Asymmetric response of transition metal cationic orbitals to applied electric field.

Understanding the quantum mechanical mechanisms underlying atomic/ionic interfacial processes and phenomena, particularly their dependence on the electronic orbital rearrangement of atoms/ions in an external electric field, remains a significant challenge. This study investigated the asymmetric response of transition metal (TM) cationic orbitals when subjected to an applied electric field. Quantum mechanical calculations were employed to quantify the newly formed hybrid orbitals and evaluate the corresponding orbital energies of the TM cations. Analysis of the quantitative contribution of asymmetric orbital hybridization to TM-surface interactions showed a significant change in orbital energy and increased effective charges of TM cations at the charged surface. This asymmetric response, induced by a negative external electric field generated from the structural charges of clay minerals (e.g., montmorillonite), repels electrons from the outer-shell orbital. This repulsion consequently increases the electron binding energy of the inner-shell orbitals, leading to new surface reactions, polarization-enhanced induction force, and polarization-induced covalent bonding between the TM cations and the charged surface. Our theoretical predictions regarding TM-clay mineral interactions are consistent with the experimental observations of TM cation adsorption. This finding has significant implications for the adsorptive removal of TM cations from wastewaters and for enhancing the catalytic efficiency of TM-surface catalysts. The unique physical and chemical characteristics exhibited by TMs at charged particle surfaces, resulting from their asymmetric response, can play pivotal roles in environmental and chemical engineering.

Enhanced soil function and health by soybean root microbial communities during in situ remediation of Cd-contaminated soil with the application of soil amendments.

The interactions between soil microbiomes at various trophic levels are essential for restoring soil functions. Legumes are considered as "pioneer crops" in degraded or contaminated soils because they can fix nitrogen through symbiotic relationships with rhizobacteria, which promotes soil fertility. However, little is known about the abilities of legumes to contribute to the health of soil contaminated with cadmium (Cd). In this research, we applied a soil amendment (commercial Mg-Ca-Si conditioner, CMC) at two rates (1,500 and 3,000 kg/ha) in a Cd-contaminated soybean field. Bulk and rhizosphere soil samples were collected to assess the amendment-induced effects on four microbial lineages (bacteria, fungi, arbuscular mycorrhizal fungi [AMF], and nematodes) and their functions including Cd stabilization, nutrient cycling, and pathogen control. Compared with the control, both CMC application rates increased the pH and reduced labile Cd fraction in the bulk and rhizosphere soils. Although the total Cd concentrations in the soil were similar, the Cd accumulation in the grains was significantly reduced in treatments of soil amendments. It was observed that the application of CMC can significantly reduce the AMF diversity but increased the diversity of the other three communities. Moreover, the biodiversity within keystone modules (identified by co-occurrence network analysis) played key roles in driving soil multifunctionality. Specifically, key beneficial groups in module 2 such as Aggregicoccus (bacteria), Sordariomycetes (fungi), Glomus (AMF), and Bursaphelenchus (nematode) were strongly associated with soil multifunctionality. By co-culturing bacterial suspensions with the soybean root rot pathogen Fusarium solani in the in vitro assays, we experimentally validated that the application of CMC promoted the suppression of soil bacterial community on pathogens by inhibiting the mycelium growth and spore germination. Also, the bacterial community was more resistant to Cd stress in soils receiving CMC amendment. Our findings provide valuable theoretical references for enhancing soil functions and health via applying a soil amendment (CMC) during Cd-contaminated soil remediation. IMPORTANCE Restoration of microbiome-driven soil functions and health is of great importance during Cd-contaminated soil remediation via soil amendment. Soybean and its symbiotic mutualism can provide abundant nitrogen and phosphorus to relieve the nutrient deficiency of Cd-contaminated soil. This study provides a novel perspective on the potential role of applying a soil amendment (CMC) in enhancing the functions and health of Cd-contaminated soils. Our results showed the distinct differences in soil microbial community responding to amendment-induced changes in edaphic properties. The biodiversity within keystone modules had major contributions to the maintenance of the soil's multifunctionality and health. Additionally, a higher CMC application rate showed more beneficial effects. Collectively, our results enhance our understanding about the effects of applying CMC, together with soybean rotation, to enhance and maintain soil functions and health during the field Cd stabilization process.

