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Ebullition is a major transport pathway of methane from aquatic ecosystems to the atmosphere. Several studies have highlighted that methane ebullition plays an important role in reservoirs, but not much data is available from non-impounded stream sections. Quantifying river methane emissions on a global scale is a challenge due to the high spatiotemporal heterogeneity in these dynamic and variable systems. A better conceptual understanding of riverine methane ebullition is needed for sound carbon budgets, both in terms of flux volumes and predictive factors for hot-spot emission zones.This study targeted the knowledge gap in riverine methane ebullition with a time-resolved observation-based analysis of the ebullitive transportation pathway in a river cross section. We installed four bubble traps in a small stream in southern Germany and monitored volumes and concentrations of the two greenhouse gases CO2 and CH4 along with carbon stable isotopes (δ13C) of CH4 over the course of a year. The bubble traps were evenly distributed over one cross-section in a curve to represent different sediment-compositions and flow regimes between the undercut slope and slip-off slope. Sediment characterization at each site included grain-size distribution curves, porosity measurements and determination of organic carbon content.Ebullitive gas fluxes were extremely high at two of the locations centrally in the river: up to 1000 ml m-2 d-1 during summer and autumn, and 100-400 ml m-2 d-1 in December. CH4 concentrations of up to 65% were measured in the gas samples and CH4 exceeded CO2 concentrations (

The hyporheic zone (HZ) is of major importance for carbon and nutrient cycling as well as for the ecological health of stream ecosystems. However, biogeochemical observations in this ecotone are complicated by a very high spatial heterogeneity and temporal dynamics. Especially the latter are difficult to observe without disturbing the system. In this field study, we tested and combined three less common methods for time-resolved measurements with high vertical resolution. We installed Rhizon samplers for repeated pore-water extraction, an optical sensor unit for in-situ measurements of dissolved oxygen, and a depth-resolved temperature monitoring system in the HZ of a small stream. While Rhizon samplers were found to be highly suitable for pore-water sampling of dissolved solutes, measured gas concentrations, here CH4, showed a strong dependency of the pump rate during sample extraction, and an isotopic shift in gas samples became evident. This was presumably caused by a different behaviour of water and gas phase in the pore-space. The manufactured oxygen-sensor could locate the oxic-anoxic interface with very high precision. This is ecologically important and allows to distinguish aerobic and anaerobic processes. Temperature data could not only be used to estimate vertical hyporheic exchange, but also depicted sedimentation and erosion processes. Overall, the combined approach was found to be a promising tool to acquire data for the quantification of biogeochemical processes in the HZ with high spatial and temporal resolution.

Abstract: Students’ vocational interests can be described by Holland’s theory of occupational choice. Holland distinguishes six interest dimensions here: realistic, investigative, artistic, social, enterprising, and conventional. Although these attributes are relatively stable during adolescence, their stability increases dramatically during university studies. Because vocational interests are often a factor in career counseling and the choice of what to study, it is essential to investigate the extent to which they develop during the first years of college. This study examines the NEPS first-year student cohort to investigate the stability of students’ interests and aspirations. The paper analyzes 2,442 male and 3,435 female students who studied within one of six major study clusters and provided data about their vocational interests at Wave 1 (study entry) and Wave 9 (about 4.5 years later close to the end their studies). The study’s results show strong and highly significant correlations for all interest dimensions, as well as a high stability of students’ aspirations. The correlations were strongest for artistic interests and weakest for conventional interests and were distinguishable between most dimensions. Furthermore, the analyses showed notable differences with respect to gender and field of study. Further analyses went beyond a variable-centered towards a person-centered approach showing that students with a stable interest vector also displayed higher profile correlations and a higher person-environment fit. The analysis shows that 28% of the sample are still developing their interests. This indicates notable adaption processes during university time that should be factored into course design, career counseling, and further research.

