DOC sources and DOC transport pathways in a small headwater catchment as revealed by carbon isotope fluctuation during storm events

[摘要] Monitoring the isotopic composition (δ¹³C_DOC) of dissolvedorganic carbon (DOC) during flood events can be helpful for locating DOCsources in catchments and quantifying their relative contribution to streamDOC flux. High-resolution (< hourly basis) δ¹³C_DOCdata were obtained during six successive storm events occurring during thehigh-flow period in a small headwater catchment in western France.Intra-storm δ¹³C_DOC values exhibit a marked temporalvariability, with some storms showing large variations (> 2 ‰), and others yielding a very restricted range ofvalues (< 1 ‰). Comparison of these results withpreviously published data shows that the range of intra-storm δ¹³C_DOC values closely reflects the temporal and spatial variationin δ¹³C_DOC observed in the riparian soils of thiscatchment during the same period. Using δ¹³C_DOC data inconjunction with hydrometric monitoring and an end-member mixing approach (EMMA),we show that (i) > 80% of the stream DOC flux flows throughthe most superficial soil horizons of the riparian domain and (ii) theriparian soil DOC flux is comprised of DOC coming ultimately from bothriparian and upland domains. Based on its δ¹³C fingerprint, wefind that the upland DOC contribution decreases from ca.~30% of thestream DOC flux at the beginning of the high-flow period to < 10% later in this period. Overall, upland domains contribute significantly tostream DOC export, but act as a size-limited reservoir, whereas soils in thewetland domains act as a near-infinite reservoir. Through this study, weshow that δ¹³C_DOC provides a powerful tool for tracing DOCsources and DOC transport mechanisms in headwater catchments, having ahigh-resolution assessment of temporal and spatial variability.

[学科分类] 地球化学与岩石