyze the relationship between hydrochemical conditions and the composition of stygofauna assemblages in the aquifer. Using hydrochemical modeling and multivariate analyses, four main hydrogeological situations were defined as occurring in the aquifer. Bores were classified as having either a high, low or no influence from or exchange with the river. The latter group was further subdivided into those of low and high salinity. Further analysis combining the biological and hydrochemical data identified two main groups of samples. The first group was composed mainly of samples related to the aquifer groundwater which had higher richness and abundance of fauna compared to samples in the second group which was comprised of samples affected by stream water leakage and samples related to the highest salinities. These results suggest that more stable conditions (mainly related to steadier groundwater head levels) and lower nitrate concentrations promoted a more diverse and abundant stygofauna community.