Local Environmental Variables Research Articles

Are drivers of microbial diatom distributions context dependent in human-impacted and pristine environments?

Species occurrences are influenced by numerous factors whose effects may be context dependent. Thus, the magnitude of the effects and their relative importance to species distributions may vary among ecosystems due to anthropogenic stressors. To investigate context dependency in factors governing microbial bioindicators, we developed species distribution models (SDMs) for epilithic stream diatom species in human-impacted and pristine sites separately. We performed SDMs using boosted regression trees for 110 stream diatom species, which were common to both data sets, in 164 human-impacted and 164 pristine sites in Finland (covering ~1,000km, 60° to 68°N). For each species and site group, two sets of models were conducted: climate model, comprising three climatic variables, and full model, comprising the climatic and six local environmental variables. No significant difference in model performance was found between the site groups. However, climatic variables had greater importance compared with local environmental variables in pristine sites, whereas local environmental variables had greater importance in human-impacted sites as hypothesized. Water balance and conductivity were the key variables in human-impacted sites. The relative importance of climatic and local environmental variables varied among individual species, but also between the site groups. We found a clear context dependency among the variables influencing stream diatom distributions as the most important factors varied both among species and between the site groups. In human-impacted streams, species distributions were mainly governed by water chemistry, whereas in pristine streams by climate. We suggest that climatic models may be suitable in pristine ecosystems, whereas the full models comprising both climatic and local environmental variables should be used in human-impacted ecosystems.

Photoluminescence and Structural Characterization of RE‐Doped Sodium Aluminosilicate Oxyfluoride Glass and Nanocrystalline Glass‐Ceramics as a Function of γ‐Irradiation Dose

Dy3+ and Eu3+‐doped oxyfluoride glass and glass nanocomposites are subjected to low and high dose of γ‐irradiation, i.e., 100 Gy and 1 kGy, respectively. The photoluminescence spectra show changes in electric to magnetic dipole ratios signifying variations in local structural environment. Glass‐ceramics depict the tendency of crystallization or the ordering of structure with increasing γ‐irradiation dose. The results are further supported with X‐ray diffraction and scanning electron microscopy (SEM) measurements. The formation of nanometer size fluoride particles in the pristine glass and glass‐ceramics after γ‐irradiation has been observed from SEM studies. Fourier transform infrared (FTIR) study reveals the restructuring of aluminosilicate network under γ‐irradiation.

Iodine solubility and speciation in glasses

The study of iodine in glasses and melts is critical in many areas, from geosciences to materials science to waste management. Glasses in the ternary system Na2O-B2O3-SiO2 were studied with the goal of identifying a glass matrix able to dissolve large quantities of this element, and to identify the main parameters affecting the solubility of iodine. Two sets of experiments were carried out: the first one with the aim of determining the solubility limit of iodine, and the second one to identify the structural variations occurring within the glass network upon iodine incorporation, and to identify the parameters influencing the most both iodine solubility and speciation. We demonstrated that there is a strong dependence of iodine incorporation on bulk chemistry and glass physical properties. A solubility limit of ~5 mol% I has been assessed for B2O3-rich glasses and of ~1 mol% for SiO2-rich ones, and this composition dependence has been explained by considering the fragility parameter of the glass network. Structural variations in the iodine local environment and in the glass network were characterized by Raman, X-ray Absorption Spectroscopy, and 11B NMR. Spectroscopy data point out the coexistence of different I species within the glasses, with iodide being the predominant one, surrounded by Na+ ions.

Estimating the minimal efficient scale and the effect of intermunicipal cooperation on service provision areas for waste treatment in Japan

We explore the difference in cost structure when municipalities participate in intermunicipal cooperation (IMC) and estimate the minimal efficient scale, which minimizes the per capita service provision cost. The unit of analysis is designated as waste treatment provision area. We specify a cost function based on the Cobb–Douglas form that considers local environment variables, and illustrate the disparity between the current population and minimal efficient scale of the public service provision area. There are several key findings. First, being in an IMC affects the cost function by generating transaction costs, such as monitoring the quality of service provision, but the costs are discounted by population size. Second, the cost function is not linear to population, a downward convex function. Third, approximately 90% of the service provision areas in Japan have the opportunity to take advantage of economies of scale. However, geographical constraints render waste treatment with the framework of IMC more difficult, since such areas are separated by natural elements such as mountains. Nevertheless, the model in this study implies the possibility that municipalities can efficiently reduce public spending by participating in IMC authorities.

