Analytical Models for Grain Size Determination of Metallic Coatings and Machined Surface Layers Using the Four-Point Probe Method.

The grain size of a metallic coating or the surface layer after the machining of metallic parts strongly impacts corrosion and wear properties along with fatigue behavior. By measuring the combined electrical resistance of this layer and the substrate using the four-point probe method, the grain size of the layer can be determined. For different grain shapes, models are derived based on an analytical approach. The parameters in the models can be determined by appropriate calibration measurements. As a result, the grain sizes can be determined quickly with a non-destructive method, which can be applied to ensure consistent coating or machining results as part of quality control routines in industrial processes.

Socio-economic or environmental benefits from pondscapes? Deriving stakeholder preferences using analytic hierarchy process and compositional data analysis.

Ponds occupy a large share of standing water worldwide and play an important role in providing various ecosystem services. There are concerted efforts of the European Union either to create new ponds, or to restore and preserve existing ponds as nature-based solutions to provide benefits to ecosystem and human well-being. As part of the EU PONDERFUL project, selected pondscapes (i.e. landscapes of ponds) in eight different countries - hereafter "demo-sites", are studied to comprehensively understand their characteristics and their efficiency to provide ecosystem services. In addition, the needs and knowledge of stakeholders who own, work, research, or benefit from the pondscapes are also important, because of their capabilities to create, manage and develop the pondscapes. Therefore, we established connection with stakeholders to study their preferences and visions on the pondscapes. Using the analytic hierarchy process, this study shows that in general stakeholders in the European and Turkish demo-sites prefer environmental benefits to economic benefits, while stakeholders in the Uruguayan demo-sites rank the economic benefits higher. More specifically, in the European and Turkish demo-sites, the biodiversity benefits, i.e. life-cycle maintenance, habitat and gene pool protection, receive the highest ranking among all groups. On the other hand, stakeholders at the Uruguayan demo-sites rank provisioning benefits as the most important, because many ponds in Uruguayan demo-sites are being used for agricultural purposes. Understanding those preferences helps policy makers to address the needs of stakeholders more correctly, when considering any action or policy for the pondscapes.

Population genetics of the African snakehead fish Parachanna obscura along West Africa's water networks: Implications for sustainable management and conservation.

An essential factor for aquatic conservation is genetic diversity or population divergence, which in natural populations reflects the interplay between geographical isolation with restricted gene flow and local evolution of populations. The long geological history of Africa may induce stronger among-population divergence and lower within-population divergence in fish populations of African watersheds. As an example, we studied population structure of the African snakehead fish Parachanna obscura. Our study aimed: (1) to develop a set of highly polymorphic microsatellite markers suitable for the analysis of genetic diversity among P. obscura and (2) to study the genetic diversity and structure of P. obscura populations from the West Africa region and mostly from Côte d'Ivoire, with respect to the effects of climate region and geographical distance on the genetic differentiation. A total of 259 specimens from 15 locations of P. obscura were collected over the West Africa region reflecting a high variability of pairwise geographical distances and variability of hydrological connectivity of the area. We developed a set of 21 polymorphic microsatellite markers for studying population genetics of the fish. The results showed relatively low intragenetic diversity for all the 15 locations, certainly attributable to confinement of fish in segregated catchments, resulting in limited gene flow. We also found evidence for local adaptation processes, suggested by five out of 21 microsatellite loci being under putative selection, according to BAYESCAN analysis. In turn, there was strong genetic differentiation (F ST > 0.5) among fish from most locations, reflecting the allopatric development in watersheds without hydraulic connectivity. Neighbor-joining dendrogram, Principal Coordinate Analysis, and analysis of ancestral groups by STRUCTURE suggested that the 15 locations can be divided into three clusters, mainly matching the dominant climate zones and the segregation of the watersheds in the region. The distinct genetic structure of the fish from the 15 locations obtained in this study suggests that conservation and sustainable management actions of this fish resource should avoid genetic mixing of potentially locally adapted populations.

Can size distributions of European lake fish communities be predicted by trophic positions of their fish species?

