Zooplankton of the Big Eau Pleine Reservoir

[摘要] Composition, abundance, and distribution of zooplanktonwere determined during September, 1973 to September,1974 in the Big Eau Pleine Reservoir, a eutrophic, 2832 ha(10.93 m^2 ) fluctuating reservoir in central Wisconsin.Yearly water level fluctuations of up to 9.6m (31.5 ft.)occur commonly, and maximum drawdown occurs during winter.The yearly drawdown appeared to have little affect on thezooplankton populations because: a) zooplankton speciescomposition in the Big Eau Pleine Reservoir was typicalfor lakes of the Great Lakes Region, b) the mean annualtotal number of 298 zooplankton per liter and biomass of362 mg/m^3 (13.8 kg/ha) for the ice-free period of September20 through December 1, 1973 and May 13 through September 5,1974, were high in comparison with other bodies of water,c) the 30-year mean annual flushing rate of 158 days isconsiderably greater than that thought to be limiting tozooplankton, and d) a winter drawdown, as in the Big EauPleine Reservoir, occurs when zooplankton numbers are lowand has less affect than if it occurred during summer,when zooplankton numbers are high.The reservoir remained thermally unstratified exceptfor a brief period during late June and early July. Lowwater transparency could probably be attributed to algaeblooms and suspended sediments during summer and suspendedsediments during winter. Dissolved oxygen was minimal in winter, reaching concentrations as low as 0.1 ppm inJanuary and February. Of 25 zooplankton taxa in thereservoir, at least 17 were found at each of 6 samplingsites. Copepod nauplii, Rotifera, and Chydorus sphaericuscomprised 66 to 75% of zooplankton numbers. As is typicalin other bodies of water, maximum biomass and number perliter occurred during summer and minima during winter.The reservoir, probably due to a lack of horizontal andvertical thermal stratification, had little horizontal orvertical differences in zooplankton number per liter, andno significant horizontal differences in zooplanktonbiomass.

[发布机构] University of Wisconsin-Stevens Point, College of Natural Resources