Comparison of automated extraction and amplification platforms on quantification of plasma HDV RNA: A multicenter study

Understanding how local environmental factors affect communities and compositional patterns are crucial to biodiversity conservation, especially in environments that were severally affected by anthropic actions. We analyzed the effects of fine-scale local environmental conditions on alpha and beta diversity of fern communities in three Atlantic forest areas and investigated the mechanisms underlying fern community responses. We sampled ferns and collected local environmental variables in 22 plots in three Atlantic forest areas and used multi-model inferences to identify the relationship between community diversity and composition and local environmental factors. We also applied multivariate analyses to verify whether community composition is constrained by local environmental factors. Finally, we analyzed beta-diversity (dissimilarity in species composition) patterns between and within forest areas and identified the contribution of turnover and nestedness to observed beta-diversity patterns. At the local scale, fern diversity was positively and strongly affected by fine-scale variations in nutrient availability and negatively influenced by soil acidity. Meanwhile, changes in community composition were also related to fine-scale variations in nutrient availability and soil rock coverage. Beta-diversity within forest areas (local scale) was as high as between forest areas (regional scale), a pattern that was virtually driven by species turnover at both scales of analysis. Our results highlight a prominent role of environmental filtering in regulating fine-scale local fern community diversity and composition, to such an extent that fine-scale local variation in species composition is as high as between spatially and climatically distant forest areas.

Freshwater Bacterioplankton Metacommunity Structure Along Urbanization Gradients in Belgium.

Urbanization is transforming and fragmenting natural environments worldwide, driving changes in biological communities through alterations in local environmental conditions as well as by changing the capacity of species to reach specific habitats. While the majority of earlier studies have been performed on higher plants and animals, it is crucial to increase our insight on microbial responses to urbanization across different spatial scales. Here, using a metacommunity approach, we evaluated the effects of urbanization on bacterioplankton communities in 50 shallow ponds in Belgium (Flanders region), one of the most urbanized areas in Northwest Europe. We estimated the relative importance of local environmental factors (35 abiotic and biotic variables), regional spatial factors and urbanization (built-up area) quantified at two spatial scales (200 m × 200 m and 3 km × 3 km). We show that urbanization at local or regional scales did not lead to strong changes in community composition and taxon diversity of bacterioplankton. Urbanization at regional scale (3 km × 3 km) explained only 2% of community composition variation while at local scale (200 m × 200 m), no effect was detected. Local environmental factors explained 13% (OTUs with relative abundance ≥ 0.1%) to 24% (12 dominant OTUs -≥ 1%) of community variation. Six local environmental variables significantly explained variation in bacterioplankton community composition: pH, alkalinity, conductivity, total phosphorus, abundance of Daphnia and concentration of copper (Cu), of which pH was partly mediated by urbanization. Our results indicate that environmental rather than spatial factors accounted for the variation in bacterioplankton community structure, suggesting that species sorting is the main process explaining bacterioplankton community assembly. Apparently, urbanization does not have a direct and strong effect on bacterioplankton metacommunity structure, probably due to the capacity of these organisms to adapt toward and colonize habitats with different environmental conditions and due to their fast adaptation and metabolic versatility. Thus, bacterioplankton communities inhabiting shallow ponds may be less affected by environmental conditions resulting from urbanization as compared to the impacts previously described for other taxa.

Beta Diversity Partitioning and Drivers of Variations in Fish Assemblages in a Headwater Stream: Lijiang River, China

