Pronk, Michiel

2009, Pronk, Michiel, Goldscheider, Nico, Zopfi, Jakob, Zwahlen, François

Recharge and contamination of karst aquifers often occur 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 (1) a first turbidity signal occurs during increasing discharge due to remobilization of particles from fractures (pulse-through turbidity); (2) 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 Escherichia coli/100 mL; and (3) PSD allows differentiation between the two types of turbidity. A relative increase of fine particles (0.9 to 1.5 mu m) coincides with microbial contamination. These findings help quantify water storage and percolation in the epikarst and better understand contaminant transport and attenuation. The use of PSD as "early-warning parameter" for microbial contamination in karst water is confirmed.

2008, Pronk, Michiel, Goldscheider, Nicola, Zopfi, Jakob, Zwahlen, François

Recharge and contamination of karst aquifers often occur 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 (1) a first turbidity signal occurs during increasing discharge due to remobilization of particles from fractures (pulse-through turbidity); (2) 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 Escherichia coli/100 mL; and (3) PSD allows differentiation between the two types of turbidity. A relative increase of fine particles (0.9 to 1.5 μm) coincides with microbial contamination. These findings help quantify water storage and percolation in the epikarst and better understand contaminant transport and attenuation. The use of PSD as "early-warning parameter" for microbial contamination in karst water is confirmed.

2007, Pronk, Michiel, Goldscheider, Nico, Zopfi, Jakob

Continuous monitoring of particle-size distribution (PSD), total organic carbon (TOC), turbidity, discharge and physicochemical parameters, together with analyses of fecal indicator bacteria, particularly Escherichia 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, 4.8–6.3 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 (0.9–10 µm) 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.

2009, Pronk, Michiel, Goldscheider, Nicola, Zopfi, Jakob

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.

2008, Goldscheider, Nicola, Meiman, Joe, Pronk, Michiel, Smart, Christopher

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.

2006, Pronk, Michiel, Goldscheider, Nicola, Zopfi, Jakob

La dynamique du carbone organique, de la turbidité, des bactéries indicatrices de contamination fécale et d’autres paramètres physico-chimiques a été étudiée dans un système karstique proche de la ville d’Yverdon-les-Bains, Suisse. Des mesures en continu ainsi que des échantillonnages ont été effectués à une perte drainant une zone agricole (input), et à deux groupes sourciers (output) qui montrent fréquemment une contamination bactérienne. En période d’étiage, un essai de traçage à l’uranine a été réalisé depuis la perte. Le traceur est apparu aux sources 10–12 jours après l’injection; la masse de restitution totale a été de 29%. Des essais précédents, réalisés en hautes eaux, ont montré des temps de transit plus court. Suite à un événement pluvieux important, un pic de turbidité primaire, synchrone avec l’augmentation du débit, est observé aux sources, indiquant une re-mobilisation des sédiments autochtones de l’aquifère. Un pic de turbidité secondaire apparaît quelques jours plus tard aux sources, suggérant l’arrivée de matériel allochtone de la perte. Cette dernière est accompagnée de pics plus larges de carbone organique et des bactéries indicatrices de contamination fécale. La microbiologie moléculaire (PCR-DGGE) a permis la caractérisation des communautés bactériennes de la perte et des sources. Ces résultats démontrent l’importante influence de la perte sur la qualité de l’eau souterraine, alors que sa contribution au débit du système est négligeable. Le carbone organique semble être un meilleur indicateur de la présence de contamination bactérienne que la turbidité., 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 10–12 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., Se ha estudiado la dinámica del carbono orgánico, turbiedad, una bacteria indicadora de fecales, y parámetros fisicoquímicos en un sistema kárstico cerca de Yverdon, Suiza. Se realizaron mediciones en línea y muestreo en un sumidero que drena una superficie agrícola (la entrada), y dos grupos de manantiales (las salidas) que frecuentemente muestran contaminación bacterial. Un trazador fluorescente que se inyectó en el sumidero durante condiciones de flujo bajo arribó en los manantiales por vez primera 10–12 días después de que fue inyectado; el ritmo total de recuperación fue de 29%. Las pruebas de trazadores realizadas con anterioridad bajo condiciones de flujo alto aportaron tiempos de viaje más cortos. Después de una tormenta fuerte se observó un pico de turbiedad primario en los manantiales. El pico coincide con el limbo ascendente del hidrograma indicando remobilización de partículas alóctonas provenientes del acuífero. Un pico de turbiedad secundario ocurre varios días más tarde sugiriendo el arribo de partículas alóctonas provenientes del sumidero. Se observaron simultáneamente picos más amplios de carbono orgánico y bacteria. La aplicación de métodos de microbiología molecular (PCR-DGGE) permitieron caracterizar las comunidades de bacteria en el sumidero y los manantiales. Los resultados demuestran que el sumidero es una fuente importante de contaminación de aguas subterráneas mientras que su contribución a la recarga del acuífero es insignificante. El carbono orgánico parece ser un mejor indicador de contaminación bacterial que la turbiedad.

