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Geothermal waters provide a great resource to generate clean energy, however, there is a notorious lack of high quality data on these waters. The scarcity of deep geothermal aquifer information is largely due to inaccessibility and high analysis costs. However, multiple operators use geothermal wells in Lower Bavaria and Upper Austria for balneological (medical and wellness) applications as well as for heat mining purposes. The state of the art sampling strategy budgets for a sampling frequency of 1 year. Previous studies have shown that robust groundwater data requires sampling intervals of 1–3 months, however, these studies are based on shallow aquifers which are more likely to be influenced by seasonal changes in meteorological conditions. This study set out to assess whether yearly sampling adequately represents sub-yearly hydrochemical fluctuations in the aquifer by comparing yearly with quasi-continuous hydrochemical data at two wells in southeast Germany by assessing mean, trend and seasonality detection among the high and low temporal resolution data sets. Furthermore, the ability to produce reliable forecasts based on yearly data was examined. In order to test the applicability of virtual sensors to elevate the information content of yearly data, correlations between the individual parameters were assessed. The results of this study show that seasonal hydrochemical variations take place in deep aquifers, and are not adequately represented by yearly data points, as they are typically gathered at similar production states of the well and do not show varying states throughout the year. Forecasting on the basis of yearly data does not represent the data range of currently measured continuous data. The limited data availability did not allow for strong correlations to be determined. We found that annual measurements, if taken at regular intervals and roughly the same production rates, represent only a snapshot of the possible hydrochemical compositions. Neither mean values, trends nor seasonality was accurately captured by yearly data. This could lead to a violation of stability criteria for mineral water, or to problems in the geothermal operation (scalings, degassing). We thus recommend a new testing regime of at least 3 samples a year. While not a replacement for the detailed analyses, under the right circumstances, and when trained with more substantial data sets, viertual sensors provide a robust method in this setting to trigger further actions.

Walking is a complex task. To prevent falls and injuries, gait needs to constantly adjust to the environment. This requires information from various sensory systems; in turn, moving through the environment continuously changes available sensory information. Visual information is available from a distance, and therefore most critical when negotiating difficult terrain. To effectively sample visual information, humans adjust their gaze to the terrain or—in laboratory settings—when facing motor perturbations. During activities of daily living, however, only a fraction of sensory and cognitive resources can be devoted to ensuring safe gait. How do humans deal with challenging walking conditions when they face high cognitive load? Young, healthy participants (N = 24) walked on a treadmill through a virtual, but naturalistic environment. Occasionally, their gait was experimentally perturbed, inducing slipping. We varied cognitive load by asking participants in some blocks to count backward in steps of seven; orthogonally, we varied whether visual cues indicated upcoming perturbations. We replicated earlier findings on how humans adjust their gaze and their gait rapidly and flexibly on various time scales: eye and head movements responded in a partially compensatory pattern and visual cues mostly affected eye movements. Interestingly, the cognitive task affected mainly head orientation. During the cognitive task, we found no clear signs of a less stable gait or of a cautious gait mode, but evidence that participants adapted their gait less to the perturbations than without secondary task. In sum, cognitive load affects head orientation and impairs the ability to adjust to gait perturbations.

Deep groundwater aquifers are exploited for a variety of purposes. In general, impermeable rock layers protect these aquifers from anthropogenic influences. As such, they are a last resort for groundwater in a pre-industrial state, and a crucial resource in cases of emergency, such as floods contaminating shallow groundwater. The EU Water Framework Directive (WFD) provides the regulatory framework to protect its quality and quantity. Recent monitoring of the hydrochemical state of Upper Jurassic wells in Bavaria and Austria has shown fluctuations that were connected to new exploitation activities and might indicate an unsustainable development of the aquifer. We propose a new workflow in accordance with the WFD which uses clustering algorithms to assess these fluctuations. Our data consists of 5 to 42 hydrochemical analyses per well with yearly sampling intervals spanning up to 30 years. From the cluster analysis we derived thresholds for two corridors: Natural Range Corridor (NC) and Action Corridor (AC). While the NC represents a well-specific natural variation range, the AC hints towards unsustainable development and should trigger a detailed (re)assessment. To show the potential of the new method, the workflow was applied to two wells with different geological characteristics. Distinct fluctuation events were clearly recognized and can be used in the context of an early warning system, such that malign hydrochemical variations can be detected before they become legally problematic to well operators. Our workflow thus provides a novel, robust, and reproducible method to assess the grade of sustainability at which a well is exploited and ensures a good status of a unique and important resource.

