Paula Andrea Rodríguez Zorro

B. Hermanowski, M. Lima da Costa and H. Behling, Department of Palynology and Climate Dynamics, University of Göttingen, Alemania []

Changes in vegetation and climate using multi-proxy analysis in an oxbow lake in southwestern Amazonia during the late Holocene

Oxbow lakes dynamics are related with the variation in the flood pulse of the rivers. The flux of water and sediments that enter into these systems are regulating the configurations of the ecosystems that are growing there, influencing the biodiversity in the flood plains. The focus of this research is to find different changes in vegetation, during the late Holocene in southwestern Brazilian Amazonia, specifically in Amapá Lake, an oxbow lake as a result of a meander of Acre River. Our first results based on pollen counting, show a huge influence of Acre River in the establishment of the vegetation in the lake. This area is dominated by Tropical rain forest with the dominance of Cecropia, Moraceae/Urticaceae, Fabaceae and Melastomataceae. Along the record, pollen concentration is low with values between 5000 and 13000 grains/cm3; there are different peaks in the percentage of tropical rain forest, and Cecropia, as pioneer plant indicator, is showing high and low frequency pattern, with values reaching up 50%. We interpret those results as a different successional stages caused by flooding phases of Acre River; when Cecropia reduces its frequency there is an increase in the representation of other elements of tropical rain forest as Sapindaceae, Annonaceae and Moraceae, showing a possible pattern of colonization in the area. According to these preliminary results and as a first approach into the changes in vegetation in oxbow lakes in Amazonia floodplains, we are going to use a multi proxy analysis, with radio carbon dating, X-ray fluorescence spectrometry, stratigraphy and statistical analysis to corroborate that these fluctuations in the vegetation are related with the effect of the flood pulse of Acre River into Amapá Lake during the last 600 years BP. Key words: amazon, oxbow lake, Holocene.