Internal Seiche Research Articles

Strong bottom currents in large, deep Lake Geneva generated by higher vertical-mode Poincaré waves

Although internal seiches are ubiquitous in large, deep lakes, little is known about the effect of higher vertical-mode seiches on deepwater dynamics. Here, by combining entire summer season current and temperature observations and 3D numerical modeling, we demonstrate that previously undetected vertical mode-two and mode-three Poincaré waves in 309-meter deep Lake Geneva (Switzerland/France) generate bottom-boundary layer currents up to 4 cm s−1. Poincaré wave amphidromic patterns revealed three strong cells excited simultaneously. Weak hypolimnetic stratification (N2 ≈ 10−6s−2), typical of deep lakes, significantly modified the wave structure by shifting the lower vertical node in the lake’s center from ~75-meter depth (without stratification) to ~150-meter depth (with stratification). This shift induces shear in the middle of the hypolimnion and strengthens bottom currents, with important implications for hypolimnetic mixing and sediment-water exchange. Our findings demonstrate that classical concepts based on constant temperature layers cannot correctly characterize higher vertical-mode Poincaré seiches in deep lakes.

The wash zone and habitat use among three benthic fish species in stratified lakes

AbstractMixing processes in lakes are important in determining sedimentation zones and in setting the so‐called “wash zone”, the area of lake bottom in contact with an oscillating thermocline during wind‐driven internal seiche events. The wash zone also aligns with a sharp change in sediment roughness and hardness. Taken together, these rapid changes in temperature and sediment indicate that the wash zone is a distinctive ecotone in stratified lakes. Depth stratified randomised netting was used to develop count‐based habitat use models for three common benthic fish species as a function of depth or temperature covariates. Using data from two lakes with quite different wash zone depths, we show the wash zone to describe fish habitat for two of three benthic fish species by utilising the top 50% of estimated fish abundance as an indicator of habitat use. White sucker (Catostomus commersoni) habitat use was within the boundaries of the wash zone. Lake whitefish (Coregonus clupeaformis) habitat was adjacent and within the wash zone. Longnose sucker (C. catostomus) habitat use was in the deep areas of lakes dominated by sediment focusing and did not overlap white sucker. Lake whitefish habitat use overlapped both catostomids, but peak abundance of both lake whitefish and white sucker overlapped pointing to potential interactions between these species. Smaller lakes have less vigorous mixing processes and a narrower wash zone, so with a decline in lake size the likely area of the wash zone as habitat for benthic feeding fish would become smaller.

Abnormal surges and the effects of the Seto Inland Sea circulation in Hiroshima Bay, Japan

The Seto Inland Sea (SIS) is the largest semienclosed coastal sea in Japan and has three connections with the outer seas. When a typhoon approached the SIS in September 2011, spatial variations of sea level elevation were observed across the SIS. Additionally, an unusual sea level rise (abnormal surge) occurred in Hiroshima Bay approximately 8 days after the typhoon passed, with the Itsukushima Shrine in the bay flooded by the surge. To understand the mechanism of the abnormal surge in the bay and the relationship between sea level variations and circulation in the SIS, we investigated the 2011 event by applying a high-resolution numerical ocean circulation model using SCHISM with bias correction for sea surface heights (SSHs) at the open boundary. The overall easterly throughflow due to the west-high east-low SSH pattern in the SIS and temporary SSH disturbances due to typhoons were well reproduced in the model results. Among the three connections, the Bungo Channel mainly determined the overall net flux into the SIS and contributed significantly to sea level variations within the SIS. Additionally, the Kii Channel played more crucial roles in shaping the circulation and local sea level variations. The Kanmon Strait exhibited minor impacts. The abnormal tide in Hiroshima Bay was mainly attributed to seawater flux input from the outer seas, in conjunction with the subtidal internal seiche with the bay. The results will help us to further understand the physical processes of the ocean and establish evidence-based safety plans for reducing natural hazard damage.

