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

Water Resources Research
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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 (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.

Publication type Article
Publication Subtype Journal Article
Title Concentration-discharge relationships of dissolved rhenium in Alpine catchments reveal its use as a tracer of oxidative weathering
Series title Water Resources Research
DOI 10.1029/2021WR029844
Edition Online First
Year Published 2021
Language English
Publisher American Geophysical Union
Contributing office(s) Geosciences and Environmental Change Science Center
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