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δ 15 N of zooplankton species in subarctic lakes in northern Sweden: effects of diet and trophic fractionation
Author(s) -
Karlsson J.,
Jonsson A.,
Meili M.,
Jansson M.
Publication year - 2004
Publication title -
freshwater biology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.297
H-Index - 156
eISSN - 1365-2427
pISSN - 0046-5070
DOI - 10.1111/j.1365-2427.2004.01208.x
Subject(s) - trophic level , zooplankton , pelagic zone , bacterioplankton , subarctic climate , phytoplankton , plankton , trophic state index , ecology , biology , nutrient , environmental science
Summary 1. To assess the use of stable nitrogen isotopes ( δ 15 N) for reconstructing trophic relationships in planktonic food webs, crustacean zooplankton species and pelagic dissolved and particulate matter were analysed in 14 subarctic lakes in northern Sweden. The lakes are situated along an altitudinal gradient and show a substantial variation in nutrient content and energy mobilization by bacterioplankton and phytoplankton. 2. The δ 15 N of dissolved and particulate matter was comparatively low, suggesting efficient N recycling and low losses of depleted N from the pelagic zone of these unproductive lakes. 3. Copepods had a systematically higher δ 15 N than cladocerans, with an average difference of 3.1–4.9‰ within lakes, implying different trophic positions of the two groups. Comparisons of nitrogen pools and energy fluxes suggest that the low cladoceran δ 15 N was a result of feeding on bacteria. 4. The difference in δ 15 N between copepods and cladocerans declined with decreasing bacterioplankton production among lakes, due either to increasing trophic isotope fractionation or decreasing relative importance of bacteria in the diet of cladocerans.