An organism's body size plays an important role in ecological interactions such as predator-prey relationships. As predators are typically larger than their prey, this often leads to a strong positive relationship between body size and trophic position in aquatic ecosystems. The distribution of body sizes in a community can thus be an indicator of the strengths of predator-prey interactions. The aim of this study was to gain more insight into the relationship between fish body size distribution and trophic position in a wide range of European lakes. We used quantile regression to examine the relationship between fish species' trophic position and their log-transformed maximum body mass for 48 fish species found in 235 European lakes. Subsequently, we examined whether the slopes of the continuous community size distributions, estimated by maximum likelihood, were predicted by trophic position, predator-prey mass ratio (PPMR), or abundance (number per unit effort) of fish communities in these lakes. We found a positive linear relationship between species' maximum body mass and average trophic position in fishes only for the 75% quantile, contrasting our expectation that species' trophic position systematically increases with maximum body mass for fish species in European lakes. Consequently, the size spectrum slope was not related to the average community trophic position, but there were negative effects of community PPMR and total fish abundance on the size spectrum slope. We conclude that predator-prey interactions likely do not contribute strongly to shaping community size distributions in these lakes.

Predator Group Composition Indirectly Influences Food Web Dynamics through Predator Growth Rates.

AbstractConsiderable theoretical work predicts that intraspecific trait variation can have profound ecological consequences by altering species interactions. Because of their high flexibility, behavioral traits may be especially relevant in mediating how species respond to one another, thus affecting food web dynamics and ecosystem functioning. However, empirical evidence supporting this idea is limited. Here, we generated predator groups where we manipulated the composition of behavioral types within the groups to assess effects on predator growth rates, prey communities, basal resources, and ecosystem functioning in replicated outdoor ponds. Using European perch (Perca fluviatilis), we created three types of predator populations: two where all individuals expressed either bold or shy phenotypes and one that contained a mix of individuals of the two behavioral types. Bold perch grew faster in mixed populations, indicating that predator growth depends on each individual's behavioral type and that of its group members. However, there was no evidence that the behavioral composition of the perch population directly altered the dynamics of lower trophic levels. Instead, final perch biomass, not behavioral composition, had the strongest influence on lower trophic levels. Thus, the central question may not be whether predator behavior matters at all for trophic dynamics but rather when behavioral effects will predominate over effects of other influences, such as predator biomass variation.

European fish-based assessment reveals high diversity of systems for determining ecological status of lakes.

Triggered by the adoption of the Water Framework Directive, a variety of fish-based systems were developed throughout Europe to assess the ecological status of lakes. This paper provides a comprehensive overview of all existing systems and summarizes sampling methods, fish community traits (metrics) and the relevant anthropogenic pressures assessed by them. Twenty-one European countries developed fish-based assessment systems. Three countries each developed two distinct systems to approach different ecoregions, either to use different data, or to assess different lake types leading to a total number of 24 systems. The most common approach for the setting of reference conditions, used in seventeen systems, was the utilisation of fish communities in comparably undisturbed natural lakes as reference. Eleven used expert judgment, nine historical data and eight modelled relationships. Fourteen systems combined at least two approaches. The most common fish sampling method was a standardized fishing procedure with multimesh-gillnets. Many countries applied combinations of fishing methods, e.g. non-standard gillnets, fyke nets and electrofishing. Altogether 177 metrics were used for index development and each system combined 2-13 metrics. The most common ones were total standardized catches of number and biomass, relative abundance of Perca fluviatilis, Rutilus rutilus, and Abramis brama, feeding preferences, sensitive species, and non-natives. The pressure-response-relationships for these metrics were supported with both correlations established during system development and scientific publications. However, the metrics and their combinations were highly diverse and no metric was applied universally. Our analysis reveals that most fish-based assessment systems address multiple pressures (eutrophication, hydromorphological alterations, fishery pressure and occurrence of non-natives), whilst few are pressure-specific, tackling only eutrophication or acidification. We argue that the value of fish-based systems for lakes lies in their capacity to capture the effect of many different pressures and their interactions which is lacking for most assessment systems based on other biota.

