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Urban shallow groundwater is highly impacted in terms of hydrogeology and water quality by anthropogenic activities and infrastructure, such as heating and cooling, surface sealing, leaking sewage pipes, and underground buildings. For a sustainable management of urban water resources, a better understanding of biogeochemical processes and its dynamics on a spatial and temporal scale in the urban subsurface is needed. So far, data sets including a critical minimum number of key parameters and an appropriate resolution in space and time have often been missing. Here, we introduce a multi-tracer approach applied to assess the shallow aquifers in Vienna. Water samples were collected twice, in autumn 2021 and spring 2022, respectively, from 150 groundwater wells in the city limits of Vienna. A comprehensive set of parameters (e.g. major ions, nutrients, heavy metals, water and nitrate stable isotopes) were analyzed to evaluate the spatial and seasonal variations in water origin and quality. Statistical analysis revealed that driving factors influencing groundwater quality include aquifer properties, interactions between groundwater-surface water, and redox conditions. A combined interpretation of conservative tracers indicated zones influenced by surface water - groundwater interactions that also influenced the water chemistry. Microbial anaerobic processes govern groundwater quality. In particular, contamination of nitrate from septic water and manure is locally reduced by denitrification, as proven by compound-specific isotope analysis, improving water quality. At the same time, other anaerobic processes, such as iron and manganese reduction, sulfate reduction, and methanogenesis deteriorate water quality. Finally, groundwater temperatures, up to 27°C, were observed close to urban underground infrastructure, hinting at subsurface buildings and surface sealing as stressors in shallow groundwater. In conclusion, our high resolution spatial sampling with the large set of parameters will not only allow a better understanding of groundwater quality dynamics, but also allows to evaluate effects to groundwater biodiversity and develop predictive mathematical models.

Shallow urban groundwater is habitat of microorganisms as well as invertebrate fauna. Both communities are assumed to be strongly influenced by multiple stressors, such as increased groundwater temperatures and enhanced local hydraulic fluctuations, acting in the urban subsurface. To date, ecological studies mainly focused on natural and arable environments, with little attention to biodiversity and the role of anthropogenic factors in urban groundwater habitats. Our project targets the subterranean regime of the city of Halle (Saale) as an ideal benchmark to explore spatial and temporal dynamics of subsurface biodiversity on the urban scale. The unique hydrogeological setting of Halle, which covers a broad range of different aquifer types, with characteristic subsurface urban warming, allows for the evaluation of selected abiotic factors related to hydraulics, hydrochemistry and temperature trends. We expect new insight into the individual and concerted role of these factors on groundwater microorganisms and fauna.First data were collected within a field campaign in June/July 2022. Physico-chemical parameters in groundwater were recorded with a multiparameter probe at each sampling point. Hydrochemical analysis including major anions and dissolved organic carbon (DOC) was conducted with the water samples from the wells and freshly pumped groundwater. Groundwater animals were collected from the bottom of the wells with a net sampler. Animals were sorted and counted at the level of higher taxonomic groups (e.g. amphipods, copepods, isopods, ostracods, oligochaetes, nematodes, and mites). In the presentation, first results on the hydrogeology, hydrochemistry, microbiology and faunal diversity of the urban center and surroundings of Halle are introduced. We show major spatial trends and how faunal abundance and diversity relates to direct urban temperature effects and zones of anoxic conditions. Moreover, research activities planned for the near future will be discussed.

Summer periods of warm weather become longer and hotter causing “Urban Heat Islands” in large cities. Rising temperatures do not stop at the surface, but migrate into the underground, where infrastructure – such as sewage and district heating systems, buildings and shallow geothermal energy systems for cooling – amplifies the increase of groundwater temperatures. In order to be able to quantify this ongoing process and predict future temperature developments, a sound data basis is necessary. As of now, only groundwater temperature measurements have been available for different depth (one-point or multiple depth measurements) and time intervals (varying from two weeks to months) at a limited number of wells within the shallow urban aquifers in Vienna. To increase the spatial information content, the goal of this study was to measure groundwater temperature and level within the urban shallow aquifers of Vienna in two extensive field campaigns for more than 800 wells and to analyze those data statisticallyTo document the warmest and coldest conditions, measurements took place in one week each in October (2021) and April (2022). In total, groundwater temperatures in 1 m depth intervals and groundwater level were measured at 812 locations. Out of these ones, at 150 wells, water temperature was measured in pumped water. The average value of the profile equals best the pumped groundwater and thus represents the average aquifer temperature. According to our data analysis, the groundwater temperatures in Vienna vary between 6.9 °C and 30.6 °C. The highest temperatures were detected in close proximity to possible heat sources and a rapid drop in temperature with increasing distance could be demonstrated.Based on the collected data, temperature maps for both measurement dates and for different depth-intervals were derived, and display the underground urban heat islands in Vienna. The temperature maps enable the estimation of the potential for sustainable heating and cooling with groundwater in the capital of Austria.Together with historic long-term temperature data, trend analyses will be performed to allow a prognosis of thermal changes in the groundwater. The results, together with an extensive analysis of the groundwater chemistry and ecology, will feed into the development of a catalogue of measures for authorities and policymakers. Intention of the included recommendations is to counteract further groundwater warming and to ensure an efficient and sustainable use of groundwater for heating and cooling. The guidelines will therefore not only contribute to cooling the groundwater, but also to decarbonize the heating and cooling supply of Vienna.

