The Observatory on LAkes (OLA) database: Sixty years of environmental data accessible to the public

Rimet, Frédéric; Anneville, Orlane; Barbet, Denis; Chardon, Cècile; Crépin, Laura; Domaizon, Isabelle; Dorioz, Jean‐Marcel; Espinat, Laurent; Frossard, Victor; Guillard, Jean; Goulon, Chloé; Hamelet, Valérie; Hustache, Jean-Christophe; Jacquet, Stéphan; Lainé, Leslie; Montuelle, Bernard; Perney, Pascal; Quétin, Philippe; Rasconi, Séréna; Schellenberger, Antoine; Tran-Khac, Viet; Monet, Ghislaine

doi:10.4081/jlimnol.2020.1944

Cited by 62 publications

(65 citation statements)

References 55 publications

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“…The datasets used for Lake Geneva are obtained at a single sampling point referred to as SHL2 corresponding to the deepest and pelagic part of the lake. Data were obtained bi-monthly, except for the winter period, for which sampling is performed once a month (Rimet et al 2020). The one-dimensional Schmidt stability was calculated as Sc � = − ∫ 0 m 120 m g( (z) − )(z − z c ) dz .…”

Section: Comparison With Lake Genevamentioning

confidence: 99%

Inhibited vertical mixing and seasonal persistence of a thin cyanobacterial layer in a stratified lake

et al. 2021

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Harmful blooms of the filamentous cyanobacteria Planktothrix rubescens have become common in many lakes as they have recovered from eutrophication over the last decades. These cyanobacteria, capable of regulating their vertical position, often flourish at the thermocline to form a deep chlorophyll maximum. In Lake Zurich (Switzerland), they accumulate during stratified season (May–October) as a persistent metalimnetic thin layer (~2 m wide). This study investigated the role of turbulent mixing in springtime layer formation, its persistence over the summer, and its breakdown in autumn. We characterised seasonal variation of turbulence in Lake Zurich with four surveys conducted in April, July and October of 2018 and September of 2019. Surveys included microstructure profiles and high-resolution mooring measurements. In July and October, the thin layer occurred within a strong thermocline ($$N \gtrsim 0.05$$ N ≳ 0.05 s$$^{-1}$$ - 1 ) and withstood significant turbulence, observed as turbulent kinetic energy dissipation rates ($$\varepsilon \approx 10^{-8}$$ ε ≈ 10 - 8 W kg$$^{-1}$$ - 1 ). Vertical turbulent overturns –monitored by the Thorpe scale– went mostly undetected and on average fell below those estimated by the Ozmidov scale ($$L_O \approx 1$$ L O ≈ 1 cm). Consistently, vertical diffusivity was close to molecular values, indicating negligible turbulent fluxes. This reduced metalimnetic mixing explains the persistence of the thin layer, which disappears with the deepening of the surface mixed layer in autumn. Bi-weekly temperature profiles in 2018 and a nighttime microstructure sampling in September 2019 showed that nighttime convection serves as the main mechanism driving the breakdown of the cyanobacterial layer in autumn. These results highlight the importance of light winds and convective mixing in the seasonal cycling of P. rubescens communities within a strongly stratified medium-sized lake.

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Section: Comparison With Lake Genevamentioning

confidence: 99%

Inhibited vertical mixing and seasonal persistence of a thin cyanobacterial layer in a stratified lake

et al. 2021

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“…Hourly moving averages were applied to the meteorological data prior to the analysis. The data sets were complemented by CTD (conductivity‐temperature‐depth) profiles taken on a regular basis at the deepest point of the lake (SHL2 in Figure 1a) by CIPEL (CIPEL, 2019), which monitors water quality in Lake Geneva (Rimet et al, 2020).…”

Section: Methodsmentioning

confidence: 99%

Wintertime Coastal Upwelling in Lake Geneva: An Efficient Transport Process for Deepwater Renewal in a Large, Deep Lake

et al. 2020

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Combining field measurements, 3‐D numerical modeling, and Lagrangian particle tracking, we investigated wind‐driven, Ekman‐type coastal upwelling during the weakly stratified winter period 2017/2018 in Lake Geneva, Western Europe's largest lake (max. depth 309 m). Strong alongshore wind stress, persistent for more than 7 days, led to tilting and surfacing of the thermocline (initial depth 75–100 m). Observed nearshore temperatures dropped by 1°C and remained low for 10 days, with the lowest temperatures corresponding to those of hypolimnetic waters originating from 200 m depth. Nearshore current measurements at 30 m depth revealed dominant alongshore currents in the entire water column (maximum current speed 25 cm s−1) with episodic upslope transport of cold hypolimnetic waters in the lowest 10 m mainly during the first 3 days. The observed upwelling dynamics were well reproduced by a 3‐D hydrodynamic model (RMSE 0.2°C), whose results indicated that upwelled waters spread over approximately 10% of the lake's main basin surface area. Model‐based Lagrangian particle tracking confirmed that upwelled waters originated from far below the thermocline, that is, >150 m depth, and descended back to around 150–200 m depth over a wide area after wind stress ceased. Observational and particle tracking results suggest that wintertime coastal upwelling, which can occur several times during winter, is an overlooked transport process that is less sensitive to the effects of global warming than convective cooling. It can provide an effective but complex 3‐D pathway for deepwater renewal in Lake Geneva, and other large, deep lakes with a sufficiently long wind fetch.

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“…Lough Bunaveela had full water column temperature observations available at an hourly resolution from 2009 to 2019 and Windermere for 2008 and 2009. The peri-alpine Lake Bourget and Lake Geneva have full water column profiles of temperature available at a bi-monthly or monthly frequency for multiple years (Rimet et al 2020).…”

Section: Study Sitesmentioning

confidence: 99%

Warming winters threaten peripheral Arctic charr populations of Europe

et al. 2020

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As the global climate warms, the fate of lacustrine fish is of huge concern, especially given their sensitivity as ectotherms to changes in water temperature. The Arctic charr (Salvelinus alpinus L.) is a salmonid with a Holarctic distribution, with peripheral populations persisting at temperate latitudes, where it is found only in sufficiently cold, deep lakes. Thus, warmer temperatures in these habitats particularly during early life stages could have catastrophic consequences on population dynamics. Here, we combined lake temperature observations, a 1-D hydrodynamic model, and a multi-decadal climate reanalysis to show coherence in warming winter water temperatures in four European charr lakes near the southernmost limit of the species’ distribution. Current maximum and mean winter temperatures are on average ~ 1 °C warmer compared to early the 1980s, and temperatures of 8.5 °C, adverse for high charr egg survival, have frequently been exceeded in recent winters. Simulations of winter lake temperatures toward century-end showed that these warming trends will continue, with further increases of 3–4 °C projected. An additional 324 total accumulated degree-days during winter is projected on average across lakes, which could impair egg quality and viability. We suggest that the perpetuating winter warming trends shown here will imperil the future status of these lakes as charr refugia and generally do not augur well for the fate of coldwater-adapted lake fish in a warming climate.

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The Observatory on LAkes (OLA) database: Sixty years of environmental data accessible to the public

Cited by 62 publications

References 55 publications

Inhibited vertical mixing and seasonal persistence of a thin cyanobacterial layer in a stratified lake

Inhibited vertical mixing and seasonal persistence of a thin cyanobacterial layer in a stratified lake

Wintertime Coastal Upwelling in Lake Geneva: An Efficient Transport Process for Deepwater Renewal in a Large, Deep Lake

Warming winters threaten peripheral Arctic charr populations of Europe

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