Abstract
Stable carbon and nitrogen isotopes were studied in a community of a headwater stream covered with old-growth deciduous forest in central Japan, in spring. CPOM (Coarse Particulate Organic Matter), consisting mainly of tree litter such as leaves and twigs, had lower δ13C-value than epilithic algae. From comparison of mean δ13C-values, finely decomposed tree litter was the main component of FPOM (Fine Particulate Organic Matter). A dual isotope plot of δ13C and δ15N showed that most taxa of benthic invertebrates and fish (char) depended on CPOM and/or FPOM for their C and N source, and only a few taxa of benthos appeared to depend on algae. Therefore, we concluded that the food web in this stream was based on allochthonous organic matter derived from terrestrial forest, rather than on autochthonous production.
