Sources, Spreading and Fate of Antibiotic Resistance Genes and Resistant Bacteria in Vidy Bay, Lake Geneva, Switzerland

Increasing numbers of multiresistant bacterial pathogens cause severe health problems on a global scale. Large quantities of bacteria and their resistance genes are discharged into natural environments via human and animal waste. Not much is known so far about the fate and further spread of resistance determinants in the environment. There is evidence that aquatic environments may function as important compartments for preserving and exchanging antibiotic resistance genes (ARG) from sewage and drinking water. Lake Geneva is the largest fresh water reservoir of Western Europe and supplies the surrounding cities. At the same time these cities discharge sewage into the lake. Lausanne is the largest city in the lake’s catchment and discharges the highest amount of treated, as well as in case of heavy rain events, partly untreated waste waters. Also two rivers, Chambering and Flown, transport untreated sewage (bypass), in case of storm events. Only 3.4 km from the sewage discharge point lake water is pumped for drinking water preparation for Lausanne. Many studies have reported on contamination of the bay with heavy metals, inorganic nutrients, organic carbon and fecal indicator bacteria due to the sewage discharge. The present thesis aimed on investigating the sources, spreading and fate of antibiotic resistant bacteria and antibiotic resistance genes in the Vida bay, Lake Geneva. In the first part of this dissertation, a screening for antibiotic- and specifically multi-resistant bacteria was carried out as one of the first studies in a Swiss waste water stream and the receiving fresh water lake. For this purpose, a combined set of culture based (viable bacterial counts on nutrient media supplemented with antibiotics) and molecular tools (detection and quantitation of antibiotic resistance genes from environmental DNA-extracts using quantitative real-time PCR) was applied. Raw hospital and communal sewage, as well as partly treated/mixed sewage, which is discharged into the lake via an effluent pipe 700 m off shore, were taken into account. Furthermore lake water samples nearby the end of the waste water discharge pipe and the drinking water pump as well as close to the two river mouths were analyzed. Finally, the role of Lausannes WTP was evaluated for its potential to remove resistant and multiresistant bacteria, as well ARG. Results show highest levels of multiresistant bacteria and ARG in both hospital and communal sewage. Incidence was found that the WTP is a selective environment for multiresistant bacteria and resistance genes. Moreover, lake water and sediments nearby the end of the WTP discharge pipe and the two river mouths exhibited significantly higher levels of resistant determinants as compared to samples from the drinking water uptake. If the level of antibiotic resistance close to the drinking water uptake represents the natural background level of the lake or whether it is impacted by the WTP plume remained open during this first survey. The spatial distribution and persistence of ARG discharged via waste water into lake systems has been evaluated for the first time in the second part of this thesis. 22 sediment cores were sampled along two major transects (leading either into the deep lake or along the south-western shore line to the drinking water uptake) and in the vicinity of the WTP discharge pipe in the Vidy bay. A subset of samples was also analyzed for contamination with a “conventional” pollutant of sewage (mercury), for which a similar transport behavior (particle bound) as for bacteria and their resistance genes is assumed. The microbial community composition in all sediment as well as in waste water samples was analyzed using ARISA. Strong pollution with both ARG and mercury was detected in close proximity of the WTP discharge pipe and both contaminants significantly decreased along the transect into the deep lake. In general however, the spatial contamination of mercury and ARG was only moderately correlated. While the mercury contaminated sediment surface area tended to have a pollution tail in south eastern direction, ARG showed only a slow decrease along the south western transect. These findings imply differences in transport and fate of mercury and ARG in the bay, or additional sources of ARG contamination. Analysis of the microbial diversity in the samples support these hypotheses. This study revealed feasibility of qPCR as a tool to semi-quantitatively track spatial ARG contamination in fresh water lake sediments. Not much is known yet on the antibiotic resistance background level of fresh water lakes and how this may be influenced by anthropogenic activities in the surrounding catchment. Water samples from 21 Swiss lakes have been collected and were analyzed for the prevalence of different ARG (2 sulfonamide resistance genes sul1 & sul2, 3 tetracycline resistance genes tetB, tetM, tetW and one plasmid mediated fluoroquinolone resistance gene qnrA). In order to document the abundance of these genes in the bacterial populations, they were normalized to bacterial 16S rRNA gene copy numbers. The lakes differ in size, geographical position, land use pattern, and trophical status. The composition of the microbial community of all lakes was analyzed using ARISA. Sulfonamide resistance genes were detected in all investigated lakes (0.2-4%, sul1 and 0.01-0.3%, sul2), with highest levels in Lake Baldegger (21%). Lake Baldegger also contained all of the three tetracycline resistance genes, which were found in only 4 other lakes. None of the lakes was positive for qnrA. Important anthropogenic catchment activities linked to sul gene prevalence could not be identified based on our data and may require further analysis and an additional variables to complete our data set. However, our study demonstrates contamination of Swiss lakes with sulfonamide resistance genes and the potential of fresh water lakes preserve these genes, even remote from direct sources of pollution.

