A Critical Review of Groundwater Table Fluctuation: Formation, Effects on Multifields, and Contaminant Behaviors in a Soil and Aquifer System.

The groundwater table fluctuation (GTF) zone is an important medium for the hydrologic cycle between unsaturated soil and saturated aquifers, which accelerates the migration, transformation, and redistribution of contaminants and further poses a potential environmental risk to humans. In this review, we clarify the key processes in the generation of the GTF zone and examine its links with the variation of the hydrodynamic and hydrochemistry field, colloid mobilization, and contaminant migration and transformation. Driven by groundwater recharge and discharge, GTF regulates water flow and the movement of the capillary fringe, which further control the advection and dispersion of contaminants in soil and groundwater. In addition, the formation and variation of the reactive oxygen species (ROS) waterfall are impacted by GTF. The changing ROS components partially determine the characteristic transformation of solutes and the dynamic redistribution of the microbial population. GTF facilitates the migration and transformation of contaminants (such as nitrogen, heavy metals, non-aqueous phase liquids, and volatile organic compounds) through colloid mobilization, the co-migration effect, and variation of the hydrodynamic and hydrochemistry fields. In conclusion, this review illustrates the limitations of the current literature on GTF, and the significance of GTF zones in the underground environment is underscored by expounding on the future directions and prospects.

Transport and transformation of arsenic in coastal aquifer at the scenario of seawater intrusion followed by managed aquifer recharge.

Release of contaminants from aquifers at the coastal area is of increasing concern, but remains unclear due to the complex groundwater dynamics and hydrochemistry. Specifically, frequently occurring seawater intrusion and the subsequent engineering measures of managed aquifer recharge (MAR) could alter the groundwater regime, which might affect the fate and behaviors of contaminants. In this work, we investigated the transport and transformation of arsenic (As) in the coastal aquifer at the scenario of seawater intrusion followed by the injection-based MAR process. Results showed that seawater intrusion induced 10.3% more release of aqueous As in aquifers, which was attributed to the competitive desorption as a result of elevated anion concentration and pH, and the reduction of As(V) to As(III) due to the reduced redox potential and enriched As-reducing bacteria. Furthermore, seawater intrusion inhibited the recrystallization of iron (hydr)oxides and instead facilitated its conversion to iron sulfide with lower affinity to As. The subsequent MAR introduced oxygenated recharge water into aquifers and increased the redox potential, leading to the dissolution of iron sulfide followed by formation of amorphous iron (hydr)oxides. However, the competitive desorption of As with rich HCO3- under increased pH dominated continuous increase in the aquifer aqueous As during MAR process. A constructed numerical model for describing As transport based on the experimental data showed that As transported along the interface between seawater and freshwater, and MAR enhanced the release of As and expanded the spread range of As. Our findings reveal that both seawater intrusion and subsequent MAR could cause the release, transport, and transformation of As, which provides new insight on the understanding of geochemical process of As in coastal aquifers.

Constructing the active surface soil layer with ZVI-biochar amendment for simultaneous immobilization of As and Zn in both contaminated soil and groundwater: Continuous versus intermittent infiltration mode.

In this study, the zero valent iron-biochar composite (ZVI-BC) was applied to construct an active surface soil layer for the simultaneous remediation of As-Zn contaminated soil and groundwater, focusing on the influence of the infiltration mode of pumped-up groundwater into soil. The active surface soil treated more contaminated groundwater for As (4.45-5.46 L kg-1 soil) than that for Zn (2.52-3.13 L kg-1 soil) under both continuous and intermittent infiltration modes, with about 98% As and 95% Zn removed from groundwater and retained in the soil. As(V) precipitated with Fe(III) due to ZVI oxidation, which was responsible for the As immobilization. The soil under the intermittent infiltration mode was enriched by the Sphingomonas with arsenate reductase gene, which promoted more reduction of As(V) into As(III) and facilitated coprecipitation of As(III) with Fe(III). The Mn oxide determined the sorption of Zn in the active soil layer, where the Hyphomicrobium, one type of manganese oxidizing bacteria, was much higher under the continuous infiltration mode, which accounted for the more Zn immobilization. After the remediation, both As and Zn immobilized in the active surface soil showed high stability, with the average downward migration rate of only 0.207-0.368 cm year-1 within 20-year rainfall exposure. Our findings indicate that this active surface soil layer is applicable for simultaneous immobilization of As and Zn in both contaminated soil and groundwater, and the groundwater intermittent infiltration could be a better option considering the remediation effectiveness, the immobilization mechanism, the long-term stability, and the energetic efficiency.

