African river basins: catchment-scale carbon fluxes and transformations (AFRIVAL).

This project wishes to fundamentally improve our understanding of the role of tropical freshwater ecosystems in carbon (C) cycling on the catchment scale. It uses an unprecedented combination of state-of-the-art proxies (e.g., stable isotope, 14C and biomarker signatures, field measurements of relevant biogeochemical processes). We focus on tropical systems since there is a striking lack of data on such systems, even though riverine C transport is thought to be disproportionately high in tropical areas. Furthermore, the presence of landscape-scale contrasts in vegetation (in particular, C3 vs. C4 plants) are an important asset in the use of stable isotopes as natural tracers of C cycling processes on this scale. Freshwater ecosystems are an important component in the global C cycle, and the primary link between terrestrial and marine ecosystems. Recent estimates indicate that ~2 Pg C y-1 enter freshwater systems, i.e., about twice the estimated global terrestrial C sink. More than half of this is thought to be remineralized before it reaches the coastal zone, and for the Amazon basin this has even been suggested to be ~90% of the lateral C inputs. The question how general these patterns are is a matter of debate, and assessing the mechanisms determining the degree of processing versus transport of organic carbon in lakes and river systems is critical to further constrain their role in the global C cycle. This project provides an interdisciplinary approach to describe and quantify catchment-scale C transport and cycling in tropical river basins.

Keywords:Carbon cycling, Biogeochemistry, Nutrient cycling, River basins, Africa, Stable isotopes, Aquatic metabolism, CO2 fluxes

Disciplines:Soil sciences, challenges and pollution, Agriculture, land and farm management