With climate change, streams and rivers are at increased risk of droughts and flow intermittency. The full implications of these conditions for fluvial carbon (C) processing and stream-atmosphere CO2 emissions are not well understood. We performed a controlled drought experiment in outdoor hyporheic flumes. We simulated small rain events that increase sediment moisture content, but do not cause streamflow in order to investigate how these events affect streambed dissolved organic C dynamics, biofilm respiration and enzyme activity, and bacterial community composition. Flumes were subject to a non-flow phase of one month with small rain events with varying frequency (weekly, 3 × weekly, and no rain). Sediment was sampled at the surface and from the hyporheic zone at the end of the non-flow phase. We quantified microbial respiration of the dry sediments and sediment DOC leaching after simulated flow resumption. We found that, at the surface, more frequent rain events significantly increased microbial respiration from 12.6 ± 0.25 µg CO2 g−1 DW h−1 to 26.5 ± 11.3 µg CO2 g−1 DW h−1 between the control and 3 × weekly rain events. The average amount of DOC leached from surface sediments during flow resumption was reduced by 0.813 ± 0.62 mg L−1 with more frequent rain events. More frequent rain events also resulted in the leaching of fresher DOM with increased tryptophan fluorescence and a higher BIX. This, along with higher glucosidase activity in the biofilms, indicates higher OC processing during the drought period with more frequent rain events. Small rain events also enhanced Shannon diversity of microbial communities, with a stronger presence of ‘terrestrial-like’ bacterial clades. We propose that rain events during drought, even those of small size, are highly relevant for fluvial organic C processing during the dry phase. Future research should explicitly consider small rain events when investigating C fluxes in intermittent streams to fully understand the C processing in these systems with climate change. We conclude that small rain events impact DOM dynamics during reflow and likely impact the cascading C processing in the downstream river network.

We present field data on the effects of heavy rainfall after drought on the mobility of glyphosate and redox conditions in a clayey floodplain soil. By applying glyphosate together with deuterated water as conservative tracer in combination with time resolved

In many countries, groundwater quality is routinely monitored in yearly or quarterly intervals. Such frequencies, however, may not be sufficient for investigations into the temporal dynamics of water quality, due to seasonal variability or responses to extreme events. One approach to overcome this limitation is the use of in-situ sensors, such as UV-Vis spectrometers. With a focus on nitrate as an abundant groundwater contaminant, we explored the suitability of these sensors for high-resolution groundwater monitoring in shallow unconsolidated oxic aquifers. In-situ nitrate measurements in four selected wells compared well with values from lab analyses determined in pumped groundwater samples. Most importantly, our results revealed distinct seasonal patterns and, at two sites, pronounced short-term fluctuations in nitrate concentrations concomitant to patterns observed in precipitation, hydraulic head and groundwater temperature. Such dynamics in water quality, and thus the causal relationship with hydrological events and land use, will unfortunately be overlooked when following conventional sampling schemes with the risk of non-representative time series if routine sampling is timed unfavorably. Finally, we provide practical advice for deployment of the sensor.

Aquifers contain the largest store of unfrozen freshwater, making groundwater critical for life on Earth. Groundwater temperatures infl uence stream thermal regimes, groundwater-dependent ecosystems, aquatic biogeochemical processes, water quality, and the geothermal potential. Yet little is known about how groundwater responds to surface warming across spatial and temporal scales. We simulate current and projected groundwater temperatures at the global scale and show that groundwater at the depth of the water table is projected to warm on average by 3.3 ° C between 2000 and 2099 (RCP 8.5). However, regional groundwater warming patterns vary substantially due to spatial variability in climate and water table depth. The highest warming rates are projected in Central Russia, Northern China, and parts of North America and the Amazon rainforest. Results also show that by 2099, 234 million people are projected to live in areas where groundwater exceeds the highest threshold for drinking water temperatures set by any country.

