Dynamics and interaction of organic carbon, turbidity and bacteria in a karst aquifer system

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 turbidit

Use of particulate surrogates for assessing microbial mobility in subsurface ecosystems

Mass fluxes from the ground surface can play a vital role in influencing groundwater ecosystems. Rates of delivery may influence intact ecosystem composition, while fluxes of substances associated with anthropogenic activity may critically alter the functioning of associated microbial assemblages. Field-based tracing experiments offer a valuable means of understanding mass transport rates and mechanisms, particularly in complex heterogeneous epikarst systems overlying vulnerable fissured aquifers. A short-term tracer experiment monitoring solute and particle tracer concentrations after they passed through a 10-m-thick sequence of limestone, capped by a thin soil, revealed rapid travel times and variable attenuation rates for the substances employed. Results demonstrated that particle tracers have shorter average travel times and can reach the subsurface in higher concentrations and over shorter times than non-reactive solutes. High recovery rates for the bacterial tracer Ralstonia eutropha H16 contrasted strongly with those of similarly sized fluorescent polystyrene microspheres, highlighting the importance of physico-chemical surface characteristics of particle tracers. Complementary laboratory batch experiments examined the role played by organic and inorganic soil/rock surfaces on particle tracer attenuation. Findings suggest that biofilms may significantly promote transport of particulate material below ground, i.e., the delivery of allochthonous microorganisms to karst groundwate

New insights into the transport of sediments and microorganisms in karst groundwater by continuous monitoring of particle-size distribution

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 (0.9–1.5 μm) 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. </span

Microbial communities in karst groundwater and their potential use for biomonitoring

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 discusse

Complete Genome Sequence of Alteromonas Virus vB_AspP-H4/4

Alteromonas virus vB_AspP-H4/4 is a member of the Podoviridae family and was isolated from North Sea water in the 1970s. The complete double-stranded DNA genome has 47,631 bp with 49 predicted genes

Origin and spatial-temporal distribution of faecal bacteria in a bay of Lake Geneva, Switzerland

The origin and distribution of microbial contamination in Lake Geneva's most polluted bay were assessed using faecal indicator bacteria (FIB). The lake is used as drinking water, for recreation and fishing. During 1year, water samples were taken at 23 points in the bay and three contamination sources: a wastewater treatment plant (WWTP), a river and a storm water outlet. Analyses included Escherichia coli, enterococci (ENT), total coliforms (TC), and heterotrophic plate counts (HPC). E. coli input flux rates from the WWTP can reach 2.5 × 1010CFU/s; those from the river are one to three orders of magnitude lower. Different pathogenic Salmonella serotypes were identified in water from these sources. FIB levels in the bay are highly variable. Results demonstrate that (1) the WWTP outlet at 30m depth impacts near-surface water quality during holomixis in winter; (2) when the lake is stratified, the effluent water is generally trapped below the thermocline; (3) during major floods, upwelling across the thermocline may occur; (4) the river permanently contributes to contamination, mainly near the river mouth and during floods, when the storm water outlet contributes additionally; (5) the lowest FIB levels in the near-surface water occur during low-flow periods in the bathing seaso