Abstract
Lake Saroma is the biggest coastal lagoon in Japan and the bottom water is generally oxic in recent years, while Lake Abashiri is characterized by an anoxic bottom water even in winter season. In order to characterize the oxic and anoxic surface sediments in the coastal lagoons, distributions of total organic carbon (TOC), total nitrogen (TN) and total sulfur (TS) contents have been investigated in the two lake sediments. TOC, TN and TS contents, as well as C/S and C/N ratios, seem to reflect the oxic-anoxic condition, primary production and salinity in the lakes. In the oxic environment, TOC, TN and TS contents are low, and the C/S and C/N ratios are high. On the other hand, in the anoxic environment, TOC, TN and TS contents are high, and the C/S and C/N ratios are low. These results suggest that fleshly deposited planktonic organic matter was preserved and was effectively used by sulfate reducing bacteria in the anoxic environment.
