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
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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.