Spatial patterns of modern diatom distribution in the Eilandvlei Catchment, Wilderness, South Africa

Diatom species compositions are often distributed along environmental gradients and are influenced by a number of environmental parameters. The spatial patterns of modern diatoms can be combined with palaeolimnology to provide a powerful means to assess ecological change in coastal lake systems on multiple time scales. The modern distribution of diatom assemblages in surficial sediments in the Eilandvlei catchment was studied in order to ascertain spatial patterns and explore the main environmental parameters responsible for community structure. Canonical correspondence analysis revealed that among four measured environmental variables; salinity and conductivity accounted for most of the variance in the diatom data. The species composition of the catchment was found to be dominated by brackish species. In general, the brackish species' Cocconeis placentula, Amphora coffeaeformis and Planothidium delicatulum were prevalent among all sites in the catchment, indicating the brackish nature of the system. Geographic Information System techniques were used in the analysis of the distribution of diatom species. Diatoms were classed by salinity preferences into brackish, fresh and marine taxa and their spatial distribution was analysed relative to water temperature and salinity distributions. The community pattern gave an accurate representation of ecological conditions of the sampling sites, displaying salinity and temperature gradients through the catchment. Brackish species were most abundant through the estuary while marine species were concentrated through sections of Eilandvlei and Rondevlei. Freshwater species were found at low abundances through the system. The distribution of the three classes of diatoms suggests that this assemblage is structured by salinity. This distribution of modern diatoms can provide useful analogues to interpret palaeoenvironmental reconstructions in the region in the future.