Contribution of 3D coupled hydrodynamic-ecological modeling to assess the representativeness of a sampling protocol for lake water quality assessment

Abstract

This study deals with the impact of spatio-temporal heterogeneities on the assessment of lake ecological status according to the European water framework directive (WFD). A method, based on three-dimensional coupled hydrodynamic and ecological modeling, is presented to assess the variability of lake ecological status, and to locate the most representative sampling station of Lake Geneva (France/Switzerland). Five variables used in the lake ecological status evaluation were simulated by using the free software Delft3D. The numerical simulation results showed that the simulated ecological status based on chlorophyll a and total phosphorus concentrations measured at the regulatory monitoring station depend on the choice of the sampling date. Results also indicated a strong spatial heterogeneity in ecological status that varies from “poor” to “good” along an East-West gradient. Finally, the numerical simulation results showed that the most representative point of a mean theoretical ecological quality for Lake Geneva would be located in the center of the upper basin, close to the historical sampling station.

Assessing the thermal regime of poorly monitored reservoirs with a combined satellite and three-dimensional modeling approach

“…To understand the thermal regime of lakes and reservoirs, water temperature in deeper layers is also required. Three-dimensional modelling provides a means to examine hydrodynamic and ecological processes taking place over long periods of time at high resolution throughout the lake volume (Soulignac et al 2019).…”

A Bayesian data assimilation framework for lake 3D hydrodynamic models with a physics-preserving particle filtering method using SPUX-MITgcm v1

“…In addition, to more realistically accommodate fluctuations in water transparency, we estimate a spatially uniform Secchi depth using the photosynthetically active radiation (PAR) data from the LéXPLORE moorings (Wüest et al, 2021) to determine the attenuation rate of shortwave energy in the water column. In the future, given the spatial variability of Lake Geneva (Bouffard et al, 2018;Soulignac et al, 2019), a better approach might be to use remote sensing data to estimate Secchi depth for different lake locations. Finally, we use the albedo formula of Cogley (1979) to account for seasonal changes in surface reflectivity.…”

Conclusion du colloque

“…L'évaluation DCE-LEMA est basée sur des mesures de paramètres physiques, chimiques, d'inventaires biologiques, qui sont recombinées en indicateurs de bon état, l'un chimique, l'autre écologique, souvent des combinaisons complexes de ces paramètres interprétés en regard de leurs niveaux établis sur des milieux de référence (Reyjol et al,2013;MTES ;2019). Les spécialistes du CEMAGREF en font une description qui ne cherche pas à en masquer la complexité (Souchon et Nicolas, 2011) :…”

“…Du fait de l'obligation de mise au point d'indicateurs de qualité au niveau européen, l'évaluation de l'état écologique des plans d'eau a été un long processus même pour les mesures fondamentales en limnologie comme la température de l'eau, l'oxygène, la salinité et le pH. L'optimisation de la surveillance du Léman, produite par 9 laboratoires et des traitements statistiques poussés, a conduit à la validation du point central du lac (SHL2, par 309m de profondeur), défini il y a près de 60 ans par Bernard Dussart et ses collègues, comme représentatif et utilisé depuis par la Commission Internationale du Léman (CIPEL) (Soulignac et al, 2019).…”