Beta diversity partitioning has currently received much attention in research of fish assemblages. However, the main drivers, especially the contribution of spatial and hydrological variables for species composition and beta diversity of fish assemblages are less well studied. To link species composition to multiple abiotic variables (i.e., local environmental variables, hydrological variables, and spatial variables), the relative roles of abiotic variables in shaping fish species composition and beta diversity (i.e., overall turnover, replacement, and nestedness) were investigated in the upstream Lijiang River. Species composition showed significant correlations with environmental, hydrological, and spatial variables, and variation partitioning revealed that the local environmental and spatial variables outperformed hydrological variables, and especially abiotic variables explained a substantial part of the variation in the fish composition (43.2%). The overall species turnover was driven mostly by replacement (87.9% and 93.7% for Sørensen and Jaccard indices, respectively) rather than nestedness. Mantel tests indicated that the overall species turnover (ßSOR and ßJAC) and replacement (ßSIM and ßJTU) were significantly related to hydrological, environmental, and spatial heterogeneity, whereas nestedness (ßSNE or ßJNE) was insignificantly correlated with abiotic variables (P > 0.05). Moreover, the pure effect of spatial variables on overall species turnover (ßSOR and ßJAC) and replacement (ßSIM and ßJTU), and the pure effect of hydrological variables on replacement (ßSIM and ßJTU), were not important (P > 0.05). Our findings demonstrated the relative importance of interactions among environmental, hydrological, and spatial variables in structuring fish assemblages in headwater streams; these fish assemblages tend to be compositionally distinct, rather than nested derivatives of one another. Our results, therefore, indicate that maintaining natural flow dynamics and habitat continuity are of vital importance for conservation of fish assemblages and diversity in headwater streams.

Associations between environmental variability and inversion polymorphism of Drosophila subobscura: meta-analysis of populations from the Central Balkans

CR Climate Research Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials CR 77:205-217 (2019) - DOI: https://doi.org/10.3354/cr01551 Associations between environmental variability and inversion polymorphism of Drosophila subobscura: meta-analysis of populations from the Central Balkans M. Stamenkovic-Radak1,*, B. Kenig2, M. Djurakic3, M. Jelic1, K. Eric1, M. Andjelkovic4 1Faculty of Biology, University of Belgrade, 11000 Belgrade, Republic of Serbia 2Institute of Biological Research ‘S. Stankovic’, University of Belgrade, 11000 Belgrade, Republic of Serbia 3Department of Biology and Ecology, Faculty of Sciences, University of Novi Sad, 21000 Novi Sad, Republic of Serbia 4Serbian Academy of Sciences and Arts, 11000 Belgrade, Republic of Serbia *Corresponding author: marina@bio.bg.ac.rs ABSTRACT: Ecological and evolutionary factors, together with abiotic conditions, affect biogeographic patterns of genetic entities. The spatial and temporal variability of chromosomal inversions of Drosophila subobscura suggests that this species can serve as a good model for studying the effects of environmental change on the genetic structure of natural populations. A comprehensive meta-analysis of the association of environmental and climatic variables with inversion diversity patterns was performed on 20 D. subobscura populations from the central part of the Balkan Peninsula. Environmental data consisted of 3 sets of variables related to temperature and precipitation, extracted from 2 climatic databases, averaged over a 3 month period, and using biological instead of calendar dates of sampling. Arrangement frequency patterns are likely driven by a synergistic effect of factors related to temperature and precipitation. The frequencies of standard chromosomal arrangements tend to co-vary positively with precipitation, whereas parameters related to temperature appear to favor higher frequencies of the inverted and more complex chromosomal arrangements. A complex relationship among local environmental variables is evident from the results and reflects the probable effect of an altitudinal shift; the altitudinal gradient of inversions is different from their latitudinal gradient. The pattern of inversions is generally not associated with environmental variables, and a particular inversion cannot be a predictive genetic marker of global climate change. Populations in different habitats are subjected to habitat-specific selection regimes, while demographic factors and population history also affect the genetic variability pattern observed. KEY WORDS: Adaptation · Climate · Chromosomal polymorphism · Thermal response Full text in pdf format Supplement 1Supplement 2 PreviousNextCite this article as: Stamenkovic-Radak M, Kenig B, Djurakic M, Jelic M, Eric K, Andjelkovic M (2019) Associations between environmental variability and inversion polymorphism of Drosophila subobscura: meta-analysis of populations from the Central Balkans. Clim Res 77:205-217. https://doi.org/10.3354/cr01551 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in CR Vol. 77, No. 3. Online publication date: March 28, 2019 Print ISSN: 0936-577X; Online ISSN: 1616-1572 Copyright © 2019 Inter-Research.

Multi-scalar drivers of biodiversity: local management mediates wild bee community response to regional urbanization.

