Abstract: The use of groundwater as a drinking water resource requires knowledge of its microbiological status and quality. In contrast to conventional microbiological monitoring of groundwater, the present study not only considers faecal indicator bacteria, but also covers a wide spectrum of microorganisms, including bacterial pathogens (verotoxin-producing E.coli, Campylobacter spp. and Salmonella spp., as well as Pseudomonas aeruginosa), human enteric viruses (norovirus, enterovirus, rotavirus and adenovirus) and parasitic protozoa (Cryptosporidium oocysts and Giardia cysts). Samples collected at karst sites of the Swiss National Groundwater Monitoring network revealed the presence of a large diversity of microorganisms of faecal origin, the occurrence of which could be linked to specific hydrogeological settings and situations. The findings represent a âsnapshotâ of the microbiological status at the monitoring sites and provide a national overview of the types and presence of microorganisms in Swiss karst groundwater. In addition to microbiological parameters related to faecal contamination, the overall bacterial load in groundwater was assessed using cell density measurements (i.e. total cell count), which yielded typical ranges for this ecological parameter. The study highlights differential vulnerability of karst groundwater to microbiological contamination, as well as its relationship with the microbial biocenoses, i.e. the interplay of allochthonous and autochthonous microbial components. On the basis of this data set, a microbiological classification of karst aquifers is proposed and discussed with respect to spring dynamics and vulnerability.
Abstract: Mobile particles play crucial roles for contaminant transport in karst aquifers, but few studies have investigated the relationships between sediment dynamics and contaminants. This is partly due to the difficulty in monitoring suspended particles: Turbidity is easy to measure but does not deliver detailed information on the size and type of particles; mineralogical laboratory analyses are laborious and not suitable for continuous monitoring. A portable particle counter was used for the study presented here. The instrument delivers time-series of particle-size distribution (PSD), i.e. the number and diameter of suspended particles, grouped into different size-classes ranging from 0.9 to 139 µm. The test site is a karst system near the city of Yverdon-les-Bains, Switzerland. A swallow hole draining agricultural land is connected to two karst springs, 4.8 and 6.3 km away, which are occasionally contaminated by faecal bacteria at highly variable levels. Turbidity alone turned out not to be a reliable indicator for microbial contamination. To obtain more insight into bacteria and particle transport towards the springs, a comprehensive research program was carried out, including tracer tests and monitoring of PSD, turbidity, total organic carbon (TOC), faecal bacteria (E. coli) and various hydrologic and physicochemical parameters. Results show that there are two types of turbidity: A primary turbidity signal occurs shortly after rainfall during the rising limb of the hydrograph; a secondary signal typically occurs during spring flow recession. The first signal is explained by remobilization of conduit sediments due to a hydraulic pressure pulse (autochthonous or pulse-through turbidity). The second peak indicates the arrival of water from the swallow hole, often together with TOC and faecal bacteria (allochthonous or flow-through turbidity). PSD analyses revealed that autochthonous turbidity is composed of a broad mixture of fine and large particles, while allochthonous turbidity predominantly consists of very fine particles. This is explained by sedimentation of larger particles between the swallow hole and the springs. During allochthonous turbidity periods, very good correlation between the finest particles (0.9â1.5 micro-m) and E. coli was found (R2 = 0.93). The relative increase of fine particles can consequently be used as an "early-warning parameter" for microbial contamination of karst spring water. Further applicability and limitations of this approach are also discussed.
