Department of Biology
Master of Science
A study of the seasonal and spatial distribution of phytoplankters in relation to physio-chemical parameters and discharge regime was conducted in Barren Lake, Kentucky, a flood control reservoir with a dam equipped with a multilevel outlet, from February, 1970, through January, 1971. Paired samples were collected every two weeks from April through October and every three weeks from November through March. Samples were obtained from eight depths in the main pool area of the reservoir and from the tailwater. Reservoir discharge was primarily from the upper 3 m from April through September. At other times, discharge incorporated lower levels to reach and maintain lower winter pool levels. Based upon chemical and biological characteristics, Barren Lake may be considered to be mesotrophic. The alkalinity levels of the lake (range: 44-129 mg/1) averaged 91 mg/1 over the study period. An anaerobic hypolimnion developed in the late summer, and pH was consistently slightly alkaline. The phytoplankton community was dominated by taxa considered to be characteristic of both eutrophic and oligotrophic waters, but maxima were relatively low (77000 - 155000 cells/1). During the study, five major phytoplankton populations were present: March-April, Melosira italica; June, Ceratium hirundinella; July, Asterionella formosa and Dinobryon sertularia; August, Fragilaria crotonensis; and December, Melosira granulata. Two distinct minima occurred in February and May. The main controlling factors for seasonal and spatial succession were concluded to be the physical effects of changing light, temperature, turbidity, turbulence, and discharge. Nutrients, which fluctuated with plankton populations, were always above reported limiting values. Zooplankton, although inversely correlated with phytoplankton populations in the spring, were not felt to affect significantly the phytoplankton populations due to the species composition of the phytoplankton community. The February minimum of 2159 cells/1 coincided with high discharge (3600 cfs), high turbidity (123.8 mg/1), and low temperature (3.3 C). The March-April pulse coincided with the spring increases of light, temperature, and nutrients. The main factors contributing to the pulse was a reduction in discharge (500 cfs), high turbulence, and the improvement in general growing conditions. During May, increasing effects of stratification on turbulence and the rise of discharge rate to 3600 cfs contributed to the spring minimum. In June, Ceratium hirundinella pulsed during high alkalinity (118.8 mg/1) and high temperature (22-24 C). It declined as alkalinity decreased to a seasonal low (72.9 mg/1) and disappeared in the fall when temperature dropped below 7. 5 C. Asterionella formosa achieved dominance (2384 cells/1) in July below the 6 m level, being restricted there due to its inability to tolerate the high temperature (24-29 C) and light intensity (35000 lux @ 0.5 m) in more shallow waters. Its occurrence so late in the year was attributed to its inability to compete with the Melosira populations of early spring. The decline of A. formosa correlated with increases in temperature and decreases in light at the lower depths. Dinobryon sertularia was associated seasonally and spatially with the populations of A. formosa. Fragilari a crotonens is dominated the phytoplankton maximum of 155754 cells/1 in August. It succeeded A_. formosa due to its ability to tolerate higher temperatures (24-29 C) and to utilize nutrients, particularly silica, more efficiently. Its subsequent decline corresponded to decreases in temperature, an increase in discharge (1000 cfs), and a decrease in light in late September. Following the decline of F. crotonensis, Melosira granulata produced a maximum of 45062 cells/1 in December. Its succession was attributed to the return of homothermy and the resulting increases in turbulence and nutrients at fall overturn. The size of the population may have been influenced by the surge in discharge (3600 cfs) in November. In January, a sharp decline in the population coincided with a surge in discharge (3600 cfs) and decreases of temperature and light to seasonal lows. Tailwater plankton populations generally correlated with main pool populations. Tailwater phytoplankton populations tended to be somewhat lower than those of the main pool. Discrepancies, when they occurred, were attributed to difficulties with sampling equipment, high discharge (3600 cfs), and stratification of plankton populations when discharge occurred from levels not associated with those populations.
Wright, John, "Seasonal and Spatial Distribution of the Plankton of Barren Lake, Kentucky, with Special Reference to the Phytoplankton Community" (1973). Masters Theses & Specialist Projects. Paper 1014.