Interaction between the microbial community and invading Escherichia coli O157:H7 in soils from vegetable fields.

The survival of Escherichia coli O157:H7 in soils can contaminate vegetables, fruits, drinking water, etc. However, data on the impact of E. coli O157:H7 on soil microbial communities are limited. In this study, we monitored the changes in the indigenous microbial community by using the phospholipid fatty acid (PLFA) method to investigate the interaction of the soil microbial community with E. coli O157:H7 in soils. Simple correlation analysis showed that the survival of E. coli O157:H7 in the test soils was negatively correlated with the ratio of Gram-negative (G(-)) to Gram-positive (G(+)) bacterial PLFAs (G(-)/G(+) ratio). In particular, levels of 14 PLFAs were negatively correlated with the survival time of E. coli O157:H7. The contents of actinomycetous and fungal PLFAs in the test soils declined significantly (P, <0.05) after 25 days of incubation with E. coli O157:H7. The G(-)/G(+) ratio declined slightly, while the ratio of bacterial to fungal PLFAs (B/F ratio) and the ratio of normal saturated PLFAs to monounsaturated PLFAs (S/M ratio) increased, after E. coli O157:H7 inoculation. Principal component analysis results further indicated that invasion by E. coli O157:H7 had some effects on the soil microbial community. Our data revealed that the toxicity of E. coli O157:H7 presents not only in its pathogenicity but also in its effect on soil microecology. Hence, close attention should be paid to the survival of E. coli O157:H7 and its potential for contaminating soils.

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.

Survival of Escherichia coli O157:H7 in soils from vegetable fields with different cultivation patterns.

Escherichia coli O157:H7 survived longer in soils from plastic-greenhouse cultivation than soils from the open field. Soil pH, organic carbon levels, and the ratio of bacterial phospholipid fatty acids (PLFAs) to fungal PLFAs played the significant roles in survival of O157:H7. Greater attention should be paid to the control of pathogen contamination under conditions of plastic-greenhouse cultivation.

Mitigating iodomethane emissions and iodide residues in fumigated soils.

Although long-regarded as an excellent soil fumigant for killing plant pests, methyl bromide (MeBr) was phased out in 2005 in the USA, because it can deplete the stratospheric ozone layer. Iodomethane (MeI) has been identified as an effective alternative to MeBr and is used in a number of countries for preplant pest control. However, MeI is highly volatile and potentially carcinogenic to humans if inhaled. In addition, iodide anions, a breakdown product of MeI, can build up in fumigated soils and potentially cause plant toxicity and contaminate groundwater via leaching. In order to overcome the above two obstacles in MeI application, a method is proposed to place reactive bags containing ammonium hydroxide solution (NH4OH) on the soil surface underneath an impermeable plastic film covering the fumigated area. Our research showed that using this approach, over 99% of the applied MeI was quantitatively transferred to iodide. Of all the resulting iodide, only 2.7% remained in the fumigated soil, and 97.3% was contained in the reactive bag that can be easily removed after fumigation.

Application of graphene for the analysis of pharmaceuticals and personal care products in wastewater.

A novel and reliable analytical method based on a graphene adsorbent for solid-phase extraction (SPE) derivatized with N-tert-butyldimethylsilyl-N- methyltrifluoroacetamide and analyzed by gas chromatography-mass spectrometry was developed for determination of nine pharmaceuticals and personal care products (PPCPs) in wastewater samples. Different ratios of graphene/silica gel were tested, with 20 % graphene/silica gel giving the best performance as an SPE adsorbent. The mean recoveries of the target analytes obtained by 20 % graphene/silica gel SPE ranged from 58.1 to 87.6 %. The limit of quantification ranged from 30 to 259 ng/L and from 13 to 115 ng/L for the influent and effluent, respectively. By comparing the accuracy and precision of 20 % graphene/silica gel and Oasis HLB SPE cartridges, we demonstrated that the method can be satisfactorily used for the analysis of PPCPs in wastewater samples. We applied the method to wastewater samples from a sewage treatment plant near Riverside, California, to track the concentration change of PPCPs in the treatment processes.