Metagenomic and machine learning-aided identification of biomarkers driving distinctive Cd accumulation features in the root-associated microbiome of two rice cultivars.

Developing low-cadmium (Cd) rice cultivars has emerged as a promising avenue for food safety in Cd-contaminated farmlands. The root-associated microbiomes of rice have been shown to enhance rice growth and alleviate Cd stress. However, the microbial taxon-specific Cd resistance mechanisms underlying different Cd accumulation characteristics between different rice cultivars remain largely unknown. This study compared low-Cd cultivar XS14 and hybrid rice cultivar YY17 for Cd accumulation with five soil amendments. The results showed that XS14 was characterized by more variable community structures and stable co-occurrence networks in the soil-root continuum compared to YY17. The stronger stochastic processes in assembly of the XS14 (~25%) rhizosphere community than that of YY17 (~12%) suggested XS14 may have higher resistance to changes in soil properties. Microbial co-occurrence networks and machine learning models jointly identified keystone indicator microbiota, such as Desulfobacteria in XS14 and Nitrospiraceae in YY17. Meanwhile, genes involved in sulfur cycling and nitrogen cycling were observed among the root-associated microbiome of these two cultivars, respectively. Microbiomes in the rhizosphere and root of XS14 showed a higher diversity in functioning, with the significant enrichment of functional genes related to amino acid and carbohydrate transport and metabolism, and sulfur cycling. Our findings revealed differences and similarities in the microbial communities associated with two rice cultivars, as well as bacterial biomarkers predictive of Cd-accumulation capacity. Thus, we provide new insights into taxon-specific recruitment strategies of two rice cultivars under Cd stress and highlight the utility of biomarkers in offering clues for enhancing crop resilience to Cd stresses in the future.

Assembly of root-associated bacterial community in cadmium contaminated soil following five-year consecutive application of soil amendments: Evidences for improved soil health.

Soil amendments have been extensively used to remediate heavy metal contaminated soils by immobilizing or altering edaphic properties to reduce the bioavailability of heavy metals. However, the potential influences of long-term soil amendments applications on microbial communities and polluted soil health are still in its infancy despite that have been applied for decades. We used amplicon sequencing and q-PCR array to characterize the root-associated microbial community compositions and rhizosphere functional genes in a five-year field experiment with consecutive application of four amendments (lime, biochar, pig manure, and a commercial Mg-Ca-Si conditioner). Compared with the control, soil amendments reduced the available Cd (CaCl2 extractable Cd) in soils and strongly affected bacterial community compositions in four root-associated niches. Five rare keystone bacterial species were found belonging to the family Gallionellaceae (1), Haliangiaceae (1), Anaerolineaceae (2), and Xanthobacteraceae (1), which significantly correlated with soil pH and the functional genes nifH and phoD. Random forest analysis showed that rhizosphere soil pH and microbial functions, and root-associated keystone bacterial community compositions mainly influenced the Cd concentrations in rice grains. Altogether, our field data revealed five-year consecutive application of soil amendments regulated root-associated microbial community assembly and enhanced microbial functions, thereby improved rhizosphere health of Cd-contaminated soils.

Effects of reclaimed wastewater irrigation on soil-crop systems in China: A review.

Reclaimed wastewater (RW) use represents a substantial opportunity to alleviate the growing scarcity of water for irrigation of agricultural crops in China. However, insufficient understanding of the effects and fates of possible contaminants in RW promotes concerns over crop safety and prevents the extensive incorporation of RW in agriculture. We reviewed the characteristics of contaminants in RW, the fate of contaminants in soil-crop systems, and the effects of RW irrigation on soil quality and crop growth in China. We found that concentrations of heavy metals in RW were higher than the permissible limits in some areas. The total concentrations and main categories of emerging contaminants and pathogens in RW varied markedly among municipal wastewater treatment plants, and the greatest risks of contamination were posed by ofloxacin, sulfamethoxazole, and erythromycin, the most frequently observed compounds with risk quotients >1. The negative effects of salts and nutrients in RW on soil quality and crop growth were minor and manageable. The accumulation of heavy metals and emerging contaminants in soils irrigated with RW did not pose an immediate risk to soils and crops. Changes in soil microbial populations, diversity, and activity caused by RW irrigation increased crop yields and protected crops against contaminants. However, attention is necessary to the risks of bioaccumulation in soils and crops of heavy metals, emerging contaminants, intermediate metabolites, and pathogens, and their effects on human health with long-term RW irrigation. We recommend irrigation practices, crop screening, soil treatments, prioritizing the risks of contaminants, and comprehensive management to increase safety in RW used for agricultural irrigation.