2008, Pronk, Michiel, Zwahlen, François, Goldscheider, Nico

Karst aquifers represent an important groundwater resource world-wide. They are, however, highly vulnerable to contamination due to fast transport and limited contaminant attenuation processes encountered in such systems. Pathogenic microorganisms are among the most frequent and problematic contaminants in groundwater from karst aquifers. It is generally accepted that the presence of faecal indicator bacteria, such as Escherichia coli and enterococci, in groundwater indicates the possible presence of pathogenic bacteria, protozoa and viruses. Monitoring microbial water quality relies, however, on sterile water sampling and subsequent laboratory analyses. Moreover, the sampling intervals and the relatively long time lag between sampling and results are often too long to prevent microbially polluted water entering the distribution network. Therefore, establishing a correlation between the microbial water quality and parameters that can easily be measured online – using it as an “early-warning” parameter – constitutes the first main objective of this work. Most microorganisms in groundwater are harmless. Enumeration of pathogenic and water quality indicator bacteria thus provides an incomplete picture of the microbial assemblages. These microbial communities are of growing interest, as aquifers, which include habitats for a wide range of organisms, are increasingly considered as ecosystems harbouring their proper biocenoses. These ecosystems have to be better understood in order to ensure the sustainable management of groundwater resources. Furthermore, as bacteria are abundant and ubiquitous, thriving even in extreme habitats, the potential use of microbial communities for groundwater biomonitoring has been raised. However, the understanding of microbial diversity, their distribution patterns and their dynamics in karst aquifer ecosystems are actually still in an early stage and rather sparse and constitute therefore the second main objective of this research project. The occurrence, dynamics and transport processes of suspended matter and faecal indicator bacteria were investigated at two karst aquifer systems (the Yverdon-les-Bains and Noiraigue test sites, Switzerland), which are characterised by allochthonous point recharge, and several shallow cave sites located in the unsaturated zone of karst aquifers (the Vers-chez-le-Brandt, Grand-Bochat and Gänsbrunnen test sites, Switzerland). Classical hydrogeological parameters, such as discharge, temperature, electrical conductivity, organic carbon and turbidity, were monitored continuously online, along with event-based, high-frequency analyses of Escherichia coli and enterococci. In order to gain more insight into the origin and behaviour of suspended particles in karst groundwater, particle-size distribution (PSD) was also monitored continuously. Results demonstrated that suspended particles in karst spring water either originated from the remobilisation and scouring of intrakarstic particulate material due to increasing flow velocities (i.e. autochthonous turbidity) and / or the transfer of particles from land surface and sinking streams (i.e. allochthonous turbidity), which entered the system following rainfall events. These allochthonous turbidity events coincided with increased faecal indicator bacteria and organic carbon levels. PSD allowed distinguishing both types of turbidity: autochthonous turbidity consisted of particle concentration increases over a wide range of particle sizes (from colloidal sizes up to 0.1 mm), whereas allochthonous turbidity periods were characterised by a predominance of finer particles (0.9 to 10 µm). PSD is therefore proposed as surrogate indicator for possible microbial contamination of groundwater from karst aquifers. The structure, diversity and temporal variability of microbial communities from a swallow hole draining agricultural land and two connected karst springs (Yverdon-les-Bains karst aquifer system) were investigated using molecular microbiological methods (PCR-DGGE and cloning / sequencing) and related to hydrological and physico-chemical 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 profiles) 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 in the water entering the swallow hole. Conversely, high similarities among spring water samples with low allochthonous contribution provided evidence for a stable autochthonous endokarst microbial community. This autochthonous endokarst microbial community was characterised by a high diversity with only a few dominant species. δ-Proteobacteria, Acidobacteria and Nitrospira species were important members of this community. The high percentage of unknown sequences (i.e. sequences revealing similarities lower than 97 % to already known sequences) suggests that many karst aquifer bacteria are still undiscovered. Moreover, it highlights that karst aquifers are rarely studied, unique habitats and that sequences from shallow subsurface ecosystems are currently underrepresented in databases. In conclusion, the high sensitivity of PSD analysis allows consequently proposing it as an “early-warning” surrogate for real-time monitoring of possible microbial contamination of groundwater from karst aquifers. The method permits optimising water treatment and identifying periods when spring water must be rejected. Furthermore, this study represents a first step towards a better understanding of the microbial ecology in karst aquifer systems and may serve as a starting point for developing biomonitoring tools.

2007, Pronk, Michiel, Goldscheider, Nico, Zwahlen, François, Zopfi, Jacob