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 (

Hydrochemical stimulation by acidification of geothermal wells is a standard procedure to remove drilling mud and to improve hydraulic contact between borehole and reservoir. Several successive stimulations using hydrochloric acid were monitored by both online measurement and conventional analysis. The results show recovery curves with distinct two-step exponential temporal decrease of the chloride concentration. The initial decrease is fast, representing water and acid flow along pathways which are very well connected to the borehole. After the fluid from these flow paths has been recovered, the concentration decreases at a lower rate. This can be attributed to water flowing in less well connected flow paths. With additional stimulations the chloride concentration curve approaches a mono-exponential decrease. This indicates that the flow paths within the reach of the stimulation get more homogeneous.A numerical model of flow and solute transport in the borehole and the surrounding geothermal reservoir was developed in order to simulate the observed chloride-recovery behaviour in the course of a number of successive hydrochemical stimulations. The finite-element model was adapted to match the observed hydraulic and hydrochemical data range.Simulation hereby allows to separate time-dependent single contributions from the different flow paths to the total recovery concentration. Based on this information, indications of structural change due to the successive acidification steps can be derived from the chloride-recovery curves of each step. Furthermore, for typical settings the minimum time and volume of solution can be estimated which is required to achieve a significant structural signalThe derived structural information can be useful to predict the long-term behaviour of a geothermal injection well which during operation is exposed to a mild but constant chemical stimulation by the injected cold and, with respect to chloride in the rock matrix, undersaturated water.

Scaling summarizes precipitation of solids on the surface of pipes, heat exchangers, and other equipment in various industrial processes, including geothermal systems. Scalings in carbonate systems, which make up one of the most important geothermal reservoirs, are caused by a disruption of the lime-carbonic acid-equilibrium. Increasing temperatures (e.g. at the motor of a pump) lead to oversaturation. Decreasing pressure itself also leads to oversaturation but also to the formation of gas bubbles and stripping of CO2. The latter causes a shift to higher pH-values and massive oversaturation and affects most facilities in the North-Alpine Foreland Basin. The omnipresent scalings reduce the efficiency and may cause significant downtimes. It is therefore important to predict the amount of scalings along the geothermal cycle.While current hydrogeochemical models are capable to predict the risk and position of scalings, they are falling short with regard to the temporal development. They generally over-predict the amount of scalings which indicates that limiting processes, e.g. diffusion limited crystal growth, partial volume effects, and local equilibria have to be considered. This requires a combination of a fluid dynamics model and a hydrogeochemical model. Since the geothermal fluids are quite heterogeneous in their hydrochemical composition (from fresh water to brine) and both, equilibrium constants and kinetic rate constants, depend on the hydrochemical composition, coupling to an established hydrogeochemical model is favored to shorthand implementations of individual reactions.Benchmark data for such improved models can be obtained from bubble columns. Here, a gas is injected at the bottom of a usually transparent pipe filled with a fluid of known chemical composition and the effects of stripping (or gas augmentation) can be monitored with high temporal and spatial resolution. The fluid flow is accessible through tracking of particles and gas bubbles. Bubble columns are also used in different industrial processes, providing additional applications for the developed model.In this contribution we show the coupling of OpenFOAM, a very versatile computational fluid dynamics model, with PhreeqC, a widely used hydrogeochemical model, to simulate the effects of stripping on the formation of carbonate precipitates on the pipe walls and in dispersion. The model is compared to experimental data and a hybrid hydrogeochemical model which used an effective mass transfer rate for the gas-water exchange reaction as fitting parameter to cover the rate limiting processes.

