Original paper

Energy input from a riparian forest into a headwater stream in Hokkaido, Japan

Kochi, Kaori; Yanai, Seiji; Nagasaka, Akiko

Abstract

We investigated the amounts and types of organic matter that entered a coastal forest stream in Hokkaido, northern Japan. Organic matter input from the riparian forest was collected using litter traps, and benthic organic matter was collected from the streambed. Plant parts were weighed, and monthly nitrogen and carbon inputs were calculated. Organic matter input was highest in October, accounting for 58% of the total annual amount, whereas input between May and August comprised only 22% of the total amount. Frass and various plant parts, such as flowers and green leaves, contributed nitrogen from May to August, and the total input during this period accounted for 39% of the annual input, which was comparable to the input recorded in October. In May and June, senescent leaves accounted for 30-40% to the total standing crop although only green leaves entered the stream during this period. To explore the relationship between benthic organic matter and stream macroinvertebrate density, we collected the two dominant summer growing shredder species (Goerodes complicatus [Trichoptera] and Sternomoera rhyaca [Gammaridea]). Densities of S. rhyaca were significantly related to the standing crop of detritus; G. complicatus showed the same trend, although the relationship was not significant. During spring and summer, plant matter that contained high levels of nitrogen contributed to increased nutrient resources in the stream. This organic matter probably affected the growth and development of stream macroinvertebrates when resources were scarce during early summer.

Keywords

organic matternitrogen inputcarbon inputleavesmacroinvertebrates