Changes in biomass of filter feeding caddisfly in a gravel-bed stream draining from forested to pasture land in northern japan
Masanori Nunokawa, Department of Agriculture and Environment, Hokkaido College, Senshu University, 1610-1, Bibai, Hokkaido, 079-0197, Japan, Takashi Gomi, Interntional Environmental Agriculture Sciences, Tokyo University of Agriculture and Technology, 3-8-1 Harumi-cho, Fuchu-shi, Tokyo, Japan, Junjiro Negishi, Aqua Restoration Research Center, Public Works Research Institute, Mubanchi, Kanyuuchi, Kawashima-kasada-cho, Kakamigahara, Gifu, 501-6021, Japan, and Osamu Nakahara, Divison of River Management, Wako Giken Ltd., Miyanomori 3jyo-1-3-15, Chuo-ku, Sapporo, Hokkaido, 064-8507, Japan.
The changes of food resources in a stream, in association with the changes in riparian conditions from forested to pasture areas, affects species composition and biomass of benthic macroinvertebrates. Changes in land use along the river typically confound changes in catchment geomorphology, which controls in-channel physical conditions, because agriculture was conducted in flood plains. We investigated the distribution of filter feeding caddisfly (Stenopsyche marmorata) along the Jyuyonsen creek (7.5 km channel segment, N45°1’ E142°7’) draining from forested to pastureland in 2004. Biomasses of Stenopsyche and suspended particle organic matter, riparian forest conditions, and in-channel physical variables were examined. We examined the effects of riparian land use and in-channel physical conditions on the distribution of Stenopsyche. The biomass of the Stenopsyche in the pastureland was six times greater than in the forest. All physical variables in the creek were marginally changed. The biomass of Stenopsyche was positively correlated to suspended FPOM. Our results suggest that the effects of land use, via the food resources, was the dominant controlling factor for the distribution of caddisflies rather than the physical variables associated with change in catchment geomorphology.