The traditional perception of groundwater food webs is that of short and poorly structured food chains extending to only few trophic levels. This is mainly attributed to the lack of light and the shortfall of substantial primary production as well as the shortage of dissolved organic carbon and nutrients. It is frequently argued that microbes form the basis of groundwater food webs. In reality, the obvious lack of comprehensive biofilms may point to detritus as the main common food source and an opportunistic and omnivorous feeding strategy with most groups and species. Also, the relative stability of groundwater environments may have led to low trait variability. However, recent research also contrasts the paradigm of poorly structured food chains against emerging convoluted mechanisms sustaining a great range of biotic diversity and functional complexity. In summary, understanding of the ecological and functional linkages among stygofaunal groups, and their interaction with the microbial community, is still in its infancy. Stygofauna sampled from three spots of a shallow alluvial aquifer in the vicinity of the Danube River in the city of Vienna, Austria, has been analyzed by means of bulk stable carbon and nitrogen isotope and gut microbiome analysis to disentangle food web interactions. Our preliminary data revealed the following pattern: plant material, terrestrial insects, and detritus show a narrow range in carbon (-32 to -25δ13C) and a wide range in nitrogen (-1.5 to 6.5 δ15N) isotope signatures. In terms of nitrogen isotope values, the next tropic level is represented by isopods and gastropods, followed by ostracods, oligochaetes and amphipods. The broader range of stygofauna in carbon isotope signatures indicate an additional food source; most probably microbes; gut microbiome analyses indicate differences with oligochaetes, gastropods, ostracodes, isopods and amphipodes, however, with a few individuals from the later three groups sharing a very similar gut microbiome; within the amphipods, there is obviously a difference in gut microbiome composition with species and sampling sites; carbon and nitrogen isotope signatures underline amphipod-species differences; microbiome diversity in all cases was less divers in the animal guts when compared to environmental water, sediment and detritus samples. plant material, terrestrial insects, and detritus show a narrow range in carbon (-32 to -25δ13C) and a wide range in nitrogen (-1.5 to 6.5 δ15N) isotope signatures. In terms of nitrogen isotope values, the next tropic level is represented by isopods and gastropods, followed by ostracods, oligochaetes and amphipods. The broader range of stygofauna in carbon isotope signatures indicate an additional food source; most probably microbes; gut microbiome analyses indicate differences with oligochaetes, gastropods, ostracodes, isopods and amphipodes, however, with a few individuals from the later three groups sharing a very similar gut microbiome; within the amphipods, there is obviously a difference in gut microbiome composition with species and sampling sites; carbon and nitrogen isotope signatures underline amphipod-species differences; microbiome diversity in all cases was less divers in the animal guts when compared to environmental water, sediment and detritus samples. Finally, we first collected evidence for anaerobic processes taking place in animal guts living in an oxic groundwater environment. In light of our data, putative groundwater food web interactions in the shallow alluvial aquifer are discussed.

Climate change has a massive impact on the global water cycle. Subsurface ecosystems, the earth largest reservoir of liquid freshwater, currently experience a significant increase in temperature and serious consequences from extreme hydrological events. Extended droughts as well as heavy rains and floods have measurable impacts on groundwater quality and availability. In addition, the growing water demand puts increasing pressure on the already vulnerable groundwater ecosystems. Global change induces undesired dynamics in the typically nutrient and energy poor aquifers that are home to a diverse and specialized microbiome and fauna. Current and future changes in subsurface environmental conditions, without doubt, alter the composition of communities, as well as important ecosystem functions, for instance the cycling of elements such as carbon and nitrogen. A key role is played by the microbes. Understanding the interplay of biotic and abiotic drivers in subterranean ecosystems is required to anticipate future effects of climate change on groundwater resources and habitats. This review summarizes potential threats to groundwater ecosystems with emphasis on climate change and the microbial world down below our feet in the water saturated subsurface.

Riverbank filtration is an established and quantitatively important approach to mine high-quality raw water for drinking water production. Bacterial fecal indicators are routinely used to monitor hygienic raw water quality, however, their applicability in viral contamination has been questioned repeatedly. Additionally, there are concerns that the increasing frequency and intensity of meteorological and hydrological events, i.e., heavy precipitation and droughts leading to high and low river levels, may impair riverbank filtration performance. In this study, we explored the removal of adenovirus compared with several commonly used bacterial and viral water quality indicators during different river levels. In a seasonal study, water from the Rhine River, a series of groundwater monitoring wells, and a production well were regularly collected and analyzed for adenovirus, coliphages, E. coli, C. perfringens, coliform bacteria, the total number of prokaryotic cells (TCC), and the number of virus-like particles (TVPC) using molecular and cultivation-based assays. Additionally, basic physico-chemical parameters, including temperature, pH, dissolved organic carbon, and nutrients, were measured. The highest log10 reduction during the >72 m of riverbank filtration from the river channel to the production well was observed for coliforms (>3.7 log10), followed by E. coli (>3.4 log10), somatic coliphages (>3.1 log10), C. perfringens (>2.5 log10), and F+ coliphages (>2.1 log10) at high river levels. Adenovirus decreased by 1.6–3.1 log units in the first monitoring well (>32 m) and was not detected in further distant wells. The highest removal efficiency of adenovirus and most other viral and bacterial fecal indicators was achieved during high river levels, which were characterized by increased numbers of pathogens and indicators. During low river levels, coliforms and C. perfringens were occasionally present in raw water at the production well. Adenovirus, quantified via droplet digital PCR, correlated with E. coli, somatic coliphages, TCC, TVPC, pH, and DOC at high river levels. At low river levels, adenoviruses correlated with coliforms, TVPC, pH, and water travel time. We conclude that although standard fecal indicators are insufficient for assessing hygienic raw water quality, a combination of E. coli, coliforms and somatic coliphages can assess riverbank filtration performance in adenovirus removal. Furthermore, effects of extreme hydrological events should be studied on an event-to-event basis at high spatial and temporal resolutions. Finally, there is an urgent need for a lower limit of detection for pathogenic viruses in natural waters. Preconcentration of viral particles from larger water volumes (>100 L) constitutes a promising strategy.