It is critical to understand the specific drivers of biodiversity across multiple spatial scales, especially within rapidly urbanizing areas, given the distinct management recommendations that may result at each scale. However, drivers of biodiversity patterns and interactions between drivers are often only measured and modeled at a single scale. In this study, we assessed bee community composition at three time periods in 20 grassland and 20 agriculture sites located across two major metroplexes. We examined how local environmental variables and surrounding landscape composition impact bee abundance, richness, and evenness, including comparisons between groups with different nesting strategies and body sizes. We collected nearly 13,000 specimens and identified 172 species. We found that levels of regional land use differentially impacted bee abundance and diversity depending on local habitat management. Specifically, within agriculture sites, bee richness was greater with increasing landscape-level seminatural habitat, while in grassland sites, bee richness was similar across landscapes regardless of seminatural habitat cover. Bee evenness at both site types declined with increasing landscape-level habitat heterogeneity, due to an increase of rare species at the grassland sites, but not in the agricultural sites, further indicating that diversity is driven by the interaction of local habitat quality and landscape-level habitat composition. We additionally found that agriculture sites supported higher abundances, but not richness, of small-bodied and below-ground nesting bees, while grassland sites supported higher abundances of aboveground nesting bees, and higher richness of large-bodied species. Increased levels of local bare ground were significantly related to multiple metrics of bee diversity, including greater belowground nesting bee abundance and richness. Local floral richness was also significantly related to increases of overall bee abundance, as well as the abundance and richness of small bees. Overall, we suggest that local land managers can support bee abundance and diversity by conserving areas of bare soil and promoting native floral diversity, the latter especially critical in highly urban agricultural spaces. Our results provide the first documentation of significant interactions between local habitat management and landscape composition impacting insect communities in urban systems, indicating that bee conservation practices depend critically on land use interactions across multiple spatial scales.

Recurring cryptic ecosystems in Lower to Middle Devonian carbonate mounds of Hamar Laghdad (Anti-Atlas, Morocco)

Exceptionally well-preserved fossil cryptic communities have been discovered in submarine cavities of the Lower and Middle Devonian (Emsian to Givetian) mud mounds in the Hamar Laghdad area (Anti-Atlas, Morocco). The cryptic biota encrusted the roofs of the cavities and grew predominantly oriented upside down. These unique coelobiotic communities were dominated by various solitary rugose corals, which very often displayed a “calice-in-calice” growth pattern. Apart from the rugosans, the cavities were inhabited by other sessile invertebrates: tabulate corals, cladochonids, crinoids and lithistid sponges. Many of the skeletons were encrusted by microbial structures. The high density of organisms overgrowing each other points to intensive competition for space in all studied Devonian submarine crypts. The late Emsian to latest Givetian cavities were colonised by various sets of coelobiotic inhabitants mostly originating from the surrounding deep-water marine environments. It is suggested that the local species pool was a decisive factor in determining the ecological succession and taxonomic structure of cryptic communities. The changes in taxonomic composition and diversity, over time and space, were primarily related to variations in local physical environment. Consequently, the communities in crypts affected by venting of high-temperature fluids or hydrocarbon seepage were of low diversity and included endemic elements and characteristically small specimens.

Well-managed grassland heterogeneity promotes butterfly conservation in a corridor network

Habitat degradation is a major concern in transformed landscapes, as it reduces complexity by removing species, interactions, and ultimately biodiversity. Degradation is also of concern for ecological networks (ENs) composed of an interconnected system of conservation corridors among South Africa's commercial forestry compartments. These corridors are predominantly grasslands, and used as rangeland, so managed to optimize grazing conditions. Yet, how this management approach influences biodiversity remains unknown. Here, we studied how butterfly assemblages respond to local differences in rangeland quality (low, high and reference sites), and how this effect compared to that of local environmental variables (e.g. rockiness and bare ground), meso environmental gradients (e.g. topographic position and aspect), and landscape composition (i.e. proportion of different land cover types in the surrounding matrix). We calculated species richness and composition, Shannon's diversity index (H′), and the Butterfly Conservation Index (BCIn) representing the proportion of sensitive and range-restricted butterfly species per site. Rangeland quality was considered less important for butterflies than other environmental variables, but it was also significantly confounded with other environmental variables. At the landscape scale, proportion of grassland in the landscape matrix influenced butterfly assemblage composition, while proportion of thicket had a significant positive effect on BCIn. Moreover, the effect of elevation on assemblage composition emphasizes the value of maintaining environmental gradients within these conservation corridors. At the meso spatial scale, butterfly species richness and diversity (H′) declined with increased dominance by a single plant species, which usually occurs late in a normal fire cycle. This suggests a reliance by butterflies on recurring natural disturbances for long-term persistence. We recommend moderate patch burning and grazing, as well as occasional hot burns to reduce thicket in Afromontane grassland. This approach would improve local scale vegetation patterns, and increase heterogeneity across the landscape for conserving these butterflies into the future.