Microstructure and Corrosion Properties of AlCrFeCoNi High-Entropy Alloy Coatings Prepared by HVAF and HVOF.

High-entropy alloys (HEAs) represent an innovative development approach for new alloy systems. These materials have been found to yield promising properties, such as high strength in combination with sufficient ductility as well as high wear and corrosion resistance. Especially for alloys with a body-centered cubic (bcc) structure, advantageous surface properties have been revealed. However, typical HEA systems contain high contents of expensive or scarce elements. Consequently, applying them as coatings where their use is limited to the surface represents an exciting pathway enabling economical exploitation of their superior properties. Nevertheless, processing conditions strongly influence the resulting microstructure and phase formation, which in turn has a considerable effect on the functional properties of HEAs. In the presented study, microstructural differences between high-velocity oxygen fuel (HVOF) and high-velocity air fuel (HVAF) sprayed coatings of the alloy AlCrFeCoNi are investigated. A metastable bcc structure is formed in both coating processes. Precipitation reactions are suppressed by the rapid solidification during atomization and by the relatively low thermal input during spraying. The coating resistance to corrosive media was investigated in detail, and an improved passivation behavior was observed in the HVAF coatings.

Genetic relationships between sympatric and allopatric Coregonus ciscoes in North and Central Europe.

BACKGROUND: Sympatric speciation along ecological gradients has been studied repeatedly, in particular in freshwater fishes. Rapid post-glacial ecological divergence has resulted in numerous endemic species or ecologically distinct populations in lakes of the temperate zones. Here, we focus on the Baltic cisco (Coregonus albula) complex, to study the genetic similarity among two pairs of sympatric autumn- and spring-spawning populations from post-glacial German Lakes Stechlin and Breiter Luzin. For comparison, we included a similar pair of sympatric populations from the Swedish Lake Fegen. We wanted to explore potential genetic similarities between the three sympatric cisco population pairs in the three lakes, to evaluate whether the pairs may have emerged independently in the three lakes, or whether two different species may have colonized all three lakes independently. Furthermore, we considered allopatric C. albula populations from three Polish, three Finnish, and four Swedish locations, added one Siberian population of the sister species C. sardinella and a Swedish C. maraena (whitefish) population. By genotyping nine microsatellite markers in 655 individuals from these 18 populations, we wanted to elucidate how strongly the cisco populations differ across a larger geographical area within Europe. Finally, we compared the genetic differences between the spring- and autumn-spawning populations of ciscoes in the two German lakes to infer the potentially deteriorating effect of strong anthropogenic pressure on the lakes. RESULTS: Dendrogram, Principal Coordinate Analysis and admixture analysis all indicated strong correspondence between population differentiation and geographical location for most cisco populations in Europe, including the Siberian population of C. sardinella. However, populations from some Swedish lakes deviated from this general pattern, by showing a distinct genetic structure. We found evidence for independent evolution of the three sympatric population pairs, because the populations co-occurring in the same lake were always most closely related. However, genetic differentiation was weak in the two German population pairs, but strong in the Swedish Lake Fegen, indicating that the weak differentiation in the German pairs reported earlier has eroded further. CONCLUSIONS: Our results suggest that the genetic differentiation at neutral genetic markers among populations of the Baltic cisco complex has evolved (and is maintained) by random genetic drift in isolated populations. However, earlier studies on the Swedish populations combining mitochondrial DNA and microsatellite data indicate that also post-glacial immigration from separate glacial refugia has shaped the present genetic population structure. The low neutral differentiation of the German sympatric pairs in contrast to the Swedish pair suggests that recent anthropogenic effects on the lakes in Germany may put the endemic spring-spawners at risk to extinction.

Capacity challenges in water quality monitoring: understanding the role of human development.

