Songhu Yuan

Fe(II)-bearing clay minerals are widespread reductants of hexavalent chromium (Cr(VI)) in subsurface environments. However, the influences of coexisting Fe (hydr)oxides on Cr(VI) reduction by Fe(II)-bearing clay minerals remain elusive. Here, Cr(VI) reduction was investigated in premixed systems of reduced nontronite NAu-2 (rNAu-2) and various Fe (hydr)oxides. Results showed that coexisting ferrihydrite significantly facilitated Cr(VI) reduction during the quick stage (0–2.5 min) across pH 5.5–9.0. During the subsequent slow stage (2.5–205 min), ferrihydrite inhibited Cr(VI) reduction at pH 5.5–7.0 but enhanced it at pH 9.0. In contrast, coexisting goethite had negligible effects. Without Fe (hydr)oxides, direct reduction by rNAu-2 dominated for Cr(VI) removal. In the presence of Fe (hydr)oxides, competitive adsorption was found to inhibit direct Cr(VI) reduction, yet Fe (hydr)oxide-mediated electron transfer effectively offset this inhibitory effect. Both competitive adsorption and mediated electron transfer were influenced by the type and dosage of Fe (hydr)oxides, as well as solution pH. Kinetic modeling revealed that ferrihydrite-mediated electron transfer contributed 1.8–71.5% of the total Cr(VI) reduction, with greater contributions observed at higher solution pH and ferrihydrite dosage. Our findings provide new insights into mineral–mineral electron transfer and its role in regulating Cr(VI) fate in subsurface environments.

In situ chemical reduction (ISCR) is an efficient process for groundwater remediation, whereas the injection of reductants poses secondary contamination risks. Here, we propose a new strategy of electron injection for contaminant reduction in groundwater without the injection of reductants. The reductants are physically separated from the contaminants in aquifers, and electron transfer from reductants to contaminants was achieved by two connected electrodes due to the potential difference. Results showed that 0.1 mM Cr(VI) (pH 2.5) was removed by 98% within 2 h in a laboratory batch system using 10 mM sodium dithionite (pH 11.8) as the electron source. Electrochemically stable electrodes, such as graphite and mixed metal oxides, exhibited high performance in Cr(VI) removal. Over 85% of Cr(VI) removal was maintained in 10 cycles of consecutive treatments. This electron injection system could remove 81% of Cr(VI) within 60 h in a simulated aquifer. By leveraging electron injection, this approach provides a feasible pathway for aquifer redox regulation, thereby reducing the reliance on massive chemical inputs and minimizing secondary environmental disturbances caused by traditional ISCR.

In situ chemical oxidation (ISCO) is widely used for groundwater remediation, whereas the influence of aquifer heterogeneity, that is, the difference in physical structure and chemical compositions, on oxidant retention and consumption remains poorly understood. In low-permeability lens-containing sand columns, we found that the retention and consumption of oxidant (KMnO4) were largely influenced by the chemical reactivity of the lens besides the well-known permeability. Inert lens (represented by kaolin) mainly altered the transport pathways of oxidant, whereas chemically reactive lenses (represented by real sediments with different electron-donating capacities) further enhanced the retention and consumption within the lenses. A higher electron-donating capacity led to more oxidant retention and consumption. Moreover, the reduced components released from the reactive lens could also increase the oxidant consumption. This study highlights the importance of chemical reactivity besides the physical structure of lenses in heterogeneous aquifers for oxidant transport, retention, and consumption and also implicates the consideration of chemical reactivity for designing the injection dosages and position of oxidants in ISCO remediation.