Soil indigenous microorganisms weaken the synergy of Massilia sp. WF1 and Phanerochaete chrysosporium in phenanthrene biodegradation.

Biodegradation is a promising way to reduce phenanthrene (PHE) in environment. PHE biodegradation by bioaugmentation of axenic and mixed cultures of Massilia sp. WF1 (a highly efficient PHE-degrading bacteria) and Phanerochaete chrysosporium (P. chrysosporium, an extensively researched model fungus in organic pollutant bioremediation) was investigated in aqueous and autoclaved/un-autoclaved soil cultures. In the liquid cultures, the strain WF1 could use PHE (ca. 10 mg L-1) as the sole carbon source, and the presence of d-fructose (500 mg L-1) had no obvious effect on its PHE degradation; while the opposite was observed for P. chrysosporium. The bioaugmentation of strain WF1 and P. chrysosporium co-culture showed the highest PHE-degradation efficiency, especially in the aqueous and the autoclaved soil (PHE, ca. 50 mg kg-1) cultures, indicating a synergistic interaction of the co-culture during PHE dissipation. It was further observed that the indigenous microorganisms (mainly the Gram-positive bacteria) played a dominant role during PHE biodegradation and showed an antagonistic action against the strain WF1-P. chrysosporium co-culture, which weakened the synergistic action of the co-culture in the un-autoclaved soil. Besides, the abundances of PAH-RHDα GP and nidA genes were negatively correlated with residual PHE in the soil. Our findings provide the scientific support for bioremediation of PAHs in environment.

Metabolic interactions in a bacterial co-culture accelerate phenanthrene degradation.

A highly eff ;ective phenanthrene (PHE)-degrading co-culture containing Rhodococcus sp. WB9 and Mycobacterium sp. WY10 was constructed and completely degraded 100 mg L-1 PHE within 36 h, showing improved degradation rate compared to their monocultures. In the co-culture, strain WY10 played a predominant role in PHE degradation. 1-hydroxy-2-naphthoic acid was an end-product of PHE degradation by strain WB9 and accumulated in the culture medium to serve as a substrate for strain WY10 growth, thereby accelerating PHE degradation. In turn, strain WY10 degraded PHE and 1-hydroxy-2-naphthoic acid intracellularly to form phthalate and protocatechuate that were exported to the culture medium through efflux transporters. However, strain WY10 cannot take up extracellular phthalate due to the absence of phthalate transporters, restricting phthalate degradation and PHE mineralization. In the co-culture, phthalate and protocatechuate accumulated in the culture medium were taken up and degraded towards TCA cycle by strain WB9. Therefore, the metabolic cross-feeding of strains WB9 and WY10 accelerated PHE degradation and mineralization. These findings exhibiting the synergistic degradation of PHE in the bacterial co-culture will facilitate its bioremediation application.

Non-bioavailability of extracellular 1-hydroxy-2-naphthoic acid restricts the mineralization of phenanthrene by Rhodococcus sp. WB9.

Rhodococcus sp. WB9, a strain isolated from polycyclic aromatic hydrocarbons contaminated soil, degraded phenanthrene (PHE, 100 mg L-1) completely within 4 days. 18 metabolites were identified during PHE degradation, including 5 different hydroxyphenanthrene compounds resulted from multiple routes of initial monooxygenase attack. Initial dioxygenation dominantly occurred on 3,4-C positions, followed by meta-cleavage to form 1-hydroxy-2-naphthoic acid (1H2N). More than 95.2% of 1H2N was transported to and kept in extracellular solution without further degradation. However, intracellular 1H2N was converted to 1,2-naphthalenediol that was branched to produce salicylate and phthalate. Furthermore, 131 genes in strain WB9 genome were related to aromatic hydrocarbons catabolism, including the gene coding for salicylate 1-monooxygenase that catalyzed the oxidation of 1H2N to 1,2-naphthalenediol, and complete gene sets for the transformation of salicylate and phthalate toward tricarboxylic acid (TCA) cycle. Metabolic and genomic analyses reveal that strain WB9 has the ability to metabolize intracellular 1H2N to TCA cycle intermediates, but the extracellular 1H2N can't enter the cells, restricting 1H2N bioavailability and PHE mineralization.

