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Nitrogen‐stable isotopic signatures of basal food items, primary consumers and omnivores in rivers with different levels of human impact
Author(s) -
Kohzu Ayato,
Tayasu Ichiro,
Yoshimizu Chikage,
Maruyama Atsushi,
Kohmatsu Yukihiro,
Hyodo Fujio,
Onoda Yukio,
Igeta Akitake,
Matsui Kiyoshi,
Nakano Takanori,
Wada Eitaro,
Nagata Toshi,
Takemon Yasuhiro
Publication year - 2009
Publication title -
ecological research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.628
H-Index - 68
eISSN - 1440-1703
pISSN - 0912-3814
DOI - 10.1007/s11284-008-0489-x
Subject(s) - omnivore , δ15n , benthic zone , trophic level , food web , ecology , biology , stable isotope ratio , shrimp , δ13c , nutrient , organic matter , detritus , eutrophication , predation , physics , quantum mechanics
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 (δ 15 N) 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 δ 15 N 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.