Structure and status of the intertidal wetlands of the Knysna Estuary

Abstract

The intertidal wetlands of the Knysna Estuary cover an area of 1000 hectares and are important both to the ecology of the estuary as well as to the tourism-orientated economy of Knysna. Little research, however, has been conducted on these wetlands. The aim of this research was to investigate the floristic structure of the wetlands in relation to both the salinity and inundation gradients that typify an estuary. An herbarium of 54 species was collected of which 27 were saltmarsh or estuarine species. A vegetation map was compiled illustrating that the lower and middle reaches of the estuary were dominated by succulent, herbaceous saltmarsh species while the upper reaches were estuarine and dominated by reeds and rushes. The structure of the communities in the low and middle reaches was determined primarily by the regular tidal inundation patterns experienced by the marshes while in the upper reaches it was the infrequent tidal inundation, coupled with the presence of a large brackish water body adjacent to the marsh, that determined the community structure here. A qualitative assessment of anthropogenic impacts on the wetlands is also made.