Numerical modeling investigations of colloid facilitated chromium migration considering variable-density flow during the coastal groundwater table fluctuation.

Fluctuation of the groundwater table in the coastal zone influences the migration of colloids in vadose zone, which can further carry contaminants to transport. To capture the variable-density water flow and the migration processes, this study developed a colloid-facilitated migration model by adjusting the adsorption coefficient and considering the relationship between colloid and salinity based on the experimental observations. This model was further applied to explore the effects of freshwater and seawater fluctuations on the migration and transformation of colloids and Cr in coastal vadose zones. The greater the hydraulic conductivity of the saturated aquifer was, the more Cr were discharged into the ocean by submarine groundwater discharge. Furthermore, the increase in the freshwater fluctuation amplitude expanded the pollution ranges of colloidal Cr and dissolved Cr. The rise of the seawater fluctuation amplitude had a more obvious reduction effect on the total solid retained Cr in the contaminant source, compared with that of the freshwater fluctuation. As the seawater fluctuation amplitude increased from 0.1 m to 0.8 m, the ratio of total solid retained Cr reduction in the contaminant source to the initial value increased from 1.8 % to 7.8 %. The results obtained from this study deepens our understanding of how colloids and contaminants migrate across a coastal area from vadose zone induced by the groundwater table fluctuation.

Colloid formation and facilitated chromium transport in the coastal area soil induced by freshwater and seawater alternating fluctuations.

Seawater seasonal fluctuation results in its close interaction with freshwater in the coastal area, which may affect behavior of contaminants there. This study was conducted to explore the transport and transformation of soil colloid and associated Cr during freshwater and seawater alternating fluctuations by laboratory experiment and numerical simulation. Such a fluctuation brought downward migration of Cr from upper contaminated soil and induced reduction of Cr(VI) into Cr(III). An obvious increase of retained Cr(III) was observed at the lower layers of soil due to the reducing environment. More importantly, the colloids with average sizes between 800-1500 nm was formed during the fluctuation and mainly composed of microcline and Fe/Mn oxides minerals, which determined the Cr transport. Compared with the previous freshwater fluctuation, seawater fluctuations generated more and larger-sized colloids due to its high ionic strength. These colloids carried over 94% Cr in the effluent and Cr(III) accounted for over 95% of total Cr. A colloid-facilitated Cr transport modeling showed that the soil retained Cr decreased by about 14% after eight rounds of fluctuation on an actual soil-contaminated site scale. Our study provides insight for the understanding of geochemical process of Cr in the coastal area under freshwater and seawater fluctuation conditions.

Dispersion and transport of microplastics in three water-saturated coastal soils.

The coastal area is one of the key zones for transport and fate of microplastics (MPs). This study investigated the transport behaviors of different sized MPs in three water-saturated coastal soils, with the aim to explore effects of properties of three different coastal soils on the dispersion and migration of three-sized MPs (0.3, 0.5, and 1 µm). All three-sized MPs had the strongest dispersion in Soil 3 solution, followed by that in Soil 1 solution and then that in Soil 2 solution. The strongest dispersion of MPs in Soil 3 solution was attributed to the lowest ionic strength. Such a high dispersion favored MPs movement in soil solution but readily be sorbed and fixed by rich Fe and Al oxides in Soil 3 solid through strong electrostatic attraction, leading to the lowest transport rate (20.5-41.2%). The high ionic strength in the Soil 1 solution decreased the dispersion of MPs, but the presence of high content of humic acid enhanced the electrostatic repulsion and steric hindrance between MPs and soil particles, resulting in the highest transport ability of MPs in Soil 1 (39.4-72.5%). The large amount of dissolved Ca2+ and Mg2+ in Soil 2 solution favored MPs bridged with fulvic acid, resulting in the highest aggregation of MPs and relatively lower transport ability (34.1-49.6%). Large-sized MPs had higher electrostatic repulsion between the particles, thus increasing the dispersion and transport capacity of MPs in soil. Modeling showed the experiment-consistent results that Soil 3 had the lowest MPs transport after 600 mm of heavy rainfall, with the maximum migration distance of 7.50-10.5 cm, which was smaller than that in Soil 2 (8.10-12.0 cm) and that in Soil 1 (9.00-18.3 cm). These results indicated that MPs transport in coastal soil is significant and soil solution and solid composition plays an important role in the dispersion and transport of MPs, respectively. These findings afforded a great basis for the assessment of the fate and risk of MPs in coastal areas.

