Alpine Karst Research Articles

Differences in aquatic microcrustacean assemblages between temporary and perennial springs of an alpine karstic aquifer

Microcrustacean (Copepoda, Ostracoda) assemblages were investigated at the interface of the vadose and phreatic zones in the alpine karstic aquifer from the Julian Alps in Slovenia (SE Europe). Two temporary and one perennial karstic outlets were sampled by filtering the water several times over 2 years. Concurrently, benthos from the mouth of a perennial spring and from an adjacent spring brook were collected. Altogether 24 microcrustacean species were recorded. The spatial and temporal variation in drift densities and species composition was high indicating complex groundwater hydrological pathways being dependent on precipitation regime. Non-metric Multidimensional Scaling (NMDS) clearly separated drift samples from temporary springs and other sample groups (drift in perennial spring, spring mouth and spring brook benthos). ANOSIM revealed statistically significant differences between all sample groups (Diacyclops zschokkei, Elaphoidella phreatica and Mixtacandona sp. B contributed over 50 % to the observed differences among sample groups. Three species (Nitocrella sp., Speocyclops infernus, Lessinocamptus pivai), known to be typical epikarst species, were collected only in the drift from one temporary spring (T2). Mao Tau species accumulation curves did not reach asymptote for the drift from temporary springs, but did for the drift from perennial spring, and for the spring mouth and the spring brook benthos. The results on drift composition indicated the variation in the origin of the water discharging at the interface of vadoze and phreatic zones depending greatly on water level conditions, while the drift densities were higher in the water presumably discharging from phreatic zone (perennial spring and temporary springs during low water levels). Julian Alps; alpine karst; groundwater; drift; Copepoda; Ostracoda

Dynamics of natural prokaryotes, viruses, and heterotrophic nanoflagellates in alpine karstic groundwater

Seasonal dynamics of naturally occurring prokaryotes, viruses, and heterotrophic nanoflagellates in two hydro-geologically contrasting alpine karst springs were monitored over three annual cycles. To our knowledge, this study is the first to shed light on the occurrence and possible interrelationships between these three groups in karstic groundwater. Hydrological and microbiological standard indicators were recovered simultaneously in order to estimate surface influence, especially during rainfall events. Data revealed a strong dependence of the microbial communities on the prevailing hydrological situation. Prokaryotic numbers averaged 5.1 × 107 and 1.3 × 107 cells L−1, and heterotrophic nanoflagellate abundance averaged 1.1 × 104 and 3 × 103 cells L−1 in the limestone spring type (LKAS2) and the dolomitic spring type (DKAS1), respectively. Viral abundance in LKAS2 and DKAS1 averaged 9.4 × 108 and 1.1 × 108 viruses L−1. Unlike in DKAS1, the dynamic spring type LKAS2 revealed a clear difference between base flow and high discharge conditions. The virus-to-prokaryotes ratio was generally lower by a factor of 2–3, at higher average water residence times. Furthermore, the high prokaryotes-to-heterotrophic nanoflagellate ratios, namely about 4700 and 5400 for LKAS2 and DKAS1, respectively, pointed toward an uncoupling of these two groups in the planktonic fraction of alpine karstic aquifers.Seasonal dynamics of naturally occurring prokaryotes, viruses and heterotrophic nanoflagellates in two hydro-geologically contrasting alpine karst springs were monitored over three annual cycles. Data revealed a strong dependence of the microbial communities on the prevailing hydrological situation.

Structural–tectonic controls and geomorphology of the karst corridors in alpine limestone ridges: Southern Carpathians, Romania

The relationship between surface karst development and the geological frame is widely acknowledged in the study of karst landforms. It is of considerable interest especially in alpine environments (e.g. Alpine–Dinaric–Carpathian orogenic system). Karst corridors are generally known as kluftkarren or bogaz and form by solution of limestone along a lithoclase network. The Vânturariţa-Buila Massif (Carpathians, Romania) is a typical alpine karst ridge and a former carbonate platform of Upper Jurassic age in which geologically-controlled karst features have been developing over a geologic timescale. Field research and mapping were useful in extracting geologic features. Joint- and structure-controlled karst corridors are common in the upper section of the mountain, between 1600 and 1850m. First, a complex system of lithoclases (fissures, joints and faults) occurred; then, surface runoff or meltwater solutionally enlarged them. Tension fractures strike in a northeast–southwest direction, parallel to homoclinal limestone layers. The exposed fault walls often preserve draperies and speleothem remnants. Further, statistical analysis of joint, fault and bogaz orientations has shown the close relation between the three datasets, and morphometric analysis centered only on the karst corridor system. Results derived from the statistical analysis of orientation data show that there is a strong preferred orientation of the bogaz or bogaz-like forms along the directional faults and that they commonly develop in extensional (tectonically active) environments. Additional features typical to fluviokarst are also present — subterranean connections between the karst corridors and the headwalls of the pocket valleys, generating headward recession both by continuous sapping of karst springs at the headwall base followed by collapses. An extremely poor surface drainage network developed in the upper pavement facing southeast, compared to that on the middle and lower sides.