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.

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.

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.

Root-induced changes to cadmium speciation in the rhizosphere of two rice (Oryza sativa L.) genotypes.

Our aim was to investigate rhizosphere effects on the chemical behavior of Cd. This was done in a glasshouse experiment, where two rice cultivars (Zhenong54 and Sixizhan) were grown in soil spiked with cadmium (Cd) at two levels, 3.9 ± 0.5 and 8.3 ± 0.5 mg kg(-1) soil, placed in a rhizobox until ripening stage. Chemical forms of cadmium near the root surface were then assessed using a sequential extraction procedure (SEP). There were significant differences in Cd species, especially exchangeable Cd (EXC-Cd) between the two rice cultivars as affected by rice roots. The lowest EXC-Cd with Zhenong54 appeared in the near-rhizosphere area with little difference between tillering stage and ripening stage while Sixizhan had its lowest EXC-Cd concentration in the root compartment. Both cultivars had slight changes in the Fe/Mn oxide-bound fraction of Cd (FMO-Cd) at the grain ripening stage while the control treatments without plants had a significant increase in FMO-Cd at the same time, indicating a transformation from a less bioavailable form (FMO-Cd) to more bioavailable forms (EXC-Cd). Soil microbial biomass in the vicinity of the root surface had opposite trends to some extent with EXC-Cd, partly because of the root-induced changes to bioavailable Cd. Unlike Zhenong54, Sixizhan had a higher Cd concentration in the root, but only a small proportion of Cd translocated from the root to grain.

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.

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.

Leaching potential of nonsteroidal anti-inflammatory drugs in soils.

Nonsteroidal anti-inflammatory drugs (NSAIDs) in soils resulting from application of municipal wastewater or biosolids may migrate through soils intact or be transformed and reach groundwater. In the present study, the leaching potential of four NSAIDs (ibuprofen, naproxen, ketoprofen, and diclofenac sodium) in three U.S. cropland soils was evaluated, and the effect of CaCl(2) solution (as an index of salinity), dissolved organic matter (DOM), and polyacrylamide (PAM) amendment was investigated. The soils were spiked with selected NSAIDs, incubated for 24 h followed by 7-d storage in glass flasks, and then packed into stainless steel columns and leached with deionized water (DIW), 10 mM CaCl(2), DOM (DOC 34 mg/L), and PAM solution (1.0 mg/L) by gravity. Initial concentrations of ibuprofen, naproxen, ketoprofen, and diclofenac sodium in the three packed soils were 1.93 to 2.07, 1.74 to 2.27, 1.79 to 2.16, and 1.99 to 2.13 mg/kg, respectively. Maximum concentrations of the above NSAIDs in column effluents were 1.23, 0.92, 0.69, and 1.12 mg/L, respectively, when the soil was leached with 10 pore volumes of water, which occupied 17.4, 11.1, 9.6, and 15.2% of the total chemicals in each soil column. Dissolved organic matter or PAM solution did not facilitate the NSAIDs release from soils. The CaCl(2) solution, however, reduced the amounts of NSAIDs leached from all three soils. Leaching of NSAIDs differed among the three tested soils. The results suggest that the leaching of NSAIDs through soil to water is significant, and the mobility of NSAIDs in soil is related to their chemicals' characteristics (such as pK(a) values) and soil properties (such as soil organic matter and clay content). Amending soil with DOM or PAM does not significantly affect the leaching behavior of NSAIDs in soil, whereas increasing the salinity of the irrigation water may decrease the extent of contamination of groundwater posed by NSAIDs.

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.

Leachability of some emerging contaminants in reclaimed municipal wastewater-irrigated turf grass fields.

