Temporal variations in organic carbon species and fluxes from the Chena River, Alaska

Abstract

Water samples were collected biweekly from the Chena River, Alaska, during 2005‐2006 for analysis of dissolved organic carbon (DOC), dissolved inorganic carbon (DIC), total dissolved carbohydrate (TCHO), including monosaccharide (MCHO) and polysaccharide (PCHO), particulate organic carbon (POC) and its isotopic compositions, and Si(OH)4. Carbon species exhibit strong temporal variations with elevated DOC, POC, and TCHO but depleted DIC and Si(OH)4 during the spring freshet and decreased DOC, POC, and TCHO but elevated DIC and Si(OH)4 concentrations under winter ice. Organic matter is mostly derived from surface soil leaching, whereas DIC and Si(OH)4 are associated with groundwater and mineral layer leaching. On average, DIC was the predominant carbon species, accounting for 77% ± 13% of the total carbon pool, whereas DOC and POC comprised 19% ± 10% and 4% ± 4%, respectively. However, DOC became the dominant carbon species during the spring freshet. TCHO comprised 15% ± 4% of DOC with higher CHO:DOC ratios during spring runoff and summer. Within the TCHO pool, MCHO was the predominant CHO component (89% ± 10%), leaving 11% ± 10% as PCHO. The particulate organic matter source during the summer drought season was mostly autochthonous, with low POC: chlorophyll a and C:N but high POC: suspended particulate matter ratios and depleted δ13C values. The annual yields of DOC, DIC, and POC from the basin are 133 ± 8, 361 ± 7, and 27 ± 4 x 103 mol C km‐2, corresponding to an export flux of 6.9 ± 0.4, 18.8 ± 0.4, and 1.4 ± 0.2 x 108 mol C yr‐1, respectively. Anticipated changes in hydrological and biogeochemical cycles in high‐latitude watersheds undergoing climate warming will likely be reflected in the chemical and phase speciation of carbon and other elements.