Hydrodynamic Control of Sediment‐Water Fluxes: Consistent Parameterization and Impact in Coupled Benthic‐Pelagic Models

AbstractBenthic oxygen dynamics and the exchange of oxygen and other solutes across the sediment‐water interface play a key role for the oxygen budget of many limnic and shallow marine systems. The sediment‐water fluxes are largely determined by two factors: sediment biogeochemistry and the thickness of the diffusive boundary layer that is determined by near‐bottom turbulence. Here, we present a fully coupled benthic‐pelagic modeling system that takes these processes and their interaction into account, focusing especially on the modulation of the sediment‐water fluxes by the effects of near‐bottom turbulence and stratification. We discuss the special numerical methods required to guarantee positivity and mass conservation across the sediment‐water interface in the presence of rapid element transformation, and apply this modeling system to a number of idealized scenarios. Our process‐oriented simulations show that near‐bottom turbulence provides a crucial control on the sediment‐water fluxes, the oxygen penetration depth, and the re‐oxidation of reduced compounds diffusing upward from the deeper benthic layers especially on time scales of a few days, characterizing oceanic tides, internal seiching motions in lakes, and mesoscale atmospheric variability. Our results also show that the response of benthic‐pelagic fluxes to rapid changes in the forcing conditions (e.g., storm events) can only be understood with a fully coupled modeling approach.

Physical mechanisms of internal seiche attenuation for non-ideal stratification and basin topography

The dynamics of vertical mixing and the occurrence of basin-scale internal waves (internal seiches) in lakes and reservoirs are often classified and described based on the force balance of wind shear and horizontal pressure gradients resulting from wind-generated currents (the Wedderburn number). The classification schemes consider specific time scales that are derived based on a simplified vertical density distribution, a rectangular basin shape, and a constant water depth. Using field measurements and numerical simulations with a validated hydrodynamic model, we analyzed the transfer of energy from wind to the internal seiche field in a small reservoir. Our results demonstrate that the basin shape has a strong influence on the energy dissipation and on the transfer of energy to propagating high-frequency internal waves, thereby attenuating the generation of basin-scale internal seiches. Most of the energy loss of the internal seiche occurs at the sloping boundary, where the internal seiche is susceptible to shoaling and breaking. These findings suggest that the Wedderburn number can be used to predict the occurrence of internal seiche activity in continuously stratified systems. As the Wedderburn number and derived mixing classifications are widely applied also for the interpretation of observed ecological and biogeochemical processes, its application to basins with sloping bathymetry and complex shape should be critically scrutinized, and deviations from predicted dynamics, including the presence of hotspots of turbulent mixing, should be considered.

Scale interactions between an internal seiche and double diffusion

Scale interactions between an internal seiche and double diffusion

Factors influencing summer phytoplankton biomass in a large river system with impoundments: retention time, zooplankton grazing, thermal stratification and internal seiching in a hydro lake

ABSTRACT Phytoplankton production as indicated by chlorophyll a concentrations in Lake Karāpiro, the last hydro power station lake on the Waikato River, shows high seasonal variability but a long term trend of decrease, despite an abundance of nutrients (N and P) in the river. Early studies pre-2005 of the river system’s eight hydro dams identified that only Lakes Ohakuri and Arapuni thermally stratified in summer, and it was hypothesised that thermal stratification could enhance phytoplankton productivity through increased retention time. During. a more recent study (2013–2014), Lake Karāpiro was also found to be thermally stratified with the thermocline around the depth of the power station intake. In this study we found that thermal stratification enhanced phytoplankton growth by confining them to the well-lit epilimnion. However, growth was limited as the nutrient supply became depleted and zooplankton grazing was found to adversely impact phytoplankton biomass, with highest grazing pressure in spring and lowest in late summer to autumn, consistent with an increase in chlorophyll a concentration. We found that wind stress along the lake axis can induce an internal seiche, which causes a substantial stepwise change in water quality downstream as the thermocline sweeps up and down across the power station intake.

