Masters Theses

Date of Award

5-1997

Degree Type

Thesis

Degree Name

Master of Science

Major

Botany

Major Professor

Clifford Amundsen

Committee Members

Patricia L. Walne, Raymond W. Holton

Abstract

Watts Bar Reservoir (WBR), one of nine Tennessee Valley Authority (TVA) regulated mainstream impoundments of the Tennessee River, is intimately associated with a unique seasonal reservoir riparian environment. The impoundment of WBR caused a complete disruption of the riverine biological system and brought about an abrupt formation of a new lacustrine biological system, abutting unadapted, truncated. mesic slopes. The new successional hydric community is threatened by erosion of the unstable shorelines, which may reduce allochthonous organic input, may influence the rate of cultural eutrophication, and may limit the composition and productivity of algal communities due to reduced transparency. The most recent in-depth published information on the ecological health of WBR was conducted by TVA in 1993, and contained phytoplankton productivity estimates based on chlorophyll a concentrations. TVA retains many preserved phytoplankton collections from WBR that have never been taxonomically evaluated. The purpose of this 20 month field-study was to list the phytoplankton genera of WBR and to place their existence into a broader perspective based on the environmental variables recorded in this study and in the literature. Fifty-six phytoplankton samples were collected on 24 days between September 1994 and May 1996. Approximately ten locations on WBR were sampled primarily with a Wisconsin-style plankton net. The study showed that of the 110 phytoplankton genera assigned an identification, all the genera with more than a 50% frequency thrived in all four seasons, usually occurred abundantly in the full study range of pH, conductivity, and temperature, and thus were considered the dominant algae of WBR. In decreasing order of relative occurrence in 56 samples these genera were Pediastrum, Fragilaria, Melosira, Asterionella, Scenedesmus, Euglena, Tabellaria, Anabaena, Bumilleria, and Oscillatoria. Phytoplankton genera that were present in every season were considered seasonal generalists in WBR, and those that fared better in only one or two seasons were considered seasonal specialists. Watts Bar Reservoir supports a very diverse phytoplankton assemblage with a high generic diversity value of 0.976, determined from an adapted version of Simpson’s diversity index. Chlorophytes were found in highest frequency at 48.2%, followed by chrysophytes at 27.3%, cyanophytes at 15.5%, euglenophytes at 4.5%, and pyrrhophytes at 4.5%. Environmental variables were addressed in respect to three categories: 1) season 2) habitat, and 3) physio-chemical factors. Seasonal phytoplankton community similarity indices (Sorensen’s and Jaccard’s Indices) for WBR indicated that summer and fall phytoplankton communities were the most similar, followed by spring and fall. spring and summer, winter and spring, winter and summer, and fall and winter communities. Chrysophytes were found to thrive in winter conditions, at which time the frequency of chlorophytes and pyrrhophytes dwindled. The highest total number of phytoplankton genera per sample day (43) was found on August 26, 1996, along with the highest number of genera collected in any one of 56 sample sets (36). In relation to habitat location, phytoplankton communities in cove-embayment areas had a higher generic richness than main channel-collected phytoplankton, which was probably related to the higher averages for pH, conductivity, and temperature in the cove-embayment areas. Phytoplankton communities from sample locations or combinations of similar types of sample locations selected for community similarity comparisons ranged from 76.9% to 43.6% in similarity according to Sorensen’s Index. When phytoplankton were distributed by genus along three continua between the field-recorded minimum and maximum ranges of the physio-chemical factors, pH, conductivity, and temperature, cyanophytes were found to occur in a higher than average pH and temperature. Phytoplankton community similarity comparisons indicated that the reported communities of selected southern reservoirs had less than 50% of their phytoplankton in common with those of WBR, according to Sorensen’s Index.

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