Bayesian Monitoring Design for Streambed Heat Tracing: Numerical Simulation and Sandbox Experiments.

Heat tracing methods have been widely employed for subsurface characterization. Nevertheless, there were very few studies regarding the optimal monitoring design for heat tracing in heterogeneous streambeds. In this study, we addressed this issue by proposing an efficient optimal design framework to collect the most informative diurnal temperature signal for Bayesian estimation of streambed hydraulic conductivities. The data worth (DW) was measured by the expected relative entropy between the prior and posterior distributions of the conductivity field. An adaptively refined Gaussian process surrogate was employed to alleviate the computational burden, resulting in at least three orders of magnitude of speed-up. The applicability of the optimal experimental design framework was evaluated by both numerical and sandbox experimental cases. Results showed that the most informative locations centered in the transition zones among the main patterns of the hydraulic conductivity field, while the most informative times centered in a short period after the minimum/maximum temperature appeared. With the fixed number of measurements, extending the calibration period was more beneficial than increasing the monitoring frequency in improving the estimation results. To our best knowledge, this work is the first study on Bayesian monitoring design for streambed characterization with the heat tracing method. The method and results can provide guidance on selecting monitoring strategies under budget-limited conditions.

Factors influencing the accuracy of the denitrifier method for determining the oxygen isotopic composition of nitrate.

The denitrifier method is widely used as a novel pretreatment method for the determination of nitrogen and oxygen isotope ratios as it can provide quantitative and high-sensitivity measurements. Nevertheless, the method is limited by relatively low measurement accuracy for δ18O. In this study, we analyzed the factors influencing the accuracy of δ18O determination, and then systematically investigated the effects of dissolved oxygen concentrations and nitrate sample sizes on estimates of the δ15N and δ18O of nitrate reference materials. The δ18O contraction ratio was used to represent the relationship between the measured difference and true difference between two reference materials. We obtained the following main results: (1) a gas-liquid ratio of 3:10 (v/v) in ordinary triangular flasks and a shaking speed of 120 r/min produced an optimal range (1.9 to 2.6 mg/L) in the concentration of dissolved oxygen for accurately determining δ18O, and (2) the δ18O contraction ratio decreased as nitrate sample size decreased within a certain range (1.0 to 0.1 µmol). Our results suggested that δ18O contraction is influenced mainly by dissolved oxygen concentrations in pure culture, and provided a model for improving the accuracy of oxygen isotope analysis.

Salicylate and phthalate pathways contributed differently on phenanthrene and pyrene degradations in Mycobacterium sp. WY10.

Mycobacterium sp. WY10 was a highly effective PAHs-degrading bacterium that can degrade phenanthrene (PHE, 100 mg L-1) completely within 60 h and 83% of pyrene (PYR, 50 mg L-1) in 72 h. In this study, ten and eleven metabolites, respectively, were identified in PHE and PYR degradation cultures, and a detailed PHE and PYR metabolism maps were constructed based on the metabolic results. The strain WY10 degraded PHE and PYR with initial dioxygenation mainly on 3,4- and 4,5-carbon positions, respectively. Thereafter, PYR degradation entered the PHE degradation pathway via the ortho-cleavage. It was observed that the "lower pathway" of PHE and PYR degradations were different. Based on the kinetics of residual metabolites, PHE was degraded in a dominant phthalate pathway and a minor salicylate pathway. However, both phthalate and salicylate pathways played important roles on PYR degradation. The WY10 genome revealed there were fifty-three genes related to PAHs degradations, including a complete gene set for PHE and PYR degradation via the phthalate pathway. The candidate gene/ORF, BOH72_19755, encoding salicylate synthase might contribute in the salicylate pathway.

A process-based model for pentachlorophenol dissipation in a flooded paddy soil.