Compound-specific isotope analysis (CSIA) can reveal mass-transfer limitations during biodegradation of organic pollutants by enabling the detection of masked isotope fractionation. Here, we applied CSIA to monitor the adaptive response of bacterial degradation in inoculated sediment to low contaminant concentrations over time. We characterized Aminobacter sp. MSH1 activity in a flow-through sediment tank in response to a transient supply of elevated 2,6-dichlorobenzamide (BAM) concentrations as a priming strategy and took advantage of an inadvertent intermittence to investigate the effect of short-term flow fluctuations. Priming and flow fluctuations yielded improved biodegradation performance and increased biodegradation capacity, as evaluated from bacterial activity and residual concentration time series. However, changes in isotope ratios in space and over time evidenced that mass transfer became increasingly limiting for degradation of BAM at low concentrations under such stimulated conditions, and that activity decreased further due to bacterial adaptation at low BAM (μg/L) levels. Isotope ratios, in conjunction with residual substrate concentrations, therefore helped identifying underlying limitations of biodegradation in such a stimulated system, offering important insight for future optimization of remediation schemes.

info:eu-repo/semantics/publishedVersion

Subterranean ecosystems are among the most widespread environments on Earth, yet we still have poor knowledge of their biodiversity. To raise awareness of subterranean ecosystems, the essential services they provide, and their unique conservation challenges, 2021 and 2022 were designated International Years of Caves and Karst. As these ecosystems have traditionally been overlooked in global conservation agendas and multilateral agreements, a quantitative assessment of solution-based approaches to safeguard subterranean biota and associated habitats is timely. This assessment allows researchers and practitioners to understand the progress made and research needs in subterranean ecology and management. We conducted a systematic review of peer-reviewed and grey literature focused on subterranean ecosystems globally (terrestrial, freshwater, and saltwater systems), to quantify the available evidence-base for the effectiveness of conservation interventions. We selected 708 publications from the years 1964 to 2021 that discussed, recommended, or implemented 1,954 conservation interventions in subterranean ecosystems. We noted a steep increase in the number of studies from the 2000s while, surprisingly, the proportion of studies quantifying the impact of conservation interventions has steadily and significantly decreased in recent years. The effectiveness of 31% of conservation interventions has been tested statistically. We further highlight that 64% of the reported research occurred in the Palearctic and Nearctic biogeographic regions. Assessments of the effectiveness of conservation interventions were heavily biased towards indirect measures (monitoring and risk assessment), a limited sample of organisms (mostly arthropods and bats), and more accessible systems (terrestrial caves). Our results indicate that most conservation science in the field of subterranean biology does not apply a rigorous quantitative approach, resulting in sparse evidence for the effectiveness of interventions. This raises the important question of how to make conservation efforts more feasible to implement, cost-effective, and long-lasting. Although there is no single remedy, we propose a suite of potential solutions to focus our efforts better towards increasing statistical testing and stress the importance of standardising study reporting to facilitate metaanalytical exercises. We also provide a database summarising the available literature, which will help to build quantitative knowledge about interventions likely to yield the greatest impacts depending upon the subterranean species and habitats of interest. We view this as a starting point to shift away from the widespread tendency of recommending conservation interventions based on anecdotal and expert-based information rather than scientific evidence, without quantitatively testing their effectiveness., This study is funded by the European Commission via the Marie Sklodowska-Curie Individual Fellowships program (H2020-MSCA-IF-2019; project number 882221), awarded to S.M. Additional support is provided by the PRIN SHOWCAVE “A multidisciplinary research project to study, classify and mitigate the environmental impact in tourist caves” (project number 2017HTXT2R; funded by the Italian Ministry of Education, University and Research). M.B.M. acknowledges support from the Kone Foundation (project number 202007611). T.D., C.F., V.Z., and M.Z. were supported by the Slovenian Research Agency, through core programme P1-0184 and P6-0119. O.T.M. was supported by a grant of the Romanian Ministry of Research, Innovation and Digitization, CNCS/CCCDI— UEFISCDI, project number 2/2019 (DARKFOOD), within PNCDI III. S.I.S. acknowledges funding by MEMOBIC (EU Operational Programme Research, Development and Education No. CZ.02.2.69/0.0/ 0.0/16_027/0008357), and by the Ministry of Education, Youth and Sports of the Czech Republic (grant number CZ.02.1.01/0.0/0.0/16 025/0007417). E.P. is supported by the PON “Research and Innovation” Programme (Axis IV “Education and Research for recovery” – Action IV.6 “Research contracts on Green themes”).

