Theses and Dissertations


Title: The penetration of light and the concentration of dissolved oxygen in fertilized pond waters infested with Microcystis

Name: Beasley, Philip Gene

Degree: MS

Chair: Dr. John M. Lawrence

Resides: FAA Library

University: Auburn

Location: Auburn, Alabama

Date: 1962

Pages: 70

Keywords: Light,Dissolved Oxygen,Fertilized Pond Waters,Microcystis.

Abstract:

This project was initiated as an exploratory study of the penetration of light into fertilized pond waters infested with Microcystis. Five earthen experimental ponds which were fertilized with inorganic fertilizer or received daily applications of fish food or both were used in this experiment.Weekly measurements were made of light intensity, dissolved oxygen concentration, free carbon dioxide concentration, and water temperature at various depths in these ponds. Surface and subsurface light intensities were measured in microamperes with submersible Weston Photronic photoelectric cells connected to a microammeter. Surface light intensity was measured in foot-candles with a Weston sunlight illumination meter. Surface and subsurface light intensities measured in microamperes were subsequently converted to foot-candles. The dissolved oxygen concentration and temperatures were measured with an oxygen-temperature meter. Counts of Microcystis and zooplankters were made from vertical plankton net hauls. Copper sulfate was periodically applied to control Microcystis.The depth at which the light intensity was less than 1 foot-candle varied with the degree of infestation of Microcystis. With heavy infestation the light intensity was below1 foot-candle at 5 feet: with low infestation the light intensity was not below 1 foot-candle at 7.5 feet: with moderate infestation the light intensity fluctuated above and below 1 foot-candle at 7.5 feet.The dissolved oxygen concentration at 5 feet in the pond heavily infested with Microcystis was usually above 1 ppm and above 3 ppm in the moderately infested ponds. In the ponds with relatively low abundance of Microcystis the dissolved oxygen concentration was usually above 1 ppm at 7.5 feet.Relatively high light intensities were sometimes recorded at depths where the dissolved oxygen concentration was less than 1 ppm. At depths where the dissolved oxygen concentration was less than 1 ppm, the temperature was somewhat lower than the upper stratum. Generally, the depth to which relatively constant temperatures extended decreased with the infestation of Microcystis. This suggests that dense growths of Microcystis contribute to thermal stratification by absorbing heat and decreasing the depth at which cooler waters are found. The cooler water then limits the descent of phytoplankton and thereby limits the amount of dissolved oxygen at lower depths as a result of a scarcity of phytoplankton.Applications of copper sulfate generally resulted in an increase of light penetration by reduction of Microcystis. Due to the infrequency of sampling dates (at weekly intervals) it was impossible to definitely establish the relationship between reduction of Microcystis by treatment with copper sulfate and the resulting concentration of dissolved oxygen.

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