Basin-scale internal waves provide the driving forces for vertical and horizontal fluxes in a stratified lake below the wind-mixed layer. Thus, correct modeling of lake mixing and transport requires accurate modeling of basinscale internal waves: examining this capability with a hydrostatic, z-coordinate three-dimensional (3D) numerical model at coarse grid resolutions is the focus of this paper. It is demonstrated that capturing the correct thermocline forcing with a 3D mixed-layer model for surface dynamics results in a good representation of low-frequency internal wave dynamics. The 3D estuary and lake computer model ELCOM is applied to modeling Lake Kinneret, Israel, and is compared with field data under summer stratification conditions to identify and illustrate the spatial structure of the lowest-mode basin-scale Kelvin and Poincaré waves that provide the largest two peaks in the internal wave energy spectra. The model solves the unsteady Reynolds-averaged Navier-Stokes equations using a semi-implicit method similar to the momentum solution in the TRIM code with the addition of quadratic Euler-Lagrange discretization, scalar (e.g., temperature) transport using a conservative flux-limited approach, and elimination of vertical diffusion terms in the governing equations. A detailed description is provided of turbulence closure for the vertical Reynolds stress terms and vertical turbulent transport using a 3D mixed-layer model parameterized on wind and shear energy fluxes instead of the convential eddy viscosity/diffusivity assumption. This approach gives a good representation of the depth of the mixed-layer at coarse vertical grid resolutions that allows the internal waves to be energized correctly at the basin scale.Wind stresses, surface heating, and density currents form the driving energy fluxes of a stratified lake. The basin-scale energy flux from the wind is of particular interest because of its dominant role in setting the thermocline in motion, which, in the absence of inflows and outflows, is the primary energy store for transport and mixing below the wind-mixed layer. Thus, modeling the basin-scale internal wave behavior is an a priori requirement to modeling and quantifying the flux paths of nutrients in a stratified lake (Imberger 1994). This paper takes a first step in this direction by analyzing our ability to model basin-scale internal waves that are seen in Lake Kinneret, Israel.Energy flux path in a stratified lake-Energy flux through a stratified lake has a fundamental dependence on forced and free baroclinic motions. The wind imparts both momentum and turbulent kinetic energy (TKE) to the water in the surface layer. The TKE distributes momentum vertically in the 1 Corresponding author

The response of the water column to varying conditions of stratification and wind forcing was investigated in Lake Kinneret (Israel) using data collected from thermistor chains and acoustic Doppler current profilers during 1997 and 1998. The strong daily sea breeze was found to generate a vertical mode 1 internal Kelvin wave and basin-scale internal Poincaré waves of vertical modes 1, 2, and 3. The Kelvin wave, the dominant component of the internal wave field, was responsible for alongshore velocities in the nearshore regions. In the upwind nearshore regions, velocities were dominated by the forced response to the wind and were cross-shore in nature. In the lake interior, the Kelvin wave effect on the horizontal velocity field was minor compared to the higher vertical mode Poincaré waves. The Kelvin wave is shown to exist in resonant and nonforced states with the wind, whereas the vertical mode 1 Poincaré wave energy remained relatively constant, despite large variability in the forcing conditions. The energy in the higher mode Poincaré waves varied greatly, both on daily and seasonal timescales. The results demonstrate that the wind energy forces multiple basin-scale internal wave modes and that prior motion in the water column must be considered when determining the subsequent internal wave response in periodically forced systems.