Monitoring the qualitative status of freshwaters is an important goal of the international community, as stated in the Sustainable Development Goal (SDGs) indicator 6.3.2 on good ambient water quality. Monitoring data are, however, lacking in many countries, allegedly because of capacity challenges of less-developed countries. So far, however, the relationship between human development and capacity challenges for water quality monitoring have not been analysed systematically. This hinders the implementation of fine-tuned capacity development programmes for water quality monitoring. Against this background, this study takes a global perspective in analysing the link between human development and the capacity challenges countries face in their national water quality monitoring programmes. The analysis is based on the latest data on the human development index and an international online survey amongst experts from science and practice. Results provide evidence of a negative relationship between human development and the capacity challenges to meet SDG 6.3.2 monitoring requirements. This negative relationship increases along the course of the monitoring process, from defining the enabling environment, choosing parameters for the collection of field data, to the analytics and analysis of five commonly used parameters (DO, EC, pH, TP and TN). Our assessment can be used to help practitioners improve technical capacity development activities and to identify and target investment in capacity development for monitoring.

Strain-rate sensitive ductility in a low-alloy carbon steel after quenching and partitioning treatment.

We investigate an extraordinarily high ductility in a low alloy carbon steel at an elevated temperature after a quenching and partitioning (Q&P) treatment. The conventional (quenched and tempered) reference material does not show similar behavior. Interestingly, the Q&P treated material's ductility is considerably reduced at increasing strain rates while strength remains almost constant. These results indicate the presence of a diffusion-controlled deformation mechanism at elevated temperatures. Our research shows that interlath retained austenite is more stable during deformation at higher temperatures, resulting in a delayed transformation to martensite and therefore to a more pronounced contribution to plastic deformation at (and in the vicinity of) the many interfaces inherently present in this multi-phase steel.

Short-term fish predation destroys resilience of zooplankton communities and prevents recovery of phytoplankton control by zooplankton grazing.

Planktivorous fish predation directly affects zooplankton biomass, community and size structure, and may indirectly induce a trophic cascade to phytoplankton. However, it is not clear how quickly the zooplankton community structure and the cascading effects on phytoplankton recover to the unaffected state (i.e. resilience) once short-term predation by fish stops. The resilience has implications for the ecological quality and restoration measures in aquatic ecosystems. To assess the short-term zooplankton resilience against fish predation, we conducted a mesocosm experiment consisting of 10 enclosures, 6 with fish and 4 without fish. Plankton communities from a natural lake were used to establish phytoplankton and zooplankton in the mesocosms. High biomasses (about 20 g wet mass m-3) of juvenile planktivorous fish (perch, Perca fluviatilis) were allowed to feed on zooplankton in fish enclosures for four days. Thereafter, we removed fish and observed the recovery of the zooplankton community and its cascading effect on trophic interactions in comparison with no fish enclosures for four weeks. Short-term fish predation impaired resilience in zooplankton community by modifying community composition, as large zooplankton, such as calanoids, decreased just after fish predation and did not re-appear afterwards, whereas small cladocerans and rotifers proliferated. Total zooplankton biomass increased quickly within two weeks after fish removal, and at the end even exceeded the biomass measured before fish addition. Despite high biomass, the dominance of small zooplankton released phytoplankton from grazer control in fish enclosures. Accordingly, the zooplankton community did not recover from the effect of fish predation, indicating low short-term resilience. In contrast, in no fish enclosures without predation disturbance, a high zooplankton:phytoplankton biomass ratio accompanied by low phytoplankton yield (Chlorophyll-a:Total phosphorus ratio) reflected phytoplankton control by zooplankton over the experimental period. Comprehensive views on short and long-term resilience of zooplankton communities are essential for restoration and management strategies of aquatic ecosystems to better predict responses to global warming, such as higher densities of planktivorous fish.

Testing the devil's impact on southern Baltic and North Sea basins whitefish (Coregonus spp.) diversity.

