LINKS BETWEEN LANDSCAPE AND LAKESCAPE IN EAST AFRICA, INFERENCES FOR CONSERVATION PALEOECOLOGY FROM LAKE TANGANYIKA

Food security is a grave concern for rapidly growing populations in the tropics. Processes at work on landscapes as well as in lakes are critical to supporting agriculture and inland fisheries that provide protein for millions of rural poor. Climate and vegetation influence productivity both directly and indirectly through weathering; however, evaluating the effects of each and feedbacks between systems has yet to be accomplished in many regions. A detailed understanding of how these processes interact is important for setting conservation priorities where profound alterations to both the biosphere and geosphere are anticipated. This is further complicated by intensifying land-use within tropical watersheds, which decouples vegetation change from climate; it is yet unclear what the direct effects of vegetation change may be on erosion and weathering when operating independent of climate. Long term observational records of the critical zone do not exist in tropical Africa, however, sedimentary paleo-records from lakes are often of sufficient length and resolution to record the impact of bioclimatic variability.

We combine long (60ka) and intermediate-length (400yrs) lake sediment records from Lake Tanganyika (Tanzania) to document relationships among climate, vegetation, weathering, and aquatic ecosystems at multiple scales. These records illustrate that glacial-interglacial climate change did not significantly alter weathering intensity. Instead, weathering responses occurred during a major vegetation reorganization attributable to Iron Age human activity. Furthermore, anthropogenic landscape alteration and historical land-use resulted in widespread soil erosion. In combination with a high-resolution record that documents interannual changes in lacustrine primary production, we develop a conceptual model for understanding the interactive effects of climate and land-use change associated with agricultural intensification on fisheries. This shows that impacts to pelagic and benthic communities related to vegetation structure and warming are decoupled and asymmetrical; however, conservation strategies focused on local mitigation of forest loss have the potential for successful outcomes in lakes and on land.