Alpine Karst Aquifers Research Articles

Unraveling the functioning of the vadose zone in alpine karst aquifers: New insights from a tracer test in the Migovec cave system (Julian alps, NW Slovenia)

The aquifers of alpine karst and high karst plateaus are abundant water resources. They are difficult to characterise due to their complex, partly glaciokarstic, evolution in active tectonic environments, and an unsaturated zone up to two kilometres thick. We present and discuss the results of a tracing test in the alpine karst of the Julian Alps (Slovenia), more precisely in the Migovec System, the longest cave system in Slovenia (length = 43 km, depth = 972 m). The cave extends below a mountain ridge that separates the Soča and Sava Valleys, thus forming a topographic divide between the Adriatic and Black Sea basins, which gives the test greater regional significance. In early September 2019, three kilograms of uranine were injected into a perched lake in a remote part of the system, approximately 900 metres below the plateau and 100 metres above the low water table. All known springs in the valleys on either side of the mountain were monitored by manual or instrumental sampling and a field fluorometer. Due to the unexpectedly dry season, no tracer was detected at any site for two months until a heavy rainfall event in early November. Subsequently, about 60-65 % of the tracer mass appeared within 60 hours in the Tolminka River. No tracer was detected at other sites, either becauseit was not present or because it was highly diluted. The study suggests that the lake containing the tracer is bypassed by the vadose flow and that the tracer was only mobilised during large events when the lake became part of the epihreatic flow. The linear peak flow velocity from the injection site to the Tolminka Spring was only about 1.7 m/h. However, assuming that the tracer was only mobilised by the large rain event, the velocity would be 70 m/h. The study highlights the challenges and pitfalls of water tracing in alpine karst systems and suggests ways to avoid them.

Improved understanding of dynamic water and mass budgets of high‐alpine karst systems obtained from studying a well‐defined catchment area

AbstractLarge areas of Europe, especially in the Alps, are covered by carbonate rocks and in many alpine regions, karst springs are important sources for drinking water supply. Because of their high variability and heterogeneity, the understanding of the hydrogeological functioning of karst aquifers is of particular importance for their protection and utilisation. Climate change and heavy rainfall events are major challenges in managing alpine karst aquifers which possess an enormous potential for future drinking water supply. In this study, we present research from a high‐alpine karst system in the UNESCO Biosphere Reserve Großes Walsertal in Austria, which has a clearly defined catchment and is drained by only one spring system. Results show that (a) the investigated system is a highly dynamic karst aquifer with distinct reactions to rainfall events in discharge and electrical conductivity; (b) the estimated transient atmospheric CO2 sink is about 270 t/a; (c) the calculated carbonate rock denudation rate is between 23 and 47 mm/1000a and (d) the rainfall‐discharge behaviour and the internal flow dynamics can be successfully simulated using the modelling package KarstMod. The modelling results indicate the relevance of matrix storage in determining the discharge behaviour of the spring, particularly during low‐flow periods. This research and the consequent results can contribute and initiate a better understanding and management of alpine karst aquifers considering climate change with more heavy rainfall events and also longer dry periods.

Geochemical insights into groundwater movement in alpine karst, Bear River Range, Utah, USA

Alpine karst aquifers control the availability and longevity of some water resources, but are not well understood. A conceptual model of the alpine karst aquifer system in the Bear River Range of northern Utah (USA) has been developed by geochemical analysis (major ions, δ18O, δ2H and δ13C values) of seasonal water samples from seven perennial springs, and residence-time assessment (3H and CFCs) of two low- and two high-discharge springs. All spring data can be explained by reaction paths dominated by the dissolution of calcian dolomite. The δ13C values align well with reaction paths for open-system dissolution. Saturation indices and low Ca:Mg molar ratios indicate that incongruent dissolution exerts a strong control on water–rock interactions, complicating interpretation of natural solute tracers. Values of δ18O and δ2H in springs follow the Utah meteoric water line. Snow δ18O values correlate with elevation, but not with increasing rainout distance, providing qualitative estimates of recharge elevation that generally align with previous dye-traces to five of the seven springs. Concentrations of 3H and CFCs likely are best described by binary mixing of subannual recharge with 60–65-year-old groundwater, suggesting that the alpine karst aquifer system in the Bear River Range is best represented by a double-porosity model. Subannual recharge documented by dye traces implies that caverns are the primary flowpaths to the springs, but the presence of decadal-age water may indicate that lower permeability flowpaths dominate during baseflow. No evidence was found for a longer-residing flow component, suggesting high sensitivity to future climate variability.