BACKGROUND: The diversity and phylogeny of whitefish of the genus Coregonus is complex, and includes many endemic species of high conservation concern. However, because of commercial importance of whitefish fisheries, stockings and translocations have occurred repeatedly, which challenges the identification of local populations as conservation units. This study analyses the phylogenetic relationships of 15 contemporary and two historical populations of lake-resident and anadromous whitefish (Coregonus spp.) from the southern Baltic and North Sea basins. We elucidated the complex history of Lake Schaal (northern Germany) whitefish, for which a local tale suggests that the devil threw whitefish from the Central European Lake Constance into this lake. Studies from the early twentieth century indeed suggested numerous stocking events for Lake Schaal from Lake Constance, from Estonian/Russian Lake Peipsi and from the anadromous whitefish of the Baltic Sea. RESULTS: Analyses of 13 microsatellite markers showed that Lake Constance whitefish are unrelated to any northern Germany whitefish population, including the contemporary whitefish population from Lake Schaal. Comparison with four historical specimens further showed that the native Lake Schaal whitefish (C. holsatus) vanished from the lake, but has survived as a non-native population in the north German Lake Drewitz. The whitefish currently occurring in Lake Schaal and three adjacent lakes are identified as C. maraenoides, introduced from Lake Peipsi. The contemporary anadromous whitefish populations from the Baltic (German and Finnish coast) and the German River Treene (North Sea basin, stocked from Danish River Vida) grouped together, but showed significant genetic differentiation. The 14 historical specimens of C. oxyrinchus from Rivers Rhine and Schelde were assigned to several contemporary whitefish populations, but among them only one specimen was assigned to the contemporary River Treene population. Therefore, we do not support the view that the whitefish from River Vida/Treene are identical with the historical C. oxyrinchus. CONCLUSIONS: Our study demonstrates that lake and anadromous whitefish in the Baltic and North Sea basins reflect a complex phylogeography, which is further blurred by the effects of repeated stocking and translocations. To identify conservation units, the genetic identity of each population has to be scrutinized.

Ecological conditions drive pace-of-life syndromes by shaping relationships between life history, physiology and behaviour in two populations of Eastern mosquitofish.

The pace-of-life syndrome (POLS) hypothesis predicts variation in behaviour and physiology among individuals to be associated with variation in life history. Thus, individuals on the "fast" end of POLS continuum grow faster, exhibit higher metabolism, are more risk prone, but die earlier than ones on the "slow" end. Empirical support is nevertheless mixed and modelling studies suggested POLS to vary along selection gradients. Therefore, including ecological variation when testing POLS is vastly needed to determine whether POLS is a fixed construct or the result of specific selection processes. Here, we tested POLS predictions between and within two fish populations originating from different ecological conditions. We observed opposing life histories between populations, characterized by differential investments into growth, fecundity, and functional morphology under identical laboratory conditions. A slower life history was, on average, associated with boldness (latency to emergence from a refuge), high activity (short freezing time and long distance travelled), and increased standard metabolism. Correlation structures among POLS traits were not consistent between populations, with the expression of POLS observed in the slow-growing but not in the fast-growing population. Our results suggest that POLS traits can evolve independently from one another and that their coevolution depends upon specific ecological processes.

Variation in flexural stiffness of the lepidotrichia within and among the soft fins of yellow perch under different preservation techniques.

Although the ray-finned fishes are named for their bony, segmented lepidotrichia (fin rays), we are only beginning to understand the morphological and functional diversity of this key vertebrate structure. Fin rays support the fin web, and their material properties help define the function of the entire fin. Many earlier studies of fin ray morphology and function have focused on isolated rays, or on rays from only one or two fins. At the same time, relatively little is known about how different preservation techniques affect the material properties of many vertebrate structures, including fin rays. Here, we use three-point bending tests to examine intra- and inter-fin variation in the flexural stiffness of fin rays from yellow perch, Perca flavescens. We sampled fin rays from individuals that were assigned to one of three preservation treatments: fresh, frozen, and preserved with formalin. The flexural stiffness of the fin rays varied within and among fins. Pelvic-fin rays were the stiffest, and pectoral fin rays the least stiff. The fin rays of the dorsal, anal, and caudal fins all had similar stiffness values, which were intermediate relative to those from the paired fins. The flexural stiffness of the fin rays was higher in rays that were at the leading edge of the fin. This variation in flexural stiffness was associated with variation in joint density and the relative length of the unsegmented proximal base of the fin rays. There was no significant difference in flexural stiffness between fresh and frozen specimens. In specimens preserved with formalin, there is a small but significant effect on stiffness in smaller fin rays.

