Concentration-discharge relationships of dissolved rhenium in Alpine catchments reveal its use as a tracer of oxidative weathering

Robert Hilton; Jens M. Turowski; Matthew Winnick; Mathieu Dellinger; Patrick Schleppi; Kenneth H. Williams; Corey Lawrence; Katharine Maher; Martin West; Amanda Hayton

doi:10.1029/2021wr029844

USGS · 70226212

Concentration-discharge relationships of dissolved rhenium in Alpine catchments reveal its use as a tracer of oxidative weathering

Robert Hilton·Jens M. Turowski·Matthew Winnick·Mathieu Dellinger·Patrick Schleppi·Kenneth H. Williams·Corey Lawrence·Katharine Maher·Martin West·Amanda Hayton

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Abstract

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 (OC petro ) 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]/[SO 4 2- ] ratios, which indicate a dominance of Re from OC petro . Despite differences in rock type and hydro-climatic setting, the three catchments have a positive correlation between river water [Re]/[Na + ] and [Re]/[SO 4 2- ] 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 CO 2 release by OC petro 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 OC petro in river sediments is large, and the findings call for more measurements of OC petro oxidation in mountains and rivers as thet cross floodplains.

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Robert Hilton, Jens M. Turowski, Matthew Winnick, Mathieu Dellinger, Patrick Schleppi, Kenneth H. Williams, Corey Lawrence, Katharine Maher, Martin West, Amanda Hayton. 2021-11-23. Concentration-discharge relationships of dissolved rhenium in Alpine catchments reveal its use as a tracer of oxidative weathering. https://doi.org/10.1029/2021wr029844

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