Periodic boundary layer separation and lateral intrusions observed above a sloping lakebed

AbstractLateral intrusions flowing from the boundaries of lakes and oceans might influence basin‐scale distributions of heat, chemical solutes, sediments, and organisms. Here, observations of numerous intrusions from multiple locations in a small lake were used to examine the relation of intrusions to a lakewide internal seiche, and to estimate mean exchange between sloping bottom boundary layers (BBLs) and the lake interior. BBL waters were observed periodically separating from the bed and flowing laterally offshore. Boundary layer separation was initiated where strong downslope flows encountered upslope‐propagating temperature fronts. These separation events propagated upslope, coherent with the vertically propagating internal seiche, resembling previously reported cases of upslope‐propagating internal bores. Following separation, jets flowed offshore immediately above temperature fronts, transporting boundary layer water at least 61 m into the interior. Jet propagation could be traced upwards, from the bed at 9.4 m depth to the base of the surface mixed layer. Mean offshore transport was most intense within the metalimnion (4–7 m depth). Intruding intermediate‐temperature thermocline water was likely supplied both by river inputs and by boundary mixing of cold and warm waters. These findings suggest that periodic jets, resulting from seiche‐induced boundary layer separation, transported significant quantities of water from the boundary layer toward the stratified lake interior, with possible implications for distributions of sediments, solutes, and organisms.

Influence of internal seiche dynamics on vertical movement of fish

Abstract Internal seiches are common in stratified lakes, with significant effects on stratification patterns, hydrodynamics and vertical nutrient transport. In particular, seiches can change the vertical distribution of the thermocline and the cold hypolimnetic and warm epilimnetic water masses by several metres on a timescale of a few hours, leading to rapid and strong changes in temperature profiles and oxygen availability, with profound effects on mobile and sessile organisms. This could affect fish communities directly, through physiological stress and elevated mortality, and indirectly, through prey distribution. The aim of this study was to analyse the effects of internal seiche dynamics on lacustrine fish behaviour, and to characterise fish reaction patterns, with the main focus on vertical movement of fish in the vicinity of a shifting thermocline, and avoidance of cold hypolimnetic water. The analysis was based on acoustic telemetry data from Lake Milada, a post‐mining lake in the Czech Republic, with a total of 61 tracked individuals of four species: northern pike (Esox lucius), wels catfish (Silurus glanis), tench (Tinca tinca) and rudd (Scardinius erythropthalmus). The effects of seiche dynamics on the four species studied were weak but significant during the day, while at night they affected only rudd. Upward seiches elicited stronger responses in fish than downward seiches, and the impacts occurred only during the strongest seiche events. Thermocline shifting during seiche events may induce a transient reduction in habitat for seiche‐reacting species, and thus affect predation and other inter‐ and intra‐specific interactions, as well as fish community dynamics.

An Estimation of Precipitation Retention Time Using Depth Metres in the Northern Basin of Lake Biwa

To facilitate climate change adaptations and water management, estimates of precipitation retention time (time required for precipitation to reach a lake) can help to accurately determine a water body’s terrestrial water storage capacity and water cycle. Although estimating the precipitation retention time on land is difficult, estimating the lag between precipitation on land and a rise in lake water levels is possible. In this study, the delay times (using a depth metre installed in the mooring system in the northern basin of Lake Biwa from August 2017 to October 2018) were calculated using response functions, and it evaluated the precipitation retention time in the catchment. However, as several delays between the river surface flow (<1 d) and shallow subsurface flow (≈45 d) remained unidentified, the delay times resulting from direct precipitation on the lake as well as from internal seiches were determined. The results suggest that delay times of approximately 20 d correspond to the paddy–waterway system between the river inflow and the subsurface flow, and that this effect corresponds to that of large rivers such as the Ane River. These findings can enhance water management strategies regarding the regulation of river flows, adapting to climate change-induced fluctuations in precipitation.

Bottom boundary layer mixing processes across internal seiche cycles: Dominance of downslope flows

AbstractIn a stratified lake, where an internal seiche maintained an oscillating bottom boundary layer (BBL), processes including strain‐induced periodic stratification (SIPS), a downslope mean flow, and upslope‐propagating internal waves controlled fluctuating BBL mixing rates. To investigate these processes, high‐resolution temperature and velocity profiles were measured within 2 m of the sloping bed, through more than 100 cycles of upslope and downslope flows. The associated seiche‐induced velocity reversals coincided with the arrival of upslope‐propagating cold fronts. Although fronts are sometimes associated with internal wave breaking, in this lake the measured frontal slopes were small and breaking did not occur. When fronts were not propagating past instruments, near‐bed stratification was consistent with SIPS, being intensified by downslope flows and reduced by upslope flows. Owing to a downslope near‐bed mean flow, which was previously shown to cancel an upslope internal‐wave Stokes drift, peak downslope velocities regularly exceeded peak upslope velocities. Given these strong downslope velocities, turbulent dissipation rates were most intense during downslope phases. Therefore, during downslope flow, creation of stratification by SIPS coincided with elevated dissipation, creating conditions for effective mixing. Correspondingly, two simple parameterizations for mixing efficiency suggest that most of the total near‐bed buoyancy flux (≥ 82%), and most of the irreversible flux (87%), occurred during the downslope‐flow phase of internal seiche cycles. The observed mechanism for dominant mixing during downslope flow has potential to act in other environments where internal waves propagate up sloping beds.