Empirical correspondence between trophic transfer efficiency in freshwater food webs and the slope of their size spectra.

The density of organisms declines with size, because larger organisms need more energy than smaller ones and energetic losses occur when larger organisms feed on smaller ones. A potential expression of density-size distributions are Normalized Biomass Size Spectra (NBSS), which plot the logarithm of biomass independent of taxonomy within bins of logarithmic organismal size, divided by the bin width. Theoretically, the NBSS slope of multi-trophic communities is exactly -1.0 if the trophic transfer efficiency (TTE, ratio of production rates between adjacent trophic levels) is 10% and the predator-prey mass ratio (PPMR) is fixed at 104 . Here we provide evidence from four multi-trophic lake food webs that empirically estimated TTEs correspond to empirically estimated slopes of the respective community NBSS. Each of the NBSS considered pelagic and benthic organisms spanning size ranges from bacteria to fish, all sampled over three seasons in 1 yr. The four NBSS slopes were significantly steeper than -1.0 (range -1.14 to -1.19, with 95% CIs excluding -1). The corresponding average TTEs were substantially lower than 10% in each of the four food webs (range 1.0% to 3.6%, mean 1.85%). The overall slope merging all biomass-size data pairs from the four systems (-1.17) was almost identical to the slope predicted from the arithmetic mean TTE of the four food webs (-1.18) assuming a constant PPMR of 104 . Accordingly, our empirical data confirm the theoretically predicted quantitative relationship between TTE and the slope of the biomass-size distribution. Furthermore, we show that benthic and pelagic organisms can be merged into a community NBSS, but future studies have yet to explore potential differences in habitat-specific TTEs and PPMRs. We suggest that community NBSS may provide valuable information on the structure of food webs and their energetic pathways, and can result in improved accuracy of TTE-estimates.

Influence of Titanium on Microstructure, Phase Formation and Wear Behaviour of AlCoCrFeNiTix High-Entropy Alloy.

The novel alloying concept of high-entropy alloys (HEAs) has been the focus of many recent investigations revealing an interesting combination of properties. Alloying with aluminium and titanium showed strong influence on microstructure and phase composition. However, detailed investigations on the influence of titanium are lacking. In this study, the influence of titanium in the alloy system AlCoCrFeNiTix was studied in a wide range (molar ratios x = 0.0; 0.2; 0.5; 0.8; 1.0; 1.5). Detailed studies investigating the microstructure, chemical composition, phase composition, solidification behaviour, and wear behaviour were carried out. Alloying with titanium showed strong influence on the resulting microstructure and lead to an increase of microstructural heterogeneity. Phase analyses revealed the formation of one body-centred cubic (bcc) phase for the alloy without titanium, whereas alloying with titanium caused the formation of two different bcc phases as main phases. Additional phases were detected for alloys with increased titanium content. For x ≥ 0.5, a minor phase with face-centred cubic (fcc) structure was formed. Further addition of titanium led to the formation of complex phases. Investigation of wear behaviour revealed a superior wear resistance of the alloy AlCoCrFeNiTi0.5 as compared to a bearing steel sample.

Reconciling the opposing effects of warming on phytoplankton biomass in 188 large lakes.

Lake ecosystems are deeply integrated into local and regional economies through recreation, tourism, and as sources of food and drinking water. Shifts in lake phytoplankton biomass, which are mediated by climate warming will alter these benefits with potential cascading effects on human well-being. The metabolic theory of ecology suggests that warming reduces lake phytoplankton biomass as basal metabolic costs increase, but this hypothesis has not been tested at the global scale. We use satellite-based estimates of lake surface temperature (LST) and lake surface chlorophyll-a concentration (chl-a; as a proxy for phytoplankton biomass) in 188 of the world's largest lakes from 2002-2016 to test for interannual associations between chl-a and LST. In contrast to predictions from metabolic ecology, we found that LST and chl-a were positively correlated in 46% of lakes (p < 0.05). The associations between LST and chl-a depended on lake trophic state; warming tended to increase chl-a in phytoplankton-rich lakes and decrease chl-a in phytoplankton-poor lakes. We attribute the opposing responses of chl-a to LST to the effects of temperature on trophic interactions, and the availability of resources to phytoplankton. These patterns provide insights into how climate warming alters lake ecosystems on which millions of people depend for their livelihoods.

