Shallow Impoundments

Shallow impoundments, those often or continuously fully mixed, behave differently from deep ones. A relatively greater area of lake bottom is less than 5 m in depth and within the reach of significant wind generated shear cur rents. Phytoplankton and detritus are resuspended from the bottom during windy conditions and reduce the pene tration of light for a period sufficient to impair phytoplankton production, resulting in oscillations of biomass.

The longitudinal gradients characteristic of deep impoundments is not seen among shallow ones, because dispersion of solutes and suspended matter is influenced much more by wind. The effect of wind mixing can be magnified by long water retention times. Horizontal distri bution ofboth phytoplankton and zooplankton is especially sensitive to fluctuations in the direction of wind.

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