[en] Lake Tanganyika, East Africa, has a simple pelagic food chain, and trophic relationships have been established previously from gut-content analysis. Instead of expected isotopic enrichment from phytoplankton to upper level consumers, there was a depletion of 15N in August 1999. The isotope signatures of the lower trophic levels were an indicator of a recent upwelling event, identified by wind speed and nitrate concentration data, that occurred over a 4-d period several days prior to sampling. The isotope structure of the food web suggests that upwelled nitrate is a nutrient source rapidly consumed by phytoplankton, but the distinctive signature of this nitrate is diluted by time averaging in the upper trophic levels. This time averaging is a consequence of the fact that the isotopic signature of an organism is related to variable nitrogen sources used throughout the life of the organism. This study illustrates the importance of recognizing differences in time averaging among trophic levels.
Disciplines :
Aquatic sciences & oceanology
Author, co-author :
O'Reilly, C.M.; Department of Hydrology and Water Resources, University of Arizona, Tucson, AZ 85721-0011, United States
Hecky, R.E.; Department of Biology, University of Waterloo, Waterloo, ON N2L 3G1, Canada
Cohen, A.S.; Department of Geosciences, University of Arizona, Tucson, AZ 85721-0077, United States
Plisnier, Pierre-Denis ; Université de Liège - ULiège > Département d'astrophysique, géophysique et océanographie (AGO) > Chemical Oceanography Unit (COU) ; Royal Museum for Central Africa, Tervuren, Belgium
Language :
English
Title :
Interpreting stable isotopes in food webs: Recognizing the role of time averaging at different trophic levels
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