Facing the challenges of climate change, policy making relies on sound greenhouse gas (GHG) budgets. Rivers and streams emit large quantities of the potent GHG methane (CH4), but their global impact on atmospheric CH4 concentrations is highly uncertain. In situ data from the hyporheic zone (HZ), where most CH4 is produced and some of it can be oxidized to CO2, are lacking for an accurate description of CH4 production and consumption in streams. To address this, we recorded high-resolution depth-resolved geochemical profiles at five different locations in the stream bed of the river Moosach, southern Germany. Specifically, we measured pore-water concentrations and stable carbon isotopes (δ13C) of dissolved CH4 as well as relevant electron acceptors for oxidation with a 1 cm vertical depth resolution. Findings were interpreted with the help of a numerical model, and 16S rRNA gene analyses added information on the microbial community at one of the locations. Our data confirm with pore-water CH4 concentrations of up to 1000 µmol L−1 that large quantities of CH4 are produced in the HZ. Stable isotope measurements of CH4 suggest that hydrogenotrophic methanogenesis represents a dominant pathway for CH4 production in the HZ of the river Moosach, while a relatively high abundance of a novel group of methanogenic archaea, the Candidatus “Methanomethyliales” (phylum Candidatus “Verstraetearchaeota”), indicate that CH4 production through H2-dependent methylotrophic methanogenesis might also be an important CH4 source. Combined isotopic and modeling results clearly implied CH4 oxidation processes at one of the sampled locations, but due to the steep chemical gradients and the close proximity of the oxygen and nitrate reduction zones, no single electron acceptor for this process could be identified. Nevertheless, the numerical modeling results showed potential not only for aerobic CH4 oxidation but also for anaerobic oxidation of CH4 coupled to denitrification. In addition, the nitrate–methane transition zone was characterized by an increased relative abundance of microbial groups (Crenothrix, NC10) known to mediate nitrate and nitrite-dependent methane oxidation in the hyporheic zone. This study demonstrates substantial CH4 production in hyporheic sediments, a potential for aerobic and anaerobic CH4 oxidation, and underlines the high spatiotemporal variability in this habitat.

Rivers and streams are often supersaturated in methane (CH4) and emit significant amounts of this potent greenhouse gas to the atmosphere. Methane is produced by methanogenic archaea in anaerobic sediments where energetically more favorable redox processes are substrate-limited. Diffusing up towards the sediment surface, methane can be oxidized in the hyporheic zone (HZ) aerobically with oxygen or anaerobically with nitrate, nitrite, sulfate or iron and manganese oxides as electron acceptors. Yet, knowledge about net carbon emissions from streams is restricted, because high spatial heterogeneities in production and consumption zones make bottom-up global estimations particularly challenging.In this study we want to increase process understanding of riverine methane cycling, in particular production and oxidation in hyporheic stream sediments. Several studies have investigated predictors for potential methane production and oxidation in river sediments using incubation experiments. We chose a different approach by measuring high-resolution depth-dependent geochemical profiles at five different locations across a stream bed. An in-situ equilibrium dialysis sampler (peeper) was used to obtain pore-water samples with a 1 cm depth-resolution for the measurement of dissolved oxygen, relevant anion and cation concentrations as well as methane concentrations and stable carbon isotopes (δ13C) of methane. In the methanogenic zone stable carbon isotopes may provide information about the most relevant methane production pathway, while an isotopic enrichment in δ13C-CH4 towards the sediment surface linked with decreasing methane concentrations may indicate microbial degradation. Production and oxidation rates were estimated using inverse numerical modeling of measured concentration gradients. Additionally, the concentration of 16S rRNA genes (a measure of bacteria biomass) was quantified from one of the locations using quantitative PCR, which revealed an increase in microbial biomass at the nitrate-methane transition zone. Sequencing of the 16S rRNA genes shows clear shifts in microorganisms driving the streambed methane cycle at and below the nitrate-methane transition zone.The measured δ13C-CH4 values between -75 ‰ and -70 ‰ indicate that hydrogenotrophic methanogenesis is the dominant production pathway. However, we found that methane fluxes into the surface water were low. Mainly responsible for a strong decrease in methane concentrations towards the sediment surface were most likely diffusive processes. Decreasing methane concentrations linked with a significant enrichment in δ13C towards heavier isotopes was only observed at one of the sampling locations. The isotopic shift together with modeling results and microbiological analyses may reveal microbially driven aerobic and anaerobic methane oxidation in the HZ, but in most locations methane is only oxidized at low rates where the environment is already methane depleted by diffusion. Limiting for both aerobic and anaerobic methane oxidation was supposedly the low methane concentration in zones with available electron acceptors.

