Environmental and hydrologic controls on sediment and organic carbon export from a subalpine catchment: insights from a time series
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Published:2022-12-13
Issue:23
Volume:19
Page:5591-5616
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ISSN:1726-4189
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Container-title:Biogeosciences
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language:en
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Short-container-title:Biogeosciences
Author:
Schwab Melissa SophiaORCID, Gies Hannah, Freymond Chantal Valérie, Lupker MaartenORCID, Haghipour Negar, Eglinton Timothy Ian
Abstract
Abstract. Studies engaging in tracking headwater carbon signatures
downstream remain sparse, despite their importance for constraining transfer
and transformation pathways of organic carbon (OC) and developing
regional-scale perspectives on mechanisms influencing the balance between
remineralization and carbon export. Based on a 40-month time series, we
investigate the dependence of hydrology and seasonality on the discharge of
sediment and OC in a small (350 km2) Swiss subalpine watershed (Sihl
River basin). We analyze concentrations and isotopic compositions (δ13C, F14C) of particulate OC and use dual-isotope mixing and
machine learning frameworks to characterize and estimate source
contributions, transport pathways, and export fluxes. The majority of transferred OC is sourced from plant biomass and soil material. The relative
amount of bedrock-derived (petrogenic) OC, abundant in headwater streams,
progressively decreases downstream in response to a lack of source material
and efficient overprinting with biospheric OC, illustrating rapid organic
matter alteration over short distances. Large variations in OC isotopic
compositions observed during baseflow conditions converge and form a
homogenous mixture enriched in OC and characterized by higher POC-F14C
values following precipitation-driven events. Particulate OC isotopic data
and model results suggest that storms facilitate surface runoff and the
inundation of riparian zones, resulting in the entrainment of loose
plant-derived debris and surficial soil material. Although particle
transport in the Sihl River basin is mainly driven by hydrology, subtle
changes in bedrock erosivity, slope angle, and floodplain extent likely have profound effects on the POC composition, age, and export yields.
Funder
Schweizerischer Nationalfonds zur Förderung der Wissenschaftlichen Forschung
Publisher
Copernicus GmbH
Subject
Earth-Surface Processes,Ecology, Evolution, Behavior and Systematics
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