Effects of Heat Fluxes on the Phytoplankton Distribution in a Freshwater Lake

2021 ◽  
Vol 34 (6) ◽  
pp. 603-610
Author(s):  
B. O. Tsydenov
Keyword(s):  
Heat Fluxes ◽  
Freshwater Lake ◽  
Phytoplankton Distribution

Evaluation of the CLM4 Lake Model at a Large and Shallow Freshwater Lake*

2013 ◽  
Vol 14 (2) ◽  
pp. 636-649 ◽  
Author(s):  
Bin Deng ◽  
Shoudong Liu ◽  
Wei Xiao ◽  
Wei Wang ◽  
Jiming Jin ◽  
...  
Keyword(s):  
Latent Heat ◽  
Lake Taihu ◽  
Large Fraction ◽  
Heat Fluxes ◽  
Freshwater Lake ◽  
Sediment Layer ◽  
Local Climate ◽  
Community Land Model ◽  
Numerical Predictions ◽  
Lake Model

Abstract Models of lake physical processes provide the lower flux boundary conditions for numerical predictions of weather and climate in lake basins. So far, there have been few studies on evaluating lake model performance at the diurnal time scale and against flux observations. The goal of this paper is to evaluate the National Center for Atmospheric Research Community Land Model version 4–Lake, Ice, Snow and Sediment Simulator using the eddy covariance and water temperature data obtained at a subtropical freshwater lake, Lake Taihu, in China. Both observations and model simulations reveal that convective overturning was commonplace at night and timed when water switched from being statically stable to being unstable. By reducing the water thermal diffusivity to 2% of the value calculated with the Henderson–Sellers parameterization, the model was able to reproduce the observed diurnal variations in water surface temperature and in sensible and latent heat fluxes. The small diffusivity suggests that the drag force of the sediment layer in this large (2500 km2) and shallow (2-m depth) lake may be strong, preventing unresolved vertical motions and suppressing wind-induced turbulence. Model results show that a large fraction of the incoming solar radiation energy was stored in the water during the daytime, and the stored energy was diffused upward at night to sustain sensible and latent heat fluxes to the atmosphere. Such a lake–atmosphere energy exchange modulated the local climate at the daily scale in this shallow lake, which is not seen in deep lakes where dominant lake–atmosphere interactions often occur at the seasonal scale.

Near-surface mixing in a freshwater lake

1991 ◽  
Vol 42 (6) ◽  
pp. 655 ◽  
Author(s):  
L Padman
Keyword(s):  
Heat Content ◽  
Heat Fluxes ◽  
Freshwater Lake ◽  
Wave Number ◽  
Temperature Profiles ◽  
Measured Temperature ◽  
High Wave Number ◽  
Near Surface ◽  
Vertical Heat ◽  
Surface Mixing

Mixing rates in the upper 10 m of a freshwater lake during the spring heating season are examined by means of fine-structure temperature profiles. Dissipation rate, eddy diffusivity, and vertical heat flux are estimated from 'Thorpe reordering' of measured temperature profiles, a technique that allows these parameters to be obtained from the energy-containing scales of the turbulence rather than from the much smaller scales at which kinetic energy dissipation and scalar diffusion actually occur. The estimated vertical heat fluxes agree reasonably well with the seasonal variability of the lake's total heat content and with the observed short-term variability in mixed-layer temperature. These results suggest that satisfactory estimates of turbulent vertical diffusivities in the surface mixing layer can be obtained from Thorpe reordering. This technique can be applied to data that are considerably simpler and cheaper to obtain than are the measurements of microscale shear required for the more usual 'dissipation' method. Concurrent measurements of vertically averaged shear from a nearby surface mooring are used to study the use of Richardson numbers as a parameter in diffusion models. It is shown that considerable mixing can occur even when the Richardson number based on vertical and temporal averages of shear and density gradient is much larger than the assumed critical value of O(1). Therefore, in regions where the shear and strain variances evaluated over a fixed vertical scale cannot be related either observationally or by means of modelled spectra to the unresolved high wave-number variances, the use of diffusivity parametrizations based on measured, averaged Richardson numbers cannot be justified.

Contribution of large bacteria to bacterial biomass in a deep freshwater lake (Lake Biwa, Japan)

2020 ◽  
Vol 85 ◽  
pp. 131-139
Author(s):  
S Shen ◽  
Y Shimizu
Keyword(s):  
Cell Volume ◽  
Bacterial Cell ◽  
Lake Biwa ◽  
Bacterial Biomass ◽  
Spatial Variations ◽  
Freshwater Lake ◽  
Heterotrophic Nanoflagellates ◽  
Bacterial Productivity ◽  
Transmission Electron ◽  
Seasonal And Spatial Variations

Despite the importance of bacterial cell volume in microbial ecology in aquatic environments, literature regarding the effects of seasonal and spatial variations on bacterial cell volume remains scarce. We used transmission electron microscopy to examine seasonal and spatial variations in bacterial cell size for 18 mo in 2 layers (epilimnion 0.5 m and hypolimnion 60 m) of Lake Biwa, Japan, a large and deep freshwater lake. During the stratified period, we found that the bacterial cell volume in the hypolimnion ranged from 0.017 to 0.12 µm3 (median), whereas that in the epilimnion was less variable (0.016 to 0.033 µm3, median) and much lower than that in the hypolimnion. Additionally, in the hypolimnion, cell volume during the stratified period was greater than that during the mixing period (up to 5.7-fold). These differences in cell volume resulted in comparable bacterial biomass in the hypolimnion and epilimnion, despite the fact that there was lower bacterial abundance in the hypolimnion than in the epilimnion. We also found that the biomass of larger bacteria, which are not likely to be grazed by heterotrophic nanoflagellates, increased in the hypolimnion during the stratified period. Our data suggest that estimation of carbon flux (e.g. bacterial productivity) needs to be interpreted cautiously when cell volume is used as a constant parametric value. In deep freshwater lakes, a difference in cell volume with seasonal and spatial variation may largely affect estimations.

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