Nitrogen-stable isotopic signatures of basal food items, primary consumers and omnivores in rivers with different levels of human impact

Autor: Kiyoshi Matsui, Fujio Hyodo, Ichiro Tayasu, Eitaro Wada, Akitake Igeta, Chikage Yoshimizu, Yukihiro Kohmatsu, Toshi Nagata, Yukio Onoda, Ayato Kohzu, Yasuhiro Takemon, Takanori Nakano, Atsushi Maruyama
Rok vydání: 2008
Předmět:
Zdroj: Ecological Research. 24:127-136
ISSN: 1440-1703
0912-3814
DOI: 10.1007/s11284-008-0489-x
Popis: We examined how nitrogen-stable isotopic signatures of food web components (basal resources, primary and lower consumers, and omnivores) in rivers change with increasing levels of human population density (HPD) in their watersheds. Samples were collected from 22 rivers flowing in the Lake Biwa basin, Japan. Among three potential resources at the base of food webs (epilithon, benthic and suspended particulate organic matter), the mean isotopic values (δ15N) of the epilithon (4.5–7.8%) were consistently higher than those of other items (1.9–4.2%) and displayed the most pronounced elevation (by 3.3%) with increasing HPD. The mean δ15N values of the individual taxa of lower consumers (bivalve, snail and caddisfly) tended to increase with increasing HPD, although the pattern and the extent of the elevation were highly variable among the taxa. These results suggest a taxon-specific feature in the N source (or sources) of lower consumers. Our data suggested that human activities (e.g. nutrient loading) potentially induce changes in the N baselines of river food webs. The major N source of bivalves appeared to be shifted from suspended particulate organic matter to other items with increasing HPD. Trophic levels of goby fish (Rhinogobius sp. OR) and shrimp (Palaemon paucidens), being estimated to be at 2.4–3.8 and 2.1–3.4, respectively, did not differ significantly among rivers with different HPD levels.
Databáze: OpenAIRE
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