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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.

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.

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.

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.

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.

Das Grundwasser ist der groste und alteste kontinentale Lebensraum. Trotzdem wird in der europaischen und deutschen Rechtspraxis Grundwasser bisher als Ressource und nicht als Lebensraum behandelt. Allerdings kann der Lebensraumbezug uber die Definition des Grundwassers als Gewasser im deutschen Wasserhaushaltsgesetz bzw. als „aquatisches Okoysystem“ in der Europaischen Grundwasserrichtlinie (EG-GWRL) hergestellt werden. Die Umsetzung des Grundwasserschutzes sollte sich am okosystemaren Ansatz fur Oberflachengewasser in der Europaischen Wasserrahmenrichtlinie (EG-WRRL) und den Zielen der nationalen Biodiversitatsstrategie orientieren. Fur das Grundwasser wird die Einfuhrung der Begriffe „guter okologischer Zustand“ und „Grundwasserokosysteme“ in das Umweltrecht vorgeschlagen. Grundwasserlebensraume und -arten sollten durch die Eingriffsregelung berucksichtigt und in die FFH-Richtlinie, in das Bundesnaturschutzgesetz und die Bundesartenschutzverordnung aufgenommen werden. Fachlich und rechtlich ist die Diskriminierung der Grundwasserokosysteme gegenuber Oberflachengewassern nicht zu begrunden. Die Autoren argumentieren fur die „Gleichberechtigung“ von Oberflachen- und Grundwasser und machen Vorschlage fur die Anpassung des bestehenden Rechts im Sinne eines okologisch begrundeten Grundwasserschutzes.

Aromatic hydrocarbons belong to the most abundant contaminants in groundwater systems. They can serve as carbon and energy source for a multitude of indigenous microorganisms. Predictions of contaminant biodegradation and microbial growth in contaminated aquifers are often vague because the parameters of microbial activity in the mathematical models used for predictions are typically derived from batch experiments, which don’t represent conditions in the field. In order to improve our understanding of key drivers of natural attenuation and the accuracy of predictive models, we conducted comparative experiments in batch and sediment flow-through systems with varying concentrations of contaminant in the inflow and flow velocities applying the aerobic Pseudomonas putida strain F1 and the denitrifying Aromatoleum aromaticum strain EbN1. We followed toluene degradation and bacterial growth by measuring toluene and oxygen concentrations and by direct cell counts. In the sediment columns, the total amount of toluene degraded by P. putida F1 increased with increasing source concentration and flow velocity, while toluene removal efficiency gradually decreased. Results point at mass transfer limitation being an important process controlling toluene biodegradation that cannot be assessed with batch experiments. We also observed a decrease in the maximum specific growth rate with increasing source concentration and flow velocity. At low toluene concentrations, the efficiencies in carbon assimilation within the flow-through systems exceeded those in the batch systems. In all column experiments the number of attached cells plateaued after an initial growth phase indicating a specific “carrying capacity” depending on contaminant concentration and flow velocity. Moreover, in all cases, cells attached to the sediment dominated over those in suspension, and toluene degradation was performed practically by attached cells only. The observed effects of varying contaminant inflow concentration and flow velocity on biodegradation could be captured by a reactive-transport model. By monitoring both attached and suspended cells we could quantify the release of new-grown cells from the sediments to the mobile aqueous phase. Studying flow velocity and contaminant concentrations as key drivers of contaminant transformation in sediment flow-through microcosms improves our system understanding and eventually the prediction of microbial biodegradation at contaminated sites. Electronic supplementary material The online version of this article (10.1007/s10532-018-9824-2) contains supplementary material, which is available to authorized users.

Continuous research in the field of water and health is important to ensure high standards of hygiene and to improve microbial risk assessment and water management. Various waterborne outbreaks induced by pathogenic bacteria, viruses and protozoa have been reported in recent decades. Pathogens derived from human and animal feces have been played frequently a key role in contaminations of freshwater. Reasons for the presence of pathogens in drinking water systems are insufficient wastewater treatment, contaminated raw water or damaged water supply systems. Numerous routes of transmission and the distribution of individual pathogens by raw water and drinking water constitute potential hazards to public health. Recently, different research activities have been initiated in Germany, which focus on the examination of pathogens in water to establish a modern microbial risk assessment according to the high-tech strategy employed by the federal government. This review article provides a compilation of the pathogens that are important in German water bodies (wastewater, surface water, groundwater, and drinking water) and includes coverage of German research on pathogens and technologies for reducing these pathogens in water, challenges to research, and recent developments in concentration and detection methods for pathogens. Finally, current knowledge gaps and ongoing research questions are highlighted.

