Current Research Projects
Atmospheric acidity and its impacts on atmospheric macronutrient deposition
Exploring the functional diversity and activity of microbial communities related to mercury cycling in Lake Geneva with new omics approaches
Mercury (chemical symbol Hg) is considered as a priority pollutant, including in Europe, mainly because of the toxicity of its organic form, methylmercury (MeHg), and its propensity to biomagnify, i.e. to increase its concentration in the tissues of organisms as it travels up the food chain. It is known that the Hg methylation, the transformation of divalent Hg (HgII) to MeHg, occurs under oxygen-free conditions and depends essentially on the activity of microorganisms characterized by specific genes – the hgcAB gene cluster. In addition, HgII methylation depends on the HgII bioavailability, the abundance of electron acceptors, the abundance and nature of organic matter as well as the activity and structure of the microbial community. It is therefore instrumental to understand the compendium of metabolic processes that can affect directly or indirectly HgII methylation.
This project aims to determine and compare HgII-methylation, microbial biodiversity and activity involved in HgII methylation in contrasted physico-chemical contexts in Lake Geneva. We aim to overcome some of the current limits for predicting MeHg concentrations in the environment. This project will be a proof of concept of the interest of coupling cutting-edge high-throughput biological analysis (metagenomics and metaproteomics, i.e. global analysis of genes and proteins, respectively) with a physico-chemical characterization. An increased knowledge of the relationship between microbial community activity, physico-chemical conditions, MeHg production and demethylation is necessary to predict the variability in MeHg concentrations across environments and consequently mitigate the Hg methylation to protect environment and human health.
Effect of Nearshore Mixing on Formation of Nearshore Cold Water Density Currents
The warming of lakes due to climate change, which has been shown for lake surface waters by satellite thermal imagery, affects lake ecological processes and their biodiversity. In large lakes, such as Lake Geneva, large-scale currents, initiated by wind events, are responsible for horizontal water mass transport. Nearshore, they produce vertical currents (coastal upwelling and downwelling), which in addition to nearshore cold water density currents during winter cooling, lead to significant vertical transport. This is of great relevance to the lake energy status (global vertical mass exchange) and hence to its ecological functioning. The impact of climate change on these vertical movements, localized in nearshore regions, is still poorly understood, although they directly influence deep lake temperature. Moreover, few studies have dealt with the initiation and the development of those currents. This project will investigate the formation and the fate of nearshore cold water currents in winter and the effect of turbulent mixing on these processes in Lake Geneva. The inhibition (or not) of the formation of those cold water currents due to large-scale alongshore currents and their turbulence induced mixing will be assessed.
The Bois Chamblard lakeshore is an ideal field site where cold water nearshore currents have been studied in recent years. Existing in situ equipment will be supplemented with a new platform called the Turbulator, designed to measure in detail turbulent mixing throughout the water column. The first part of the project consists of field-testing this platform, which is equipped with high frequency temperature and velocity sensors surrounded by lower resolution sensors that measure the bulk vertical variables characterising the main current. The vertical position of the platform and the measurements will be remotely controlled via a cable laid on the lakebed. This subsurface configuration enables precise turbulence measurements, even during harsh lake surface conditions (e.g., strong wind events) that would not be possible from the surface. In addition, field campaigns will include measurements from two existing platforms, an autonomous catamaran that measures local meteorological conditions along with temperature and current profiles on predetermined paths, and a helium balloon equipped with a thermal camera for surface temperature measurements. The combination of these instruments will permit quantification of the extent of the nearshore zone.
Turbulence measurements, coupled with observations at the field site scale, will yield valuable data on the dynamics of vertical currents in the nearshore zone. The new insights gained on turbulence and entrainment due to large-scale lake currents will contribute to a better understanding of global lake vertical mixing. Furthermore, the results are expected to improve lake circulation models, particularly in the initiation of nearshore cold water density currents and, more generally, on the effect of the nearshore mixing zone on vertical water mass movement.
Lake Near-shore Hydrodynamic Phenomena
Lake Geneva is the largest lake in Western Europe. An important question affecting the biodiversity of the lake is whether it is warming due to climate change. The lake’s surface area is about 580 km2, and heat exchange at the surface is the dominant mechanism for adding heat to the lake. Even if a warmer climate increases the temperature of surface waters, this water is buoyant and does not sink. Consequently, it does not affect the majority of the lake, which is 300 m deep.
Bois Chamblard’s location on the shores of Lake Geneva, with its gently sloping nearshore bathymetry, offers an excellent opportunity for investigation of near-shore hydrodynamic phenomena. ECOL is investigating cold-water density currents, which are generated in shallow shore regions particularly during winter months when rapid nearshore cooling occurs. The increased density generates negatively buoyant water masses near the shoreline that can propagate into deep areas of the lake and so can affect the lake’s overall energy balance. To investigate their formation and propagation, ECOL has set up a long-term in situ data gathering system, using fibre-optic cables and other equipment for temperature and current profile measurements.