Fluvial pollen deposition in a mangrove ecosystem in south-eastern Brazil

Abstract

Here palynological assemblages are presented from channel surface sediment samples from the Caceribu, Guaraí and Guapimirim-Macacú rivers located in an important area of the Brazilian coast (Guanabara Bay, State of Rio de Janeiro), in order to provide information relevant for the interpretation of palaeoecological records. The data indicate the predominance of pollen types from the Atlantic Forest in all samples and a relatively low representation of mangrove pollen, suggesting distant (regional) fluvial transport. Avicennia and Rhizophora were represented in those samples closer to the intertidal zone, Rhizophora being the most important. It was possible to verify a marked difference in pollen concentration/deposition among the three rivers, probably related to the different hydrodynamic pattern of each river. A low concentration of palynomorphs occurred in the Macacú-Guapimirim River, resulting from its higher flow, and there was a high deposition of palynomorphs in the sediments of Guaraí River, in response to its isolation from the hydrographic Guanabara Bay basin. It was possible to verify other interesting data, such as low palynomorph concentration in samples from near the mouth and an increase of palynomorphs in the upstream samples, mainly due to the more active action of the tidal currents. Meanwhile, the increase in the total concentration of the palynomorphs in the upstream samples coincides with the maximum reach of the saline waters and their meeting with the internal flow of the rivers.