Internal seiches as drivers of fish depth use in lakes

AbstractInland temperate lakes undergo various physical processes, such as thermal stratification, that dictate the spatial availability of suitable temperature and dissolved oxygen conditions. Here, we use intensive limnological monitoring and acoustic telemetry transmitters implanted in wild fish to document the magnitude and frequency of thermocline deflection events (i.e., wind driven internal seiches that lead to upwelling of hypoxic hypolimnetic water) and their influence on freshwater fish depth use in a coastal embayment of Lake Ontario. The embayment experienced around 100 internal seiche events during a 3‐month period and tracking of walleye (Stizostedion vitreus) vertical positions in the water column showed clear trends of avoidance of low dissolved oxygen. Quantile regression showed a significant correlation between walleye vertical position and the depth of the 3, 4, and 5 mg L−1 oxyclines, with the 3 mg L−1 oxycline having the largest effect. Upwellings of the hypoxic hypolimnion forced walleye to use the water column above these fluctuating oxyclines (5th percentile, p < 0.001), with 94.2% of detections occurring at depths above the 3 mg L−1 oxycline. Understanding how fish respond to upwelling events (both temperature and oxygen) is important for fisheries assessment, management, and habitat restoration planning as there is clear avoidance of suboptimal oxygen conditions and sampling in the overcrowded fringes of these low‐oxygen zones could artificially inflate population estimates.

Laboratory-scale investigation of a periodically forced stratified basin with inclined endwalls

We present results of numerical simulations of a stratified reservoir with a three-layer stratification, subject to an oscillating surface shear stress. We investigate the effect of sloped endwalls on mixing and internal wave adjustment to forcing within the basin, for three different periods of forcing. The simulations are carried out at a laboratory scale, using large-eddy simulation. We solve the three-dimensional Navier–Stokes equations under the Boussinesq approximation using a second-order-accurate finite-volume solver. The model was validated by reproducing experimental results for the response of a reservoir to surface shear stress and resonant frequencies of internal waves. We find interesting combinations of wave modes and mixing under variation of the forcing frequencies and of the inclination of the endwalls. When the frequency of the forcing is close to the fundamental mode-one wave frequency, a resonant internal seiche occurs and the response is characterized by the first vertical mode. For forcing periods twice and three times the fundamental period, the dominant response is in terms of the second vertical mode. Adjustment to forcing via the second vertical mode is accompanied by the cancellation of the fundamental wave and energy transfer to higher-frequency waves. The study shows that the slope of the endwalls dramatically affects the location of mixing, which has a feedback on the wave field by promoting the generation of higher vertical modes.

Laboratory experiments on the influence of stratification and a bottom sill on seiche damping

Abstract. The damping of water surface standing waves (seiche modes) and the associated excitation of baroclinic internal waves are studied experimentally in a quasi-two-layer laboratory setting with a topographic obstacle at the bottom representing a seabed sill. We find that topography-induced baroclinic wave drag contributes markedly to seiche damping in such systems. Two major pathways of barotropic–baroclinic energy conversions were observed: the stronger one – involving short-wavelength internal modes of large amplitudes – may occur when the node of the surface seiche is situated above the close vicinity of the sill. The weaker, less significant other pathway is the excitation of long waves or internal seiches along the pycnocline that may resonate with the low-frequency components of the decaying surface forcing.

