International audienceThis paper reports a radiofrequency identification (RFID) tracing experiment implemented in a high-sedimentload mountain stream typical of alpine gravel-bed torrents. The study site is the Bouinenc Torrent, a tributary to the Bléone River in southeast France that drains a 38.9-km² degraded catchment. In spring 2008, we deployed 451 tracers with b-axis ranging from 23 to 520 mm. Tracers were seeded along eight cross-sections located in the upstream part of the lowest 2.3 km of the stream. Three tracer inventories were implemented in July 2008, 2009 and 2010. Recovery rates calculated for mobile tracers declined from 78% in 2008 to 45% in 2009 and 25% in 2010. Observations of tracer displacement revealed very high sediment dispersion, with frontrunners having travelled more than 2 km only three months after their deployment. The declining recovery rate over time was interpreted as resulting from rapid dispersion rather than deep burial. We evaluated that 64% of the tracers deployed in the active channel were exported from the 2.3-km study reach three years after the onset of the tracing experiment. Travel distances were characterized by right-skewed and heavy-tailed distributions, correctly fitted by a power-law function. This supports the idea that in gravel-bed rivers with abundant sediment supply relative to transport capacity, bedload transport can be viewed as a superdiffusive sediment dispersion process. It is also shown that tracers initially deployed in the low-flow channel were characterized by a 15- to 30-fold increase of mobility compared to tracers deployed in gravel bars

No abstract

No abstract

No abstract

edimentary rocks contain vast stores of carbon in the form of organic carbon (rock-derived OC, or OC petro ) and carbonate minerals (for example, calcite, CaCO 3 ), equating to 130,000 times that of the pre-industrial atmosphere 1 . When exhumation and erosion expose sedimentary rocks to the atmosphere and hydrosphere 2,3 , oxidative weathering processes can release carbon dioxide (CO 2 ) through three main pathways. The oxidation of OC petro by atmospheric dioxygen (O 2 ) (refs. 4,5 ) leads to CO 2 emissions to the atmosphere:The second pathway is via the oxidation of sulfide minerals (for example, pyrite, FeS 2 ) which produces sulfuric acid (H 2 SO 4 ). This can dissolve carbonate minerals and release CO 2 immediately to the atmosphere 6-8 :(2)Alternatively, the carbon can enter the bicarbonate pool of rivers and be transferred to the ocean. The CO 2 release to the atmosphere is then delayed by an order of 10 4 years, the timescale of the carbonate precipitation in the ocean 6,9 :