Erosion and weathering fluxes in granitic basins: The example of the Strengbach catchment (Vosges massif, eastern France)

This work reports on regular observations of the suspended sediment and bedload flux at the outlet of the granitic Strengbach catchment (0.8 km²) over the period 2004–2010 along with the analysis of the dissolved load. The data set allows a first determination of the physical erosion flux (3.3 t·km− 2·yr− 1) exported out of the Strengbach watershed and how it compares to the chemical weathering flux of basic cations. The data indicate that the erosion rate carried by the bedload (1.7 t·km− 2·yr− 1) can reach one third of the total erosion rate (5 t·km− 2·yr− 1) in the Strengbach watershed. The accuracy of these rates is estimated to be 20%. The study also indicates that the estimated values for the net annual weathering flux calculated for the watershed can differ by a factor of two or more depending on the corrections applied and the assumptions retained for the watershed's functioning (from an uncorrected weathering flux of basic cations of 4.76 t·km− 2·yr− 1 to an atmosphere-corrected weathering flux of 2 t·km− 2·yr− 1 for the period 2004–2010). The weathering budgets determined for the Strengbach catchment fit the general trend defined between the weathering rate and runoff for other granitic watersheds; this suggests that the anthropogenic impact due to acid perturbation or forest management has a relatively weak influence on the weathering intensity within the watershed. The relationship between weathering and erosion rates determined for the Strengbach catchment does not significantly differ from those established for other previously studied granitoid catchments.

► Dissolved and suspended matter fluxes are determined for the Strengbach catchment.
► Physical erosion and chemical weathering rates derived from the measurements are of the same magnitude (3 to 5 t·km− 2·yr− 1).
► They do not differ significantly from other granitoid catchments.