On the limnology of Spioenkop, a turbid reservoir on the upper Tugela River, with particular reference to the structure and dynamics of its plankton community

Abstract

Basic features of the physical and biological limnology of Spioenkop, a large turbid impoundment on the Thukela River, were studied between July 1989 and May 1990, following surveys in spring 1987 and 1988. The lake showed a typical monomictic pattern of summer stratification (November through April) and holomictic winter circulation (May to October). Water quality was chemically good, with little evidence of nutrient enrichment (South African DWAF records). Biological production was confined by high turbidity (SD around 25 cm, NTU values of ca 90) imposed by suspended sediments, limiting annual maximum surface chlorophyll content to below 5 µg·/G6C-1, and spring primary production to < 500 mg C·m-2·d-1. Zooplankton was dominated (numerically and/or gravimetrically) by typical turbid-water fauna; the copepods Metadiaptomus colonialis and Lovenula falcifera, and cladocerans Daphnia barbata and Moina micrura. These species and other taxa present showed considerable seasonal periodicity, but maximal total abundance of the entire community (680 mg·m-2 DW) was attained in mid-summer.

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