Describing benthic invertebrate communities in Japanese rivers using national environmental census data: spatial distributions of total biomass and major taxa

Based on quantitative survey data of 108 rivers and 724 freshwater sites collected during a national census of river environments, we determined the frequency distribution of total invertebrate biomass (total biomass) of riffles. We also examined the spatial pattern of total biomass by classifying sites according to channel gradient, bed substrate, and region. The median value of total biomass (in wet-weight) among all sites was 19.56 g m-2 for spring-winter and 10.04 g m-2 for summer-autumn. These values were similar to those previously reported for Japanese rivers, but were several times higher than those reported for rivers from other countries. The total biomass was lowest for sites with gentlest gradient classes (