Biotic Response To Altered Freshwater Inflow
Patterns To The Kromme River Estuary,
South Africa
Author(s)
T. H. Wooldridge
Abstract
The Kromme is an example of an estuary where freshwater inflow is
significantly attenuated. Completion of a second major dam in 1983 increased
total dam storage capacity above the Mean Annual Runoff (MAR) from the
catchment. Currently, less than 2% of MAR reaches the estuary. Marine
dominance is now persistent with little upstream variation in water salinity.
Amplitude and frequency of flood events have also declined and most of the
smaller floods and freshettes no longer arrive at the estuary. Sediment dynamics
have also changed, particularly in the lower reaches where less frequent scouring
enables disproportionately large sandbanks to develop. These sandbanks are only
removed by very large floods. Sediment accumulation in the lower estuary has
reduced the efficiency of tidal exchange and this exacerbates high salinity in the
upper reaches. Because of changes to natural patterns in the physico-chemical
environment, floral and faunal characteristics of the estuary have shifted.
Eelgrass (Zostera capensis) particularly, has become more extensive (a four-fold
increase in biomass compared to the natural state) due to less frequent floods.
These eelgrass beds constitute the most important habitat with respect to
invertebrate production. Invertebrate species that favour vegetated areas (e.g. the
shrimp Palaemon perengueyi) currently dominate the benthic community while
species that favour non-vegetated sediments have probably declined (e.g. the
mudprawn Upogebia africana).
Keywords: freshwater attenuation, dam, estuary, community changes.
Keywords
freshwater attenuation, dam, estuary, community changes.
Related Book
Other papers in this volume
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