The Northern Alpine Foreland Basin (NAFB) in southwest Germany is home to more deep geothermal plants than any other region in the country. The upper Jurassic, its main aquifer, consists of permeable carbonates which bear waters with temperatures of up to 150 °C on the southern border, and total dissolved salts values of up to 2 g/L. Geothermal applications in the NAFB include medical spas, geothermal district heating and power generation.In the case of heating and power generation, cooled-off waters are reinjected underground where rock-fluid interactions can lead to changes in the rock matrix and flow pathways. These interactions are thus an important factor to consider in the maintenance of geothermal plants. In carbonate systems, a decrease of temperature after heat extraction leads to an undersaturation of the previously equilibrated waters with regard to the host formation. The injected water dissolves the rock matrix along the borehole and the flow paths into the reservoir. This can increase the risk of a thermal breakthrough between injection and production well and possibly affect the borehole integrity. While the overall amount of dissolution has been monitored and modelled previously, the microscopic changes to the flow paths are still under investigation.We used rock samples coated with a 2-component paint and produced one microfracture in the coating to overcome experimental restrictions due to a limited fluid volume of the autoclave. The experiments were run at typical injection temperatures between 40°C and 75°C. The CO2 partial pressure wasadjusted to the measured values in the injection borehole. Microscopic and Raman images were taken before and after the exposition of the rock to the undersaturated waters and complemented by hydrochemical analyses.The dissolution of the limestones picked up microstructures and led to a heterogeneous development of the flow path. In an early stage of the injection, an underprediction of the increase of the hydraulic conductivity is thus expected.These assessments allow insights into the kinetics taking place at the artificial disturbance, which will make it possible to characterize and quantify the 3-dimensional pattern of calcite dissolution at a localized scale which is important for the development of the hydraulic properties, and affects further dissolution.

Climate changes in the anthropocene lead to an increase of rainfallintensity while the infiltration capacity of the soil is reducedduring extended dry periods. As a consequence surface runoff increasesand groundwater levels are reaching all-time lows: even close to thealps water becomes scarce. Keeping precipitation water local is a mustand one option is to direct flood water into local aquifers(Flood-MAR). This comes with a number of challenges, first of all, apronounced asymmetry of floods with very high volume flow in veryshort times, and droughts requiring long-term storage. From ahydrogeological perspective, infiltration of flood waves requiresextremely well-connected groundwater bodies with high hydraulicconductivity contrasting with slow groundwater flow required forlong-term storage. Geotechnical measures like sheet-pile walls or sandinjections can be used to control the release of groundwater back tothe river. The infiltrated water has to be conditioned to meethydrochemical and sanitary criteria. In contrast to conventionalmanaged aquifer recharge (MAR) the time frame for treatment isextremely limited. As floods are not occurring regularly, any treatmentsystem has to work autonomously and to be insensitive to longdowntimes between flooding events. The decision tree for theselection of suitable sites starts with the occurrence and extent offlooding events (regular flooding events with volumes less thanroughly 1 million m³), the morphology of the site (leveled withgroundwater levels below river water), and the hydrogeologicalproperties of the adjacent aquifers (ideally porous aquifers with highspecific yield and hydraulic conductivity). Further criteria are landuse (agriculture preferred), infrastructure (access to the site, nosubsurface installations), protection zones (groundwater, habitats,...) and ecosystem services, and risk factors in the catchment(hazardous substances, extended mobilization of soil during flooding,...). Three sites have been selected as pilot sites and will bepresented.

