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

Hilton Robert G. 1, Turowski Jens M. 2, Winnick Matthew 3, Dellinger Mathieu 1, Schleppi Patrick 4, Williams Kenneth H. 5,6, Lawrence Corey R. 7, Maher Katharine 8, West Martin 1, Hayton Amanda 1

1 Department of Geography, Durham University, Science Laboratories, South Road, Durham DH1 3LE, UK
2 Helmholtz-Zentrum Potsdam, GermanResearch Centre for Geosciences GFZ, Telegrafenberg, 14473 Potsdam, Germany
3 Department of Geosciences, University of Massachusetts, 627 North Pleasant Street, 233 Morrill Science Center, Amherst, MA 01003-9297, USA
4 Swiss Federal Research Institute WSL, Z├╝rcherstrasse 111, 8903 Birmensdorf, Switzerland
5 Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
6 Rocky Mountain Biological Lab, Gothic, CO 81224, USA
7 U.S. Geological Survey, Geoscience and Environmental Change Science Center, Denver, CO 80225, USA
8 Department of Earth System Science, Stanford University, Stanford, CA 94305, USA

Water Resour. Res. 57 (2021): e2021WR029844

DOI: 10.1029/2021WR029844


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.

Keywords: oxidative weathering, trace metals, rhenium, catchment hydrology, rock organic carbon