Groundwater fauna (stygofauna) comprises organisms that have adapted to the dark subterranean environment over a course of thousands and millions of years, typically having slow metabolisms and long life cycles. They are crucial players in the groundwater of oxygenic aquifers, and contribute to various ecosystem services. Today's knowledge of their sensitivity to anthropogenic impacts is incomplete and a critical analysis of the general relevance of local findings is lacking. In this review, we focus on those areas with the highest interference between humans and stygofauna: cities. Here is where local pollution by various contaminants and heat strongly stresses the unique groundwater ecosystems. It is demonstrated that it is difficult to discern the influence of individual factors from the findings reported in field studies, and to extrapolate laboratory results to field conditions. The effects of temperature increase and chemical pollution vary strongly between tested species and test conditions. In general, previous findings indicate that heating, especially in the long-term, will increase mortality, and less adapted species are at risk of vanishing from their habitats. The same may be true for salinity caused by road de-icing in cold urban areas. Furthermore, high sensitivities were shown for ammonium, which will probably be even more pronounced with rising temperatures resulting in altered biodiversity patterns. Toxicity of heavy metals, for a variety of invertebrates, increases with time and chronic exposure. Our current knowledge reveals diverse potential impacts on groundwater fauna by urban pollution, but our insights gained so far can only be validated by standardized and long-term test concepts.

Viruses, including human pathogenic viruses, can persist in water. For producing drinking water from surface water via bank filtration, natural attenuation capacities and the fate of viruses during the passage of aquatic sediments are of particular interest. Moreover, the increasing frequency of extreme hydrological events necessitate re-evaluation of the sustainability and efficacy of processes removing viruses. For this purpose, we performed bank sediment filtration experiments using a mesocosm in a technical-scale experimental facility that simulates a field situation under more tightly controlled conditions. We used the bacteriophage MS2 as a surrogate for enteric viruses to study the transport of different viral loads through the bank sediment. Additionally, we simulated a heavy rain event to investigate the re-mobilization of initially attached virus particles. We quantified the abundance of infectious MS2 phages by plaque assay and the total number of MS2 particles by qPCR. Also, we differentiated pore water concentrations by depths of the sediment column and investigated attachment to the sediment matrix at the end of the individual experimental phases. Bank filtration over a vertical distance of 80 cm through sandy sediment revealed a virus removal efficiency of 0.8 log10 for total MS2 particles and 1.7 log10 for infectious MS2 particles, with an initial phage concentration of 1.84 × 108 gene copies mL−1. A low load of infectious MS2 (1.9 × 106 plaque forming units mL−1) resulted in a greater removal efficiency (3.0 log10). The proportion of infectious MS2 phages of the total MS2 particle mass steadily decreased over time, i.e., in the course of individual breakthrough curves and with sediment depth. The simulated pulse of rainwater caused a front of low ionic strength water which resulted in pronounced phage remobilization. The high proportion of infectious MS2 among the detached phages indicated that attachment to the sediment matrix may substantially conserve virus infectivity. Therefore, the re-mobilization of previously attached viruses owing to hydrological extremes should be considered in water quality assessment and monitoring schemes.

Grundwasser ist eine unserer wichtigsten Ressourcen fur die Gewinnung von Trinkwasser. Es ist ein thermisch stabiles Okosystem, das durch seine Funktionen zur guten Wasserqualitat beitragt. Die Nutzung oberflachennaher Geothermie fur Heiz- und Kuhlzwecke kann zu variablen Temperaturverhaltnissen fuhren. Die Konsequenzen von Temperaturschwankungen auf den Verbleib potenziell pathogener Mikroorganismen und Viren sind allerdings kaum untersucht. Ziel dieser Studie war deshalb, Transport und Verbleib von zwei Modell-Viren (MS2 und T7) bei unterschiedlichen Temperaturen (4–45 °C) im Labor in Sedimentsaulen zu untersuchen. An die experimentellen Daten wurde ein mathematisches Modell zur Beschreibung des reaktiven Stofftransports angepasst und die Transportparameter ermittelt. In allen Experimenten spielte Sorption eine wichtige Rolle fur den Ruckhalt der Viren. Dabei findet sowohl Gleichgewichtssorption als auch kinetische, reversible Sorption statt. Irreversible Sorption, also eine vollstandige Eliminierung der aktiven Viren aus der wassrigen Phase, wurde durch das Modell nicht bestatigt, kann aber fur inaktive Partikel nicht komplett ausgeschlossen werden. Die Adsorptionsraten zeigten eine leichte Temperaturabhangigkeit, wobei diese Abhangigkeit fur die beiden Modellviren entweder positiv (MS2) oder negativ (T7) war. Wesentlich starkeren Einfluss auf die Adsorptionsraten hatte die Abstandsgeschwindigkeit; je schneller, desto geringer waren die Raten. Die Ergebnisse zeigen, dass sich die Temperatur im Gegensatz zu hydrologischen Variablen (Abstandsgeschwindigkeit) nur wenig auf den Verbleib aktiver Virenpartikel von MS2 und T7 ausgewirkt hat. Sorption war ein wichtiger Prozess, eliminierte Viren aber nicht komplett aus dem Porenwasser, sodass diese trotzdem mobil waren. Es bleibt weiter zu klaren, ob Temperaturanderungen oder Sorptionsprozesse zu einer zusatzlichen Inaktivierung von Virenpartikeln fuhren konnen und unter welchen Bedingungen.

