Molecular Tracing of Riverine Soil Organic Matter From the Central Himalaya. Issue 16 (19th August 2020)

• Record Type: Journal Article
• Authors: Märki, L.; Lupker, M.; Gajurel, A. P.; Gies, H.; Haghipour, N.; Gallen, S.; France‐Lanord, C.; Lavé, J.; Eglinton, T.
• Is Part Of: Geophysical research letters. Volume 47:Issue 16(2020)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2020-08-19
• Subjects: Geophysics -- Periodicals; Planets -- Periodicals; Lunar geology -- Periodicals; 550
• DOI: 10.1029/2020GL087403
• Languages: English
• ISSNs: 0094-8276

Abstract

Abstract: The isomer distribution of branched glycerol dialkyl glycerol tetraethers (brGDGTs) in soils has been shown to correlate to the local mean annual temperature. Here, we explore the use of brGDGT distributions as proxy for the elevation at which soil organic carbon is preferentially mobilized in the Central Himalaya. Soil brGDGT distributions collected along an altitudinal profile, spanning elevations from 200 to 4, 450 m asl, are linearly correlated to elevation. We use this calibration to trace the provenance of soil organic matter in suspended sediments of rivers draining the Himalaya. BrGDGT distributions of fluvial sediments reflect the mean elevation of the soil cover in most catchments. Inverse modeling of the brGDGT data set suggests similar relative contribution to soil organic carbon mobilization from different land covers within a factor 2. We conclude that riverine soil organic carbon export in the Himalaya mostly occurs pervasively and is at the catchment scale insensitive to anthropogenic perturbations. Plain Language Summary: Soil degradation influences the global climate and has direct impacts on the ability of soils to deliver economic and ecological services. Identifying the source of eroded soil‐derived carbon entrained in sediments of large rivers remains challenging. In this contribution, we use the temperature‐sensitive signature of soil microbe‐derived organic molecules to trace the source of soil carbon exported in river sediments of the rapidly eroding Central Himalaya of Nepal. Molecular signatures of soils, sampled over a wide range of elevations, and hence temperatures are plotted on an elevation profile. River sediments are then compared to soil signatures in order to identify elevations of preferential soil export through rivers. Our data shows that soil‐derived carbon is sampled uniformly over most of the catchments, indicating that soil export by Himalayan rivers is not driven by localized human perturbations such as agriculture or deforestation. Key Points: A calibration for soil branched glycerol dialkyl glycerol tetraether (brGDGT) signals against an elevation profile is developed The provenance of soil organic matter in riverine suspended sediments is traced based on corresponding brGDGT distributions Soil organic carbon in most river sediments originates from the entire soil‐covered catchment, indicating uniform soil organic matter export