In stream ecosystems, it has been pointed out that estimating the contribution of resources to an organism and its trophic level are difficult because the δ¹³C of periphytic algae greatly varies with spatio-temporal variation. Recently, estimation of the trophic levels based on δ¹⁵N of individual amino acids has been developed to resolve those problems. However, there are few applications of this tool to actual food webs.

We investigated macroinvertebrates in headwater streams in Mt. Gomadan Experiment Forest. In this area, the clear cutting is usually operated within small catchments. Therefore, it is possible to clarify the long-term effects of the clear cutting on ecosystems. We measured the bulk δ¹³C, δ¹⁵N and δ¹⁵N of amino acids of organisms in six headwater streams of stand ages ranging from 5 to >90 yr.

A dual isotope plot of δ¹³C and δ¹⁵N values showed that most of macroinvertebrates depended on both terrestrial litter and periphytic algae. The mean δ¹³C values of macroinvertebrates decreased with increasing stand ages. The result indicates that the macroinvertebrates in old stand ages depended more on allochthonous resources rather than on autochthonous resources. In the presentation, we will also discuss the results of the trophic levels using δ¹⁵N values of amino acids.