Seasonal stable isotope variations of the modern Amazonian freshwater bivalve Anodontites trapesialis

In a floodplain lake of the Amazon River near the city of Iquitos, northeastern Peru, a one-year monitoring experiment was conducted during which water samples and living bivalves (Anodontites trapesialis) were collected with the aim to investigate seasonal delta(18)O variation in and fractionation between bivalve aragonite and host water. Both host water and molluscan growth increments show more than 8parts per thousand seasonal variation in delta(18)O. In the floodplain lake under study the delta(18)O variation of the water is controlled by contrasting dry and wet season evaporation-precipitation regimes. Molluscan delta(18)O appears to be in equilibrium with the host water. Although an approximately 4.0parts per thousand offset occurs, delta(13)O records of water and bivalves are in good agreement, suggesting that both delta(18)O and delta(13)O of the shells of freshwater bivalve A. trapesialis are good recorders of (palaeo-)environmental conditions. The delta(13)O of Dissolved Inorganic Carbon (DIC) is governed by plant growth and/or by changes in aquatic chemistry, affecting the DIC pool. (C) 2003 Elsevier Science B.V. All rights reserved.