Intensive exploitation of a karst aquifer leads to Cryptosporidium water supply contamination.

Groundwater from karst aquifers is an important source of drinking water worldwide. Outbreaks of cryptosporidiosis linked to surface water and treated public water are regularly reported. Cryptosporidium oocysts are resistant to conventional drinking water disinfectants and are a major concern for the water industry. Here, we examined conditions associated with oocyst transport along a karstic hydrosystem, and the impact of intensive exploitation on Cryptosporidium oocyst contamination of the water supply. We studied a well-characterized karstic hydrosystem composed of a sinkhole, a spring and a wellbore. Thirty-six surface water and groundwater samples were analyzed for suspended particulate matter, turbidity, electrical conductivity, and Cryptosporidium and Giardia (oo)cyst concentrations. (Oo)cysts were identified and counted by means of solid-phase cytometry (ChemScan RDI(®)), a highly sensitive method. Cryptosporidium oocysts were detected in 78% of both surface water and groundwater samples, while Giardia cysts were found in respectively 22% and 8% of surface water and groundwater samples. Mean Cryptosporidium oocyst concentrations were 29, 13 and 4/100 L at the sinkhole, spring and wellbore, respectively. Cryptosporidium oocysts were transported from the sinkhole to the spring and the wellbore, with respective release rates of 45% and 14%, suggesting that oocysts are subject to storage and remobilization in karst conduits. Principal components analysis showed that Cryptosporidium oocyst concentrations depended on variations in hydrological forcing factors. All water samples collected during intensive exploitation contained oocysts. Control of Cryptosporidium oocyst contamination during intensive exploitation is therefore necessary to ensure drinking water quality.

Investigation of transport processes inside karst aquifer by means of STATIS.

Environmental data sets are often multidimensional and consequently display complex structure. This article shows the limitations of principal component analysis (PCA) for the study of such three-dimensional (3D) data sets. These limitations can be resolved by the use of the statistical tool STATIS. The inlet (a swallow hole) and the outlet (a spring) of a karst system of the Western Paris basin were sampled during three rain events of various intensities. These 3D geochemical data sets (variables x sites x dates) for a karst system were analyzed by STATIS method to identify hydrological processes. STATIS proceeds in three steps (interstructure, compromise, and intrastructure), which allows us to focus the analysis of hydrologic systems at different temporal and spatial scales. Compromise plane shows that suspended matter and flood are not simultaneous and highlights a rapid flow, characterized by turbidity and phosphate, which represents a point source contamination, and a ground water flow contaminated by nitrate. Intrastructure plane allows us to compare hydrochemical variations between the swallow hole and the spring lead. By this way, hydrological processes such as direct transfer and resuspension of intrakarstic sediments before and after the flood were identified what cannot be realized by comparison of inlet and outlet breakthrough curves. Finally, results obtained from the same data set by STATIS and a coupled study using PCA and normalized hysteresis curves were compared. This comparison shows the efficiency of STATIS at the identification of transport processes and vulnerability of karst system and its potential for hydrological applications.

Quantitative interpretation of specific conductance frequency distributions in karst.

Use of the coefficient of variation (CV) of specific conductance has been a simple and popular approach to classifying karst aquifers; however, problems with this approach arise because specific conductance frequency distributions (CFDs) are usually multimodal and the use of the CV sometimes erroneously classifies aquifers in terms of their dominant flow type or recharge type. Here, we demonstrate a more rigorous analysis of the CFD, which gives insight into the water types contributing to spring flow. The CFD for a water year is separated into an additive series of normal distributions, each related to a hydrogeochemical population. For each water type, its mean, variance, and contribution to the overall CFD can be quantified and compared between water types and water years. We applied this method to 4 years of data collected at Barton Springs, Austin, Texas. Although the overall shape of the CFD changed from year to year, it could consistently be separated into the same set of normally distributed populations. We suggest that each population represents a water type resulting from a particular mode of aquifer functioning. Changes in the parameters describing the curves reflect aquifer response to climatic variations. The results suggest that no single parameter of specific conductance can be used to describe the degree of karst behavior of an aquifer but that the degree of karst behavior itself varies from year to year depending on hydrologic conditions.

Recurrent recovery of Pseudomonas oryzihabitans strains in a karstified chalk aquifer.

Pseudomonas oryzihabitans is an uncommon pathogen that may cause catheter-associated infections, particularly in immunocompromised patients. Although it has been isolated from environment, the source of human infection is not well documented. In the present study, 14 isolates of P. oryzihabitans were recovered over a 28-month period from a karstified chalk aquifer, allowing to advance that distributed natural water could be a source of contamination. Microbiological analyses showed that the bacterium was mainly associated with suspended particulate matters. To investigate the clonality of P. oryzihabitans environmental isolates, 16S rRNA gene sequencing, antibiogram and randomly amplified polymorphic DNA (RAPD) typings were performed. Results demonstrated (i) the presence of at least three clones within the aquifer and (ii) that the presence of the bacterium in groundwater is not only the result of a biofilm bloom but also of an exogenous contamination.

Occurrence of sessile Pseudomonas oryzihabitans from a karstified chalk aquifer.

Pseudomonas oryzihabitans is an uncommon pathogen that may cause opportunistic infections. Although it has been previously isolated from the environment, the source of human infection has not been well documented. In this study, we describe the presence of P. oryzihabitans adhering on suspended particulate matters recovered from karst groundwaters. The isolated pathogen was capable of forming biofilms on silicon supports and clay beads. Adherent P. oryzihabitans cells displayed a high resistance to chlorine as compared with the same organisms cultured in the planktonic mode. These results demonstrate that aquifer biofilms are potential environmental sources for water-born P. oryzihabitans infections and that bacterial attachment might affect drinking water purification.

[Bioecological consequences of an accidental hydrocarbon discharge on the rocky shore of the high Normandy coast. Results one year after the oil pollution on the november 26th 1974]. / Conséquences bioécologiques d'un déversement accidentel d'hydrocarbures sur le platier du littoral haut-normand. Bilan un an après la marée noire du 26 novembre 1974

We have followed, during one year, the ecological consequences of an accidental oil pollution on four rocky shores of the norman coast. In the shores where the detergents have not been used, the mussels have progressively excreted the hydrocarbons accumulated in their organism ; the other fixed animals have not been changed. In the shores where the detergents have been used their spreading had not only noxious demoecological consequences, but also synecological consequences with modifications of the fixed species which have colonized the rocks. These observations prove that the use of detergents to clean the polluted shores is not without care.