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

Abstract

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 δ 13 C cycle of particulate organic matter from surface water (POM surf ) 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 nonPeridinium years, the spring δ 13 C-POM surf maxima were lower by 3.3‰. These spring δ 13 C 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 CO 2(aq) , causing a reduction in the isotopic fractionation of the algae (higher δ 13 C of POM surf ) and massive precipitation of calcium carbonate (CaCO 3 ). In non-Peridinium years, the phytoplankton cannot deplete CO 2(aq) to similar levels; the algae maintain higher isotopic fractionation, leading to lower δ 13 C 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.

Mechanisms controlling dissolved CO2 over-saturation in the Three Gorges Reservoir area

“…In recent years, isotope proxies application has become invaluable in studying the riverine carbon cycle (Tamooh et al, 2013).  13 CDIC signatures have been used to trace DIC sources, transport and transformation in inland waters based on the distinct isotopic values of various carbon sources (Barth et al, 2003;Goodwin et al, 2016;Li et al, 2010;Tamooh et al, 2013;Zhong et al, 2017). Riverine  13 CDIC dynamics are primarily controlled by both chemical weathering in the catchment and biogeochemical processes in inland waters.…”