A LIMNOLOGICAL PROFILE OF THE UPPER OKAVANGO DELTA AT LOW WATER LEVEL

Abstract

Summary Selected limnological attributes of the Okavango Delta panhandle were measured during a brief summer survey of “open-water” habitats extending from the permanent mainstream channel, through contiguous off-channel lagoons and still backwaters, to seasonally isolated floodplain lagoon and temporary pool biotopes on the left-bank of the Okavango River at Seronga. Wide ranges in most determinants were evident along this profile:- temperature (27–34°C); conductivity(4–12.7mS m−1); pH(5.7–9.2); transparency(0.2–>2.5 m Secchi depth); dissolved oxygen (20–220% saturation); PO4-P (61–110 μg l−1): SiO2—Si (6.9–14.0 mg l−1): NH4-N (30–44 μg l−1): chlorophyll (1.3–183 μ.g l−1). Zooplankton was variably diverse (species richness from ≥ 3 to 20), comprising both euplanktonic (Bosmina, Ceriodaphnia, Daphnia, Diaphanosoma, Moina, Mesocyclops, Thermocyclops, Tropodiaptomus) and more typical epiphytic crustacean taxa (Alona, Macrothrix, Pleuroxus), along with various rotifers (Brachionus, Hexarthra, Keratella, Tric...