Last Glacial warm events on Mount Hermon: the southern extension of the Alpine karst range of the east Mediterranean

This study focuses on warm Last Glacial episodes in the southernmost extension of the Alpine karst range of the Eastern Mediterranean (Levant) region through the study speleothems in Mizpe Shelagim Cave, located in Mt. Hermon. The Alpine karst range extends from Turkey through Syria and Lebanon, reaching its southern limit in Mt. Hermon at an elevation of more than 2000 m. Under present-day conditions, southern Mt. Hermon receives 1000–2000 mm precipitation, mostly as snow, that originates in the Eastern Mediterranean Sea. Speleothems deposition in this high altitude region was continuous during interglacials, but during the Last Glacial growth only occurred when average annual temperatures exceeded ∼3 °C as inferred from the study of speleothem fluid inclusions. Warming episodes occurred at: ∼65 ka, ∼56 ka, 54.5 ka, ∼52.5–51 ka, ∼49 ka, ∼42 ka, and ∼36 ka and are coincident with maximum insolation at 65 °N. The main depositional period from ∼56 ka to 51 ka coincides with Dansgaard–Oeschger interstadial 15 and 14, and warming in the northeastern basin of the Mediterranean Sea. Warming in the southern Alpine karst range of the Eastern Mediterranean was manifested by vegetation development, together with significant snow melting that resulted in the drainage of large amount of water to the Dead Sea Rift Valley.

Temperature-driven meltwater production and hydrochemical variations at a glaciated alpine karst aquifer: implication for the atmospheric CO2 sink under global warming

About two hydrological years of continuous data of discharge, temperature, electrical conductivity and pH have been recorded at the Glarey spring in the Tsanfleuron glaciated karst area in the Swiss Alps, to understand how glaciated karst aquifer systems respond hydrochemically to diurnal and seasonal recharge variations, and how calcite dissolution by glacial meltwater contributes to the atmospheric CO2 sink. A thermodynamic model was used to link the continuous data to monthly water quality data allowing the calculation of CO2 partial pressures and calcite saturation indexes. The results show diurnal and seasonal hydrochemical variations controlled chiefly by air temperature, the latter influencing karst aquifer recharge by ice and snowmelt. Karst process-related atmospheric CO2 sinks were more than four times higher in the melting season than those in the freezing season. This finding has implication for understanding the atmospheric CO2 sink in glaciated carbonate rock terrains: the carbon sink will increase with increasing runoff caused by global warming, i.e., carbonate weathering provides a negative feedback for anthropogenic CO2 release. However, this is a transient regulation effect that is most efficient when glacial meltwater production is highest, which in turn depends on the future climatic evolution.

Effect of Alpine karst on the hydrology of the Berchtesgadener Ache basin: a comprehensive summary of karst research in the Berchtesgaden Alps

The Berchtesgaden Alps are situated in the Northern Limestone Alps, characterized by individual mountain plateaus and ridges in close proximity to each other, intersected by valleys, with an altitudinal gradient of 2 100 meters. The limestone has been exposed to dissolution processes since the Cretaceous, leading to a massive karstified aquifer with a wide range of subsurface flow channels. There are hundreds of springs as groundwater recharge locations, feeding the seven rivers of the region that contribute to the Danube watershed. Several studies were conducted to examine the hydro-geological conditions and the resulting groundwater flow. This paper aims to evaluate and summarize research in the basin describing groundwater flow to identify the main drainage direction, travel times, spring dynamics and possible subsurface redistribution in the individual mountain ranges and the whole basin. To this end, we evaluate several tracer experiments, two isotope studies and a spring database. The tracer experiments are generating knowledge about flow directions in the individual mountain ranges, groundwater redistribution, water storage and mean travel times. Five experiments prove increased groundwater flow remaining within a valley and four experiments indicate groundwater redistribution through mountain ranges. The isotope studies indicate potential water storage in the Wimbach valley of an estimated 100 x 106 to 470 x 106 m3 and mean transit times of about four years. The analysis of the spring database focuses on locations and discharge classification. Overall, there are 289 springs recorded in the spring database, distributed from 600 to over 2 000 m altitude, with major springs at the northern base of the mountains Hochkalter, Watzmann and at the north shore of lake Königssee. The conclusion summarizes the effect of the karst aquifer on the hydrology of the region. The outlook introduces current research within the area and the distributed water balance modelling.