The Annual Cycle of Energy Input, Modal Excitation and Physical Plus Biogenic Turbulent Dissipation in a Temperate Lake

AbstractA year of measurements by Doppler Current Profilers, a chain of temperature sensors and a suite of meteorological instruments has been analyzed to elucidate the seasonal cycle of the dynamical response of a temperate lake (Windermere) to surface forcing. The efficiency of energy input to the lake (Eff) was determined by comparing the rate of working by the surface wind‐stress RWy with the downward flux of momentum in the atmosphere. Eff was found to increase from values of ∼0.3% in winter mixed conditions, up to ∼1.2% during summer stratification, when internal seiches were present. Water column kinetic energy was similarly enhanced during stratification. Spectral analysis of the axial velocity showed that the first vertical mode was dominant during most of the stratified period with a less prominent second mode appearing in the early part of the summer. The observed periods and vertical structure of these modes generally accorded with estimates from internal wave theory based on density profiles. During stratification, pycnocline dissipation exhibited high variability linked to the surface forcing with an average, depth‐integrated, pycnocline dissipation rate of 2.5 × 10−5 W m−2 corresponding to ∼3%–4% of RWy. Over the same period, the dissipation rate in the bottom boundary layer (BBL) exhibited a marked diurnal variation unrelated to physical forcing. Acoustic backscatter indicated the presence of vertically migrating organisms with peak aggregation in the BBL around midday coinciding with maximum dissipation. During stratification, biogenic dissipation contributed an average of ∼36% of the total BBL dissipation rate of ∼5.7 × 10−5 W m−2.

Fate of Artificially Injected Oxygen in the Hypolimnion of a Two‐Basin Lake: Amisk Lake, Revisited

AbstractBubble‐plume diffusers are increasingly used to add dissolved oxygen (DO) to the hypolimnion of lakes and reservoirs. Bubble plumes are successful at replenishing hypolimnetic DO, but they also introduce mixing energy that induces subtle changes in the thermal structure of the reservoir, driving changes in plume behavior. To account for this complex plume‐reservoir interaction, a double bubble‐plume model is coupled with a three‐dimensional hydrodynamic model. The coupled model is used to reassess a field‐scale analysis of the bubble‐plume diffuser in two‐basin Amisk Lake, aiming at evaluating the relative role of bubble‐induced circulation and internal‐seiching in driving inter‐basin transport under stratified conditions. A large‐scale plume‐induced circulation was previously thought to be the main driver of inter‐basin oxygen transport. This interpretation was based on the attribution of the time‐averaged circulation in the channel due to plume operation. However, the intrinsic complexity of the hydraulic system and the sparseness of the field data introduced large uncertainties in the previous analysis. Here, we demonstrate that the time‐averaged circulation is primarily the result of wind‐driven internal seiches. Oxygen exchange is shown to be controlled by the interaction between internal seiche‐driven horizontal transport along the channel, and, the rate at which added oxygen reaches the layers above the sill, which is mainly controlled by plume‐induced circulation. Internal‐seiche driven transport through basin constrictions will vary depending on the magnitude of the wind forcing, depth of the thermocline and the channel geometry. These results highlight the importance of understanding water movement prior to introducing restoration actions in lakes.

Intense variability of dissolved oxygen and temperature in the internal swash zone of Hamilton Harbour, Lake Ontario

ABSTRACT The thermocline of large, stratified lakes is constantly sloshing along the sloping bed, creating a spatially variable internal swash zone. Temperature and dissolved oxygen vary rapidly here, potentially impacting fish habitat on timescales of hours. Large spatial differences in the time-dependent variance of temperature around Hamilton Harbour, Lake Ontario, Canada, were partly controlled by basin shape and bathymetry. The temporal variability was nearly twice as large at sites along the mildly sloping, narrow, upwind end of the basin relative to those at a similar depth at the steeper, broad, downwind end. Because the thermocline and oxycline were coincident, the same physical mechanisms resulted in a dissolved oxygen variance also twice as great at the mild slope compared to the steeper slope. Frequent hypoxic events occurred throughout the internal swash zone, drastically reducing the availability of fish habitat for anoxia-intolerant species. In the dynamic littoral zone, weekly measurements would overlook the acute temporal variability of temperature and dissolved oxygen. Here, we demonstrate that field observations and 3-dimensional (3D) hydrodynamic modelling can predict how basin morphometry affects internal seiche dynamics and spatial variability of internal swash zones.