Sediments accommodate the dominating share of groundwater microbiomes, however the processes that govern the assembly and succession of sediment-attached microbial communities in groundwater aquifers are not well understood. To elucidate these processes, we followed the microbial colonization of sterile sediments in in situ microcosms that were exposed to groundwater for almost 1 year at two distant but hydrologically connected sites of a pristine, shallow, porous aquifer. Our results revealed intriguing similarities between the community succession on the newly-colonized sediments and succession patterns previously observed for biofilms in other more dynamic aquatic environments, indicating that the assembly of microbial communities on surfaces may be governed by similar underlying mechanisms across a wide range of different habitats. Null model simulations on spatiotemporally resolved 16S rRNA amplicon sequencing data further indicated selection of specific OTUs rather than random colonization as the main driver of community assembly. A small fraction of persistent OTUs that had established on the sediments during the first 115 days dominated the final communities (68%-85%), suggesting a key role of these early-colonizing organisms, in particular specific genera within the Comamonadaceae and Oxalobacteraceae, for community assembly and succession during the colonization of the sediments. Overall, our study suggests that differences between planktonic and sediment-attached communities often reported for groundwater environments are not the result of purely stochastic events, but that sediment surfaces select for specific groups of microorganisms that assemble over time in a reproducible, non-random way.

Droughts are expected to become more common with climate change resulting in more frequent occurrences of flow intermittency in temperate streams. As intermittency has deleterious effects on fluvial microbial biofilms, there is a need to better understand how droughts affect the microbial functioning and thereby nutrient and organic matter processing in temperate stream ecosystems. Here, the hyporheic zone is of particular importance as it has been shown to be a hot spot for biogeochemical activity under flow intermittence. This study evaluates how drought duration affects microbial biofilm dynamics in the hyporheic zone of intermittent temperate streams. To do so, we used outdoor hyporheic flumes that were subject to periods of drought ranging from 4 to 105 days. Sediment was sampled before and during the drought, and at several occasions after rewetting. Samples were analyzed for extracellular enzymatic activity, bacterial respiration, and bacterial abundances including live to dead cell ratios. The high moisture content remaining in the hyporheic zone of the flumes allowed for the sustained microbial functioning during drought, regardless of drought duration. This can be attributed to cooler temperatures in these climate zones and shading by riparian forests. The high moisture content inhibited the local habitat and community changes that the biofilm might have undergone during more severe desiccation. However, the change in the hyporheic flow regime (flow cessation and resumption) may stimulate microbial processing in these moderate drought conditions. We suggest that the hyporheic zone may act as a buffer against drought and the factors determining this buffer capacity, such as sediment characteristics and climatic regions, need to be analyzed in more detail in future.

An integrative interdisciplinary approach is currently developed to investigate groundwater systems in alpine and prealpine environments and how they respond to hydrological extremes such as droughts, heavy rain and floods in terms of water quantity, hydrochemical quality, and ecological status. The new approach is aimed at improving the understanding of the interaction between physical, chemical, and biological processes in groundwater responses to extreme events as well as developing indicators suitable for an integrative monitoring and management of the aquifers. For this purpose, observation wells of the existing state hydrographic monitoring net have been selected within the Austrian part of the Mur river basin, stretching from the alpine origin to the national border in the foreland. The investigation area thus comprises diverse hydrogeological settings and land-use types. The selected observation wells have long-term records of groundwater levels and are used for sampling campaigns under different hydrological conditions. Groundwater level fluctuations are evaluated using drought indices and statistical approaches, such as auto-correlation and cross-correlation with precipitation and stream stages. Our hydrochemical analyses of groundwater and surface waters also consider compounds indicative of agricultural sources (e.g., nitrate), wastewater-borne micro-pollutants, and stable isotopes of water. These indicators are used to identify different drivers controlling water origin and quality. The ecological status is characterized using microbiological measures, such as total number of bacteria and microbial activity, groundwater fauna, and the qualitative composition of dissolved organic matter (DOM). First results demonstrate a deterioration of water quality from groundwater to surface water and from the alpine region towards the foreland, corresponding to the more intense agricultural and urban land use in the foreland. Linkages between water quality and hydrological conditions are currently being evaluated and will be further examined using UV-Vis spectrometry for high-resolution in-situ monitoring of water quality changes (DOM and nitrate) at selected observation wells.