With global warming, a rising amount of people will be affected by water scarcity and droughts. At the same time, precipitation intensities and thus flood risks are projected to increase. Since these extremes often occur in the same location, co-management strategies of floods and droughts may offer a promising solution. The project Smart-SWS, funded by the BMBF as part of the initiative WaX – Hydrological Extreme Events, links drought prevention and flood protection with a concept for infiltrating flood waves into riverine aquifers as decentralized, technically supported underground storage. The two main challenges of the project are ensuring water quality with respect to health and environmental risks and controlling clogging of the system. The temporal asymmetry between very rapid infiltration of a flood wave and long-term storage in the aquifer, coupled with relatively long periods of no infiltration, results in stringent requirements for infiltration system design and materials.The goal of the infiltration process is to improve retention of undesirable materials while maintaining high infiltration rates. As part of this work, potential materials will be evaluated for their suitability for infiltration of flood waters into the aquifer. For this purpose, river water quality needs to be seasonally monitored. Parameterization and characterization of clogging can be performed in column experiments using different potential materials, at different hydrodynamic and hydrochemical conditions, and with defined infiltration and dry phases. Established concepts for the transport of (bio)colloids as well as the substitution of contaminants by fluorescent tracers with similar sorption properties can be used to demonstrate the efficiency of retention and the local formation of clogging in time and space.To test potential materials for the infiltration ditches and their contaminant retention behavior during wetting and drying cycles, a transparent column setup with temperature, pressure, electrical conductivity, redox potential, pH, and turbidity probes, as well as visual monitoring was established. This allows to record spatially resolved breakthrough curves, depositions, and reactions. We expect an increase of contaminant retention with an increase of filtered fines from the infiltrated water. Both, inorganic and organic colloids, are tested for this purpose and supplemented by experimental data from field sites. The shear forces in the porous materials are matched to the expected shear forces in the infiltration ditch. The hydrochemical stress due to a reduction in ionic strength during infiltration is also simulated in the experiments.With this work, the behavior of contaminants and particles in infiltration systems can be predicted and optimized in order to fulfil environmental and legal requirements for the water quality.

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.

Herein, we compare a series of solution-processible TADF polymers with different host pendant groups to achieve balanced charge transport properties through the combination of unipolar co-hosts.

Thermally activated delayed fluorescent (TADF) emitters have become the leading emissive materials for highly efficient organic light-emitting diodes (OLEDs). The deposition of these materials in scalable and cost-effective ways is paramount when looking toward the future of OLED applications. Herein, a simple OLED with fully solution-processed organic layers is introduced, where the TADF emissive layer is ink-jet printed. The TADF polymer has electron and hole conductive side chains, simplifying the fabrication process by removing the need for additional host materials. The OLED has a peak emission of 502 nm and a maximum luminance of close to 9600 cd m$_{−2}$. The self-hosted TADF polymer is also demonstrated in a flexible OLED, reaching a maximum luminance of over 2000 cd m$_{−2}$. These results demonstrate the potential applications of this self-hosted TADF polymer in flexible ink-jet printed OLEDs and, therefore, for a more scalable fabrication process.

Walking is a complex task. To prevent falls and injuries, gait needs to constantly adjust to the environment. This requires information from various sensory systems; in turn, moving through the environment continuously changes available sensory information. Visual information is available from a distance, and therefore most critical when negotiating difficult terrain. To effectively sample visual information, humans adjust their gaze to the terrain or – in laboratory settings – when facing motor perturbations. During activities of daily living, however, only a fraction of sensory and cognitive resources can be devoted to ensuring safe gait. How do humans deal with challenging walking conditions, when they face high cognitive load? Young, healthy participants (N=24) walked on a treadmill through a virtual, but naturalistic environment. Occasionally, their gait was experimentally perturbed, inducing slipping. We varied cognitive load by asking participants in some blocks to count backwards in steps of seven; orthogonally, we varied whether visual cues indicated upcoming perturbations. We replicated earlier findings on how humans adjust their gaze and their gait rapidly and flexibly on various time scales: eye- and head movements responded in a partially compensatory pattern and visual cues mostly affected eye movements. Interestingly, the cognitive task affected mainly head orientation. During the cognitive task, we found no clear signs of a less stable gait nor of a cautious gait mode, but evidence that participants adapted their gait less to the perturbations than without secondary task. In sum, cognitive load affects head orientation and impairs the ability to adjust to gait perturbations.

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.

