3D-Modelling of the inter-annual variability of the mixing regime in a shallow urban lake: Lake Créteil, France

Abstract : Modelling accurately ecological processes in shallow lakes requires modelling accurately the lake hydrodynamics. For example, full mixing episodes during summer cause sediment re-suspension and trigger consecutive phytoplankton growth. Therefore, a validated model forced with outputs of a regional climate model could be very useful to predict changes in mixing regime and to discuss the future of phytoplankton dynamics in temperate urban lakes similar to Lake Créteil. We used the 3D hydrodynamic model Delft3D-FLOW and successfully validated it using meteorological variables, water temperature and current velocity collected at high frequency (30 s) in several points of Lake Créteil, France from spring to summer (May to August) in 2012, 2013 and 2014. Calibration was performed in 2012 and verification in 2013 and 2014. Particular hydrodynamic episodes were analyzed: destratification events and periods of internal wave activity. The number of stratified days, mixed days, destratification events and the duration of thermal stratification episodes were calculated for each year to quantify the inter-annual variability. Simulation results reproduced very well the observed inter-annual polymictic patterns and internal wave characteristics for all three years.