Reconstructing the biogeochemistry of tropical aquatic ecosystems using elemental and stable isotope tracers in freshwater bivalve shells

Aquatic ecosystems are vulnerable to changes in land use, climate, and nutrient inputs, as the material they transport is directly influenced by a range of catchment characteristics. This is particularly true for tropical systems which are under increasing stress and are sensitive early indicators of catchment modifications. However, long-term datasets on discharge or aquatic biogeochemistry are virtually non-existent. An elegant method to circumvent this absence of historical data is to use well-dated biological archives to reconstruct environmental conditions. Freshwater bivalves have demonstrated the potential to store such information in their shells: the geochemical composition along the growth axis provides a history of aquatic biogeochemical and environmental conditions (e.g. discharge) during the lifetime of the bivalve. We have initiated detailed monitoring of a wide range of parameters on several African rivers at unprecedented temporal resolution, within the framework of an ERC Starting Grant (AFRIVAL) and related projects. Collections of recent bivalves from these locations offers a unique opportunity to thoroughly calibrate at high resolution the relationship between bivalve shell and discharge or aquatic geochemistry and fine-tune the information we can reliably extract from them. Then, we will apply the same methodology on archived museum shells collected from the same sites up to 125 years ago. The contrasting catchments studied will provide excellent case studies of how freshwater bivalves record known (and unknown) changes in climate and/or land-use in understudied tropical catchments.