Abstract: Die Nutzung der Ressource Grundwasser für die Trinkwasserversorgung erfordert Kenntnisse über deren mikrobiologischen Zustand. Untersuchungen an 50 Messstellen der Nationalen Grundwasserbeobachtung NAQUA erlauben einen ersten landesweiten Ãberblick zu Art und Auftreten von Mikroorganismen im Grundwasser der Schweiz. An einzelnen Messstellen wurden Bakterien, Viren und Protozoen festgestellt, allerdings ohne den Nachweis von Organismen mit infektiösen Wirkung. Art und Häufigkeit des Auftretens lassen sich mit dem Grundwasserleitertyp in Beziehung setzen, wobei Grundwasservorkommen in Lockergesteinen am wenigsten und Karst-Grundwasserleiter am meisten betroffen sind. Die Ergebnisse stellen eine Momentaufnahme des mikrobiologischen Zustands des Grundwassers an den beprobten Messstellen dar und erfassen dabei typische Situationen hinsichtlich Hydrogeologie und Bodennutzung sowie die wichtigsten Grundwasservorkommen des Landes.
Abstract: This paper discusses the roles of sediments and particles/colloids for contaminant attenuation and transport in karst groundwater and presents experimental results concerning the relations between particles and microbial contamination in a karst system in Switzerland. The test site consists of a swallow hole draining agricultural land, connected to two springs, one of which is used for water supply. A portable particle counter was used to obtain detailed time-series of Particle-Size Distribution (PSD) in spring water, along with continuous monitoring of turbidity, total organic carbon (TOC) and other parameters, and analyses of faecal bacteria (E. coli). Two types of turbidity were observed at the springs following intense rainfall: A primary signal occurred during increasing discharge and is explained by remobilisation of intrakarstic sediments due to a hydraulic pulse (autochthonous or pulse-through turbidity). A secondary turbidity is typically observed after several days and indicates the arrival of water from the swallow hole (allochthonous or flow-through turbidity), often associated with high levels of TOC, nitrate and E. coli. PSD analyses allowed further differentiation: The primary turbidity consists of a mixture of different particles sizes, while the secondary signal predominantly consists of very fine particles, because larger particles are removed by sedimentation between the swallow hole and the springs. There is good correlation between E. coli and 0.9â1.5 micro-m flow-through particles. A relative increase of very fine particles can thus be used as an "early-warning system" for microbial contamination. PSD monitoring could also help to study other problems in karst environments, not only water contamination, but also soil erosion.
Abstract: Recharge and contamination of karst aquifers often occurs via the unsaturated zone, but the functioning of this zone has not yet been fully understood. Therefore, irrigation and tracer experiments, along with monitoring of rainfall events, were used to examine water percolation and the transport of solutes, particles and fecal bacteria between the land surface and a water outlet into a shallow cave. Monitored parameters included discharge, electrical conductivity, temperature, organic carbon, turbidity, particle-size distribution (PSD), fecal indicator bacteria, chloride, bromide and uranine. Percolation following rainfall or irrigation can be subdivided into a lag phase (no response at the outlet), a piston-flow phase (release of epikarst storage water by pressure transfer) and a mixed-flow phase (increasing contribution of freshly infiltrated water), starting between 20 min and a few hours after the start of recharge event. Concerning particle and bacteria transport, results demonstrate that (i) a first turbidity signal occurs during increasing discharge due to remobilization of particles from fractures (pulse-through turbidity); (ii) a second turbidity signal is caused by direct particle transfer from the soil (flow-through turbidity), often accompanied by high levels of fecal indicator bacteria, up to 17,000 E. coli/100 mL; (iii) PSD allows differentiation between the two types of turbidity. A relative increase of fine particles (0.9 â 1.5 micro-m) coincides with microbial contamination. These findings help to quantify water storage and percolation in the epikarst and to better understand contaminant transport and attenuation. The use of PSD as âearly-warning parameterâ for microbial contamination in karst waters is confirmed.
