Zooplankton Community Abundance and Diversity in Dardanelle Reservoir, Arkansas, 1981-1990

Journal of the Arkansas Academy of Science Volume 46 Article 7 1992 Zooplankton Community Abundance and Diversity in Dardanelle Reservoir, Arkansas, 1981-1990 John D. Rickett University of Arkansas at Little Rock Robert L. Watson University of Arkansas at Little Rock Follow this and additional works at: http://scholarworks.uark.edu/jaas Part of the Fresh Water Studies Commons, Terrestrial and Aquatic Ecology Commons, and the Water Resource Management Commons Recommended Citation Rickett, John D. and Watson, Robert L. (1992) "Zooplankton Community Abundance and Diversity in Dardanelle Reservoir, Arkansas, 1981-1990," Journal of the Arkansas Academy of Science: Vol. 46 , Article 7. Available at: http://scholarworks.uark.edu/jaas/vol46/iss1/7 This article is available for use under the Creative Commons license: Attribution-NoDerivatives 4.0 International (CC BY-ND 4.0). Users are able to read, download, copy, print, distribute, search, link to the full texts of these articles, or use them for any other lawful purpose, without asking prior permission from the publisher or the author. This Article is brought to you for free and open access by ScholarWorks@UARK. It has been accepted for inclusion in Journal of the Arkansas Academy of Science by an authorized editor of ScholarWorks@UARK. For more information, please contact , . Journal of the Arkansas Academy of Science, Vol. 46 [1992], Art. 7 JOHN D. RICKETT and ROBERT L WATSON Biology Department University ofArkansas at LittleRock LittleRock, AR 72204 ABSTRACT Zooplankton samples were collected quarterly from five stations representing the discharge bay and four "control"or "dispersing impact" stations. Rotifers dominated all samples numerically and by the number of taxa. All major groups (Rotifera, Cladocera, Copepoda, and Protozoa) exhibited greatest abundances during the summer. Quarterly variations in abundance and number of taxa were documented. Except for an increase in taxonomic analysis detail between 1981 and 1984 resulting in several more taxa added to the list, no long-term increases, declines or repeating cycles were apparent. Margalef's Richness Index reflected this change and showed a long-term increase with evidence of a 5- to 6-year repeating cycle. Shannon's Heterogeneity and Pielou's Evenness Indices showed no obvious trend or cycle. When these variables at Sta. 5 (discharge) were compared with other stations, no significant differences (a = 0.05) were documented.. INTRODUCTION Environmental studies on Dardanelle Reservoir have included plankton surveys (Palko 1970; Rickett and Watson 1983a, 1983b), surveys of radionuclides (Chittenden 1979, 1980) and general water chemistry (Rickett and Watson 1985). Several of these studies, including the present one, have been funded by Arkansas Power & Light Company (presently Entergy Corporation) to determine the environmental compatibility of the operation of Arkansas Nuclear One, a generating of this facility facility located on the north shore of the reservoir. Unit I began commercial production in 197S and uses reservoir water pumped once through for condenser cooling. Rickett and Watson (1983a) described the general structure of the zooplankton community (taxa, abundances and temporal variations) between 1975 and 1983. The principal objective of this project segment has been to document longer term impacts, ifany, of plant operation on the composition and variations in the zooplankton community for the period 1981 through 1990. A secondary objective of this report was to review river discharge variations and relate such variations, ifpossible, to variations in the zooplankton community. . Figure 1 Dardanelle Reservoir in the vicinity of ANO with sampling sites noted. SITE DESCRIPTION Dardanelle Reservoir was created on the main channel of the Arkansas River by the Kerr-McClellan Navigation System in the early 1960s and has been managed by the U.S. Army Corps of Engineers. Rickett and Watson (1985) reported morphometric data on the reservoir and a general description of watershed components. Since 1985 additional housing and urban development have occurred north and west of the city of Russellville, and limited development of agriculture and silviculture has occurred elsewhere in the watershed. There have also been minor development projects such as roads, small businesses and individual housing units inthe watershed area. Five stations were established to sample different general areas of the reservoir as well as to compare four "control" stations with the discharge station (Figure 1). The intake and upstream control stations (16 and 21, respectively) were distanced beyond the influence of the thermal discharge (5), whereas the mid-lake station (11) was expected to be withinits influence. By the time discharge water reached the downstream station (15), no residual heat was expected to remain. METHODS Depth-integrated zooplankton samples were collected quarterly at five stations on the reservoir during the years 1981-1990. Two hundred liters of water were pumped through a Wisconsin-style plankton net having 80micron mesh size, and the filtrate was preserved with Meyer's fixative. Approximately two-thirds of the volume was taken from the surface to 0.3 m depth, whereas the remaining third was taken equally from 0.3 to 3.0 m, a depth generally representing the lower margin of the euphoric zone. In the lab, sample aliquots were placed in a Sedgwick -Rafter counting cell and viewed at lOOx with a Nikon inverted microscope equipped with a mechanical stage. Organisms were identified to genus and tabulated as number per liter. Community structure was described by evaluating zooplankton abundances, number of taxa, and three indices of diversity: Margalef's Richness, Shannon's Heterogeneity and Pielou's Evenness (see Appendix for formulae and notations). The Margalef formula compares the number Proceedings Arkansas Academy of Science, Vol. 46, 1992 Published by Arkansas Academy of Science, 1992 57 57 Journal of the Arkansas Academy of Science, Vol. 46 [1992], Art. 7 fiGoGrvoir^ /^iKcinSflS, iwO ii99U £Oopi9riKXon /adljnuance orivi i/iv©rsiiy in l/cJiQcJiigiiG of taxa in a sample and the total number of organisms comprising those taxa. The Shannon index evaluates how the individuals are distributed among the taxa, whereas the Pielou Evenness index is somewhat more sensitive than Shannon's in that it relates the distribution if the individuals back to the number of taxa in the sample. For all indices used, an increase in number of taxa without changing the number of individuals, or a decrease in the number ofindividuals or individuals per taxon without changing the number of taxa produces a larger calculated value, a feature which must be considered for interpretation. b For the mean number of organisms per station, the years 1981-1983 exhibited consistently low numbers (fewer than 1000 per liter), followed immediately (1984) by the highest peak (...truncated)