|| 要旨トップ | 本企画の概要 |||日本生態学会第61回全国大会 (2014年3月、広島) 講演要旨
シンポジウム S10-3 (Lecture in Symposium/Workshop)
Impacts of anthropogenic nitrogen (N) inputs on nutrient dynamics and food web structures using stable N isotope techniques in the Arida river catchment, Japan. Riverine survey utilizing 5 regular sampling points showed that δ15N of nitrate (NO3-) increased from forested upstream (~2 per mil) to the downstream (~7 per mil) due to the sewage loads and fertilizer effluents from agricultural area. Correspondingly the δ15N of benthic algae and aquatic insects increased toward the downstream. This indicates that primary producers of each reach strongly relied on the local N sources and it was utilized effectively in their food web. Simulation using a GIS based mixing model considering the spatial distributions of human population density and fertilizer effluents revealed that strongest impacts of N inputs was originated from organic fertilizers applied to orchards in the middle to lower parts of catchment. Food web structural analysis using food network unfolding technique based on observed δ15N suggested that the structure of nutrient pyramid did not differ significantly along the riverine positions, while the members of species in each trophic revel changed and the impact of anthropogenic N input was visible along the river.