We report on the physicochemical processes and the products of DNA damage involved in Ne-22 ion-beam radiation of hydrated (12 ± 3 H2O/nucleotide) salmon testes DNA at 77 K. Free radicals trapped at 77 K were identified using electron spin resonance (ESR) spectroscopy. The measurement of DNA damage using two different techniques of mass spectrometry revealed the formation of numerous DNA products. Results obtained by ESR spectroscopy showed that as the linear energy transfer (LET) of the ion-beam radiation increases along the beam track, the production of DNA radicals correspondingly increases until just before the Bragg peak is reached. Yields of DNA products along the ion-beam track were in excellent agreement with the radical production. This work is the first to use the combination of ESR spectroscopy and mass spectrometric techniques enabling a better understanding of mechanisms of radiation damage to DNA by heavy ion beams detailing the formation of DNA free radicals and their subsequent products.

The fate of engineered nanoparticles in the aquatic-terrestrial transition zone is decisive for their effect in the environment. However, our knowledge on processes within this interface is rather low. Therefore, we used a floodplain stream mesocosm to enhance our understanding of the long-term distribution and biological effects of citrate-coated silver nanoparticles (Ag-NPs) in this ecosystem. Parallel to pulsed dosing of Ag-NPs, we observed fluctuating but successively increasing concentrations of aqueous Ag, 88–97% of which was categorized as particles. The remaining dissolved fraction was mainly complexed with natural organic matter (NOM). The major Ag fraction (50%) was associated with the uppermost sediment layer. The feeding activity of benthic amphipods was largely unaffected, which could be explained by the low Ag concentration and complexation of released Ag+ with NOM. According to our hypothesis, only a small nanoparticle fraction (6%) moved to the terrestrial area due to aquatic aging and enrichment of Ag-NPs in sediments and biota. Nanoparticle infiltration in deeper sediment and soil layers was also limited. We expect that a small fraction of nanoparticles remaining in the water for several weeks can be transported over large distances in rivers. The Ag-NPs accumulated in the top layer of sediment and soil may serve as a source of toxic Ag+ ions or may be remobilized due to changing physico-chemical conditions. Furthermore, the high enrichment of Ag-NPs on algae (up to 250 000-fold) and leaves (up to 11 000-fold) bears risk for organisms feeding on those resources and for the transfer of Ag within the food web.

Solution-processing of multilayered Organic Light Emitting Diodes (OLEDs) remains a challenge that is often addressed by cross-linking polymer precursors into insoluble networks. Herein, we blend an emissive polymer carrying a Thermally Activated Delayed Fluorescence (TADF) emitter and a host species with a photo-cross-linkable polymer containing ortho-methylbenzaldehyde and maleimide groups as reactive cross-linkers to form a Semi-Interpenetrating Polymer Network (SIPN) upon irradiation at 365 nm. The progress of the cross-linking via Diels–Alder [4 + 2]-cycloaddition is monitored by FT-IR-spectroscopy and is correlated with the solvent resistance of the SIPN. Furthermore, the influence of the molecular weight and the cross-linker content on the efficiency of the cross-linking are investigated. The resulting polymer films show a high solvent resistance evidenced by photoluminescence and AFM measurements and are thus suitable for a successive solution-processed layer. Furthermore, a comonomer carrying the commercial host molecule 1,3-bis(N-carbazolyl)benzene (mCP) was synthesized in high yields, copolymerized and integrated in the emissive SIPN with good resistance against organic solvents. Lastly, the polymer blends were processed with an ink-jet printer and turned into an insoluble SIPN.