Hierarchical species distribution models in support of vegetation conservation at the landscape scale

AbstractQuestionsSpecies distribution models (SDMs) based on habitat suitability and niche quantification are powerful tools in vegetation science. Recent findings suggest that they could be applied at the landscape scale as vegetation conservation tools, but that some environmental dimensions (e.g., climate) need to be considered at larger scales. What is the importance of applying hierarchical SDMs combining information from different scales to ensure consistent local vegetation management decisions?Study SiteMainland Spain and Biosphere Reserve of Sierra del Rincón (central Spain).MethodsWe generated SDMs for five tree species at the regional scale (mainland Spain) using climatic variables plus presence/absence data from the Spanish National Forest Inventory; and at the landscape scale (Sierra del Rincón Biosphere Reserve) using local environmental variables plus locally gathered vegetation presence/absence data. Predictions of both regional and landscape models were combined at the landscape scale following two different hierarchical approaches. The four resulting predictions were compared with correlation coefficients and independently evaluated with the AUC statistic and data collected in the study area.ResultsThe regional SDMs depict suitable climatic conditions for the tree species, while the landscape SDMs capture important local ecological drivers that influence habitat suitability at finer scales. Expectedly, the regional SDMs predict larger suitable areas than the landscape SDMs. The predictions from the hierarchical approaches are reliable and provide on average better results than non‐hierarchical ones.ConclusionsSDMs can be valuable tools for local plant conservation programs. We present examples of the applicability of a hierarchical modeling approach and conceptual and methodological solutions related to the use of these tools in local vegetation conservation programs. For example, we show that landscape SDMs could be used to determine the current distribution of endangered plant species, while a hierarchical approach would be better suited to define areas to re‐vegetate within a local restoration program.

Predicting Presence of Amphibian Species Using Features Obtained from GIS and Satellite Images

The construction of transport infrastructure is often preceded by an environmental impact assessment procedure, which should identify amphibian breeding sites and migration routes. However, the assessment is very difficult to conduct because of the large number of habitats spread out over a vast expanse, and the limited amount of time available for fieldwork. We propose utilizing local environmental variables that can be gathered remotely using only GIS systems and satellite images together with machine learning methods. In this article, we introduce six new and easily extractable types of environmental features. Most of the features we propose can be easily obtained from satellite imagery and spatial development plans. The proposed feature space was evaluated using four machine learning algorithms, namely: a C4.5 decision tree, AdaBoost, random forest and gradient-boosted trees. The obtained results indicated that the proposed feature space facilitated prediction and was comparable to other solutions. Moreover, three of the new proposed features are ranked most important; these are the three dominant properties of the surroundings of water reservoirs. One of the new features is the percentage access from the edges of the reservoir to open areas, but it affects only a few species. Furthermore, our research confirmed that the gradient-boosted trees were the best method for the analyzed dataset.

Silurian records of carbon and sulfur cycling from Estonia: The importance of depositional environment on isotopic trends

The Llandovery–Wenlock carbonate-marl succession of the Baltoscandian Basin has been analyzed in the Viki drill core, western Estonia, for carbonate carbon (δ13Ccarb), organic carbon (δ13Corg), carbonate-associated sulfate (δ34SCAS) and pyrite (δ34Spyr) isotopes, along with trace element concentrations. Following the End-Ordovician glaciation and the Hirnantian carbon isotope excursion, δ13Ccarb values rise to an early Llandovery carbon isotope maximum (+2‰). Subsequently, δ13Ccarb and coeval δ13Corg record a large ∼+4.5‰ excursion in the early Wenlock, associated with a regression and biotic turnover known as the Ireviken bioevent (IBE). Overall, δ34SCAS values generally fall within a range (25‰ to 35‰) similar to that reported in other sections of comparable age. Two distinct trends are observed: low and stable δ34SCAS values are associated with deep-water facies, while δ34SCAS becomes higher and more variable in the shallow-water facies. Similarly, δ34Spyr values are low and invariant (∼−15‰) in deep-water facies but become higher and more variable (ranging between −35‰ and 16‰) in shallow-water deposits. Despite abundant recrystallization, no obvious evidence for large-scale alteration of proxies is apparent in concentrations of Fe, Sr, Mn and Mg, or in isotopic correlations, although increased variability and lower values of δ34SCAS are observed where CAS abundance is low. A large, well-resolved positive excursion in δ34SCAS observed during the IBE from a time-correlative section on Gotland (Sweden) is absent in the data presented here. This difference demonstrates that, counter to general understanding, local environmental variations can give rise to divergent δ34SCAS profiles in coeval sections. The S-isotope fluctuations in CAS and pyrite in the Viki drill core can be explained by local processes involving facies changes, early diagenetic processes and associated open vs. closed system behavior that can overprint and potentially mask basin or global signals.

