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.

Lake Superior: sediment-water exchanges and nutrient fluxes

Lake Superior is the largest freshwater body in North America, containing 10% of the world's freshwater. Its productivity is extremely limited by phosphorus, with N:P ratio in its waters being one of the highest in the world. By combining state-of-the-art modeling with experimental measurements, we are learning about the nutrient cycling in this system and, by extension, about other oligotrophic systems, such as abyssal ocean plains.

Large Lake Observatory (LLO) operates a research vessel, Blue Heron, as well as offers laboratories for physical, chemical, biological, and geological research.

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. The chemistry and microbiology of its waters depend on the particulars of physical mixing. We investigate this coupling of biogeochemistry and physics using an array of numerical tools, as well as field and laboratory measurements.

Methane is bubbling from the sediments of Lake Matano:

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 use advanced numerical tools and work 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.

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.

Predictive modeling and decision support for lake restoration

Restoration of polluted lakes is costly and the outcomes of management solutions are often uncertain. Lakes are dynamical systems. They are affected by a multitude of factors and behave differently on seasonal and multi-year time scales. Modeling is an inexpensive and powerful way to predict the effectiveness of restoration measures and to suggest the best solutions. We use detailed models to identify relevant physical and biogeochemical processes and simpler, more easily parameterizable, models capable of assisting with management decisions. Applications include lakes in Switzerland, Germany, and Israel.