A COMSOL-PHREEQC Coupled Python Framework for Reactive Transport Modeling in Soil and Groundwater.

The CPqPy framework coupling COMSOL and PHREEQC based on Python was developed. This framework can achieve the simulation of diversified situations including multi-physics coupling and geochemical reactions of soil and groundwater. The multi-physics coupling models are calculated in COMSOL, whereas PHREEQC was applied to calculate the geochemical models through the Phreeqpy library in Python. Feasibility and accuracy of CPqPy were verified and applied to two cases, including a solute transport model considering equilibrium reaction and ion exchange as well as a reactive transport model of a variable saturation soil considering kinetic reaction. The results show a high degree of credibility of CPqPy. The framework has the advantages of strong portability, and it can be further used in conjunction with multiple Python calculation libraries, which greatly extends the application of the reactive transport model.

Migration and transformation of chromium in unsaturated soil during groundwater table fluctuations induced by rainfall.

The groundwater table fluctuation zone is the main interface for contaminants to transport between the unsaturated soil and saturated aquifers which still lacks of concern. In this study, we explored the interactions of Cr(VI) in this specific zone during water table fluctuation through laboratory experiment and numerical modeling. The higher reduction of Cr(VI) was found in the lower soil layer due to the lower Eh at the bottom layer of the unsaturated zone and the Cr(III) concentration increased with rise in water level and fluctuation amplitudes. After twice water fluctuation, nevertheless, there was still about 42.2% Cr retained in the soil and dominantly present as Cr(III) form. The model coupling reaction network with hydrodynamic field showed the cumulative Cr(III) in the unsaturated soil zone had a faster increase at the higher water level rise speed compared with lower rise speed. The cumulative Cr(VI) decreases over time in the saturated aquifers, whereas the cumulative Cr(III) increased with the increase of fluctuation amplitude. Reduction of Cr(VI) into Cr(III) was accompanied with Fe(II) and organic carbon oxidation. The results indicate that the hydrodynamic conditions have impacts on the redox environment of soil which could further affect the transformation and transport of Cr.

Chemical and photo-initiated aging enhances transport risk of microplastics in saturated soils: Key factors, mechanisms, and modeling.

Microplastics (MPs) inevitably undergo aging transformation and transport process in environmental compartments. In this study, the polystyrene MPs were aged via three different oxidation methods including persulfate oxidation (PS), UV irradiation (UV), and UV irradiated persulfate oxidation (UVPS). All three treatments induced the great transformation of MPs, with the significant increase in surface roughness and in oxygen-containing functional groups, i.e., COOH or COOC. The UVPS aging showed synergetic effect due to the strengthened photo-initiated chemical oxidation, compared to UV and PS alone. All aged MPs exhibited the enhanced transport (34.9%-89.2%) in sandy and clay loam soils than pristine MPs (30.5%), and the synergetic effect was also observed in the transport behaviors of the UVPS MPs. Higher transport of MPs and aged MPs occurred in sandy soil than that in clay loam soil since the latter one contained high Fe minerals that tend to retain MPs, which was confirmed by the model quartz sand column experiment. Modeling on the migration of MPs retained in soil under a rainstorm scenario showed that the aged MPs had the stronger remobility and greater proportion of cumulative flux than pristine ones in the soil profile. These findings provided new insights on the fate and transport of MPs in natural soil and their potential risk to groundwater contamination.

Overexpressed CDR1as functions as an oncogene to promote the tumor progression via miR-7 in non-small-cell lung cancer.

