Water Level Fluctuations and the Ecosystem Functioning of African Lakes

Recent research has highlighted the influence that lake level fluctuations can have on fisheries productivity in tropical lakes and reservoirs, yet little is understood regarding their impact on ecosystem functioning in these systems.  Using food web data from 15 Ecopath models of African Lakes, we assessed food web characteristics relating to Odum’s ecosystem maturity hypothesis (e.g. system omnivory index, primary production/biomass).  We hypothesized that highly fluctuating lakes and reservoirs would show characteristics typical of systems at early stages of maturity.  The lakes studied varied greatly in terms of their physical characteristics and degree of relative lake level fluctuations, with the magnitude of relative lake level fluctuations being lowest for the deep lakes Kivu and Tanganyika and highest for the shallow lakes Naivasha and Chad.  Similarly, the food web characteristics of these systems are highly distinct, in some cases varying by more than an order of magnitude across systems.  Preliminary analyses suggest non-linear relationships between some food web characteristics and the degree of relative lake level fluctuations in these systems.  The results of this study will help scientists in understanding how anthropogenic changes to hydrological cycles (e.g. climate change, dams) will influence ecosystem functioning in African lakes and reservoirs.