Inland Waters, Vol 6, No 2 (2016)

Species-specific imprint of the phytoplankton assemblage on carbon isotopes and the carbon cycle in Lake Kinneret, Israel

Aram Goodwin, Jonathan Erez, Karl David Hambright, Nir Koren, Eugeni Barkan, Tamar Zohary
Pages: 211-223


Lakes undergoing major changes in phytoplankton species composition are likely to undergo changes in carbon (C) cycling. In this study we used stable C isotopes to understand how the C cycle of Lake Kinneret, Israel, responded to documented changes in phytoplankton species composition. We compared the annual δ13C cycle of particulate organic matter from surface water (POMsurf) between (1) years in which a massive spring bloom of the dinoflagellate Peridinium gatunense occurred (“Peridinium years”) and (2) years in which it did not (“non-Peridinium years”). In non-Peridinium years, the spring δ13C–POMsurf maxima were lower by 3.3‰. These spring δ13C maxima were even lower in POM sinking into sediment traps and in zooplankton (lower by 6.8 and 6.9‰, respectively). These differences in the isotopic composition of the major organic C components in the lake represent ecosystem-level responses to the presence or absence of the key blooming species P. gatunense . When present, the intensive, almost monospecific bloom lowers the concentrations of CO2(aq), causing a reduction in the isotopic fractionation of the algae (higher δ13C of POMsurf) and massive precipitation of calcium carbonate (CaCO3). In “non-Peridinium years, the phytoplankton cannot deplete CO2(aq) to similar levels; the algae maintain higher isotopic fractionation, leading to lower δ13C maxima. These changes are reflected higher up in the food web (zooplankton) and in sedimenting organic matter. The consequences for the ecosystem in non-Peridinium years are lower export of both organic and inorganic C.
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