In situ chemical oxidation (ISCO) has been widely used in groundwater remediation, whereas the injected chemicals pose secondary risks to the remediated aquifers. Here, we propose a noncontact oxidation scheme in which contaminants are treated by physically separated oxidants through wired electrodes, thereby eliminating the injection of chemicals into the aquifer. Groundwater circulation is applied to transport contaminated groundwater from surrounding aquifers to the in-well electrode. We serendipitously found that graphite electrodes after simple preoxidation showed superior performance to other commercial electrodes, exhibiting high and sustainable performance in mediating the long-distance electron transfer from contaminants to oxidants. For the noncontact oxidation of 10 μM phenol by 10 mM peroxysulfate (PDS), the removal reached 85% within 2 h and was maintained stable over 10 consecutive treatment cycles. Persulfate led to a larger contaminant removal than other common oxidants. Assisted with hydraulic circulation, this system achieved 95% of phenol removal within 36 h in a simulated aquifer. Contaminants with high electron-donating abilities were prone to be oxidized. Anode/contaminant and cathode/oxidant interfacial interactions played a critical role in noncontact oxidation. This noncontact oxidation strategy presents a new horizon for green groundwater remediation.

We introduce two gene‐informed approaches that, for the first time, explicitly incorporate microbial genomic information into groundwater denitrification simulations. First, we couple the dynamic flux balance analysis (DFBA, which resolves genome‐resolved metabolic networks) with the PFLOTRAN reactive transport model (RTM). The ensuing DFBA‐reactive transport model (RTM) framework provides a mechanistic, pathway‐explicit linkage between gene expression and solute transformation dynamics. Second, we develop a gene‐informed deep‐learning model that leverages environmental covariates and functional gene abundances to emulate biogeochemical reaction kinetics at orders‐of‐magnitude reduced computational cost. Using controlled batch and column experiments including alternating surface‐water/groundwater flow regimes, both models reproduce observed NO ₃ ⁻ depletion and NO ₂ ⁻ transients and outperform the conventional RTM constrained only by geochemistry. Our DFBA‐RTM elucidates pathway‐level controls on denitrification, whereas the gene‐informed deep‐learning model offers fast and accurate forecasts suitable for multi‐scenario analyses. Together, these results show that incorporating microbial genomic information substantially improves hydro‐biogeochemical modeling results and that mechanistic and data‐driven strategies are complementary. While the former supports process attribution, the latter yields efficient and scalable surrogates. The framework is readily extensible to other contaminant and redox systems, advancing hydro‐biogeochemical modeling toward genetically informed (high‐resolution) representations of subsurface environments.

Surface water-groundwater interaction zones are recognized as hotspots for reactive oxygen species (ROS) production. Entrapped gas bubbles formed due to water table fluctuations are important sinks and sources of dissolved oxygen (DO), whereas their influence on ROS production remains unknown. Here, we use column experiments to simulate surface water-groundwater interactions and quantitatively investigate the role of entrapped gas bubbles in the spatiotemporal distributions of DO and H₂O₂. During surface water recharge, gas bubbles act as O₂ sinks, which uptake O₂ from DO in the infiltrated surface water and thus restrict O₂ penetration and the resultant H₂O₂ production. For subsequent groundwater discharge, the O₂ stored in gas bubbles serves as a DO source for groundwater, which promotes H₂O₂ production. Cycles of groundwater discharge and surface water recharge experiments support the fact that the restriction and promotion effects induced by gas bubbles persist across recharge-discharge cycles. Reactive transport modeling reveals that the peak concentration and distribution area of H₂O₂ during surface water recharge decrease with the increase in the degree of gas saturation, but they increase during groundwater discharge. These findings highlight the previously overlooked dual roles of entrapped gas bubbles in ROS production and distribution under fluctuating hydrological regimes.