Geothermal energy plays an increasingly important role as a renewable energy source. However, it induces temperature changes in natural thermally static groundwater ecosystems. Temperature impacts can considerably alter the groundwater chemical composition and quality, the metabolism of organisms, and, consequently, biogeochemical processes and ecosystem functions. Combining original data from current studies with a compact review of recent findings, we show that a moderate increase in groundwater/aquifer temperature [+5 to 10 Kelvin (K)] generally causes only minor changes in water chemistry, microbial biodiversity, and ecosystem function in non-contaminated and energy-poor (oligotrophic) groundwater systems. In aquifers that are contaminated with organics, nutrients, and heavy metals—typical in urban areas and at sites with intensive land use (e.g., agriculture)—and particularly at temperatures ≥30 °C as regularly reached when heat is actively stored in aquifers, significant changes in water quality and ecological patterns can result. Here most critical are the heat-related mobilization of organic matter and contaminants (e.g., arsenic), the reduction and depletion of dissolved oxygen, and consequently the consecutive shift to anaerobic redox processes that may produce toxic and corrosive products (e.g., hydrogen sulfide) and greenhouse gases (e.g., methane and carbon dioxide). Severe temperature alterations lead to a reduced biodiversity of the aquifer’s microbial community with the establishment of atypical thermophilic assemblages. Groundwater fauna, which is specifically adapted to the cold groundwater habitat, may be sensitive to thermal changes at temperature increases of only 5 K with long-term emigration or direct lethal effects. From an ecological point of view, long-lasting or reoccurring temperature alterations need to be carefully evaluated and regulated in the future. We suggest developing local and regional vulnerability concepts for the sustainable and ecologically sound use of subterranean heat and cold.

Oberflachennahe Geothermie ist eine sich rasant entwickelnde Technologie, deren Einfluss auf die Okologie unterirdischer aquatischer Lebensraume bisher nicht ausreichend untersucht wurde. Dabei sind biologische Prozesse masgeblich von der Temperatur beeinflusst. In Feld- und Laboruntersuchungen, die Temperaturveranderungen von 2 bis 45 °C umfassten, erwiesen sich insbesondere die Diversitat und Zusammensetzung von Bakteriengemeinschaften im Aquifer als sehr temperatursensitiv, wahrend mikrobielle Biomasse und Aktivitaten zusatzlich von der Nahrstoff- und Substratverfugbarkeit im Grundwasserleiter beeinflusst waren. Echte Grundwasserinvertebraten zeigten eine geringe Temperaturtoleranz gegenuber dauerhaften Temperaturerhohungen. Die durchgefuhrten Untersuchungen erlauben erste Empfehlungen fur eine okologisch nachhaltige Planung, Genehmigung, den Bau und den Betrieb von oberflachennahen Geothermieanlagen.

Healthy aquifers deliver important ecosystem services, e.g. the purification of infiltrating water and the storage of high-quality water over decades in significant quantities. The functioning of terrestrial and surface aquatic ecosystems directly depends on groundwater and vice versa. Nowadays, legislation has started to consider groundwater not only as a resource but as a living ecosystem. The assessment of ecosystems requires consideration of ecological criteria, which, so far, are not available for groundwater systems. In the framework of a project supported by the German Federal Environment Agency (UBA), a first concept for the ecological assessment of groundwater ecosystems is developed. Steps to be taken are introduced, with a strong focus on microbes as potential bioindicators. These include (1) the typology of groundwater ecosystems, (2) the derivation of natural background values, (3) the identification of potential bioindicators, and (4) the development of an assessment model. First successes and difficulties associated with these challenges, e.g. the lack of simple correlations between abiotic and biotic variables, are discussed on the basis of a data set from a local and regional aquifer in NE Germany. The need for collaboration between ecologists, hydrogeologists and geochemists, as well as the application of modern approaches such as multivariate statistics, is emphasized.

