Phytoplankton and zooplankton population dynamics and production of a recently formed African reservoir

Abstract

The study provides a 2 .5 year record of Rhenosterkop Dam (KwaNdebele, South Africa) plankton population dynamics and production in relation to physical and chemical changes which occurred during the trophic depression and stabilization phases of the reservoir . The mean volume of the reservoir was 4 % of full storage capacity . Water temperatures ranged from 14 ° C to 27 'C . Due to inorganic suspensoids, the euphotic zone averaged 2 .6 m . An anaerobic zone developed each summer . The nitrogen, soluble reactive phosphorus (SRP) and silica concentrations did not display a seasonal pattern, but the latter two nutrients declined over the study . The dominant phytoplankton group was the cryptophytes while the zooplankton population was dominated by crustaceans . Chlorophyll a concentrations ranged from 1 .1 to 27 mg m-3 and were positively correlated to silica and SRP concentrations and inversely with NH 4-N concentrations . Primary production ranged from 22 .6 to 375 mgC m -2 h-' ; changes in A,,, a, were positively correlated to silica and SRP concentrations . Total zooplankton dry weight biomass varied from < 0 .5 to > 4 mg I -' . Annual zooplankton (secondary) production was 8 to -15 gC m -3 a -'; both primary and secondary production were greatest in the first 12 months of study and remained at low levels for the remainder, similar to the trends for silica and SRP . The data indicate that the reservoir shifted from eutrophic to mesotrophic during the study, typical of events in new reservoirs, and that changes in the plankton populations were largely the result of changing nutrient concentrations .Introduction 1990). Groundwater resources are limited and the surface waters are relied upon for urban, indusThe majority of water resources in southern Aftrial and agricultural purposes . Irrigation is the rica are riverine and south of the Zambezi River major use of surface waters in this region, adding there are very few natural lakes (Allanson et al., to the load placed on limited surface resources

Spatial distribution and secondary production of Copepoda in a tropical reservoir: Barra Bonita, SP, Brazil

“…Espíndola (1994) found four species of Notodiaptomus, namely Notodiaptomus iheringi, Notodiaptomus cearensis, Notodiaptomus conifer and Notodiaptomus nsp., during a two-year study of population dynamics of Copepoda Calanoida in Barra Bonita Reservoir. Looking back at samples collected in that 1982and 1984and Argyrodiaptomus furcatus in 1986, 1988, 1992and 1993, although in low densities. A new species of Notodiaptomus has appeared in Barra Bonita Reservoir since July 1992, starting in low numbers and progressively increasing throughout the year 1993 (Espíndola, 1994).…”

“…In Lake Rhenosterkop (South Africa), secondary production was recorded to vary from 8 to 14.8 gC.m , being greater than in the oligotrophic Lake Le Roux (Hart et al, 1983in Robarts et al, 1992, showing that eutrophic systems are more productive. Similarly, comparing the reservoirs of Barra Bonita, which is eutrophic, with the oligotrophic Lagoa Dourada Reservoir, both in Brazil, the production recorded in the present study was greater than that found in the latter.…”

Variations in the number of active bacteria in the euphotic zone of a recently flooded reservoir

“…The creation of a new reservoir and flooding of a lake may initiate a series of changes in the plankton community related to alterations in hydrology and nutrient availability that frequently result from inputs of large amounts of newly flooded terrestrial organic matter that may also stimulate bacterial activity (Paterson et al 1997). These effects almost always lead to the ecosystem evolving toward a new steady state of maturation with a trophic status generally lower than that observed immediately after flooding, and that may be achieved within years (Robarts et al 1992, Paterson et al 1997. It has been established over a broad range of aquatic systems that the number of active bacteria increases with the system's productivity (del Giogio & Scarborough 1995).…”

Limnological comparison of a new reservoir with one almost 40 years old which had been totally emptied and refilled

“…Similar results were obtained for other reser voirs during the filling phase by Pinel-Alloul and l\llethot. (1984), Kimmcl et al (1988), Robarts et al (1992), who referred to this phenomenon as a 'trophic upsurge'. A significant increase of primar y production as a result of high nu trient conce ntrations during th e 'trophic upsurge' was also obser ved by tl1ese authors.…”

“…Email: zboavida@fc.ul.pt Accepted for publication 20 November 1998. ture (Pinel-Alloul & Methot 1984) and on both phytoplankton and zooplankton dynamics (Robarts et al 1992) as well as on organic matter production and decomposition (Kimmel et al 1988) .…”