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.

Fold and fault control on the drainage pattern of a double-karst-aquifer system, Winterstaude, Austrian Alps

Lithostratigraphy and geologic structures are major controls on groundwater flow in alpine karst systems. Understanding these factors is important for the delimitation of drinking water pro­tection zones. The Winterstaude mountain chain, western Aus­tria, belongs to the Helvetic nappes and consists of Cretaceous sedimentary rocks, including two karstifiable formations: Örfla and Schrattenkalk Limestone (lower and upper karst aquifer), separated by 60 m of marl. Strata are folded and cut by faults withdisplacements of 40–70 m. Folded carbonate rocks con­tinue below the alluvial valley floor so that the karst system can be subdivided in shallow and deep phreatic zones. This area is suitable for studying the combined influence of folds and faults on groundwater flow in a double-aquifer system. A multi-trac­er test withseven injections aimed at characterising hydraulic connections and linear flow velocities. Results show that (i) plunging synclines form the main drainage pathways in the up­per karst aquifer, withmaximum linear velocities of 91 m/h, while anticlines act as water divides; (ii) recharge into the lower aquifer, whichforms the central ridge of the mountain chain, contributes to springs discharging from the upper aquifer near the foot of the mountain (local flow systems); (iii) the two aq­uifers are hydraulically connected, presumably via faults, be­cause their displacements are in the same order of magnitude as the thickness of the intervening marl; (iv) flow in the upper aquifer continues below the valley floor toward the river, withmaximum velocities of 22 m/h(intermediate flow system).

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.

Wastewater from a mountain village treated with a constructed wetland

The “Asiago-Sette Comuni” plateau (Italy) is the main contributing zone of an alpine karst aquifer supplying a multi-aquifer system in the Central Veneto plain exploited for domestic, industrial and agricultural uses. Some of the communities in the upland are connected to public sewers discharging to treatment works. Conversely, several small isolated communities, farms and tourist resorts discharge to short sewers ending in septic tanks, whose overflows feed local streams, which are most of the time dry because waters infiltrate the karst bedrock and reach the plain aquifer within 24–50 h. The two aquifers are highly vulnerable to contamination, due to fast water transport with limited attenuation processes. The aim of the present research is to evaluate the efficiency of a small subsurface constructed wetland system in improving wastewater from a mountain village. In the first 16 months of operation, removal capacity of the experimental system averaged more than 98% of pathogenic organisms, more than 90% of TSS, COD and, BOD5, about 50% of N-NH+4, N-NO-3, N-total, Cl-, SO2-4 and PO3-4, even in the cold season. The vegetal cover is good and there are no operational problems.

Multiple isotope approach to the determination of the natural attenuation potential of a high-alpine karst system

Summary 3 H, δ 18 O and δ 2 H measurements on groundwater and chemical and isotope analyses on groundwater sulfate were used to determine the origin and mean transit times of groundwater and the sources affecting groundwater sulfate in a high-alpine karstic catchment area in southern Germany. Modelling results using a lumped parameter approach yielded mean transit times of water between 4 and 12 years for different karst springs. However, results obtained from δ 18 O and δ 2 H measurements on groundwater showed that a calculated mean transit time of 12 years for groundwater flow in one karst system can only be explained by mixing of young and old tritium-free ice and snowmelt water. Groundwater sulfate characterized by δ 34 S values of around 20‰ and δ 18 O values of ca. 12‰ in concert with sulfate concentrations of approximately 11 mg/L are probably affected by evaporites. In contrast, δ 34 S values of around 6‰ and δ 18 O values up to 9.4‰ in concert with sulfate concentrations between 1 and 7 mg/L mainly derive from atmospheric deposition. However, a δ 34 S value of −7.3‰ identified for one of the karst springs demonstrates that the oxidation of sulfide-containing minerals must be considered as an additional source, affecting sulfate concentrations in groundwater. The estimated transit time distribution of groundwater shows relatively high mean transit times between 2 and 5 years with a low contribution of very short transit times of less than 1 year. The high contribution of long mean transit times of groundwater in the alpine karst system, which represents an important drinking water resource, is an important function for drinking water supplies.

