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Project

The importance of flood events and floodplain processes for the dynamics of organic carbon transport and processing in large tropical rivers systems.

Recent research has highlighted the importance of rivers within the global carbon cycle. Rivers not only transport considerable amounts of carbon to the ocean thereby connecting the terrestrial and oceanic component of the carbon cycle. Rivers can also be looked as important reactors as a large fraction of the carbon that enters the fluvial system does not reach the ocean due to within-river mineralisation of floodplain deposition. Our understanding of the role of rivers in the carbon cycle is, however, still very limited. River systems have hitherto mainly been studied through longitudinal survey whereby differences in sediment/carbon concentrations from the headwaters to the mouth are used to make inferences about the dynamics of carbon within the river system. While it is certainly true that important insights can be gained from such surveys, they neglect two very important components of river systems. The first is that rivers show a very high temporal variability in discharge and that most of the sediment and carbon is transported during so-called flood events, often grouped in flood pulses. During such flood events, sediment concentrations and carbon transport may vary drastically and it is simply impossible to assess the impact of these events on carbon transport and carbon cycling from a limited number of surveys. A second aspect to consider is that rivers cannot be seen in isolation: a large amount (often > 50%) of the sediment and carbon that they transport is deposited on floodplains where the carbon may be stored and/or mineralized. It is not possible to make a comprehensive carbon budget for a river system without accounting for the processes occurring in floodplain environments. This project will therefore focus on the temporal variability of river carbon and sediment fluxes and the role of floodplains in sediment and carbon storage and cycling within lower part of the Tana river, Kenya. This river section was chosen because (i) it has a clear flood season with several flood events and (ii) it has extensive floodplains in which sediment is stored, and (iii) due to earlier work in this catchment, we have sufficient local experience and data to guarantee the success of our proposed approach. We will use a unique combination of advanced biochemical and physical techniques to characterize the carbon and sediments transported in the river and deposited on the floodplain. By combining these data with information from radionuclide analysis we will be able to (i) quantify and understand the role of flood events in sediment and carbon throughput, (ii) understand how sediment remobilisation may affect sediment transport and carbon dynamics and (iii) quantify t he role of floodplain sedimentation in the rivers carbon and sediment budget.
Date:1 Jan 2012 →  31 Dec 2017
Keywords:River, Organic carbon, Sediment transport, Biogeochemistry, Radionuclides