Emerging pollutants inherent in reclaimed municipal wastewater, including endocrine-disrupting compounds (EDCs) and pharmaceutical and personal care products (PPCPs), often have cast uncertainties on the safety of water reuse. We examined the fate and transport behavior of several PPCP and EDC compounds through observations made at experimental turf fields irrigated with naproxen, clofibric acid, diclofenac sodium, ibuprofen, estrone, 4-tert-octylphenol, bisphenol A, 4-n-nonylphenol, and triclosan latent irrigation water. The potential of the compounds to contaminate underlying groundwater was assessed using three screening protocols that employed the attributes of soils, chemicals, and water fluxes as the estimators. No compound was detected in the leachate draining through the 89-cm profile of a loamy sand soil and a sandy loam soil turf grass field during four months of irrigation according to operations typical of golf courses in southern California (USA). Ibuprofen, naproxen, triclosan, bisphenol A, clofibric acid, and estrone were detected in the surface to 30-cm soil profiles. Higher irrigation rate and coarser textural soil enhanced the downward movement of chemicals in both soils. The pollution risk screenings identified the same six compounds as having the potential to contaminate groundwater, and under conditions of turf grass irrigation, clofibric acid and ibuprofen would be most prone to cause the pollution.

Adsorption and degradation of ketoprofen in soils.

Ketoprofen, a nonsteroidal anti-inflammatory drug (NSAID), was commonly found in treated wastewater due to its incomplete removal during sewage treatment plant processes. As treated wastewater is increasingly used for landscape irrigation, it is imperative to understand the leaching potential for ketoprofen in receiving soils. In this study, adsorption and degradation experiments were conducted in four U.S. soils with different physicochemical characteristics. Ketoprofen was not strongly adsorbed to the four soils with K(d) values ranging from 1.26 to 8.24 L kg(-1), suggesting its potential to move downward with percolating water. The adsorption was positively related to the soil organic matter (OM) content (R(2) = 0.890). Degradation experiment showed that half-lives (t(1/2)) of ketoprofen were 4.58 d in Arlington sandy loam (ASL, coarse-loamy, mixed, active, thermic Haplic Durixeralfs), 8.04 d in Hanford loamy sand (HLS, coarse-loamy, mixed, superactive, nonacid, thermic Typic Xerorthents), 15.37 d in Imperial silty clay (ISC, fine, semectitc, calcareous, hyperthermic Vertic Torrifluvents), and 27.61 d in Palouse silt loam (PSL) soil (fine-silty, mixed, superactive, mesic Pachic Ultic Haploxerolls), respectively. Degradation of ketoprofen in soils appeared to be influenced by the soil OM content. The prolonged t(1/2) by sterilization indicated that microbial degradation was the dominant pathway for ketoprofen degradation in soils, while photodegradation only contributed a small portion to the ketoprofen degradation. The t(1/2) and K(oc) values were fitted to screening models to predict the leaching potential of ketoprofen in soils. It appeared that relatively high leaching potential of ketoprofen existed in ISC and PSL soils.

Impacts of soil organic matter, pH and exogenous copper on sorption behavior of norfloxacin in three soils.

Norfloxacin sorption and the factors (soil organic matter (SOM), pH, and exogenous copper (Cu) influencing the sorption were investigated in a black soil (soil B), a fluvo-aquic soil (soil F), and a red soil (soil R). With increasing norfloxacin concentrations, sorption amount of norfloxacin increased in both the bulk soils and their SOM-removed soils, but the sorption capacity of SOM-removed soils was higher than that of their corresponding bulk soils, indicating that the process of norfloxacin sorption in soil was influenced by the soil properties including SOM. The sorption data in all bulk soils and SOM-removed soils were fitted to Freundlich and Langmuir models. The correlation coefficients suggested that the experimental data fitted better to Freundlich equation than to Langmuir equation. Furthermore, the data from soil F and SOM-removed F could not be described by Langmuir equation. The norfloxacin sorption amount decreased in soil B and soil F, whereas it increased in soil R as solution pH increased. The maximum K(D) and K(OC) were achieved in soil R when the equilibrium solution pH was 6. The norfloxacin sorption was also influenced by the exogenous Cu2+, which depended on the soil types and Cu2+ concentrations. With increasing Cu2+ concentrations in solution, generally, sorption amount, K(D) and K(OC) for norfloxacin in soils increased and were up to a peak at 100 mg/L Cu2+, and then the sorption amount decreased regardless of norfloxacin levels.

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.