Globally occurring nitrate pollution in groundwater is harming the environment and human health. In situ hydrogen addition to stimulate denitrification has been proposed as a remediation strategy. However, observed nitrite accumulation and incomplete denitrification are severe drawbacks that possibly stem from the specific microbial community composition. We set up a microcosm experiment comprising sediment and groundwater from a nitrate polluted oxic oligotrophic aquifer. After the microcosms were sparged with hydrogen gas, samples were taken regularly within 122 h for nitrate and nitrite measurements, community composition analysis via 16S rRNA gene amplicon sequencing and gene and transcript quantification via qPCR of reductase genes essential for complete denitrification. The highest nitrate reduction rates and greatest increase in bacterial abundance coincided with a 15.3-fold increase in relative abundance of Rhodocyclaceae, specifically six ASVs that are closely related to the genus Dechloromonas. The denitrification reductase genes napA, nirS and clade I nosZ also increased significantly over the observation period. We conclude that taxa of the genus Dechloromonas are the prevailing hydrogenotrophic denitrifiers in this nitrate polluted aquifer and the ability of hydrogenotrophic denitrification under the given conditions is species-specific.

Nitrate pollution of freshwaters and methane emissions into the atmosphere are crucial factors in deteriorating the quality of drinking water and in contributing to global climate change. The n-damo (nitrite-dependent anaerobic methane oxidation), nitrate-dependent anaerobic methane oxidation and the anaerobic oxidation of ammonium (anammox) represent two microbially mediated processes that can reduce nitrogen loading of aquatic ecosystems and associated methane emissions to the atmosphere. Here, we report vertical concentration and stable-isotope profiles of CH4, NO3-, NO2-, and NH4+ in the water column of Fohnsee (lake in southern Bavaria, Germany) that may indicate linkages between denitrification, anaerobic oxidation of methane (AOM), and anammox. At a water depth from 12 to 20 m, a methane–nitrate transition zone (NMTZ) was observed, where δ13C values of methane and δ15N and δ18O of dissolved nitrate markedly increased in concert with decreasing concentrations of methane and nitrate. These data patterns, together with the results of a simple 1-D diffusion model linked with a degradation term, show that the nonlinear methane concentration profile cannot be explained by diffusion and that microbial oxidation of methane coupled with denitrification under anaerobic conditions is the most parsimonious explanation for these data trends. In the methane zone at the bottom of the NMTZ (20 to 22 m) δ15N of ammonium increased by 4 ‰, while ammonium concentrations decreased. In addition, a strong 15N enrichment of dissolved nitrate was observed at a water depth of 20 m, suggesting that anammox is occurring together with denitrification. The conversion of nitrite to N2 and nitrate during anammox is associated with an inverse N isotope fractionation and may explain the observed increasing offset (Δδ15N) of 26 ‰ between δ15N values of dissolved nitrate and nitrite at a water depth of 20 m compared to the Δδ15Nnitrate-nitrite of 11 ‰ obtained in the NMTZ at a water depth between 16 and 18 m. The associated methane concentration and stable-isotope profiles indicate that some of the denitrification may be coupled to AOM, an observation supported by an increased concentration of bacteria known to be involved in n-damo/denitrification with AOM (NC10 and Crenothrix) and anammox (“Candidatus Anammoximicrobium”) whose concentrations were highest in the methane and ammonium oxidation zones, respectively. This study shows the potential for a coupling of microbially mediated nitrate-dependent methane oxidation with anammox in stratified freshwater ecosystems, which may be important for affecting both methane emissions and nitrogen concentrations in lakes.

Microcosm experiments with the well-studied denitrifier Thaurera aromatica show a link between a higher maximum membrane concentration (MMC) of the toxic organic solvents 1-octanol and 4-chlorophenol and a higher degree of saturation (DoS) of the fatty acids in the cell membrane. This coincides with less pronounced stable isotope fractionation during denitrification. We suggest that the change in cell membrane fluidity and the cell's stress response leads to a decrease in nitrate transport across the cell membrane and/or an increase in the relative ratio of respiratory nitrate reduction rate versus efflux of unreacted nitrate. Both models show that the apparent kinetic isotope effect (AKIE) approach unity and thus reduce the extent of the resulting stable isotope enrichment factor epsilon N-15-NO3 in dissolved nitrate during denitrification, as experimentally and mathematically shown in this study. This may lead to an underestimation of nitrate reduction determined by nitrate stable isotope analysis in aquatic habitats where various types of stresses may affect the physiology of the driving microorganisms. (C) 2018 Elsevier Ltd. All rights reserved.