In this presentation we provide a brief overview on the strategic selection of representative groundwater wells and lessons learned.The inter-disciplinary project “Integrative Groundwater Assessment”, looks into the effects of extreme hydro-meteorological events on the quantity and the chemical and biological quality of groundwater. Focus is on the Austrian Mur catchment, an area reaching from its alpine spring (~2000 m asl) down to the Slovenian border (~200 m asl). More than 500 state operated groundwater observation wells are available over the 400 km of the river’s course, taking private wells not into account. For state operated wells, time series for water levels are publicly available which allows for simply using all the data i.e. using big data approaches [1, 2, 3] – albeit with some issues [4].However, for water quality, such time series rarely exist and if so, they often do not cover all specific parameters one needs, asking for targeted sampling campaigns. The availability of hundreds of wells seems like a benefit. However, the identification of wells that are representative and suitable for sampling regarding both chemical and biological parameters is a challenging taskIn consequence, we went through a multi-step process of planning a sampling campaign that should fulfill the following requirements: Coverage of the entire stream section from alpine to lowland regions Coverage of different land uses in the river valley Realization of well transects from the river through the complete local aquifer Wells allow sampling of groundwater for the analysis of physical-chemical and biological parameters Historical data of groundwater quantity and quality aspects are available Assessing the available metadata and taking into account the very helpful advice of stakeholders, already reduced the number of representative wells considerably. In order to obtain a consistent data set, another set of wells had to be dismissed, to allow for the same sampling and monitoring procedures at every location. Finally, out in the field, wells that were found damaged or out of order, led to a further reduction. Thus we ended up with only 45 wells suitable for our specific purposes, However, using specific strategies for data analysis as outlined in [3] and [4] and application of a novel groundwater ecological assessment scheme (D-A-C Index [5]) showed that even the substantially reduced number of wells provides a very good coverage of the various regions in the Mur catchment. In a further step, the results from two sampling campaigns and subsequent data analysis will be used to select an even smaller subset of wells where novel multi-parameter spectral dataloggers are going to be installed, enabling us to monitor various quality data in an very high temporal resolution.References:[1] https://doi.org/10.5194/egusphere-egu2020-8148[2] https://doi.org/10.1016/j.ejrh.2019.100597[3] https://doi.org/10.1007/s12665-018-7469-4[4] Haas et al (2020)Tiny steps towards Big Data - Freud und Leid der Arbeit mit großen Grundwasserdatensätzen.Tagungsband 2020. Grundwasser und Flusseinzugsgebiete - Prozesse, Daten und Modelle.[5] https://doi.org/10.1016/j.watres.2019.114902

Bank filtration is a sustainable source for drinking water production in urbanized regions but is increasingly at risk by contamination with pathogenic bacteria and viruses from surface water receiving wastewater discharge. While recent advances have improved our process understanding for pathogen transport on laboratory scale, simulations and predictions on field scale under transient conditions, as in bank filtration, are still highly uncertain. To improve our understanding on field scale, we performed a sampling survey over 16 months at an observation well transect in a heterogeneous sand-gravel aquifer of an active bank filtration waterworks at the river Rhine in Germany. Water samples were collected from the river, the production well, and 4 multi-level observation wells. Samples were analysed for main anions/cations, and hygienic indicators (E. coli and coliform bacteria via plate counts, coliphages via plaque assay, and adenoviruses via ddPCR). A two-dimensional reactive transport model was set up using PFLOTRAN to simulate the transport of heat and dissolved species, aerobic respiration, denitrification, and colloid-based transport of bacteria and viruses. For the latter, adsorption to and desorption from the sediment, straining, blocking, and inactivation are considered. Model parameters were estimated from prior knowledge of the site or calibrated with the obtained data using particle swarm optimization.Field observations show a strong seasonal variation of river hydraulics with up to 8 m difference in water level, a prolonged low in the summer/fall and short-termed river level increases in the winter. Aerobic respiration was strongly controlled by the temperature variation (6-24°C in groundwater), leading to an increase in oxygen consumption and limited denitrification during the warm summer/fall. Bacteria and virus concentrations in the groundwater were elevated following a flood in the first winter (up to 500 MPN/100mL coliforms, 2 PFU/100mL coliphages, 1000 copies/100mL adenovirus). Measurable concentrations were still observed during the summer (e.g., up to 10 MPN/100mL coliforms, 0.7 PFU/100mL coliphages, 500 copies/mL adenovirus), but concentrations were below the detection limit for most of the second winter, where no significant flood occurred. In the well closest to the river (40 m distance), the concentration reduction compared to the river varied over time between 1 to ≥4 log-units for coliforms, 1.5 to ≥3 log-units for coliphages, and 0.5 to ≥3 log-units for adenoviruses. The model results suggest the main driving processes for the variation in the bacteria and virus concentrations are (i) the changing groundwater velocity (driven by river level variations and pumping rate), (ii) occurrence of low dissolved oxygen concentrations which lower inactivation, and (iii) transient colmation layer properties (permeability and effective grain size). The colmation layer is affected by reworking of riverbed sediments during floods, bio-clogging during summer, and physical clogging due to constant forced infiltration caused by the bank filtration plant. This is supported by the observation of high bacteria concentrations in the aquifer for a short duration after pumps were reactivated following a 40-day maintenance period. Overall, bacteria and virus attenuation during bank filtration was high, only a strong flood resulted in significantly higher contaminant concentrations in the aquifer.

