A HOLOCENE CARBON STORAGE PERSPECTIVE ON COLLUVIAL AND ALLUVIAL SEDIMENT STORAGE IN THE RHINE BASIN
Long-term, Holocene sediment budget studies suggest that sediment storage provide an important link between erosion and sediment yield. Once eroded, a large amount of sediment is deposited either on hillslopes or in floodplains. On the Holocene time scale, these sedimentary sink sequester sediment-burden carbon that might significantly contribute to the “missing sink” in the global carbon budget that is assumed to be found in terrestrial components of the carbon cycle. Thus, we present results from a synoptic study of organic carbon storage in colluvial and alluvial sinks in the Rhine basin.
The influence of the sedimentary facies in fluvial systems was investigated based on a statistical analysis of 1948 organic carbon measurements in different parts of the Rhine basin. The analysis allows the development of a conceptual carbon budget model of fluvial systems. The carbon budget was coupled with a Holocene colluvial and alluvial sediment budget model, to estimate the Holocene sequestration rates of carbon storage on hillslopes and in floodplains.
Averaged carbon sequestration rates in floodplains range between 3.4 to 25.4 g m−2year−1 with more reasonable values between 5.3 to 17.7 g m−2year−1. Colluvial carbon sequestration rates range at similar values. Compared to the recent particulate carbon export, these rates are in the same order of magnitude but somewhat smaller indicating that approximately the same amount of the exported carbon may be stored in floodplains. However, compared to sedimentary carbon sequestration rates obtained elsewhere, the presented values are at the lower limit, corresponding to the lower mean Holocene soil erosion and floodplain accumulation rates.