Overturn in a hypertrophic, warm, monomictic impoundment (Hartbeespoort Dam, South Africa)

Robarts, Richard D.; Ashton, P. J.; Thornton, J. A.; Taussig, H. J.; Sephton, Lynne M.

doi:10.1007/bf00007109

Cited by 46 publications

(34 citation statements)

References 26 publications

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“…Filtered (pre-rinsed Sartorius G/F filters) subsamples of the surface, middle and bottom samples were analyzed for ammonium-N, nitrite + nitrate-N, soluble reactive phosphorus (SRP) and silica (Si0 2) concentrations using auto-analyzers and the methods in Robarts et al (1982).…”

Section: Chemical Analysesmentioning

confidence: 99%

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

et al. 1992

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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

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Section: Chemical Analysesmentioning

confidence: 99%

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

et al. 1992

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“…This phosphorus can reach the epilimnion of the lake through diffusive processes such as have been described in Lake McIlwaine, Zimbabwe (Robarts & Ward, 1978). Robarts et al (1982) in examining the effect of overturn on the phosphorus status of Hartbeespoort Dam concluded that mixing processes affect the impoundment in direct proportion to the relative percentage of epilimnion and hypolimnion mixed. In recent years the shallow nature of the impoundment resulted in multiple mixing events (NIWR, 1985) which added phosphorus to the water column from the sediments; a low net sedimentation value was present during these periods which occurrred during early and late summer (Fig.…”

Section: Discussionmentioning

confidence: 99%

“…By 1958, the lake was equated to an oxidation pond (Chomoky, 1958) whilst subsequent studies described the impoundment as eutrophic (Allanson & Gieskes, 1961;Toerien & Steyn, 1975;Scott etal., 1977) and hypertrophic (Scott et al, 1980;Ashton, 1985b;NIWR, 1985;Thornton et al, 1986). Massive hyperscums of Mcrocystis aeruginosa Kutz emend Elenkin occur regularly in sheltered embayments and inlets (Zohary, 1985) and virtually complete de-oxygenation of the water column following overturn is common (Allanson & Gieskes, 1961;Robarts et al, 1982;NIWR 1985). Robarts (1984) and Ashton (1985b) have described Hartbeespoort Dam as one of the most grossly impacted lakes yet studied.…”

Section: The Study Areamentioning

confidence: 99%

Aspects of the phosphorus cycle in Hartbeespoort Dam (South Africa) Phosphorus loading and seasonal distribution of phosphorus in the reservoir

Thornton

Ashton

1989

Hydrobiologia

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Hartbeespoort Dam, a hypertrophic, warm monomictic impoundment in South Africa, receives extremely high phosphorus loads (14.6-25.9 g rnh2 a-') that are dominated by point source discharges from municipal wastewater treatment works. The reduced state of the phosphorus discharged from the works has led to the dominance of the dissolved phosphorus pool by low molecular weight orthophosphates which are analytically detectable as soluble reactive phosphorus (SRP; 60% of total phosphorus pool). Seasonality in the in-lake total phosphorus pool is regulated by a combination of abiotic and hydrological processes; biotic processes appear to play a minor role. Mass balance calculations indicate that between 62 and 77% of the annual total phosphorus inflow load is retained within the impoundment each year.

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“…The high phosphorus flux in Hartbeespoort Dam would appear to be a function of the extremely enriched (Robarts et al, 1982) and highly productive nature of the impoundment (Robarts, 1984) .…”

Section: Discussionmentioning

confidence: 99%

Aspects of the phosphorus cycle in Hartbeespoort Dam (South Africa)

Thornton

1989

Hydrobiologia

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The role of biotic processes in a warm, monomictic, hypertrophic African impoundment (Hartbeespoort Dam) is examined using 32 P radiobioassays . Phosphorus demand is assessed by phosphorus turnover times, alkaline phosphatase activity, cellular phosphorus status and the phosphorus deficiency index . Long turnover times indicative of an enriched system were recorded, ranging from 9 h to 1992 h, with no evidence of phosphorus stress being present . These turnover times support the hypothesis that the phosphorus cycle in Hartbeespoort Dam is dominated by the algal community which is shown to play an important role in phosphorus cycling within the water column . However, hydrological processes remain the driving force in phosphorus seasonality in the lake .

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Overturn in a hypertrophic, warm, monomictic impoundment (Hartbeespoort Dam, South Africa)

Cited by 46 publications

References 26 publications

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

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

Aspects of the phosphorus cycle in Hartbeespoort Dam (South Africa) Phosphorus loading and seasonal distribution of phosphorus in the reservoir

Aspects of the phosphorus cycle in Hartbeespoort Dam (South Africa)

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