We rely on a global sensitivity analysis (GSA) approach to identify the dominant physical and biogeochemical controls on dissolved oxygen (DO) dynamics in riparian aquifers. The study is motivated by the observation that availability of DO is key to regulating redox conditions and associated processes in the subsurface. Yet, the complexity of coupled flow and transport models, combined with model input uncertainty challenges our ability to fully characterize system behavior. To address this issue, we integrate Bayesian network‐based and variance‐based methods into a comprehensive GSA framework, enabling a robust evaluation of parameter and process sensitivities. To overcome the high computational demand of GSA for complex numerical models, we develop surrogate models using deep learning approaches (i.e., multi‐layer perceptrons and convolutional neural networks). Application of this framework to a high‐resolution model of riparian DO transport reveals that river stage dynamics (i.e., period and amplitude of water level fluctuations) are primary drivers of DO supply to the aquifer system. Hydraulic conductivity, riverine DO concentration, and the maximum DO reaction rate exhibit important but localized effects, influencing different transport pathways including river water infiltration, entrapped air dissolution, and diffusion through the unsaturated zone. In contrast, parameters such as porosity, longitudinal dispersion, and van Genuchten soil parameters exhibit negligible influence. These findings underscore the value of combining deep learning and GSA to efficiently evaluate complex environmental systems and to guide model simplification and diagnosis.

Electrokinetic bioremediation (EK-BIO) shows significant promise for organochlorine remediation in low-permeability matrices. However, its in situ application under site-relevant scenarios remains a substantial challenge. This study establishes a comprehensive EK-BIO lab-to-field framework that includes laboratory batch experiments, array optimization, pilot-scale field validation, and life cycle assessment. Primarily, batch and column experiments optimized both the additive dosage strategy and electrode array configuration, favoring a 6-day preinoculation of the niche-preparing culture and a unidirectional one-dimensional electrode setup. Guided by these findings, the 98-day EK-BIO pilot experiment achieved over 90.0% TCE removal, with a 74.0% chloroethylene-to-ethylene conversion efficiency. Microbial community analyses further revealed a notable increase in the relative abundance of putative organohalide-respiring bacteria in the EK-BIO, approximately 25.6% and 34.3% higher than in bioaugmentation and electrokinetic treatments, respectively. Additionally, life cycle assessment results underscored the advantages of EK-BIO over conventional thermal remediation alternatives, with reductions in carbon emissions, energy consumption, and remediation costs. This study validated the feasibility and reliability of EK-BIO technology, supporting its advancement for the in situ remediation of organochlorine-contaminated sites.

The great phytoplanktonic shift from green to red plastid lineage dominance in the early Mesozoic marks a primary producer revolution in marine ecosystems, facilitating the rise of modern ecosystems and impacting global carbon cycling and energy flows. The causes driving this evolutionary transition have been attributed to the changes in essential nutrients and the environmental crises of the Permian–Triassic mass extinction. Nonetheless, the underlying mechanisms driving this transition remain poorly understood. Here, we integrated culture experiments, molecular and physiological analyses, big data analysis, and phylogenomic dating analyses to uncover how environmental stresses influence algal physiology, thereby altering their evolutionary trajectories. We find that environmental and endogenous reactive oxygen species (ROS) collaboratively shape phytoplanktonic responses. The structural characteristics of red lineage phytoplankton enhance resistance to environmental ROS, facilitating physiological strategies that minimize endogenous ROS accumulation, thereby driving more adaptive evolutionary trajectories under environmental stresses in the early Mesozoic. The alignment of the turnover in diversification dynamics between the two lineages with paleoenvironmental shifts that triggered increased ROS production supports the role of ROS in driving this evolutionary transition. Our findings highlight ROS as a key underlying factor driving phytoplankton evolution, providing predictive insights into major biota–environment coevolutions throughout Earth’s history.

《地球科学》(ISSN 1000-2383;CN42-1874/P) (原刊名《地球科学——中国地质大学学报》ISSN 1000-2383;CN42-1233/P)，创刊于1957年，是由教育部主管、中国地质大学主办的综合性地学学术理论期刊，月刊，2015年改名为《地球科学》,她以反映中国地质大学教学与科研最新的、高水平的基础地质、应用地质、资源与环境地质及地学工程技术研究成果为主要任务。