Assessment of the Abundance and Distribution of the Aquatic Plants and Their Impacts in the Senegal River Delta: The Case of Khouma and Djoudj Streams1

Abstract

The restoration and management of regulated rivers is important for sustaining all types of ecosystems across the world. The northern area of the Senegal River basin has endured major ecological change after the construction of the Diama and Manantali dams. Karibaweed has become a major problem in the region. Permanent availability of freshwater in the Diama reservoir and the blockage of the seasonal seawater intrusion induced the proliferation and the extension of many macrophyte species. The abundance and distribution of invasive species and their impacts were surveyed in September and October 2002. This monitoring was combined with a malacologic survey to establish a correlation between the densities of several weed species and mollusk populations. Cattail species increased in density between the two surveys. Presence of some mollusk species were correlated with water depth and current velocity, and others were correlated with abundance of aquatic plants. The invasive plants reduced flow of water in the irrigation channels, which aggravated the sedimentation process in the infrastructures. The delta ecosystem is weakened by the regulated infrastructures, and the exploitation of macrophytes has seriously reduced the agricultural potential of the region.Nomenclature: Cattail, Typha latifolia (L.) and Typha domingensis Pers.; Karibaweed, Salvinia molesta Mitch. #3 SAVMO.Additional index words: Bilharzias, dams, invasive plants, Senegal River.Abbreviations: IRp, relative density index; SRB, Senegal River basin.