Assessing the Utility of Hydrogen, Carbon and Nitrogen Stable Isotopes in Estimating Consumer Allochthony in Two Shallow Eutrophic Lakes.

Hydrogen stable isotopes (δ2H) have recently been used to complement δ13C and δ15N in food web studies due to their potentially greater power to separate sources of organic matter in aquatic food webs. However, uncertainties remain regarding the use of δ2H, since little is known about the potential variation in the amount of exchangeable hydrogen (Hex) among common sample materials or the patterns of δ2H when entire food webs are considered. We assessed differences in Hex among the typical sample materials in freshwater studies and used δ2H, δ13C and δ15N to compare their effectiveness in tracing allochthonous matter in food webs of two small temperate lakes. Our results showed higher average amounts of Hex in animal tissues (27% in fish and macroinvertebrates, 19% in zooplankton) compared to most plant material (15% in terrestrial plants and 8% in seston/periphyton), with the exception of aquatic vascular plants (23%, referred to as macrophytes). The amount of Hex correlated strongly with sample lipid content (inferred from C:N ratios) in fish and zooplankton samples. Overall, the three isotopes provided good separation of sources (seston, periphyton, macrophytes and allochthonous organic matter), particularly the δ2H followed by δ13C. Aquatic macrophytes revealed unexpectedly high δ2H values, having more elevated δ2H values than terrestrial organic matter with direct implications for estimating consumer allochthony. Organic matter from macrophytes significantly contributed to the food webs in both lakes highlighting the need to include macrophytes as a potential source when using stable isotopes to estimate trophic structures and contributions from allochthonous sources.

Nox2 and Cyclosporine-Induced Renal Hypoxia.

BACKGROUND: We hypothesized that nicotinamide adenosine diphosphate oxidase 2 (Nox2) plays an important role in cyclosporine A (CsA)-induced chronic hypoxia. METHODS: We tested this hypothesis in Fisher 344 rats, C57BL/6 J wild type and Nox2-/- mice, and in liver transplant recipients with chronic CsA nephrotoxicity. We used noninvasive molecular imaging (blood oxygen level-dependent magnetic resonance imaging and dynamic contrast-enhanced magnetic resonance imaging) and molecular diagnostic tools to assess intrarenal oxygenation and perfusion, and the molecular phenotype of CsA nephrotoxicity. RESULTS: We observed that chemical and genetic inhibition of Nox2 in rats and mice resulted in the prevention of CsA-induced hypoxia independent of regional perfusion (blood oxygen level-dependent magnetic resonance imaging and dynamic contrast-enhanced magnetic resonance imaging, pimonidazole, HIF-1α). Nicotinamide adenosine diphosphate oxidase 2 knockout was also associated with decreased oxidative stress (Nox2, HIF-1α, hydrogen peroxide, hydroxynonenal), and fibrogenesis (α-smooth muscle actin, picrosirius red, trichrome, vimentin). The molecular signature of chronic CsA nephrotoxicity using transcriptomic analyses demonstrated significant changes in 40 genes involved in injury repair, metabolism, and oxidative stress in Nox2-/- mice. Immunohistochemical analyses of kidney biopsies from liver transplant recipients with chronic CsA nephrotoxicity showed significantly greater Nox2, α-smooth muscle actin and picrosirius levels compared with controls. CONCLUSIONS: These studies suggest that Nox2 is a modulator of CsA-induced hypoxia upstream of HIF-1α and define the molecular characteristics that could be used for the diagnosis and monitoring of chronic calcineurin inhibitor nephrotoxicity.