Karst morphology and groundwater vulnerability of high alpine karst plateaus

High alpine karst plateaus are recharge areas for major drinking water resources in the Alps and many other regions. Well-established methods for the vulnerability mapping of groundwater to contamination have not been applied to such areas yet. The paper characterises this karst type and shows that two common vulnerability assessment methods (COP and PI) classify most of the areas with high vulnerability classes. In the test site on the Hochschwab plateau (Northern Calcareous Alps, Austria), overlying layers are mostly absent, not protective or even enhance point recharge, where they have aquiclude character. The COP method classifies 82% of the area as highly or extremely vulnerable. The resulting maps are reasonable, but do not differentiate vulnerabilities to the extent that the results can be used for protective measures. An extension for the upper end of the vulnerability scale is presented that allows identifying ultra vulnerable areas. The proposed enhancement of the conventional approach points out that infiltration conditions are of key importance for vulnerability. The method accounts for karst genetical and hydrologic processes using qualitative and quantitative properties of karst depressions and sinking streams including parameters calculated from digital elevations models. The method is tested on the Hochschwab plateau where 1.7% of the area is delineated as ultra vulnerable. This differentiation could not be reached by the COP and PI methods. The resulting vulnerability map highlights spots of maximum vulnerability and the combination with a hazard map enables protective measures for a manageable area and number of sites.

Microbiological monitoring and automated event sampling at karst springs using LEO-satellites.

Data communication via Low-Earth-Orbit (LEO) Satellites between portable hydrometeorological measuring stations is the backbone of our system. This networking allows automated event sampling with short time increments also for E. coli field analysis. All activities of the course of the event-sampling can be observed on an internet platform based on a Linux-Server. Conventionally taken samples compared with the auto-sampling procedure revealed corresponding results and were in agreement with the ISO 9308-1 reference method. E. coli concentrations were individually corrected by event specific inactivation coefficients (0.10-0.14 day(-1)), compensating losses due to sample storage at spring temperature in the auto sampler.Two large summer events in 2005/2006 at an important alpine karst spring (LKAS2) were monitored including detailed analysis of E. coli dynamics (n = 271) together with comprehensive hydrological characterisations. High-resolution time series demonstrated a sudden increase of E. coli concentrations in spring water (approximately 2 log10 units) with a specific time delay after the beginning of the event. Statistical analysis suggested the spectral absorption coefficient measured at 254 nm (SAC254) as an early warning surrogate for real time monitoring of faecal input. Together with the LEO-satellite based system it is a helpful tool for early-warning systems in the field of drinking water protection.

Are Cambisols in Alpine Karst Autochthonous or Eolian in Origin?

ABSTRACTThis paper deals with a two-year study of karst soils and eolian dust deposition on the Reiteralpe paleosurface (1600 to 2000 m), Northern Calcareous Alps, Germany. Thirty soil profiles of Cambisols developed on Triassic and Cretaceous limestones are investigated. Dust samples collected periodically on snow cover provide influx rates and a seasonal dust record. Samples of soils, insoluble bedrock residue, and dust are characterized by pedological (e.g. grain size) and mineralogical (e.g. heavy minerals) data.The data indicate that limestone subtypes with varying crack-fillings (ferrous clays) determine the colors and amounts of residue. Both correlate positively with the thickness of reddish Bo-horizons, supporting their autochthonous character. The topsoils, however, show substantial eolian addition (silt, fine sand, mica). In winter, far-traveled red Saharan dust without organic material prevails, carried to the area by strong foehn winds. In early springtime, browner dust (organic rich) is observed which contains periglacial silicate-rich detritus from regional sources such as the Crystalline Austrian Alps.The measured winter dust influx rates are 4.8 cm per 10,000 years (related to 210 winter days). This is more than twice the calculated thickness of Holocene residue accumulation out of limestone weathering (2.3 cm per 10,000 years, related to 210 winter days), which indicates that eolian dust is a major contributor to alpine karst soil development.

Terrestrial gastropods (Mollusca, Gastropoda) of the Bulgarian part of the Alibotush Mts.