Geothermal ressources for heat and power generation are an integral part of the transition from fossil fuels to clean and sustainable energy and have been successfully developed in the North Alpine Foreland Basin since the 2000s. The timeframe since the first exploration activities is rather short and data on induced changes in the aquifer is scarce. It might be a good idea to take a look at the development classical groundwater ressources for comparison, even more so, if the geothermal facility also includes a net withdrawal for eg. medical or wellness applications.Most deep groundwater aquifers are of vital importance but strongly limited as ressources for drinking water. Depletion of these aquifers is easy to assess and usually handled well in the legislative procedure. The development of the hydrochemical state and the possible occurrence of mobile persistent trace pollutants, on the other hand, is hard to predict. Here, the current assessment framework which is based on the protection of the aquifer by impermeable layers falls short: together with groundwater renewal the age structure of the aquifer has to change. Old groundwater is replaced by more recent groundwater. Substances with a similar transport behaviour as wateritself will sooner or later show up in these deep groundwater ressources. Examples from bottled water producers show that the development from a state without any traces of anthropogenic substances to a the first occurrence is sharp and irreversible.Future development concepts for deep groundwater aquifers have to take the age structure of the aquifer into account when defining acceptable withdrawal rates, groundwater protection zones and technical operations which influence the integrity of the protecting layers.We present a conceptual assessment and monitoring concept for deep groundwater aquifers which includes the risks posed by unconventional uses of the impermeable layers (foundations, corroded wells, geothermal, ...).

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.

Multiple operators use geothermal wells in Lower Bavaria and Upper Austria for balneological (medical and wellness) applications and for energy and/or heat mining purposes. These applications depend heavily on the well‘s hydrochemical and geophysical stability (mineralization, pressure, temperature).At the moment, wells are submitted to inspection once a year, which includes the analysis of ions, pH, pressure, temperature etc. These „offline“ analyses, while covering a large set of parameters, obviously fail to show intra-annual variability within the measured parameters. On the other hand, some geothermal wells are being monitored quasi-continually. These „online“ sensors, however, only cover a small set of selected parameters, such as electric conductivity, temperature and pressure.This study aims at forecasting hydrochemical and physical stability based on annual measurements by assessing the degree of intra-annual variability covered or neglected by the yearly measurements. The results are required for a sound assessment of possible adverse effects of other exploration activities and short term variations of the withdrawal rates reflecting the demand for heat, energy and/or spa water. To do this, we followed the concept of virtual sensors and their correlation to detailed yearly measurements.We found that, while annual measurements, when taken approximately in the same season of the year, do match the data sampled online quite well, intra-annual variability at the examined wells was quite strong for some parameters and not represented by the offline data. Thus, annual data can be used to make predictions regarding long-term variability. In order to forecast intra-annual variability, higher temporal resolution is necessary. While not a replacement for the detailed analyses, the virtual sensors presented here provide a robust method to trigger further actions.

Successful development of the geothermal energy sector requires an understanding of the geological systems and processes that occur within. In the North Alpine Foreland Basin, a hydrogeothermal play type, most sites are affected by inorganic precipitates which reduce the efficiency and safety of plants. Although the gas concentrations in the geothermal waters are generally low, any formation of an independent gas phase induces carbonate precipitation. A quantitative prediction of the precipitates, however, is not yet possible because kinetic data for gas phase induced precipitates is not available.To address this issue laboratory experiments were run where a gas (CO2, air) was induced into a column containing an aqueous solution (tap water, water with high salinity). The scalings produced were analyzed by Raman spectroscopy, a mass balance of the process including the dissolving of scaling by inducing CO2 into the scaled column was based on ion chromatography data. The experiments show that by injecting air into tap water a full stripping of CO2 occurs which is the experimental proof of the disruption of the lime carbonic acid equilibrium by gas bubbles. The salinity of the initial solution influences - in agreement to previous investigations - the polymorph: only aragonite crystals were detected in tap water (ionic strength: 8.5e-03 mol/L), whereas only calcite crystals showed up in tap water with additional 0.2 g/L NaCl (ionic strength: 1.2e-02 mol/L). Precipitation was inhibited when 120 g/L NaCl were added to the tap water before stripping (ionic strength: 2.1 mol/L).The data were evaluated using a combination of hydrogeochemical calculation and precipitation kinetics (PhreeqC) with gas bubble kinetics (Python) and PEST++ for the final parameter adjustment. We successfully modelled the process of stripping, CO2-injection and the experiments with higher salinity with one model. This experimental proof of the gas phase induced carbonate precipitation and the new adequate description of the scaling process is a further step to predictive maintenance for geothermal sites and a more reliable holistic site assessment during the planning stage. Together, this improves the sustainability and the attractiveness of the geothermal energy sector to investors.