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

Abstract

Concentrations of stable and radioactive carbon isotopes of organic matter were determined for suspended solids in surface water from the shallow and semi-closed Lake Kiba, Japan during June 2014-March 2016. Particulate organic carbon (POC) concentrations were 0.44-5.01 mg L-1 , and δ 13 C and ∆ 14 C values were, respectively,-30.3 to-22.8 ‰ and-156 to-33 ‰. The organic matter in suspended solid samples consistently showed depleted 14 C, with an average ∆ 14 C value of-81 ± 37‰. The carbon isotopes showed seasonal variation, being higher in summer, and with a positive correlation to POC contents. These results suggest that the POC characteristics are controlled by a mixture of two endmembers, organic matter produced by phytoplankton activity within the lake and the watershed organic matter, under a shallow and semi-closed environment.