This work presents results of two years collecting efforts within the project “The role of the alpine karst area in Bulgaria as reservoir of species diversity”. It summarizes distribution data of 44 terrestrial gastropods from the Bulgarian part of Alibotush Mts. Twenty-seven species are newly recorded from the Alibotush Mts., 13 were confirmed, while 4 species, previously known from the literature, were not found. In the gastropod fauna of Alibotush Mts. predominate species from Mediterranean zoogeographic complex. A large part of them is endemic species, and this demonstrates the high conservation value of large limestone areas in respect of terrestrial gastropods.

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.

Temporal variation of chemical and isotopic signals in major discharges of an alpine karst aquifer in Turkey: implications with respect to response of karst aquifers to recharge

Proper management of karst aquifers requires a better understanding of flow and transport mechanisms in these systems. Flow in karst aquifers is inherently very complex due to the non-linear and non-stationary relationship between recharge and discharge. Information on this relationship has been acquired for a large (1,000 km2), mountainous (>3,500 m asl) karst aquifer with a deep unsaturated zone (>2,000 m) in the Aladaglar mountain range of south-central Turkey. All major discharges from the aquifer, which drain almost all the recharge, have been observed periodically for specific electrical conductivity, tritium and oxygen-18 variations during a period of 12 months. Observations reveal that the system’s response to recharge depends strongly on the competition between the infiltration and drainage velocities. These velocities, which are controlled by variables such as the time of precipitation, time of infiltration, intensity, and continuity of recharge, determine the degree of dominance of different types of flow mechanisms in the aquifer. Bypass, well-mixed and piston flow mechanisms are used to explain the response of the aquifer to the spatio-temporal variations in recharge. It appears that the aquifer switches among these flow mechanisms depending on the prevailing recharge mode and the competition between infiltration and drainage velocities.

Intrinsic vulnerability assessment of Sette Comuni Plateau aquifer (Veneto Region, Italy)

Maps illustrating the different degrees of vulnerability within a given area are integral to environmental protection and management policies. The assessment of the intrinsic vulnerability of karst areas is difficult since the type and stage of karst development and the related underground discharge behavior are difficult to determine and quantify. Geographic Information Systems techniques are applied to the evaluation of the vulnerability of an aquifer in the alpine karst area of the Sette Comuni Plateau, in the Veneto Region of northern Italy. The water resources of the studied aquifer are of particular importance to the local communities. This aquifer must therefore be protected from both inappropriate use as well as possible pollution. The SINTACS and SINTACS P RO K ARST vulnerability assessment methods have been utilized here to create the vulnerability map. SINTACS P RO K ARST is an adaptation of the parametric managerial model (SINTACS) to karst hydrostructures. The vulnerability map reveals vast zones (81% of the analyzed areas) with a high degree of vulnerability. The presence of well-developed karst structures in these highly vulnerable areas facilitate water percolation, thereby enhancing the groundwater vulnerability risk. Only 1.5 of the studied aquifer have extremely high-vulnerability levels, however these areas include all of the major springs utilized for human consumption. This vulnerability map of the Sette Comuni Plateau aquifer is an indispensable tool for both the effective management of water resources and as support to environmental planning in the Sette Comuni Plateau area.

Steady‐ and unsteady‐state lumped parameter modelling of tritium and chlorofluorocarbons transport: hypothetical analyses and application to an alpine karst aquifer

AbstractDetermination of a groundwater's mean residence time with the aid of environmental tracers is common in hydrogeology. Many of the lumped parameter (LP) applications used for this purpose have been based on steady‐state models. However, the results may be misleading if a steady LP model is used to simulate the environmental tracer transport in an unsteady aquifer. To test this hypothesis, the results of steady and unsteady versions of several LP models were evaluated theoretically and in an alpine karst aquifer case by using tritium, oxygen‐18 and chlorofluorocarbons (CFCs). The results reveal that the mean residence times obtained may be significantly different between the steady and unsteady versions of the same model. For the karst aquifer investigated, a serially connected exponential and a plug flow model were run under unsteady conditions. It is shown that outflux calibration with an unsteady model provides a firm basis in evaluating the results of models. An outflux‐calibrated unsteady model predicted reasonably the observed series of water isotopes. The calibrated model's CFCs output overpredicts the observed concentrations, probably because of the time lag in the unsaturated zone of the alpine karst aquifer. Copyright © 2005 John Wiley & Sons, Ltd.

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.