High Contribution of Recalcitrant Organic Matter to DOC in a Japanese Oligotrophic Lake Revealed by ¹⁴C Measurements

Abstract

ABSTRACT. Carbon isotopes ( 14 C and 13 C) of dissolved organic carbon (DOC) in a Japanese oligotrophic lake (Lake Towada) were measured to study the origin and cycling of dissolved organic matter (DOM) in Lake Towada. Lake water samples were collected at 3 depths (0, 30, and 80 or 85 m) during 4 months (April, June, August, and October) in 2006. 14 C measurements of DOC were performed by accelerator mass spectrometry (AMS) at the National Institute for Environmental Studies (NIES-TERRA) in Japan.  14 C and  13 C values of DOC in Lake Towada showed light carbon isotopic values ranging from 750 to 514‰ and 29.0 to 27.8‰, respectively. These values are similar to those of humic substances reported. The very low carbon isotopic values of DOC in Lake Towada suggest a very small contribution of DOC derived from fresh phytoplankton to the lake DOC. There is an extremely high linear relationship between the  14 C and  13 C of DOC in Lake Towada when all data points are plotted (r 2 0.818, p < 0.01), suggesting that the DOC in Lake Towada has 2 specific sources contributing heavy and light carbon isotopes. Although the freshly produced DOC of phytoplankton origin can be decomposed easily, the variation in the autochthonous DOC should influence the carbon isotopic values of DOC in Lake Towada.

Young, Old, and Weathered Carbon-Part 1: Using Radiocarbon and Stable Isotopes to Identify Carbon Sources in an Alkaline, Humic Lake

“…Inorganic carbon is derived from the atmosphere, whereas microbial decay of terrestrial vegetation and geological weathering each represent a stable isotope and radiocarbon end member (Broecker and Walton 1959;France 1995;Carpenter et al 2005;Cole et al 2006;Nara et al 2010;Zigah et al 2011). …”

“…It has been demonstrated that δ 13 C values of aquatic photosynthetic plants and plankton utilizing inorganic carbon in lakes are variable due to differences in carbon availability and kinetic fractionation (Farquhar et al 1989;McConnaughey et al 1997). Inorganic carbon is derived from the atmosphere, whereas microbial decay of terrestrial vegetation and geological weathering each represent a stable isotope and radiocarbon end member (Broecker and Walton 1959;France 1995;Carpenter et al 2005;Cole et al 2006;Nara et al 2010;Zigah et al 2011).…”

Source and quantity of carbon influence its sequestration in Rostherne Mere (UK) sediment: a novel application of stepped combustion radiocarbon analysis

“…Interpretation of bulk geochemical measures in sediments as indicators of OC source, such as d 13 C or carbon/nitrogen (C/N) ratios, are hampered by natural variability and overlapping values between OC pools (Holtvoeth et al 2016;Lacey et al 2018). Natural abundance radiocarbon methods have utility for source partitioning of OC in lakes and their sediments (McGeehin et al 2004;Nara et al 2010;Rosenheim et al 2013;Keaveney et al 2015). We used D 14 C, defined as the ratio between the international standard 14 C/ 12 C, corrected for year of measurement (base year AD 1950) and sample 14 C/ 12 C, both corrected for d 13 C fractionation (Stuiver and Polach 1977), to evaluate OC source in Rostherne Mere, UK.…”

Characterization ascertained from δ¹³C and Δ¹⁴C of particulate organic matter in surface water from a shallow and semi-closed Lake Kiba

“…Riverine particulate organic matter (POM) from wetlands has lower δ 13 C and higher ∆ 14 C than those of rivers in forests and fluvial plains, which indicates a greater contribution of apparently younger organic matter in wetland river systems. In lake environments, carbon isotopes have been applied to elucidate biogeochemical cycles and freshwater reservoir effect ranges and variations over time [6,10,11]. The phytoplankton ∆ 14 C reflects the ∆ 14 C of dissolved CO 2 , which might be a mixture of aged and modern carbon [12][13][14].…”