Carbon cycling at the sediment–water interface in a eutrophic mountain lake (Jezero na Planini pri Jezeru, Slovenia)

The biogeochemical processes that dominantly influence carbon cycling at the sediment–water interface in a eutrophic mountain lake (Jezero na Planini pri Jezeru, Slovenia) were studied for 2 years using measurements of the stable isotopic composition of carbon, as well as chemical analyses of the pore waters and sediment. According to the isotopic mass balance the major contribution of the most important aquatic carbonate species (dissolved inorganic carbon— DIC) is derived from methanogenesis (67–92%) and much less from decomposition of sedimentary organic carbon with other electron acceptors (8–23%). The contribution of calcite dissolution was observed only in 1999 when it varied throughout the year from 3–16% and did not influence DIC production appreciably. The lake sediment is an important sink of organic carbon that accumulates at the bottom of the lake.