In aquatic ecosystems, the biomass, activity and composition of microorganisms are determined to a large extent by local and regional environmental conditions. While karst aquifers are an important source for drinking water, the ecology of microbial communities in karst waters has hardly been studied. This study examined the regional variations and seasonal dynamics of microbial communities in pristine karst spring waters of Slovenia (Central Europe). Fifteen springs distributed across 5 eco-regions exhibiting a strong altitudinal gradient were sampled 4 times a year. Evaluation of the microbial communities included quantification of prokaryotic biomass via total cell counts and microbial activity estimated via measurements of electron transport system activity. The taxonomic structure of the bacterial communities was analysed by terminal restriction fragment length polymorphism fingerprinting. Biological measures were complemented by a set of physico-chemical parameters, including dissolved organic carbon, nutrients, major ions, temperature, electrical conductivity, pH, and dissolved oxygen. Bacterial community structure differed significantly with seasons and eco-regions, with the latter causing greater variation. While the overall power of the environmental variable tested was a moderate factor (15%) in explaining the variability in microbial community structure, catchment altitude was a key determinant. Prokaryotic cell density and microbial activity in spring water decreased with an increase in catchment altitude and were significantly positively correlated. For a better understanding of karst ecosystems and the ecosystem service of water purification, future investigation should address karst microbial communities at a higher phylogenetic and functional resolution.

Organic contaminant degradation by suspended bacteria in chemostats has shown that isotope fractionation decreases dramatically when pollutant concentrations fall below the (half-saturation) Monod constant. This masked isotope fractionation implies that membrane transfer is slow relative to the enzyme turnover at μg L–1 substrate levels. Analogous evidence of mass transfer as a bottleneck for biodegradation in aquifer settings, where microbes are attached to the sediment, is lacking. A quasi-two-dimensional flow-through sediment microcosm/tank system enabled us to study the aerobic degradation of 2,6-dichlorobenzamide (BAM), while collecting sufficient samples at the outlet for compound-specific isotope analysis. By feeding an anoxic BAM solution through the center inlet port and dissolved oxygen (DO) above and below, strong transverse concentration cross-gradients of BAM and DO yielded zones of low (μg L–1) steady-state concentrations. We were able to simulate the profiles of concentrations and isotope ratios of the contaminant plume using a reactive transport model that accounted for a mass-transfer limitation into bacterial cells, where apparent isotope enrichment factors *ε decreased strongly below concentrations around 600 μg/L BAM. For the biodegradation of organic micropollutants, mass transfer into the cell emerges as a bottleneck, specifically at low (μg L–1) concentrations. Neglecting this effect when interpreting isotope ratios at field sites may lead to a significant underestimation of biodegradation., Please provide a synopsis

The science of the total environment 769, 144324 (2021). doi:10.1016/j.scitotenv.2020.144324, Published by Elsevier Science, Amsterdam [u.a.]

The assessment and monitoring of the ecological quality and status of groundwater is a timely issue. At present, various assessment tools have been developed that now await application and validation. One of these, the D‑A‑C index, evaluates the microbiological-ecological quality of groundwater based on of prokaryotic cell counts, microbial activity measurements, and the qualitative characterization of dissolved organic carbon (DOM). The purpose of this paper is to illustrate the different ways of application of the D‑A-(C) index making use of a recently collected data set (n = 61) from the river Mur valley, Austria. First, we present an extension of the D‑A-(C) index by including measurements of dissolved organic matter quality (DOM) derived from fluorescence spectroscopy as additional variables to supplement the analysis of microbial cell density and activity levels. Second, we illustrate how the definition of a reference status for a ‘good’ microbiological-ecological state can improve the analysis and allow for a more sensitive and accurate detection of impacts on groundwater ecosystems. Based on our results, we advocate that the analysis be performed by making use of expert knowledge for the definition of reference sites to which target sites are to be compared.

Groundwaters host vital resources playing a key role in the near future. Subterranean fauna and microbes are crucial in regulating organic cycles in environments characterized by low energy and scarce carbon availability. However, our knowledge about the functioning of groundwater ecosystems is limited, despite being increasingly exposed to anthropic impacts and climate change-related processes. In this work we apply novel biochemical and genetic techniques to investigate the ecological dynamics of an Australian calcrete under two contrasting rainfall periods (LR—low rainfall and HR—high rainfall). Our results indicate that the microbial gut community of copepods and amphipods experienced a shift in taxonomic diversity and predicted organic functional metabolic pathways during HR. The HR regime triggered a cascade effect driven by microbes (OM processors) and exploited by copepods and amphipods (primary and secondary consumers), which was finally transferred to the aquatic beetles (top predators). Our findings highlight that rainfall triggers ecological shifts towards more deterministic dynamics, revealing a complex web of interactions in seemingly simple environmental settings. Here we show how a combined isotopic-molecular approach can untangle the mechanisms shaping a calcrete community. This design will help manage and preserve one of the most vital but underrated ecosystems worldwide.