Quantifying the sources and the transit times of sediment using fallout radionuclides (7Be, 137Cs, 210Pbxs) in contrasted cultivated catchments across the world
Abstract
Soil erosion and fine sediment supply to rivers are exacerbated in intensively cultivated catchments. Information on the sediment sources and transit times in rivers is required to improve our understanding of these processes and to guide the implementation of effective conservation measures. Accordingly, natural (7Be, 210Pb) and artificial (137Cs) fallout radionuclide concentrations were measured in overland flow and suspended sediment collected during the erosive season in contrasted cultivated catchments. In Laos, samples were collected in a steep catchment (Houay Pano, 12 km²) covered with cropland and teak plantations during the first flood of the monsoon in 2014. Cropland surface sources dominated the supply of sediment at the upstream sampling location (55%), whereas subsurface sources (channel, landslides) contributed the majority of material at the outlet (60%). Furthermore, the material exported from the catchment mainly consisted of re-suspended sediment. In Central France, the study was conducted in a flat and drained cultivated catchment (Louroux, 25 km²) during a sequence of winter events in 2013-2014 and 2016. Only surface material enriched in 137Cs was found to transit through the river during floods. The results demonstrated the initial re-suspension of material accumulated in the river channel during the first winter flood before the direct supply of sediment recently eroded from the hillslopes during the next events. In Peru, sediment was collected during a series of summer flood events (2017) in a river draining páramos (Ronquillo, 42 km²) that were recently put in cultivation. Preliminary results show that subsurface re-suspended material dominates the exports from this catchment. These results confirmed the utility of coupling continuous river monitoring and fallout radionuclide measurements on sediment collected in both tropical and temperate rivers to better understand sediment dynamics in these endangered habitats. The main challenges for the future application of this technique are related to the availability of detectors to analyze a large set of samples rapidly after collection, as well as the access to ultra-low background gamma spectrometry facilities.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2017
- Bibcode:
- 2017AGUFMEP53E..03E
- Keywords:
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- 1051 Sedimentary geochemistry;
- GEOCHEMISTRY;
- 1804 Catchment;
- HYDROLOGY;
- 1825 Geomorphology: fluvial;
- HYDROLOGY;
- 1862 Sediment transport;
- HYDROLOGY