Environmental and hydrologic controls on sediment and organic carbon export from a subalpine catchment: insights from a time series

[摘要] Studies engaging in tracking headwater carbon signaturesdownstream remain sparse, despite their importance for constraining transferand transformation pathways of organic carbon (OC) and developingregional-scale perspectives on mechanisms influencing the balance betweenremineralization and carbon export. Based on a 40-month time series, weinvestigate the dependence of hydrology and seasonality on the discharge ofsediment and OC in a small (350 km 2 ) Swiss subalpine watershed (SihlRiver basin). We analyze concentrations and isotopic compositions ( δ 13 C, F 14 C) of particulate OC and use dual-isotope mixing andmachine learning frameworks to characterize and estimate sourcecontributions, transport pathways, and export fluxes. The majority of transferred OC is sourced from plant biomass and soil material. The relativeamount of bedrock-derived (petrogenic) OC, abundant in headwater streams,progressively decreases downstream in response to a lack of source materialand efficient overprinting with biospheric OC, illustrating rapid organicmatter alteration over short distances. Large variations in OC isotopiccompositions observed during baseflow conditions converge and form ahomogenous mixture enriched in OC and characterized by higher POC-F 14 Cvalues following precipitation-driven events. Particulate OC isotopic dataand model results suggest that storms facilitate surface runoff and theinundation of riparian zones, resulting in the entrainment of looseplant-derived debris and surficial soil material. Although particletransport in the Sihl River basin is mainly driven by hydrology, subtlechanges in bedrock erosivity, slope angle, and floodplain extent likely have profound effects on the POC composition, age, and export yields.

[学科分类] 大气科学