Aquatic-terrestrial linkages in Afrotropical lakes and rivers using stable hydrogen isotopes

Understanding ecological functioning of large aquatic ecosystems provides an essential framework for conservation and management of aquatic resources. The degree to which aquatic and terrestrial primary production fuel Afrotropical aquatic food webs remains poorly understood, since quantifying the relative contributions of these resources is methodologically challenging. Carbon and nitrogen stable isotope ratios have provided valuable insights regarding the contributions of terrestrial resources, but this approach has limitations in its resolving power. Recently, the promising use of stable hydrogen isotope ratios (δ2H) has gained attention to complement those ‘traditional’ isotopes for aquatic food webs due to their greater power of separation between aquatic and terrestrial subsidies. However, measurements of δ2H of complex organic materials have faced several methodological issues related to the isotopic H exchange and the effect of residual moisture in samples. This proposal will combine the expertise of applicant in H isotopes and the host group expertise in tropical aquatic biogeochemistry to link terrestrial inputs to invertebrate and fish productivity in the Congo River basin and Lake Edward to understand their ecosystem functioning, building on a large set of available samples (Congo River) as well as new fieldwork (L. Edward). The aims of this research are: to test new preparation systems to control H exchangeability and absorbed water for H isotope analysis; and to quantify to which extent aquatic communities in the Congo River basin and L. Edward depend on aquatic and terrestrial primary production using a multiple tracer approach during different hydrological conditions, and over different temporal scales (recent versus historical, using museum-archived specimens). The information obtained through this project will be of direct relevance for the conservation and management of important goods and services offered by these ecosystems (i.e. fisheries).