Spring Water of an Alpine Karst Aquifer Is Dominated by a Taxonomically Stable but Discharge-Responsive Bacterial Community.

Alpine karst aquifers are important groundwater resources for the provision of drinking water all around the world. Yet, due to difficult accessibility and long-standing methodological limitations, the microbiology of these systems has long been understudied. The aim of the present study was to investigate the structure and dynamics of bacterial communities in spring water of an alpine limestone karst aquifer (LKAS2) under different hydrological conditions (base vs. event flow). The study was based on high-throughput 16S rRNA gene amplicon sequencing, study design and sample selection were guided by hydrology and pollution microbiology data. Spanning more than 27 months, our analyses revealed a taxonomically highly stable bacterial community, comprising high proportions of yet uncultivated bacteria in the suspended bacterial community fraction. Only the three candidate phyla Parcubacteria (OD1), Gracilibacteria (GN02), Doudnabacteria (SM2F11) together with Proteobacteria and Bacteroidetes contributed between 70.0 and 88.4% of total reads throughout the investigation period. A core-community of 300 OTUs consistently contributed between 37.6 and 56.3% of total reads, further supporting the hypothesis of a high temporal stability in the bacterial community in the spring water. Nonetheless, a detectable response in the bacterial community structure of the spring water was discernible during a high-discharge event. Sequence reads affiliated to the class Flavobacteriia clearly increased from a mean proportion of 2.3% during baseflow to a maximum of 12.7% during the early phase of the studied high-discharge event, suggesting direct impacts from changing hydrological conditions on the bacterial community structure in the spring water. This was further supported by an increase in species richness (Chao1) at higher discharge. The combination of these observations allowed the identification and characterization of three different discharge classes (Q1–Q3). In conclusion, we found a taxonomically stable bacterial community prevailing in spring waters from an alpine karst aquifer over the entire study period of more than 2 years. Clear response to changing discharge conditions could be detected for particular bacterial groups, whereas the most responsive group – bacteria affiliated to the class of Flavobacteriia – might harbor potential as a valuable natural indicator of “system disturbances” in karst aquifers.

Opening the black box of spring water microbiology from alpine karst aquifers to support proactive drinking water resource management.

Over the past 15 years, pioneering interdisciplinary research has been performed on the microbiology of hydrogeologically well‐defined alpine karst springs located in the Northern Calcareous Alps (NCA) of Austria. This article gives an overview on these activities and links them to other relevant research. Results from the NCA springs and comparable sites revealed that spring water harbors abundant natural microbial communities even in aquifers with high water residence times and the absence of immediate surface influence. Apparently, hydrogeology has a strong impact on the concentration and size of the observed microbes, and total cell counts (TCC) were suggested as a useful means for spring type classification. Measurement of microbial activities at the NCA springs revealed extremely low microbial growth rates in the base flow component of the studied spring waters and indicated the importance of biofilm‐associated microbial activities in sediments and on rock surfaces. Based on genetic analysis, the autochthonous microbial endokarst community (AMEC) versus transient microbial endokarst community (TMEC) concept was proposed for the NCA springs, and further details within this overview article are given to prompt its future evaluation. In this regard, it is well known that during high‐discharge situations, surface‐associated microbes and nutrients such as from soil habitats or human settlements—potentially containing fecal‐associated pathogens as the most critical water‐quality hazard—may be rapidly flushed into vulnerable karst aquifers. In this context, a framework for the comprehensive analysis of microbial pollution has been proposed for the NCA springs to support the sustainable management of drinking water safety in accordance with recent World Health Organization guidelines. Near‐real‐time online water quality monitoring, microbial source tracking (MST) and MST‐guided quantitative microbial‐risk assessment (QMRA) are examples of the proposed analytical tools. In this context, this overview article also provides a short introduction to recently emerging methodologies in microbiological diagnostics to support reading for the practitioner. Finally, the article highlights future research and development needs.This article is categorized under: 1Engineering Water > Water, Health, and Sanitation2Science of Water > Water Extremes3Water and Life > Nature of Freshwater Ecosystems