Pure cultures of Thauera aromatica were stressed by the addition of the toxic solvents 1-octanol and 4-chlorophenol causing adaptive modifications in their cell-membrane fatty acid composition. At the same time, we investigated the isotopic fractionation in δ15N-NO3- during denitrification. We observed a change in the degree of saturation (DoS) of the bacteria as a reaction to solvent stress and a higher degree of saturation was directly correlated to the concentration of solvents in the cell membrane. The enrichment factor ε15N-NO3- during denitrification showed a linear dependency to the DoS as well as to the membrane solvent concentration. Denitrifying bacteria thus may express less negative ε15N-NO3- when they are exposed to environmental stress that changes their cell membrane composition.

The stable isotopes 15N/14N and 18O/16O of nitrate are frequently used to determine sources of nitrate and to assess denitrification processes in the environment. Nitrate isotope ratios are thought to be conservative unless involved in (bio-) chemical conversion processes. Thus, stable isotopes are considered to be a reliable tool to determine sources of nitrate in aquatic habitats even after transport and dilution has occurred. Denitrification is known to shift both isotope ratios towards higher δ-values. A fixed ratio of 0.5 for Δδ18O/Δδ15N has been proposed and has been widely used to detect denitrification in terrestrial environments, predominantly in aquifers. However, it is observed in environmental and laboratory studies that this ratio actually varies between less than 0.5 and 1 for uncertain reasons with laboratory studies usually describing a ratio close to 1. Here we report results of anoxic incubation experiments with natural populations of nitrate-reducing microorganisms using sediments from three different environments. In our experiments we used water with a δ18O in excess of 500‰ and found a microbially mediated influence of the oxygen isotopic composition of ambient water on the isotopic composition of the residual dissolved nitrate. We found up to 5.7 ± 2.3% of the oxygen-atoms in the residual dissolved nitrate was exchanged by oxygen-atoms from ambient water within the limited timeframe of the experiments. The fastest incorporation of oxygen-atoms from water into dissolved nitrate correlated with the highest intermittent nitrite concentrations observed in our experiments. In a second series of batch experiments we also found that pure cultures of the nitrite-oxidizing bacterium Nitrobacter vulgaris promoted the incorporation of oxygen atoms from ambient water into dissolved nitrate under anoxic conditions. Presumably this happens via a reoxidation of intermediary formed nitrite by the enzyme “nitrite oxidoreductase” (NXR) in concurrence with respiratory nitrate reduction. In this context, our hypothesis is a reversibility of the reactions at the NXR enzyme even in the absence of external electron acceptors for nitrite oxidation. We suggest that the presence of nitrite-oxidizing microorganisms in aquatic environments may catalyse such an incorporation of oxygen-atoms stemming from ambient water into nitrate. This process may thus mask the original δ18O value of nitrate sources during denitrification and also distort the observed enrichment of 18O that is ascribed to denitrification. Our results are highly likely an explanation of the deviation of the described variable Δδ18O/Δδ15N ratios for denitrification in terrestrial field studies from the values observed in the laboratory on pure cultures.