Trait–environment relationships in Amazon stream fish assemblages

AbstractStudies of trait–environment relationships provide important tools for the prediction of the response of biological communities to environmental alterations. The Amazon basin presents enormous potential for the development of research on this type of relationship, given the diversity of both its fish fauna and the aquatic ecosystems this fauna inhabits. The present study investigated the association between local environmental variables and the functional traits of fish in 54 streams of six major Amazonian basins. We identified the relationship between the characteristics of the streams (channel morphology, channel habitat units, riparian vegetation cover, large woody fragments and instream cover for aquatic organisms) and fish traits related to locomotion, habitat use and feeding behaviour. The fish fauna of the broader, deeper and more slowly flowing streams was dominated by nektobenthic species that exploit autochthonous resources such as fish and invertebrates. In narrow, fast‐flowing streams, by contrast, there was a predominance of benthic fishes with varying feeding habits, including periphytivorous and invertivorous species. Narrow, shady streams were inhabited by nektonic species adapted for the exploitation of resources from the marginal vegetation. The results of this study contribute to the understanding of the association between the functional structure of fish assemblages and local environmental variables in Amazonian streams. We hope that these findings will stimulate further research into the natural variation in stream fish assemblages that will ensure the development of more effective management strategies that better protect these important aquatic ecosystems.

River Regulation Causes Rapid Changes in Relationships Between Floodplain Oak Growth and Environmental Variables.

The radial growth of pedunculate oak (Quercus robur), a species often ecologically dominating European deciduous forests, is closely tied up with local environmental variables. The oak tree-ring series usually contain a climatic and hydrologic signal that allows assessing the main drivers of tree growth in various ecosystems. Understanding the climate-growth relationship patterns in floodplains is important for providing insights into the species persistence and longevity in vulnerable riverine ecosystems experiencing human-induced hydrology alteration. Here, we use 139 years long instrumental records of local temperature, precipitation, and water levels in the Dnipro River in Kyiv to demonstrate that the implementation of river regulation has decoupled the established relationship between the radial growth of floodplain oak and local hydro-climatic conditions. Before the river flow has been altered by engineering modifications of 1965–1977, the water level in the Dnipro River was the key driver of oak radial growth, as reflected in the tree-ring width and earlywood width. The construction of two dams has altered the seasonal distribution of water level diminishing the positive effect of high water on oak growth and subsequently reversing this trend to negative, resulting from a seasonal ground water surplus. The decrease in the correlation between oak growth indices and the river’s water level in April–June was unprecedentedly rapid and clearly distinguishable among other changes in the growth-to-climate relationship. Our findings further demonstrate that trees growing in areas exposed to urban development are the most susceptible to downside effects of river regulation.

Distribution of bacterial polycyclic aromatic hydrocarbon (PAH) ring-hydroxylating dioxygenases genes in oilfield soils and mangrove sediments explored by gene-targeted metagenomics.

PAH ring-hydroxylating dioxygenases (PAH-RHDα) gene, a useful biomarker for PAH-degrading bacteria, has been widely used to examine PAH-degrading bacterial community in different contaminated sites. However, the distribution of PAH-RHDα genes in oilfield soils and mangrove sediments and their relationship with environmental factors still remain largely unclear. In this study, gene-targeted metagenomics was first used to investigate the diversity of PAH-degrading bacterial communities in oilfield soils and mangrove sediments. The results showed that higher diversity of PAH-degrading bacteria in the studied samples was revealed by gene-targeted metagenomics than traditional clone library analysis. Pseudomonas, Burkholderia, Ralstonia, Polymorphum gilvum, Mycobacterium, Sciscionella marina, Rhodococcus, and potential new degraders were prevailed in the oilfield area. For mangrove sediments, novel PAH degraders and Mycobacterium were predominated. The spatial distribution of PAH-RHDα gene was dependent on geographical location and regulated by local environmental variables. PAH content played a key role in shaping PAH-degrading bacterial communities in the studied samples, which would enrich PAH-degrading bacterial population and decrease PAH-degrading bacterial diversity. This work brings a more comprehensive and some new insights into the distribution and biodegradation potential of PAH-degrading bacteria in soil and sediments ecosystems.

