Isotopic (δ13C) evidence for the autochthonous origin of sediment organic matter in the small and acidic Lake Katanuma, Japan

Sources of sediment organic matter from the strongly acidic Lake Katanuma (0.14 km2; average pH 2.2), in Japan, were determined from an analysis of carbon stable isotope ratios (δ13C). Organic carbon was derived mainly from the benthic diatom, Pinnularia braunii, and particulate organic matter (POM) primarily from the phytoplankton, Chlamydomonas acidophila, and not from emergent or terrestrial C3 plants such as Phragmites australis, Sasa kurilensis or Fagus crenata. Although the sediment organic matter of most small lakes, especially strongly acidic lakes, is commonly thought to be of allochthonous origin, the sources of sediment organic matter in the small and acidic Lake Katanuma were clearly autochthonous.