Turbulent mixing within the metalimnion of a stratified lake was investigated using a portable flux profiler (PFP) capable of resolving all three components of the velocities, the conductivity, and the temperature microstructure. Presented is a detailed description of the techniques used in the data processing, particularly in the separation of the turbulence from the internal wave signal. The sampling, carried out in Lake Kinneret (Israel) during the summer for 3 consecutive years, showed that most of the time the vertical flux through the metalimnion was negligible, but, at times, the eddy diffusivity did reach values as high as 10 Ϫ2 m 2 s Ϫ1 . A comparison between direct measurement of the vertical fluxes obtained from the PFP data with that from indirect estimates of the fluxes shows good agreement for the 6 Յ Fr ␥ Ͻ 100 range. Scaling of the turbulence based on Fr ␥ and Ri reveal two classes of turbulent regimes: (1) due to traumata characteristic of internal wave-wave interaction and, another, (2) more energetic and due to shear-driven turbulence. The PFP penetrated the water relatively slowly (0.1 m s Ϫ1) allowing the measurement of temperature fluctuations down to 1 mm and, at the same time, also providing information of the velocity fluctuations. This is different from previous oceanographic measurements, which are always gathered with instrument traversing the water column at velocities closer to 1 m s Ϫ1 , preventing regime (1) from being detected.The vertical exchange between the surface and deep waters in stratified lakes is a central issue in the understanding of the fluxes of particles and nutrients and, consequently, the eutrophication in these water bodies. Imberger (1998) drew a conceptual model of these flux paths in a stratified lake where the wind induces mixing in the surface layer and energizes basin scale internal waves that, in turn, distribute this energy around the lake, leading to mixing mainly near the boundaries (Gloor et al. 1994;Lemckert and Imberger 1998) and reduced fluxes through the metalimnion in the interior of the lake.Even though the vertical fluxes in the metalimnion are small, their quantification is essential for the interpretation of observed biological and chemical parameter variations (Nishri et al. 2000). Naturally, two questions arise as we approach the mixing in the metalimnion: first, what is the magnitude and, second, what are the mechanisms energizing the mixing. Direct measurements of the buoyancy fluxes carried out in the ocean (Moum 1990(Moum , 1996a Yamazaki and Osborn 1993) show the difficulties in making these measurements and provide the first comparison between the direct determination of the fluxes with the more easily ob-1 Corresponding author (saggio@iris.ufscar.br).

Thermistor chain data collected in Lake Biwa (Japan) during a period of strong stratification were used to determine the nature of the water column response to wind forcing. The evolution of the basin-scale waves in the lake were reproduced in three-dimensional numerical simulations and the time variability of the internal wave spectrum is discussed based on spectral analysis of the thermistor chain records. Severe winds associated with the passage of three typhoons during the sampling period excited basin-scale Kelvin and PoincarC waves, which, by interaction with the topography of the lake and non-linear effects, generate trains of high-frequency internal waves. Time-frequency analysis of the temperature signals suggests that the u-* slope of the internal wave spectrum is probably the result of the composition of groups of waves with high intermittence travelling through the wave guide. The observed rapid decay of internal wave energy after severe wind events seemed to be due mostly to high dissipation at the sloping boundaries of the lake.

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Eutrophication is a process characterized by an increase in the aquatic system productivity, which causes profound changes in the structure of its communities. Owing to the high environmental sensitivity of planktonic species, the study of their communities can indicate the deterioration of the environment. The Jaguari and Jacareí reservoirs are part of the Cantareira System, supplying water to Sã o Paulo inhabitants and that has been affected by several forms of continuous human interference.Here we analyze some properties of the zooplankton community as bioindicators of eutrophication and water quality change. In situ physical and chemical measurements were carried out, water was collected for analysis and quantitative zooplankton samples were taken at eight sites in the two reservoirs, in both seasons, dry and rainy. Species were identified and their numerical abundances and biomasses were determined and used to estimate two biological indices. The overall trophic state and zooplankton structure, the Calanoida/Cyclopoida ratio and the k-dominance curves were associated with the disturbance levels, mainly represented by nutrient river inputs and by water level fluctuations. The Jaguari Reservoir was more eutrophicated than the Jacareí Reservoir, as evidenced by the obtained indices values. The zooplankton community properties used as indicators of the reservoir trophic state were useful monitoring tools. Keywords: zooplankton, ABC curves, Calanoida/Cyclopoida ratio, Cantareira System, environmental impact.GAZONATO NETO, A.J., SILVA, L.C., SAGGIO, A.A., ROCHA, O Comunidades zooplanctônicas como bioindicadoras de eutrofização em reservatórios tropicais.http://dx.doi. org/10.1590/1676-06032014001814Resumo: A eutrofização é um processo caracterizado pelo aumento da produtividade do sistema aquá tico, o que provoca profundas alteraçõ es na estrutura de suas comunidades. Devido à alta sensibilidade ambiental das espécies planctô nicas, o estudo de suas comunidades pode indicar a deterioraçã o do ambiente. Os reservató rios Jaguari e Jacareí sã o parte do Sistema Cantareira, que fornece á gua para os habitantes de Sã o Paulo e que tem sido afetado por diversas formas de contínua interferência humana. Neste trabalho vamos analisar algumas propriedades da comunidade zooplanctô nica como bioindicadoras de eutrofizaçã o e alteraçã o da qualidade da á gua. Foram realizadas mediçõ es in situ de variá veis físicas e químicas, amostras de á gua foram coletadas para aná lises e amostras quantitativas de zooplâ ncton foram coletadas em oito localidades compreendendo os dois reservató rios, em duas estaçõ es, seca e chuvosa. As espécies foram identificadas e suas abundâ ncias numéricas e biomassas foram determinadas e utilizadas para estimar dois índices bioló gicos. O estado tró fico e a estrututa do zooplâ ncton, a relaçã o Calanoida / Cyclopoida e as curvas de k-dominâ ncia foram associados com os níveis de perturbaçã o, representada principalmente pela entrada de nutrientes transportados pelo rio e pelas flutuaçõ ...