KARSYS hydrogeological 3D modeling of alpine karst aquifers developed in geologically complex areas: Picos de Europa National Park (Spain)

Karst aquifers are valuable groundwater resources whose management requires the use of functioning hydrogeological models. The KARSYS approach provides an explicit 3D conceptual model of the geometry and the functioning of karst aquifers that has been successfully applied in Swiss and Slovenian aquifers. In this work, KARSYS is applied in a complex geological area: the Picos de Europa National Park (Spain). The hydrogeological 3D model (500 km2) shows an alpine karst aquifer compartmentalized into 32 groundwater bodies dammed up by subvertical barriers creating elevated saturated zones (water tables at 1153 m asl) and lower ones (water tables at 145 m asl). The recharge is through 18 spring catchment areas. The groundwater flows to the saturated zones pass through vertical to inclined trajectories, and phreatic flows are oriented toward NW, NE and N. KARSYS can be applied to any geologically complex area at a regional scale, although the geological structure should be simplified and the precision in some places is low. Nevertheless, KARSYS helps to identify the hydrogeological behavior of karst areas and is a useful guide for future hydrogeological researches.

The spectral absorption coefficient at 254 nm as a real-time early warning proxy for detecting faecal pollution events at alpine karst water resources.

Because spring water quality from alpine karst aquifers can change very rapidly during event situations, water abstraction management has to be performed in near real-time. Four summer events (2005-2008) at alpine karst springs were investigated in detail in order to evaluate the spectral absorption coefficient at 254 nm (SAC254) as a real-time early warning proxy for faecal pollution. For the investigation Low-Earth-Orbit (LEO) Satellite-based data communication between portable hydrometeorological measuring stations and an automated microbiological sampling device was used. The method for event triggered microbial sampling and analyzing was already established and described in a previous paper. Data analysis including on-line event characterisation (i.e. precipitation, discharge, turbidity, SAC254) and comprehensive E. coli determination (n>800) indicated that SAC254 is a useful early warning proxy. Irrespective of the studied event situations SAC254 always increased 3 to 6 hours earlier than the onset of faecal pollution, featuring different correlation phases. Furthermore, it seems also possible to use SAC254 as a real-time proxy parameter for estimating the extent of faecal pollution after establishing specific spring and event-type calibrations that take into consideration the variability of the occurrence and the transferability of faecal material It should be highlighted that diffuse faecal pollution from wildlife and live stock sources was responsible for spring water contamination at the investigated catchments. In this respect, the SAC254 can also provide useful information to support microbial source tracking efforts where different situations of infiltration have to be investigated.

