SEMINAIRES Talence - UMR EPOC

1. SEMINAIRES Talence - UMR EPOC Lundi 14 Septembre 2009 10h45en Salle Stendhal Lignin phenols as organic matter tracer in aquatic Amazon ecosystems Marcelo Bernardes Environment Geochemistry Program Universidade Federal Fluminense, Brazil Lignin phenols analyses have been used to quantify and assess vascular plant material in riverine particles and sediments. Recently, this approach has been applied in lacustrine environments to evaluate the aquatic plants growth and relate its occurrence with hydrological seasonality. When Amazon River fills the floodplains it supplies the lakes with materials that are degraded and processed by primary producers. The balance from heterotrophic to autotrophic activities will determine the aquatic metabolism. To assess the importance of terrigenous organic matter in the aquatic carbon cycle of those floodplain lakes, lignin amount and quality evaluation should be an important role once it discriminates terrigenous from aquatic vascular plants. In the case of a phytoplankton contribution lignin will be absence. The forms and composition of lignin phenols in sediments of floodplain lakes were evaluate in white and black water lakes. Higher value of Cinamil, a typical leaf compound were related to aquatic behavior of floated macrophytes allowing a more leaf growth against a more Syringil structure phenol necessity, typical from terrestrial plants. The superficial sediments samples results appeared to be influenced by (1) the forest lowland proximity, (2) the Amazon River influence and (3) by the interconnection among the productivity of the floodplain lakes. Those alochthone versus autochthones sources added to the degradation conditions determined the composition of organic matter deposited. Black water lakes, as Curumucuri and Açaí, situated at Curuai Varzea, PA, Brazil, presented a high alochthone organic matter contribution from the drainage of the neighborhood forest. Differences found in degradation rates were related to the hydrological dynamic of those black water lakes. The more closed Açai lake showed a higher degradation rate in relation to Cumurucuri Lake that presented a less degraded organic matter due to a intense influence from floodplain system and a fast water renew. The organic matter from white water lakes sediments presented high autochthones proximate sources (aquatic plants) and less alochthone ultimate source (terrestrial plants). Differences in degradation rates give by a preferred degraded ratio between lignin phenols were related with water circulation, where a more open system seems to present a less degraded rate.