Process-based models have been widely used for predicting environmental fate of contaminants. Nevertheless, accurate modeling of pentachlorophenol (PCP) dissipation in soils at the millimeter-scale remains a challenge due to the scarcity of observation data and uncertainty associated with model assumptions and estimation of the model parameters. To provide quantitative analysis of PCP-dissipation at the anaerobic/aerobic interface of a rhizobox experiment, this study implemented Bayesian parameter estimation for a process-based reactive chemical transport model. The model considered the main transport and transformation processes of chemicals including diffusion, sorption and degradation. The contributions of the processes to PCP dissipation were apportioned both in space and time. Using the maximum-a-posteriori (MAP) estimation of parameters, our model fitted the experimental data better compared with the previous work. Our results indicated that the most reactive zone for PCP dissipation occurred in the layer of 0-2.4 mm where degradation in solid phase dominated the PCP dissipation, while upward diffusion was the main mechanism for the reduction of PCP concentration in deeper layer (2.4-4.8 mm). By considering the coupled reactive transport of PCP and Cl-, the average degrees of PCP dechlorination in each layer were estimated from corresponding total concentrations of PCP and Cl-. The degrees of PCP dechlorination in the ponding water and the top layer of soil profile were highest, while 2,3,4,5- TeCP and 3,4,5- TCP were identified as the main dechlorination products in the soil. This study demonstrated that combining Bayesian estimation with process-based reactive chemical transport model can provide more insights of PCP dissipation at the millimeter-scale. This approach can help to understand complex dissipation mechanisms for other contaminants.

Apportionment and uncertainty analysis of nitrate sources based on the dual isotope approach and a Bayesian isotope mixing model at the watershed scale.

Identifying and eliminating pollutant sources of water bodies is critical for drinking water safety. In this research, river water, reservoir water and groundwater samples (n = 259) were collected from November 2015 to January 2017. Spatial Analysis was made of the isotopic compositions of potential nitrate sources (i.e., manure, sewage, chemical nitrogen fertilizer, soil organic nitrogen and rainfall) so as to obtain the site source isotopic signatures. Different sources pools and fractionation factors were loaded to a Bayesian isotope mixing model to ensure posterior estimates with less uncertainty. Results showed that the total nitrogen (TN) concentrations in Hexi Reservoir watershed were higher than the Environmental Quality Standards for Surface Water of China (GB 3838-2002), and NO3--N was the dominant form of TN (accounting for 68.63% on average). There are significant spatio-temporal variations in the isotope data (δ15N-NO3- and δ18O-NO3-) and the dominant nitrate sources, which were related to the land use types. Loading the site source isotopic signatures to the Bayesian isotope mixing model effectively improved the accuracy and precision of nitrate source apportionment. Chemical nitrogen fertilizer (NF) was the foremost largest contributor of NO3--N (38.82%), especially for Hexi North Stream (34.19%) and Yangmei Stream (44.39%), while atmospheric deposition (AD) contributed the least to NO3--N (0.47%) of river water in the watershed; soil organic nitrogen (NS) contributed more to NO3--N in the dry season than in the wet season; and manure and sewage (M&S) contributed approximately 30.22% in the whole study period, 53.60% in September 2016 and 41.33% in Hexi South Stream. This research suggests that combination of Spatial Analysis and the Bayesian isotope mixing model with the measured isotopic signatures of potential nitrate sources accurately apportion the nitrate source contributions.

The regulatory role of endogenous iron on greenhouse gas emissions under intensive nitrogen fertilization in subtropical soils of China.