Since nearly one hundred years Traunsee experiences the import of tons of liquid and solid waste originating from salt and soda production. Today, the lake exhibits chloride concentrations of up to 170 mg L-1 and 19% of the lake floor are directly or indirectly influenced by industrial deposits (ID). Based on the comparison of several microbial parameters in unaffected, directly affected and intermediate lake bottom sediments, the ecological integrity of the lake was evaluated. The highly alkaline ID, which were exclusively colonized by microorganisms, harbored a bacterial community reduced by a factor of 10 in abundance and biomass compared to undisturbed sediment areas within the lake. The bacterial community of ID was furthermore characterized by a reduced content of actively respiring cells (INT-formazan reduction), a lower frequency of dividing cells (FDC) and a significantly reduced cell and biomass production. A 80 to 90% reduction in carbon recycling is estimated for the area exclusively covered by ID. Protists, although occasionally absent from the industrial sediments, were in general found to be less sensitive to the contaminant stress. Differences in alkalinity and dissolved organic carbon (DOC) concentrations of sediment porewaters as well as the total organic content and C/N ratios of sediments partly explain the microbial pattern observed at the various sampling sites. Possible consequences of the continuous industrial tailings for the whole lake ecosystem and the validation of the ecological integrity are discussed.

The holomictic Traunsee is the deepest and second largest lakein Austria. The special characteristic of this ecosystem isthe fact that local salt and soda industries presumably alterthe lake by the discharge of waste materials. Since thebeginning of the 20th century salt and soda works areannually releasing up to 50,000 tons of solid wastes and up to150,000 tons of chloride into Traunsee. To assess potentialeffects of these anthropogenic impacts on the bacterioplanktonthree sampling sites, influenced as well as not influenced bythe industrial discharge, were chosen for comparison andsampled monthly from November 1997 to October 1998. Bacterialabundance ranged between 0.4 to 3.0 × 106 cells ml-1 with decreasing numbers along the depth profile. Theproportion of actively respiring bacteria, i.e. INT [2-(4-iodophenyl)-3-(4-nitrophenyl)-5-phenyltetrazolium chloride]reducing cells, never exceeded 10% of DAPI (4',6'-diamidino-2-phenylindole) stained cells. Fluorescence in situ hybridization (FISH) was used to examine the seasonal and spatial distribution of dominant phylogenetic groups of thebacterioplankton. Up to 84% of bacteria detected with DAPIcould be detected via FISH applying the universal bacterialprobe EUB338. Percentages of alpha- and beta-Proteobacteriaand members of the Cytophaga-Flavobacterium cluster did notexceed 60% of DAPI-stained cells.Beta-Proteobacteriaappeared to be the most abundant group, not only in Traunsee butalso in two reference lakes, Attersee and Hallstattersee. No significant differences in any of the bacterial parameters couldbe detected between the three sampling sites and all measurementswere found in the range reported for oligotrophic lakes. The highdischarge of the Traun River, resulting in a lake water renewaltime of only one year, may diminish possible effects of industrial waste discharge in the pelagic zone.

Traunsee is a deep oligotrophic lake in Austria characterised by an artificial enrichment of chloride in the hypolimnion (up to 170 mg L-1) caused by waste disposal of soda and salt industries. Protists were collected monthly over one year, observed alive and after Quantitative Protargol Staining (ciliates) or via epifluorescence microscopy (heterotrophic flagellates). Three sites within the lake (0–40 m depths) were compared to deeper water layers from 60–160 m depths where chloride concentrations and conductivity were increased. In addition, we observed the protozooplankton of two neighbouring lakes, i.e. reference systems, during one sampling occasion. In Traunsee the abundance of ciliates was low (200–36 600 cells L-1) in contrast to high species diversity (at least 60 different species; HS = 2.6) throughout the year. The main pelagic species in terms of abundance were small oligotrichs and prostomatids like Rimostrombidium brachykinetum/hyalinum, Balanion planctonicum and Urotricha spp. throughout the investigation period. Among free-living heterotrophic flagellates, which occurred at densities of 40–2800 cells mL-1, small morphotypes dominated in the pelagial. No differences at the community level between the three lakes could be observed and pelagic ciliates and flagellates seemed not to be affected by increased chloride concentrations or by enhanced conductivity.

Linked to diverse biological processes, groundwater ecosystems deliver essential services to mankind, the most important of which is the provision of drinking water. In contrast to surface waters, ecological aspects of groundwater systems are ignored by the current European Union and national legislation. Groundwater management and protection measures refer exclusively to its good physicochemical and quantitative status. Current initiatives in developing ecologically sound integrative assessment schemes by taking groundwater fauna into account depend on the initial classification of subsurface bioregions. In a large scale survey, the regional and biogeographical distribution patterns of groundwater dwelling invertebrates were examined for many parts of Germany. Following an exploratory approach, our results underline that the distribution patterns of invertebrates in groundwater are not in accordance with any existing bioregional classification system established for surface habitats. In consequence, we propose to develope a new classification scheme for groundwater ecosystems based on stygoregions.