Biological diversity and competition among species in ecosystems are sensitive to changes in macronutrient supply and pollution exposure.
Human activity is intensively and extensively altering macronutrient cycles from a regional to a global scale with emission rates that are greater or
comparable to natural ones. Moreover, anthropogenic pollution exposes ecosystems to additional stress which threats their stability and productivity. These processes can have a strong impact on local ecosystems where atmospheric transport plays a central role in spreading macronutrients and pollutants.
Within this project we propose to characterise the atmospheric deposition fluxes of bioavailable macronutrients and pollutants at the Bois-Chamblard site and their potential impact on local biodiversity. The interaction of biogenic and anthropogenic constituents air masses transported to the site will be a research focus.

The exposure of the site to macronutrients imbalance will be explored by quantification of total nitrogen (N) and phosphorous (P) in gas, rain water and airborne particles in four different seasons. To evaluate the importance of atmospheric deposition as a nutrient path for soil the atmospheric total N and P will be compared with N:P ra<o in local soil and plants. Additionally, gas and particle phase pollutants, such as gas-phase oxidants (O3 and NOx), heavy
metal ions, and organic aerosol fraction will be quantified together with aerosol and particle properties such as aerosol pH and particle oxidative potential. Standard methodologies and techniques developed “ad-hoc” in our group will be applied altogether for the first time to have a more comprehensive understanding of atmospheric to soil exchange.

PI: Dr Andrea M. Arangio,
Co-PIs: Dr Kalliopi Violaki, Prof. Athanasios Nenes

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 (Hg^II) 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, Hg^II methylation depends on the Hg^II 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 Hg^II methylation.

This project aims to determine and compare Hg^II-methylation, microbial biodiversity and activity involved in Hg^II 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.

PI : Dr Jean-Luc Loizeau
Co-PI: Dr Claudia Cosio

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.

PI: Prof. D. Andrew Barry and Dr François Mettra

Link to project ECOL-EPFL

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.

Prof. D. Andrew Barry – Rafael Reiss (PhD)