Anaerobic batch experiments were conducted to study the regulatory role of endogenous iron in greenhouse gas emissions under intensive nitrogen fertilization in subtropical soils of China. Fe2+, Fe3+, and NO3--N dynamics and N2O, CH4, and CO2 emissions, as well as the relationships between N fertilizer, endogenous iron, and greenhouse gas emissions were investigated. The emissions of N2O increased to different extents from all the test soils by N1 (260 mg N kg-1) application compared with N0. After 24 days of anaerobic incubation, the cumulative emissions of N2O from red soils in De'an (DR) were significantly higher than that from paddy soils in De'an (DP) and Qujialing (QP) under N1. However, N application enhanced CH4 and CO2 emissions from the red soils slightly but inhibited the emissions from paddy soils. The maximal CH4 and CO2 emission fluxes occurred in DP soil without N input. Pearson's correlation analysis showed that there were significant correlations (P < 0.01) between Fe2+ and Fe3+, NO3--N, (N2O + N2)-N concentrations in DP soil, implying that Fe2+ oxidation was coupled with nitrate reduction accompanied by (N2O + N2)-N emissions and the endogenous iron played a regulatory role in greenhouse gas emissions mainly through the involvement in denitrification. The proportion of the electrons donated by Fe2+ used for N2O production in denitrification in DP soil was approximately 37.53%. Moreover, positive correlations between Fe2+ and CH4, CO2 were found in both DR and QP soils, suggesting that endogenous iron might regulate the anaerobic decomposition of organic carbon to CH4 and CO2 in the two soils. Soil pH was also an important factor controlling greenhouse gas emissions by affecting endogenous iron availability and C and N transformation processes.

Assessing soil bacterial community and dynamics by integrated high-throughput absolute abundance quantification.

Microbial ecological studies have been remarkably promoted by the high-throughput sequencing approach with explosive information of taxonomy and relative abundance. However, relative abundance does not reflect the quantity of the microbial community and the inter-sample differences among taxa. In this study, we refined and applied an integrated high-throughput absolute abundance quantification (iHAAQ) method to better characterize soil quantitative bacterial community through combining the relative abundance (by high-throughput sequencing) and total bacterial quantities (by quantitative PCR). The proposed iHAAQ method was validated by an internal reference strain EDL933 and a laboratory strain WG5. Application of the iHAAQ method to a soil phenanthrene biodegradation study showed that for some bacterial taxa, the changes of relative and absolute abundances were coincident, while for others the changes were opposite. With the addition of a microbial activity inhibitor (NaN3), the absolute abundances of soil bacterial taxa, including several dominant genera of Bacillus, Flavobacterium, and Paenibacillus, decreased significantly, but their relative abundances increased after 28 days of incubation. We conclude that the iHAAQ method can offer more comprehensive information to reflect the dynamics of soil bacterial community with both relative and absolute abundances than the relative abundance from high-throughput sequencing alone.

Use of an improved high-throughput absolute abundance quantification method to characterize soil bacterial community and dynamics.

High-throughput sequencing has dramatically expanded our understanding of bacterial communities based on the information of the species types and their relative abundances. Recently, researchers have also become aware of a deficiency in not considering the absolute abundance in this technique. Combining two or more different methods has typically been used to achieve absolute quantification of microbial communities. However, making a combination of different methods not only is time-consuming but also involves potential uncertainty due to variations in the experimental conditions. To simplify the experimental procedure and improve the high-throughput absolute abundance quantification (HAAQ) of a soil bacterial community, we propose an HAAQ method that uses an internal standard strain (ISS) HAAQ-GFP to simultaneously obtain both the relative and absolute abundances in the soil bacterial community. The results showed that a soil bacterial community and its dynamics can be better characterized by the HAAQ method when the optimal concentrations of ISS HAAQ-GFP (105 to 107cellsg-1) were used, and a 16S rRNA gene copy number adjustment was applied. Based on the HAAQ method, we first found that soil bacterial absolute abundances at the genus level fitted well to the partial log-normal distribution function, and most genera concentrations were in the range of 103.5 to 106.5cellsg-1 in the test soils. Our case studies also indicated that more comprehensive descriptions of soil bacterial communities and their dynamics can be achieved by both the relative and absolute abundances than by the relative abundance alone. The improved HAAQ method can be potentially applied to other microbial ecological studies and to stimulating the development of quantitative bacterial ecology studies.

The effective migration of Massilia sp. WF1 by Phanerochaete chrysosporium and its phenanthrene biodegradation in soil.

