Molecular Tracing of Riverine Soil Organic Matter From the Central Himalaya

L Märki,C France‐Lanord,S Gallen,J Lavé,N Haghipour,H Gies,M Lupker,A P Gajurel,T Eglinton

doi:10.1029/2020gl087403

Abstract

AbstractThe 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.

Highlights

Soils represent the largest organic carbon (OC) reservoir exposed at the Earth's surface (Jobbagy & Jackson, 2000)
The MAT reconstruction calculated from branched glycerol dialkyl glycerol tetraethers (brGDGTs) distributions of surface soils (MATGDGT) is in good agreement with the temperature estimated from climate data (MATest., Figure 1d) (r2 1⁄4 0.82, p < 0.05, RMSE 1⁄4 3.0°C)
Due to the absence of any systematic relation between soil brGDGT concentrations and elevation, it is possible to directly use the MATGDGT of soil brGDGTs as an elevation proxy. This soil MATGDGT‐elevation calibration is used to trace the elevational provenance of soil OC (SOC) in suspended sediments of Central Himalayan rivers in order to identify possible zones of preferential soil organic matter mobilization

Summary

Introduction

Soils represent the largest organic carbon (OC) reservoir exposed at the Earth's surface (Jobbagy & Jackson, 2000). The overall carbon budget of soil erosion on short time scales remains a subject of debate (Stockmann et al, 2013) It may act either as a carbon source with respect to atmospheric CO2 due to degradation and mineralization of SOC exposed during erosion (Jacinthe & Lal, 2001; Schlesinger, 1995) or as a carbon sink through effective OC sequestration and stabilization for instance in sediment accumulating areas (Berhe et al, 2012; Smith et al, 2001; Stallard, 1998). These considerations are relevant in light of increasing anthropogenic pressure on soil systems that have led to up to a 2 orders of magnitude increase in soil erosion rates (Montgomery, 2007) and represent a significant perturbation of the modern carbon cycle (Wang et al, 2017)

Methods

Results

Discussion

Conclusion