Internal seiches in a karstic mesotrophic lake (Prošće, Plitvice Lakes, Croatia)

A lake temperature experiment was performed at the Prošće, Plitvice Lakes, Croatia during a 4-month observational period (6 July–4 November, 2019) to investigate the occurrence and characteristics of internal seiches in the lake. Two-minute mean lake temperatures were measured at a single lake point at fifteen depths ranging from 0.2 to 27 m. Analysis of these data provided insight into the previously unknown and rather complex Prošće Lake seiching. Power spectral densities (PSDs) and magnitude-squared coherences (γ2), together with corresponding cross-spectrum phases that were obtained from the hourly mean lake temperature, air pressure and wind speed data, suggested the presence of three vertical modes of an internal seiche. The first mode (V1H1, period of 6.09 h) corresponds to free baroclinic oscillations; the second mode (V2H1, period of 11.64 h) and the third mode (V3H1, period of 25.60 h) are associated with forced baroclinic oscillations of the lake interior. Excitation of the higher vertical modes is attributed to the influence of dense tributary water. Due to this water influence, vertical temperature gradients in the lake interior were relatively weak; consequently, a single thick metalimnion and/or two metalimnetic layers were established, which resulted in the presence of the V2H1 and V3H1 modes, respectively. Additionally, due to the influence of tributary water, the lake did not attain the typical stratification that is characterized by hypolimnetic temperatures of ≈ 4°C. Instead, during the entire observational period, the hypolimnetic temperatures were consistently above 7.6 °C.

Speed of sound gradients due to summer thermal stratification can reduce the detection range of acoustic fish tags: results from a field study in Hamilton Harbour, Ontario

Understanding detection range is a key factor for the use of acoustic telemetry in fisheries research. Lakes have strong seasonal changes in thermal stratification, as well as short-term changes due to internal seiches. These thermal gradients in lakes imply strong sound-speed gradients that can refract and diverge acoustic signals, leading to acoustic attenuation and smaller detection range. Using field-based range testing and the Bellhop acoustic model, we investigated how changes in stratification lead to changes in detection range within Hamilton Harbour, Ontario, Canada. During the summer stratified period, the detection range was less than 350 m, whereas in the isothermal fall, range was up to 500 m. Range test data from three separate field observations showed a good correlation with Bellhop predictions. Owing to the intense internal seiches in Hamilton Harbour, the stratification in the shallower littoral regions essentially switched between stratified and isothermal conditions over short timescales, which is predicted to lead to high temporal variability in detection range that must be accounted for during the analysis and interpretation of telemetry-derived data.

Influences of upstream reservoir stratification and downstream tidal fluctuations on the summer thermal regime of a regulated coastal river

AbstractThis study focused on the effects of upstream reservoir thermal dynamics and downstream tidal influences on temperatures in a 25‐km reach of Alouette River (coastal British Columbia, Canada) below a control dam and upstream of its confluence with Pitt River. Temperature was monitored during summer 2013 using 25 sensors. Water was released from the reservoir through a low level outlet at approximately 2.7 m3 s−1, except during late spring when a higher flow was released over the dam spillway. Temperature variations in the lowest section of Alouette River, and in the lower portion of a tributary, were distinct from those further upstream due to backwatering effects associated with a semi‐diurnal tide, which can cause flow reversals in Pitt River. An internal seiche was identified in the reservoir during mid‐summer that resulted in oscillating releases of warmer and cooler water with an amplitude of up to 6°C and a period of approximately 12 hr. Wavelet analysis and band‐pass filtering indicated that the 12‐hr signal declined in strength with downstream distance, but remained detectable about 15 km below the dam. In contrast, the 24‐hr diel signal increased in strength with distance below the dam. Travel times computed via cross‐correlation of the 12‐hr signals with that at the low level outlet were within ±10% of those estimated from measured mean velocities. Lagrangian tracking of water parcels using the derived travel times indicated that the cooling effect of periodic releases of cold water during the seiching period persisted to the lower extent of the non‐tidal reach. The tidally influenced locations experienced higher temperatures than those recorded in the non‐tidal portion of Alouette River, although the relative roles of heating in the upstream tidal reach versus upstream advection of water associated with tide‐driven flow reversals in Pitt River require further study.