In lentic freshwater ecosystems, patterns of thermal stratification play a considerable part in determining the population dynamics of phytoplankton. In this study we investigated how these thermal patterns and the associated hydrodynamic processes affect the vertical distribution of phytoplankton during two consecutive diel cycles in a warm polymictic urban reservoir in the metropolitan region of São Paulo, Brazil. Water samples were taken and physical, chemical and biological data collected at half-meter intervals of depth along a water column at a fixed site, every 3 hours throughout the 48-hour period. Two events of stratification, followed by deepening of the thermocline occurred during the study period and led to changes in the vertical distribution of phytoplankton populations. Aphanocapsa delicatissima Nägeli was the single dominant species throughout the 48-hour period. In the second diel cycle, the density gradient induced by temperature differences avoided the sedimentation of Mougeotia sp. C. Agardh to the deepest layers. On the other hand, Pseudanabaena galeata Böcher remained in the 4.0-5.5 m deep layer. The thermal structure of the water was directly affected by two meteorological factors: air temperature and wind speed. Changes in the cell density and vertical distribution of the phytoplankton were controlled by the thermal and hydrodynamic events.Keywords: phytoplankton, thermohydrodynamics, thermal stratification, diel variation, Guarapiranga reservoir. Estratificação térmica de curto prazo e eventos de desestratificação parcial em um reservatório polimítico quente: efeitos sobre a distribuição da comunidade fitoplanctônica ResumoEm ecossistemas de água doce, os padrões de estratificação térmica têm uma influência considerável sobre a dinâmica populacional do fitoplâncton. Neste estudo nós investigamos como os padrões de estratificação térmica e os processos hidrodinâmicos afetaram a distribuição vertical do fitoplâncton durante dois ciclos nictemerais consecutivos em um reservatório urbano na cidade de São Paulo. As amostragens e medidas das variáveis físicas e químicas foram realizadas a cada três horas durante um período de 48 horas, ao longo de um perfil vertical. Ocorreram dois eventos de estratificação e subsequente abaixamento da termoclina acarretando alterações na distribuição vertical do fitoplâncton. Aphanocapsa delicatissima Nägeli foi a principal espécie dominante durante todo o período avaliado. No segundo ciclo nictemeral o gradiente de densidade criado pelas diferenças de temperatura impediu o afundamento de Mougeotia sp. C. Agardh para as camadas mais profundas. Por outro lado Pseudoanabaena galeata Böcher se manteve nas camadas de 4.0 e 5.5 m. A estrutura térmica da água foi diretamente afetada pelos fatores meteorológicos temperatura do ar e velocidade do vento. As mudanças na densidade e na distribuição vertical do fitoplâncton foram controladas pelos eventos térmicos e hidrodinâmicos.Palavras-chave: fitoplâncton, termohidrodinâmica, estratificação térmica, variação ...

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