Heterotrophic prokaryotic production in ultraoligotrophic alpine karst aquifers and ecological implications

Spring waters from alpine karst aquifers are important drinking water resources. To investigate in situ heterotrophic prokaryotic production and its controlling factors, two different alpine karst springs were studied over two annual cycles. Heterotrophic production in spring water, as determined by [(3)H]leucine incorporation, was extremely low ranging from 0.06 to 6.83 pmol C L(-1) h(-1) (DKAS1, dolomitic-karst-spring) and from 0.50 to 75.6 pmol C L(-1) h(-1) (LKAS2, limestone-karst-spring). Microautoradiography combined with catalyzed reporter deposition-FISH showed that only about 7% of the picoplankton community took up [(3)H]leucine, resulting in generation times of 3-684 days. Principal component analysis, applying hydrological, chemical and biological parameters demonstrated that planktonic heterotrophic production in LKAS2 was governed by the respective hydrological conditions, whereas variations in DKAS1 changed seemingly independent from discharge. Measurements in sediments recovered from LKAS2, DKAS1 and similar alpine karst aquifers (n=12) revealed a 10(6)-fold higher heterotrophic production (average 19 micromol C dm(-3) h(-1)) with significantly lower generation times as compared with the planktonic fraction, highlighting the potential of surface-associated communities to add to self-purification processes. Estimates of the microbially mediated CO(2) in this compartment indicated a possible contribution to karstification.

Prokaryotic community analysis with CARD-FISH in comparison with FISH in ultra-oligotrophic ground- and drinking water

We compared the applicability of catalysed reporter deposition fluorescence in situ hybridization (CARD-FISH) and FISH to enumerate prokaryotic populations in ultra-oligotrophic alpine groundwaters and bottled mineral water Fluorescent oligonucleotide probes EUB338 and EUB338mix (EUB338/EUB338-II/EUB338-III) were used to enumerate bacteria and probes EURY806 and CREN537 for Euryarchaea and Crenarchaea, respectively. Improved detection of Planctomycetales by probe EUB338-II was tested using a different permeabilization step (proteinase K instead of lysozyme). Total detection efficiency of cells in spring water of four different alpine karst aquifers was on average 83% for CARD-FISH and only 15% for FISH. Applying CARD-FISH on bottled natural mineral waters resulted in an average total hybridization efficiency of 89%, with 78% (range 77-96%) bacteria and 11% (range 3-22%) identified as Archaea. CARD-FISH resulted in substantially higher recovery efficiency than FISH. Hence, CARD-FISH appears very suitable for the enumeration of specific prokaryotic groups in ground- and drinking water. This study represents the first evaluation of CARD-FISH on ultra-oligotrophic ground- and drinking water. Results are relevant for basic research and drinking water distributors. Archaea can comprise a significant fraction of the prokaryotic community in bottled mineral water.

Bacterial dynamics in spring water of alpine karst aquifers indicates the presence of stable autochthonous microbial endokarst communities

Spring water of two alpine karst aquifers differing in hydrogeology but of nearby catchments were investigated for their bacterial population dynamics. Dolomite karst aquifer spring 1 (DKAS 1) represents a dolomitic-limestone karst aquifer spring showing high average water residence time and relative constant flow. Limestone karst aquifer spring 2 (LKAS 2) constitutes a typical limestone karst aquifer spring with a dynamic hydrological regime and discharge. Dolomite karst aquifer spring 1 yielded constantly lower cell counts and biomasses (median of 15 x 10(6) cells l(-1) and 0.22 microg C l(-1)) as the LKAS 2 (median of 63 x 10(6) cells l(-1) and 1.1 microg C l(-1)) and distribution of morphotypes and mean cell volumes was also different between the considered systems, indicating the influence of hydrogeology on microbial spring water quality. Molecular bacterial V3 16S-rDNA profiles revealed remarkable constancy within each spring water throughout the investigation period. Time course analysis of a flood event in LKAS 2 further supported the trend of the temporal constancy of the microbial community. Except for one case, retrieval of partial and full length 16S rDNA gene sequences from the relative constant DKAS 1 revealed similarities to presently known sequences between 80% to 96%, supporting the discreteness of the microbial populations. The gathered results provide first evidence for the presence of autochthonous microbial endokarst communities (AMEC). Recovery of AMEC may be considered of relevance for the understanding of alpine karst aquifer biogeochemistry and ecology, which is of interest as many alpine and mountainous karst springs are important water resources throughout the world.