Chapter 4 - From benthic to floating: phytoplankton dynamics in African freshwater lakes and reservoirs

Abstract

This chapter reviewed phytoplankton communities in African freshwater lakes and reservoirs and further assessed the latitudinal diversity gradient (LDG) which has been used to explain species variations in other taxonomic groups. The chapter also identified freshwater reservoirs on the continent, heavily impacted by anthropogenic impacts, and assessed how these have led to changes in phytoplankton communities. From the systematic review, phytoplankton information was available for 51 reservoirs in Africa with 1633 freshwater phytoplankton species belonging to nine taxa recorded from the 51 reservoirs. There was strong evidence that supports LDG for phytoplankton species richness increased from the poles toward the Equator. Species that highly occurred in all reservoirs included Microcystis aeruginosa among other species. Despite the basal trophic importance of phytoplankton, undesirable phytoplankton blooms have been reported from several reservoirs on the continent. The increase in human activity is causing an increased industrial, agricultural, and wastewater deposition into African reservoirs, thereby, enriching them with nutrients and resulting in the proliferation of harmful algal blooms (HAB), particularly Cyanophyta. The cyanotoxins produced by HAB have had lethal effects on various animals and humans in Africa. Besides nutrients, increasing water temperatures are driving HABs development in African reservoirs. Warming because of climate change could, therefore, favor HAB growth, thus augmenting risks associated with the blooms. Measures that reduce nutrient loading in freshwater systems should be put in place by responsible authorities to prevent biodiversity loss as well as serious human health issues. Phytoplankton monitoring and assessments should be periodically conducted in African aquatic systems to provide insights into temporal changes while assessments indicate the status of these ecosystems.