Spatial and temporal variation in the summer zooplankton community of a riverine reservoir

Zooplankton community structure was examined at five stations in Normandy Reservoir, Tennessee, on six dates from 11 July to 15 September 1980. Four physical and chemical parameters at three depths at each station were used to discriminate statistically among areas of the reservoir over time; a similar analysis based on nine taxonomic and ecological categories of zooplankton was also completed. Each of the two multi-variate analyses provided a matrix of similarities among station-times (n = 30) in the reservoir. The two similarity matrices were compared by the Mantel test and were found to be not significantly concordant, suggesting that physical-chemical variation among areas in the reservoir during the summer months was not precisely reflected by zooplankton community structure. The lack of congruence between physically- and chemically-determined reservoir structure and structure implied by zooplankton taxa or functional groups was also observed in the results of a random-effects-model ANOVA of physical and chemical parameters and zooplankton densities. ANOVA of zooplankton densities revealed that spatial variation was generally greater than temporal variation, although most of the spatial variation was ephemeral (station-time interaction) rather than fixed (station effects). An ANOVA of physical and chemical variables revealed considerable fixed spatial variation over the same time scale.