Micropollutants in Large Lakes: From Potential Pollution to Risk Assessments

David Andrew Barry, Florence Bonvin, Neil Graham, Luca Rossi

This book is divided into six additional chapters: Chapter 2 deals with the agricultural source of micropollutants; Chapter 3 with the urban source of micropollutants; Chapter 4 with lake circulation; Chapter 5 with the influence of a wastewater treatment plant on a bay; Chapter 6 with the input of sediments and their transport in a bay; and Chapter 7 with the risk assessment of the mixture of the compounds present in lake water. A last chapter (8) synthesizes the main findings and presents perspectives for future studies. More specifically: Chapter 2 is dedicated to the micropollutants that enter lakes through agriculture. These are mainly pesticides. After a review of the different types of compounds, the authors will put forth the main pathways these compounds follow to enter lakes. The case of glyphosate, an herbicide used worldwide, will be discussed. Chapter 3 illustrates the urban sources of pollutants with pharmaceuticals and biocides. Two models will be covered that allow estimating the load and dynamics of these chemicals that may exit from an urban catchment and therefore reach lakes. Special attention will be paid to the “end of pipe” removal of these compounds at a WWTP. Chapter 4 is dedicated to lake circulation. The aim of this chapter is to present an overall description of lake hydrodynamics, which is driven by three factors: wind, temperature and Coriolis forces. The main inflow to Lake Geneva is provided by the Rhône River. In addition, the topography surrounding the lake varies rapidly, for example, with mountains in the eastern part. As a consequence, the lake’s currents can vary markedly. To achieve our objective, we will utilise hydrodynamic modelling. A model will be proposed that permits describing the behavior of the top layer of the lake based on wind direction. The importance of stable hydrogen and oxygen isotopes for characterising the sources of water and mixing processes in the lake will be described and illustrated with the example of the Rhône river interflow to it. The measured variations of the isotopic compositions within the lake can serve as verification of the lake hydrodynamic models. However, the emphasis of the chapter will be on explaining the major current features and how they relate to wind forcing, which is one of the main drivers. Chapter 5 and 6 are devoted to the Vidy Bay in the Lausanne area of Lake Geneva. This bay receives the treated effluents of the largest wastewater treatment plant of the lake catchment. The latter represents therefore one of the major point sources of contaminants for the lake. These two chapters will focus on the various processes that control the transfer of contaminants (associated with particles or in a dissolved state) discharged into the bay and transported to the lake’s main water body. More specifically, Chapter 5 describes the WWTP plume dynamics. In relation to hydrodynamics (Chapter 4), specifically the behaviour of the plume formed through the treatment plant effluent release, field measurements are utilised to attempt to determine the plume behavior under various lake conditions. Furthermore, it investigates the degradation of organic pollutants. Photodegradation and other degradation processes are studied with theoretical, experimental and modelling approaches. Chapter 6 focuses on sediment path tracing. The pollutants associated with particles (trace metals, hydrophobic components, etc.) settle to the lakebed, but can be remobilized and transported to deeper parts of the lake. Bottom currents, and other physical forces, can cause resuspension and advection. Tracers used to identify this advection comprise natural and anthropogenic radioisotopes along with mercury as a major toxic trace element. Chapter 7 concentrates on one major issue of micropollutants in aquatic systems, like lakes, i.e., the risk of the mixture. The evaluation of the risk of mixture of micropollutants is not trivial and we will first present critically the models that allow doing so. We will also demonstrate their validity as predictive tools with the example of herbicide mixtures in Lake Geneva. Finally, we will map the risk of micropollutants around the lake. Finally in Chapter 8, we synthesize the main findings of all chapters and discuss recommendations for the management of mid-sized lakes regarding micropollution.

