Environmental Controls on the Distribution of Aquatic Macrophytes in Ugandan Crater-lakes

This research is part of an integrated paleoecological project which aims at coupling reconstructions of past vegetation and water-quality changes with climate variability. Crater-lakes from East Africa are favourable to the conservation of proxy indicators such as plant macrofossils used to reconstruct the lake ecosystem. The study of modern macrophytic communities related to present environmental parameters was the first step of this research. Phytosociologic and environmental data were collected in 36 crater-lakes in South-western Uganda. Species abundance and habitat conditions were described in 216 relevés arranged along transects from the lakeshore to the depth limit of aquatic plant development. A cluster analysis identified 8 macrophytes communities and their indicator species were highlighted. Combining two levels of analysis (lake or relevé) with different kind of ordinations (CA and CCA), main parameters explaining community variability were conductivity, pH, Human Impact index, vegetation zonation and productivity (Chlorophyll-a and total nitrogen). Multiple species response curves to environmental parameters were performed to assess the ecological amplitude at the individual level and select species with a good proxy-indicator value.
These results give some trends about the ecology of macrophytes communities and the ecological significations of macrofossils.