Response of micro-algae in the Kromme Estuary to managed freshwater inputs

Abstract

The Kromme is a permanently open estuary that receives little freshwater input because the capacity of the dams is equivalent to the mean annual runoff from the catchment. The estuary is marine dominated and phytoplankton chlorophyll a is low because of the low freshwater pulses that introduce nutrient-rich freshwater. Water released (2 x 10 6 m 3) from the Mpofu Dam in 1998 produced little micro-algal response in the estuary. The study reported here addresses further runoff scenarios to see which might be beneficial in stimulating microalgal production. Recent surveys together with past research were used to describe the present state and reference condition of the estuary. Average intertidal chlorophyll a was 12.9 ± 2.5 µg·g-1 of sediment and 4.9 ± 0.4 µg·g-1 of sediment during November 2003 and July 2004. These concentrations are relatively low but comparable to those found in intertidal sediments in other South African estuaries and might indicate that intertidal microalgal biomass is not severely limited by low freshwater inputs.

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