CRC Press & EPFL Press2018

Global and local anthropogenic effects on hydrodynamics of lakes

Carl Love Mikael Råman Vinnå

In many countries water quality is a major concern for drinking water management authorities. Freshwater is a limited resource and the demand for good-quality water from natural aquatic systems is therefore high. Additional stress arises from anthropogenic emissions of nutrients, chemicals, pathogens, heat and hydrological alterations as well as from the ongoing global climate change. In this thesis the relevant recent past, present and future factors affecting water quality in the perialpine Lake Biel, used as a source for drinking water, was investigated. Through measurements in the field combined with hydrodynamic logical modelling in one and three dimensions, optimal locations for forthcoming lake water intakes was identified. Water quality properties considered were temperature, oxygen, suspended sediment concentration (SSC) and the risk of subaqueous mass movements. The results identified the forthcoming changes expected in Lake Biel due to the upcoming decommission of the Mühleberg Nuclear Power Plant (MNPP) in 2019. This plant currently release ~700 MW of heat into the upstream Aare River in the form of cooling water. The removal of this anthropogenic thermal source will decrease future lake temperature by ~0.3 °C (volume average). Due to seasonal river discharge patterns, the main impact of the plant closure will occur during winter. Minor effects are expected in summer in the form of moderately weaker lake stratification. Furthermore, the current fate of thermal pollution emitted from MNPP was linked to the hydraulic residence time of Lake Biel. While short-term anthropogenic thermal impacts in Lake Biel can be large, the system is additionally experiencing continuous warming up to ~0.1 °C per decade (volume average) by the ongoing climate change. The climate effect on Lake Biel and its primary tributary, the Aare River, was investigated as well as compared to the much larger Lake Geneva and Rhône River. Climate change causes seasonal river discharge shifts resulting in enhanced river warming in summer and diminished warming in winter, while at the same time SSC increases in winter and decreases in summer. Differences in temperature as well as warming rates between rivers and lakes in turn resulted in a discharge and hydraulic residence time-dependent decrease in climate warming of lakes. Furthermore, deep-water renewal in both lakes is predicted to increase in summer and decreases in winter, possibly influencing the replenishment of deep water oxygen. Additionally, sedimentation patterns in Lake Biel were examined and linked to the historical diversion of the Aare River into the lake. The majority of sediment supplied to Lake Biel (~80 %) came from large SSC events in the Aare. These events resulted in a selective particle settling pattern, which concentrated sedimentation on the shallow shelf area North-East of the Aare delta. Both the large SSC events as well as this selective sedimentation pattern were connected to weather fronts coming in from the Atlantic Ocean. The research performed here opens up for further promising interdisciplinary research between Meteorology, Climatology, Hydrology and Sedimentology. Inland water management would benefit through increased knowledge regarding the propagation of particles and/or anthropogenic heat, from river catchments into downstream lakes and sediments.

EPFL2018

Participatory research to monitor lake water pollution

Rachel Aronoff, Luc Patiny, Carlos Vivar Rios

A participatory research team, concerned about water quality around Lake Geneva, particularly in the Montreux Bay region where some were lifeguards, ran sampling campaigns to determine summertime levels of lake water pollution. The participants were brought together serendipitously through a course organized by academic researchers and 'biohackers' from the community laboratory, Hackuarium. After discussion about lifeguards' gastrointestinal and dermatological ailments each season, the decision to pursue this participatory research project was made. In order to assess water quality, thereby testing the hypothesis that unsuspected pollution enters the lake each summer season, microbiological plating of water samples was proposed. Volunteers collected and analysed water samples over summer seasons (8 weeks in 2016, 2017 and 2020) from three sites around Montreux Bay, with tap and local river water samples as controls. Contamination of lake water was measured using standard microbiological methods, with growth media allowing quantitative assessment of abundance of several bacterial species. In particular, the focus was to quantify Escherichia coli, the classic bioindicator organism for raw sewage contamination. These open science data reveal peaks of bioindicator and other bacterial pollution in lake water samples during all sampling years. For the initial two sampling campaigns, increased microbial burdens occurred during a popular music festival, and were not simply dependent upon rainfall. In contrast, only scattered, lower level bioindicator pollution events occurred across the sampling period during the pandemic summer of 2020, when the festival was cancelled. This study confirms the power of participatory research: dedicated people on a budget can do meaningful environmental monitoring. These analyses suggest that better management, both to support water quality monitoring and for event organization, is essential, as sewage treatment facilities near many popular festivals, internationally, may need to cope with increased wastewater from visitors.

WILEY2021