Hypoxic layers in the hypolimnion of lakes are regions where Dissolved Oxygen (DO) is < 4 mg/L, and most life cannot be sustained. In Lake Geneva, the deep hypolimnion can become hypoxic. However, the hydrodynamics of the deep hypolimnion are not well understood, since at present, they are mainly based on data from a single monitoring station located in the deepest part of the lake (309 m; SHL2; Figure 1). Lake Geneva is composed of two basins: the narrow, shallow Petit Lac and the large, deep Grand Lac. During cold winters, the Petit Lac cools much faster and its dense, oxygen rich, cold waters flow into the deep hypolimnion of the Grand Lac, which allows re-oxygenation of its oxygen poor waters. In order to quantify the amount of oxygen flowing into the Grand Lac, the three-dimensional MITgcm model was calibrated to simulate dissolved oxygen dynamics during the exceptionally cold winter of 2012. For the simulation, three different lake areas were considered: (i) the whole lake, (ii) only the Grand Lac basin, and (iii) the coastal zones of the whole lake. We quantified the contribution of oxygen originating from the Petit Lac and from the coastal zones, and demonstrated that the main source of oxygen renewal in the deep hypolimnion of the Grand Lac was water that came from the Petit Lac. During winter 2012, complete water overturning due to convective cooling did not occur in the Grand Lac. Therefore, the flow of cold, oxygen rich Petit Lac waters makes a significant contribution to the oxygen budget of the deep Grand Lac hypolimnion and can thus improve the water quality of this layer. This beneficial water exchange process between the two lake basins can also occur during other cold winters.The results of this research contribute to improving future lake ecosystem investigations.
Primary Presenter: Congrong Yu, Hohai University (congrongyu@126.com)
Authors:
Congrong Yu, College of Hydrology and Water Resources, Hohai University, Nanjing, China (congrong.yu@epfl.ch)
Ulrich Lemmin, Ecological Engineering Laboratory (ECOL), Faculty of Architecture, Civil and Environmental Engineering, Ecole Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland ()
Naifu Peng, Ecological Engineering Laboratory (ECOL), Faculty of Architecture, Civil and Environmental Engineering, Ecole Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland ()
Rafael Reiss, Ecological Engineering Laboratory (ECOL), Faculty of Architecture, Civil and Environmental Engineering, Ecole Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland ()
Andrew Barry, Ecological Engineering Laboratory (ECOL), Faculty of Architecture, Civil and Environmental Engineering, Ecole Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland ()
Dissolved oxygen dynamics in the deep hypolimnion of Lake Geneva during an exceptionally cold winter
Category
Scientific Sessions > SS050 Disentangling Complex Long-Term pH and O2 Trends in Coastal and Estuarine Systems From Global and Regional Drivers
Description
Time: 06:30 PM
Date: 7/6/2023
Room: Mezzanine