Oxidative weathering of sedimentary rocks plays an important role in the global carbon cycle. Rhenium (Re) has been proposed as a tracer of rock organic carbon (OCpetro) oxidation. However, the sources of Re and its mobilization by hydrological processes remain poorly constrained. Here we examine dissolved Re as a function of water discharge, using samples collected from three alpine catchments that drain sedimentary rocks in Switzerland (Erlenbach, Vogelbach) and Colorado, USA (East River). The Swiss catchments reveal a higher Re flux in the catchment with higher erosion rates, but have similar [Re]/[Na+] and [Re]/[SO42-] ratios, which indicate a dominance of Re from OCpetro. Despite differences in rock type and hydro-climatic setting, the three catchments have a positive correlation between river water [Re]/[Na+] and [Re]/[SO42-] and water discharge. We propose that this reflects preferential routing of Re from a near-surface, oxidative weathering zone. The observations support the use of Re as a proxy to trace rock-organic carbon oxidation, and suggest it may be a hydrological tracer of vadose zone processes. We apply the Re proxy, and estimate CO2 release by OCpetro oxidation of 5.7 +6.6/-2.0 tC km-2 yr-1 for the Erlenbach. The overall weathering intensity was ∼40%, meaning that the corresponding export of un-weathered OCpetro in river sediments is large, and the findings call for more measurements of OCpetro oxidation in mountains and rivers as thet cross floodplains.
|Title||Concentration-discharge relationships of dissolved rhenium in Alpine catchments reveal its use as a tracer of oxidative weathering|
|Authors||Robert Hilton, Jens M. Turowski, Matthew Winnick, Mathieu Dellinger, Patrick Schleppi, Kenneth H. Williams, Corey Lawrence, Katharine Maher, Martin West, Amanda Hayton|
|Publication Subtype||Journal Article|
|Series Title||Water Resources Research|
|Record Source||USGS Publications Warehouse|
|USGS Organization||Geosciences and Environmental Change Science Center|