Nonlinear Dynamics of the Nearshore Boundary Layer of a Large Lake (Lake Geneva)

Self Cite

Lake Geneva, the largest freshwater lake in Western Europe, is subject to important environmental pressures from its densely populated shores and watershed. To maintain and improve water quality in this lake, as well as in other enclosed or semi-enclosed basins, it is essential to understand and be able to predict how nutrients and pollutants are transported within it. A 3D numerical modeling study of Lagrangian transport in Lake Geneva is presented, showing the dispersion of water (based on tracking inert water particles) inflowing from the lake's main tributary, the Rhône River. The relation between dominant winds, circulation patterns, and transport was analyzed. The results demonstrated that transport within the lake is highly inhomogeneous in space and intermittent in time, because water mass movements are controlled by the wind-induced formation of large-scale gyres and their subsequent breakdown into smaller ones. Particle spreading was shown to be sensitive to the depth of the initial particle release, and to the mean depth of the particles' trajectory. However, several preferential pathways could be identified. Some water particles rapidly (days) traveled across the entire lake, through the near-shore region in the upper layer, while others remained trapped for months, particularly in the central region of the lake at depth. Deeper particles tended to remain longer in the lake, due to the insulating effect of stratification, bathymetry obstacles, and slower currents at greater depth.

“…As demonstrated by Cimatoribus et al (), the model realistically reproduced the stratification, mean flow, and internal seiche variability observed in the lake. As an example, in Fig.…”

Section: Methodssupporting

confidence: 59%

Section: Methodsmentioning

confidence: 70%

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

mentioning

confidence: 99%

See 3 more Smart Citations

Tracking Lagrangian transport in Lake Geneva: A 3D numerical modeling investigation

Cimatoribus

Lemmin

Barry

2019

Self Cite

Insights into the dynamics of the deep hypolimnion of Lake Geneva as revealed by long‐term temperature, oxygen, and current measurements

Lemmin

2020

In order to identify or shed light on dominant long‐term processes of the deep hypolimnion of Lake Geneva (309 m depth), time series of temperature and horizontal currents and profiles of temperature and oxygen, taken for over a decade in the deepest part of the lake, were analyzed. The focus was on the summer stratification period (May to October). During that period, temperatures near the bottom always increased quasi‐linearly with the same gradient and small amplitude variability. Vertical mean temperature gradients in the lowest 60 m of the water column remained nearly constant over the years and were comparable to those of the deep ocean. Mean current velocity at the deepest point was 3.0 ± 0.5 cm s−1 and ever‐present inertial motions clearly dominated currents. Oxygen decreased quasi‐linearly and eutrophication appeared not to affect this rate of decrease. It is suggested that as in the deep ocean, breaking internal waves and friction from decaying inertial motion occurring in the deep hypolimnion strongly contribute to turbulent mixing in that layer. The climate change‐induced long‐term warming trend seen in the upper layers of the lake was not detected in the deep hypolimnion. Instead, year‐to‐year climate change‐induced variability strongly affected the deep hypolimnion. During cooling in cold winters, lateral advection contributed more to temperature decrease and oxygen renewal in the deep hypolimnion than vertical convection. The present analysis has shown that the dynamics of this layer are highly three‐dimensional and that the processes occurring therein cannot be correctly described by traditional one‐dimensional concepts.

The setup and relaxation of spring upwelling in a deep, rotationally influenced lake

Roberts

Egan

Forrest

et al. 2020

Strong and sustained winds can drive dramatic hydrodynamic responses in density‐stratified lakes, with the associated transport and mixing impacting water quality, ecosystem function, and the stratification itself. Analytical expressions offer insight into the dynamics of stratified lakes during severe wind events. However, it can be difficult to predict the aggregate response of a natural system to the superposition of hydrodynamic phenomena in the presence of complex bathymetry and when forced by variable wind patterns. Using an array of current, temperature, and water quality measurements at the upwind shore, we detail the hydrodynamic response of deep, rotationally influenced Lake Tahoe to three strong wind events during late spring. Sustained southwesterly winds in excess of 10 m s−1 drove upwelling at the upwind shore (characteristic of non‐rotational upwelling setup), with upward excursions of deep water exceeding 70 m for the strongest event. Hypolimnetic water, with elevated concentrations of chlorophyll a and nitrate, was advected toward the nearshore, but this water rapidly returned to depth with the relaxation of upwelling after the winds subsided. The relaxation of upwelling exhibited rotational influence, highlighted by an along‐shore, cyclonic front characteristic of a Kelvin wave‐driven coastal jet, with velocities exceeding 25 cm s−1. The rotational front also produced downwelling to 100 m, transporting dissolved oxygen to depth. More complex internal wave features followed the passage of these powerful internal waves. Results emphasize the complexity of these superimposed hydrodynamic phenomena in natural systems, providing a conceptual reference for the role upwelling events may play in lake ecosystems.