Abstract: The structure, diversity and dynamics of microbial communities from a swallow hole draining agricultural land and two connected karst springs (Switzerland) were studied using molecular microbiological methods and related to hydrological and physicochemical parameters. Storm responses and an annual hydrological cycle were monitored to determine the short- and long-term variability, respectively, of bacterial communities. Statistical analysis of bacterial genetic fingerprints (16S rDNA PCR-DGGE) of spring water samples revealed several clusters that corresponded well with different levels of the allochthonous swallow hole contribution. Microbial communities in spring water samples highly affected by the swallow hole showed low similarities among them, reflecting the high temporal variability of the bacterial communities infiltrating at the swallow hole. Conversely, high similarities among samples with low allochthonous contribution provided evidence for a stable autochthonous endokarst microbial community. Three spring samples, representative for low, medium and high swallow hole contribution, were analysed by cloning/sequencing in order to identify the major bacterial groups in the communities. The autochthonous endokarst microbial community was mainly characterized of δ-Proteobacteria, Acidobacteria and Nitrospira species. A high percentage of unknown sequences suggested further that many karst aquifer bacteria are still undiscovered. Finally, the potential use of groundwater biomonitoring using microbial communities is discussed.
Abstract: This article presents an introduction to the fundamentals of tracing techniques and their application in cave and karst environments, illustrated by case studies from the Mammoth Cave, USA, and a small experimental site in Switzerland. The properties and limitations of the most important artificial tracers are discussed, and the available methods of tracer injection, sampling, online monitoring and laboratory analysis are presented. Fully quantitative tracer experiments result in continuous or discrete concentration-time data series, i.e. breakthrough curves, and concomitant discharge data, which make it possible to obtain detailed information about groundwater flow and contaminant transport. Within the frame of speleological investigations, tracer tests can help to resolve the active and often inaccessible part of cave and conduit networks and to obtain indications about the geometry and volume of the conduits. For hydrogeological studies, caves can in turn be used as natural experimental and monitoring sites inside the unsaturated or saturated zone of karst aquifer systems.
Abstract: Continuous monitoring of particle-size distribution (PSD), total organic carbon (TOC), turbidity, discharge and physicochemical parameters, together with analyses of fecal indicator bacteria, particularly E. coli, made it possible to better understand the processes governing pathogen transport in karst groundwater and to establish PSD as indicator for possible microbial contamination of drinking water from karst springs. In the study area near Yverdon-les-Bains, Switzerland, tracer tests proved connection between a sinking stream draining agricultural land and several springs, 4.8â6.3 km away. Tracing and monitoring results demonstrate that (i) suspended particles (turbidity) in the spring water either originate from remobilization of sediments inside the aquifer (autochthonous) or from the sinking stream and land surface (allochthonous); (ii) allochthonous turbidity coincides with increased E. coli and TOC levels; (iii) PSD makes it possible to distinguish the two types of turbidity; (iv) a relative increase of finer particles (0.9â10 micro-m) indicates allochthonous turbidity and thus possible fecal contamination. The method permits to optimize water treatment and identify periods when the spring water must be rejected. Findings from other test sites confirm the feasibility of this approach.
Abstract: The dynamics of organic carbon (OC), turbidity, faecal indicator bacteria and physicochemical parameters was studied in a karst system near Yverdon, Switzerland. Online measurements and sampling were done at a swallow hole draining an agricultural surface (the input), and two groups of springs (the outputs) that often show bacterial contamination. A fluorescent tracer that was injected into the swallow hole during low-flow conditions first arrived at the springs 10â12 days after injection; the total recovery rate was 29%. Previous tracer tests during high-flow conditions gave shorter travel times. After a major rainfall event, a primary turbidity peak was observed at the springs. It coincides with the rising limb of the hydrograph, indicating remobilisation of autochthonous particles from the aquifer. A secondary turbidity peak occurs several days later, suggesting the arrival of allochthonous particles from the swallow hole. Wider peaks of OC and bacteria were observed simultaneously. Applying methods from molecular microbiology (PCR-DGGE) allowed characterisation of the bacterial communities at the swallow hole and the springs. The results demonstrate that the swallow hole is an important source of groundwater contamination, while its contribution to aquifer recharge is insignificant. OC appears to be a better indicator for bacterial contamination than turbidity.
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