Current research

Physics, chemistry, and biology under water: Sediment early diagenesis

                                                                  “There is plenty of room at the bottom.”                                                                      

Richard Feynman, 1959

Bottom sediments of lakes and oceans are not passive recipients of falling debris. They are intense reactors that process the deposited organic material and other substances using a tightly interwoven network of microbial reactions. Together with physical transport and the actions of animals, these reactions determine which substances will be returned to the overlying water (and become nutrients or pollutants), and which will be permanently buried. We investigate these complex non-equilibrium systems using state-of-the-art models, combined with field and laboratory investigations.

Projects:

Lake Superior: sediment-water exchanges and nutrient fluxes

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Biogeochemistry and physics of permanently stratified tropical lakes

Temperate lakes experience seasonal temperature variations and typically overturn twice a year, but tropical lakes are more stably stratified. Their deep water, often deprived of oxygen, can  accumulate high concentrations of reduced chemical substances, as well as dissolved gases. In the past, catastrophic gas releases from African lakes have claimed several thousand human lives. In a deep Indonesian Lake Matano, permanently anoxic conditions created a “limnologist’s El Dorado” – a unique environment conducive to geochemical microbial reactions that have not been described anywhere else. 

Projects:

Lake Matano, Indonesia: the hydrodynamics of mixing and geochemical cycles

Lake Kivu, Rwanda: towards the safe use of limnic methane gas for energy production 

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Methane bubbling from lake sediments

Methane is an important greenhouse gas and lakes supply a lot of it. Methane is produced in the sediments from the decomposition of organic matter but it rarely reaches the lake surface because it is converted to CO2 when oxydized. Bubbles offer an express way for methane to be transported to the atmosphere. Methane bubbles break through the sediment and quickly reach the surface. Data suggest that ebullition can account for up to 95% of all methane fluxes from boreal lakes. However, quantifying those fluxes are not trivial. We look at the physics of how the bubbles form and move within the sediment and use laboratory measurements to quantify methane fluxes in Minnesota lakes.

Response of aquatic biogeochemical systems to oxygen depletion

Hypoxia (oxygen depletion below the levels harmful for aquatic organisms) is an increasingly frequent phenomenon affecting the coastal waters of industrialized nations. We have used advanced numerical tools and worked in partnership with the leading researchers in Canada to understand this phenomenon and predict its effects on the water chemistry and the functioning of ecosystems in the Estuary and Gulf of St. Lawrence.