Spatially limited antiferromagnetic order in a cluster glass compound Tb2Ni0.90Si2.94

In the present study, the synthesis of a new ternary intermetallic compound Tb2Ni0.90Si2.94 has been reported. The detailed studies on structure, static and dynamical magnetic properties of the compound have been investigated by means of powder x-ray diffraction, compositional analysis, dc & ac magnetization, non-equilibrium dynamics, heat capacity and neutron diffraction measurements. The dc & ac magnetic susceptibility reveal that the compound undergoes spin cluster-glass behaviour below 9.9 K. The frequency dependence of the freezing temperature have been analysed on the basis of dynamic scaling laws such as power-law divergence and Vogel-Fulcher law, which further confirm the cluster-glass state formation for the compound. A detailed study on non-equilibrium dynamical behaviour associated with cluster-glass state has been carried out through magnetic relaxation behaviour along with magnetic memory effect in zero-field-cooled (ZFC) as well as field-cooled (FC) conditions and associated aging effect. The zero-field neutron diffraction study reveals the presence of a spatially limited antiferromagnetic phase in addition to the magnetically frustrated cluster-glass state. This result has also been supported through zero-field heat capacity studies. The variation in local electronic environment among the magnetic rare-earth ions caused by the structural disorder associated with Ni/Si ions have been argued to be responsible for the coexistence of different magnetic phases.

Relative importance of local and landscape variables on fish assemblages in streams of Brazilian savanna

AbstractUnderstanding variability in the composition of aquatic assemblages requires a multiscale perspective, since processes operating at different spatial scales (from regional to local) drive the community assembly. Here, the relative importance of environmental variables on fish species composition in streams of the Brazilian savanna (Cerrado) is assessed and quantified at local and landscape scales. The importance of both local and landscape environmental variables in structuring fish assemblages was supported. Local variables explained a substantially higher amount of variance of fish assemblages than landscape variables. However, the shared explanation indicate that landscape variables had a complementary effect. The streams sampled were mostly headwaters at similar altitudes and with similar watershed sizes, so the sensitivity of the fish assemblages, even to small landscape gradients, is highlighted. Maintaining these important instream habitat characteristics close to natural conditions seems to be essential for conserving stream fish species, and for this, the landscape context should be taken into account. Considering the near‐pristine condition of the streams studied, these findings can be used as a reference for further studies addressing the effects of human modifications on stream fish biodiversity of the Cerrado.

Color-tunable visible photoluminescence of Eu:CaF2single crystals: variations of valence state and local lattice environment of Eu ions

In this article, Eu-activated CaF2 single crystals were synthesized by Bridgman-Stockbarge method. The dependence of photoluminescence properties of Eu: CaF2 crystals in UV-Vis regions on EuF3 doping concentrations were investigated. While the EuF3 doping concentration is increased from 0.6% to 6.0%, the CIE (Commission Internationale de L'Eclairage) color coordinates of Eu: CaF2 crystals can be tuned from (0.28, 0.12) to (0.60, 0.38), corresponding to the luminescence color from blue to orange. XPS (X-ray Photoelectron Spectroscopy) measurements indicated that Eu2+ and Eu3+ ions both existed in the crystals. With EuF3 doping concentration increasing, the proportion of Eu3+ ions increase from 16.73% to 39.00%, while that of Eu2+ ions decrease from 83.27% to 61.00%. Moreover, the integrated intensity ratio (R) of the 614 nm to 593 nm of Eu3+ ions increase from 0.38 to 0.44, indicating the local lattice environment symmetry of Eu3+ ions become lower with higher EuF3 doping concentrations. Furthermore, the CIE chromaticity coordinates of Eu: CaF2 crystals greatly depend on the excitation wavelength. The warm white-light emission has been realized in 0.6%Eu: CaF2 crystal when the excitation wavelength is around 322 nm.