BACKGROUND: Circular RNA (circRNA) is a novel member of the noncoding RNA and function as efficient microRNA sponges with gene-regulatory potential, especially the circular RNA ciRS-7 (CDR1as)/tumor suppressor miRNA-7 (miR-7) signals. However, the function of CDR1as/miR-7 in non-small cell lung cancer (NSCLC) is unknown. METHODS: Normal lung tissues (n=20), adjacent non-tumor tissues (n=60), and NSCLC tissues (n=60) were collected to determine the expression and significance of CDR1as/miR-7. Lung cancer cell lines A549 and H460 were overexpressed or knocked down of CDR1as, miR-7 to determine the tumor growth etc. The CDR1as/miR-7-related pathway were analyzed. RESULTS: CDR1as levels was robustly increased with the development of NSCLC (P<0.001) and the NSCLC tissues harbored highest expression of CDR1as, which negatively correlated to the expression of miR-7. Patients with high expression of CDR1as had high TNM stage (P=0.004), more lymph nodes metastasis (LNM) (P=0.021) and shorted overall survival time (OS) (P=0.0135). The CDR1as level was an independent prognostic factor for the patients with NSCLC. Overexpression of CDR1as induced increased cell vitalities and growth, which could be abrogated by knockdown of CDR1as or overexpressed miR-7 to induce apoptosis and G1/S arrest. Mechanistically, CDR1as functioned as miR-7 sponges to up-regulate the key target genes of miR-7 including EGFR, CCNE1 and PIK3CD. The results in vivo further confirmed that CDR1as functioned as oncogene to inhibit the anti-tumor effects of tumor suppressor miR-7 by up-regulation of proliferation index Ki-67, EGFR, CCNE1 and PIK3CD levels. CONCLUSION: Overexpressed CDR1as in NSCLC functions promotes the tumor progression via miR-7 signals.

Assessment of uncertainty in discrete fracture network modeling using probabilistic distribution method.

There have been widespread concerns about solute transport problems in fractured media, e.g. the disposal of high-level radioactive waste in geological fractured rocks. Numerical simulation of particle tracking is gradually being employed to address these issues. Traditional predictions of radioactive waste transport using discrete fracture network (DFN) models often consider one particular realization of the fracture distribution based on fracture statistic features. This significantly underestimates the uncertainty of the risk of radioactive waste deposit evaluation. To adequately assess the uncertainty during the DFN modeling in a potential site for the disposal of high-level radioactive waste, this paper utilized the probabilistic distribution method (PDM). The method was applied to evaluate the risk of nuclear waste deposit in Beishan, China. Moreover, the impact of the number of realizations on the simulation results was analyzed. In particular, the differences between the modeling results of one realization and multiple realizations were demonstrated. Probabilistic distributions of 20 realizations at different times were also obtained. The results showed that the employed PDM can be used to describe the ranges of the contaminant particle transport. The high-possibility contaminated areas near the release point were more concentrated than the farther areas after 5E6 days, which was 25,400 m2.

Transcriptome analysis of distinct long non-coding RNA transcriptional fingerprints in lung adenocarcinoma and squamous cell carcinoma.

Non-small cell lung cancer (NSCLC) is one of the leading causes of cancer-related death, including two major pathologic subtypes, adenocarcinoma (AD) and squamous cell carcinoma (SCC). There are significant differences in the aberrant gene profiling and molecular characteristics among LUAD and LUSC, which lead to the different chemotherapeutic regimens administered to the two NSCLC subtypes. Therefore, unique genetic or epigenetic accurately distinguishing these two subtypes is critical for the diagnosis and treatment of patients. In this study, we tried to develop and validate novel long non-coding RNA (lncRNA)-based signatures to facilitate the diagnosis and individualized treatment of LUAD and LUSC. To analyze the distinct lncRNA profiling in LUAD and LUSC, the paired tissue samples of RNA sequencing or microarray data from The Cancer Genome Atlas (TCGA) and Gene Expression Omnibus (GEO) was used. We found that lncRNA expression pattern is different in LUAD and LUSC, and three up-regulated and down-regulated lncRNAs expressions in LUAD and LUSC tissues were validated. In addition, knockdown of the up-regulated lncRNA AFAP1-AS1 and LINC00511 impaired LUAD cell proliferation, while knockdown of PVT1 inhibited LUSC cell growth. Furthermore, four 6-lncRNAs signature expression patterns were found to be significantly associated with LUAD and LUSC patient overall and progression-free survival. Taken together, the different lncRNAs signature might accurately distinguish LUAD and LUSC and predict clinical outcome for these two different subtypes of NSCLC.