Pollutant-degrading bacteria migrated by fungi may enhance the contacts between microorganisms and pollutants and improve the bioremediation efficiency of persistent organic pollutants in soil. Here, the migration of phenanthrene (PHE)-degrading bacteria Massilia sp. WF1 and Mycobacterium sp. WY10 by the hydrophobic fungi Phanerochaete chrysosporium (P. chrysosporium) and its effects on the PHE biodegradation in soil were investigated. Migration of the hydrophilic bacterium WF1 was better than that of the hydrophobic bacterium WY10 by P. chrysosporium mycelia since strain WF1 possesses flagellum and the type III secretion system. The interaction energy change of P. chrysosporium-WF1 was lower, but the interaction forces (van der Waals attractions, capillary forces, and cross-linking effects) were stronger than those of P. chrysosporium-WY10. Thus, the adhesive attraction between strain WF1 and P. chrysosporium was stronger, and consequently, strain WF1 was migrated by P. chrysosporium to a greater extent than WY10. The corresponding migration mechanism was inferred to be a bacterial 'passive' method: bacteria adhered to mycelia before they migrated with the growing mycelia. Moreover, migrated strain WF1 via P. chrysosporium showed effective PHE biodegradation in soil. Fungus-mediated migration of pollutant-degrading bacteria may play an important role in the bioremediation of pollutants in soil.

Bayesian inference for kinetic models of biotransformation using a generalized rate equation.

Selecting proper rate equations for the kinetic models is essential to quantify biotransformation processes in the environment. Bayesian model selection method can be used to evaluate the candidate models. However, comparisons of all plausible models can result in high computational cost, while limiting the number of candidate models may lead to biased results. In this work, we developed an integrated Bayesian method to simultaneously perform model selection and parameter estimation by using a generalized rate equation. In the approach, the model hypotheses were represented by discrete parameters and the rate constants were represented by continuous parameters. Then Bayesian inference of the kinetic models was solved by implementing Markov Chain Monte Carlo simulation for parameter estimation with the mixed (i.e., discrete and continuous) priors. The validity of this approach was illustrated through a synthetic case and a nitrogen transformation experimental study. It showed that our method can successfully identify the plausible models and parameters, as well as uncertainties therein. Thus this method can provide a powerful tool to reveal more insightful information for the complex biotransformation processes.

Expressing lead isotopic compositions by fractional abundances for environmental source apportionment.

Lead (Pb) isotope has been extensively used to identify sources of Pb and apportion their contributions in the environment. Conventionally, isotope ratios are used to express Pb isotopic composition. However, the linear combination of Pb isotope ratios is not consistent with mass balance. Moreover, the graphical presentations based on Pb isotope ratios are always inconsistent when different Pb isotope ratios are used. In this study, we proposed to use fractional abundance to express Pb isotopic composition to achieve more accurate and reliable source apportionment. A new method (rotation-projection method) based on fractional abundance was developed in this research. The new method compared favorably to the isotopic ratio-based method and to another fractional abundance based method using default 204Pb value (0) (Walraven's method). It allows to present four-dimensional (4-D) Pb isotope fractional abundance data in a 3-D plot. In the meantime, due to the low variation of the fractional abundance of 204Pb in the terrestrial ecosystem, the terrestrial Pb isotope fractional abundance data fell nearly on a plane, which further allows to plot the Pb isotope fractional abundance data on a two-dimensional diagram. Proper presentation of the isotopic composition data helps to achieve more accurate and reliable source identification and apportionment.

A mathematical model for the transfer of soil solutes to runoff under water scouring.

The transfer of nutrients from soil to runoff often causes unexpected pollution in water bodies. In this study, a mathematical model that relates to the detachment of soil particles by water flow and the degree of mixing between overland flow and soil nutrients was proposed. The model assumes that the mixing depth is an integral of average water flow depth, and it was evaluated by experiments with three water inflow rates to bare soil surfaces and to surfaces with eight treatments of different stone coverages. The model predicted outflow rates were compared with the experimentally observed data to test the accuracy of the infiltration parameters obtained by curve fitting the models to the data. Further analysis showed that the comprehensive mixing coefficient (ke) was linearly correlated with Reynolds' number Re (R(2)>0.9), and this relationship was verified by comparing the simulated potassium concentration and cumulative mass with observed data, respectively. The best performance with the bias error analysis (Nash Sutcliffe coefficient of efficiency (NS), relative error (RE) and the coefficient of determination (R(2))) showed that the predicted data by the proposed model was in good agreement with the measured data. Thus the model can be used to guide soil-water and fertilization management to minimize nutrient runoff from cropland.