In batch experiments, we studied the isotope fractionation in N and O of dissolved nitrate during dentrification. Denitrifying strains Thauera aromatica and "Aromatoleum aromaticum strain EbN1" were grown under strictly anaerobic conditions with acetate, benzoate, and toluene as carbon sources. (18)O-labeled water and (18)O-labeled nitrite were added to the microcosm experiments to study the effect of putative backward reactions of nitrite to nitrate on the stable isotope fractionation. We found no evidence for a reverse reaction. Significant variations of the stable isotope enrichment factor ε were observed depending on the type of carbon source used. For toluene (ε(15)N, -18.1 ± 0.6‰ to -7.3 ± 1.4‰; ε(18)O, -16.5 ± 0.6‰ to -16.1 ± 1.5‰) and benzoate (ε(15)N, -18.9 ± 1.3‰; ε(18)O, -15.9 ± 1.1‰) less negative isotope enrichment factors were calculated compared to those derived from acetate (ε(15)N, -23.5 ± 1.9‰ to -22.1 ± 0.8‰; ε(18)O, -23.7 ± 1.8‰ to -19.9 ± 0.8‰). The observed isotope effects did not depend on the growth kinetics which were similar for the three types of electron donors. We suggest that different carbon sources change the observed isotope enrichment factors by changing the relative kinetics of nitrate transport across the cell wall compared to the kinetics of the intracellular nitrate reduction step of microbial denitrification.

We analysed carbon (delta(13)C) and nitrogen (delta(15)N) isotope ratios of organisms and biogenic tissues from Comau Fjord (southern Chile) to characterise benthic food webs and spatial isotope variability in this ecosystem. These values were intended to serve as a baseline for detecting anthropogenic impacts on Patagonian marine fjord ecosystems in later studies. Benthic macroalgae and invertebrate suspension feeders were primarily considered, with some supplementary data from cyanobacteria, plankton, fish, and coastal vertebrates. Six depth transects typified the lateral salinity gradients from the innermost part of the fjord to its mouth, as well as the vertical density gradients caused by freshwater inflow. Carbon isotope signatures indicated predominant consumption of either CO(2) or HCO(3)(-) for benthic macroalgal. All CO(2) users belonged to rhodophytes. The delta(15)N values of benthic macrophytes decreased with decreasing salinity, both vertically and along the fjord axis. This implies the influence of (15)N-poor terrestrial dissolved inorganic nitrogen (DIN) at these sites. Enhanced influence of freshwater influx also lowered N contents and increased C/N ratios in algal tissues. Exceptionally high macroalgae delta(15)N values at the seabird and sealion colony Isla Liliguapi point to animal faeces as an additional source of (15)N-enriched DIN. Thus, DIN sources not originating from the open sea are additionally utilised by the benthic macroalgae in the fjord. In contrast, mussel tissue from the same locations was much less influenced by varying DIN sources. Among benthic suspension feeders, mytilids (Mytilus chilensis, Aulacomya ater) had the lowest and scleractinian corals (Desmophyllum dianthus) had the highest delta(15)N values, and Balanidae (Elminius kingii) and gorgonians (Primnoella sp.) showed values in between. The preference for specific size classes of marine particulate organic matter (seston) as food serves as an explanation for the delta(15)N variability observed between the different benthic suspension feeders.

Background: Phonological cueing is often applied to assist spoken word retrieval in anomia. Phonological cues usually comprise auditory and visual information. Yet while the auditory channel provides full information about a cued phoneme, the mouth shape only contains information about certain features of a segment, e.g., place of articulation. Aims: This study aimed to investigate the immediate effectiveness of visual phonological information in anomic participants, as compared with auditory cueing, in assisting spoken word retrieval. Methods & Procedures: In a group of 16 anomic participants, spoken picture-naming tasks were administered using mouth shapes of initial segments of target words as visual cues, and initial phonemes as auditory cues. Outcomes & Results: Reaction time analyses revealed significant facilitation effects for both the visual and the auditory cues. Single-case analyses revealed selective effects: participants benefited either from auditory or from visual phonological information. ...

Background : Investigations of prosodic processing in brain-damaged patients have primarily focused on hemispheric specialisations in the processing of prosodic structures. Most studies of receptive prosodic abilities in brain-damaged people share a common methodological approach, i.e., they are based on explicit tasks. No attention has been paid so far to the impact of explicit or implicit experimental methodologies. Aims : The aim of this study was to compare implicit and explicit experimental paradigms of receptive prosodic processing in patients with focal left and right hemisphere lesions. Methods & Procedures : Two implicit processing paradigms were used to investigate the comprehension of turn-related prosody (turn-detection task) and of prosodic focus (phoneme-detection task) in patients with focal cerebro-vascular lesions to the left or right cerebral hemisphere. The results were compared with explicit processing data of two matched patient groups selected from a larger sample of an earlier study...