To properly conserve, restore and manage riverine ecosystems and the services they provide, it is pertinent to understand their functional dynamics. This thesis explores the functioning of tropical African streams and savanna rivers by assessing the spatial and temporal dynamics in organic processing and carbon flow in riverine food webs. The thesis contributes to the theory of riverine ecosystem functioning and has improved understanding of the structure and functioning of African tropical streams in terms of shredder diversity and their role in organic matter processing. The thesis also presents data showing that large mammalian herbivores enhance terrestrial-aquatic food webs linkages in savanna rivers via their transfer of terrestrial organic matter into streams and rivers. The findings of this research are useful for defining future research needs and actions for sustainable management of agriculturally influenced streams and savanna rivers in landscapes witnessing declining wildlife populations.