Zooplankton community response to reservoir aging

Abstract

Changes in zooplankton diversity and density in response to reservoir aging in Pawnee Reservoir were investigated. Zooplankton samples collected from April 1992 through April 1993, were compared to a similar study conducted after initial impoundment by Helzer (1971Helzer ( ), in 1968Helzer ( -1970. Since this initial study, increases in turbidity and resulting changes in biotic interactions significantly altered the zooplankton community. A significant increase in total zooplankton density and a decrease in species richness were observed between study periods. Density increased from 24.6 to 95.4 individuals L-t, while the number of taxa declined from fourteen to ten. During this time period, Cyclops vemalis became the dominant zooplankter in the reservoir. The density of this predatory copepod increased significantly, from SO.1 1-l in 1968-1970, to 44.3 1-r in 1992-1993, which accounted for most of the increase in total zooplankton density. Though a greater spring maximum of another dominant, Bosmina spp. was found during the 1992-1993 study period, the annual density of this cladoceran was not significantly different between study periods. Similar trends for Daphnia ambigua and D. pan&a were also observed, as greater spring maxima levels were attained, however overall annual densities were not significantly different. The dominance of C. vernalis (46% of annual density) and Bosmina spp. (33%), indicate that these two zooplankters were tolerant of changes in physical conditions resulting from reservoir aging and biotic interactions that followed in the reservoir during the 22 years between study periods.

Riverine and Reservoir Influences on Year Class Strength and Growth of Upper Great Plains Paddlefish

“…Trophic upsurge is typically short lived, however, and within a few years after a reservoir is filled, primary production declines, along with production at higher trophic levels as the reservoir ages (Benson, 1982), a response referred to as trophic depression (Popp and Hoagland, 1995;Popp et al, 1996;Holz et al, 1997). According to Kimmel and Groeger (1986), several factors are associated with or contribute to trophic depression, including "decreased internal nutrient loading, .…”

“…Several investigators have described trophic upsurge (Baranov, 1961;Benson, 1982) and the resulting ecological changes within reservoirs in the years soon after impoundment (Eschmeyer and Jones, 1941;Abell and Fisher, 1953;Chamberlain, 1972, Popp and Hoagland, 1995, Popp et al, 1996Holz et al, 1997). Ellis (1941) and Kimmel and Groeger (1986) summarized the increases in habitat, increased nutrient loading, increased availability of detritus, and higher primary and secondary production associated with the process of reservoir filling.…”

Comparison between the fish communities of lakes, reservoirs and rivers: can natural systems help define the ecological potential of reservoirs?

“…Although opposed in terms of hydrology, lakes and rivers share a common natural origin that may account for this similarity. When compared to reservoirs that are "recent" systems (on an ecological time scale) undergoing rapid aging processes (Kubecka, 1993;Popp et al, 1996;Thouvenot et al, 2000), natural systems may be considered as "mature" systems. This means that a number of processes underlying community structure, such as competitive interactions or colonisation events, may not have operated long enough to generate community patterns in reservoirs.…”

Managing potential impacts of reservoir enlargement on threatened Macquaria australasica and Gadopsis bispinosus in southeastern Australia

“…The trophic upsurge following inundation of new terrestrial habitats is well documented for reservoirs worldwide (Kimmel & Groeger 1986, Popp et al 1996, Gunkel et al 2003 and can persist for more than a decade (e.g. Gunkel et al 2003).…”

“…Gunkel et al 2003). Trophic upsurge results from the release of nutrients from soil or inundated vegetation, which drives increases in phytoplankton, then zooplankton and usually fish populations (Kimmel & Groeger 1986, Popp et al 1996. Trophic upsurge in the enlarged Cotter Reservoir is likely to result in a significant increase in fish species such as goldfish, a common dietary item of cormorants in southeastern Australia (McKeown 1944, Miller 1979).…”