Source and Transport of Terrigenous Organic Matter In the Upper Yukon River: Evidence From Isotope (????C-13, ΔC-14, and ????N-15) Composition of Dissolved, Colloidal, and Particulate Phases

• Main Authors: Guo, Laodong, Macdonald, Robie W.
• Format: Text
• Language: unknown
• Published: The Aquila Digital Community 2006
• Subjects: dissolved organic matter; radiocarbon; soil organic carbon; Life Sciences; Marine Biology; Yukon; Ice; permafrost; Yukon river
• Online Access: https://aquila.usm.edu/fac_pubs/2367; https://aquila.usm.edu/context/fac_pubs/article/3366/viewcontent/Guo_et_al_2006_Global_Biogeochemical_Cycles.pdf

Natural organic matter was collected from the upper Yukon River and size fractionated into the (LMW-DOC), colloidal (COC, 1 kDa to 0.45 mu m) and particulate organic carbon (POC, > 0.45 mu m) phases for characterization of elemental (C and N) and isotopic (C-13, C-14 and N-15) composition to examine their sources and transport. Concentrations of total organic carbon (TOC) decreased from 3010 mu M in mid-May to 608 mu M in September, accompanying an increase in river water delta O-18 from the snowmelt to summer and early fall. COC was the predominant OC species, comprising, on average, 63 +/- 8% of the TOC, with 23 +/- 5% partitioned in the LMW-DOC and 14 +/- 5% in the POC fraction. Annual riverine export flux to the ocean was 2.02 +/- 10(12) g-C for TOC, 7.66 x 10(10) g-N for total organic nitrogen (TON), and 3.53 x 10(12) g-C for dissolved inorganic carbon (DIC), respectively. The C/N molar ratios were distinctly different between colloidal organic matter (COM, 46 +/- 3) and particulate organic matter (POM, 15 +/- 1.4). Similar delta C-13 values were found for LMW-DOM (-27.9 +/- 0.5 parts per thousand), COM (-27.4 +/- 0.2 parts per thousand), and POM (-26.2 +/- 0.7 parts per thousand), although there was a general increase with increasing size, suggesting a common terrigenous organic source. In contrast, distinct D 14 C values were found for LMW-DOC (-155 to +91 parts per thousand), COC (40 to 140 parts per thousand), and POC (-467 to -253 parts per thousand) with a decreasing trend from snowmelt to ice-open season, suggesting that turnover pathways and transport mechanisms vary with organic matter size fractions. The high abundance of COC and its contemporary C-14 ages points to a predominant source from modern terrestrial primary production, likely from the leaching/decomposition of fresh plant litter in the upper soil horizon. The predominately old POC (average 3698 +/- 902 years B. P.), in contrast, was largely derived from riverbank erosion and melting of permafrost. These results imply that ice-opening ...