A dinâmica da vegetação nas planícies de maré do delta do rio Doce durante o holoceno tardio.

Abstract

The goal of this work was to study the vegetation dynamics on the tidal plain of the Doce River Delta – southeastern Brazil – under the climate change influence and relative sea-level change during the late Holocene (2350 cal yr BP). Thus, 14C dating, sedimentary features, and pollen date, obtained from two cores denominated URU1 (0.5 m depth) and URU2 (4 m depth), sampled with a peat sampler were used. The cores presented four typical sedimentary facies of tidal plain: i) Flaser heterolithic bedding (Hf); ii) Wavyheterolithic bedding; iii) Lenticular heterolithic bedding (Hl) and iv) Parallel mud (Mp). The pollen analysis of URU1 showed herbs predominance, trees and shrubs in all intervals, besides rising of aquatic vegetation towards surface. The URU2 core showed a mangrove and foraminifera influence close to the bottom and middle depth, possibly due to a higher marine/estuarine influence until 2250 cal yr BP. However, close to the surface of this core, occurred a mangrove and foraminifera decrease, followed by freshwater aquatic vegetation increasing, indicating a decrease in the marine influence. This can be a result of a relatively humid climate since at least 2250 cal y BP, which resulted in higher rainfall and flow of rivers. Furthermore, the palynological data shows anthropic or natural alterations that occurred after 2250 cal yr BP demonstrated decreased coverage of palm trees in the tidal plain, further of a higher presence of Cecropia and Typha angustifolia pollen. Therefore, an increase of freshwater flow and wet climate conditions since at least 2000 cal yr BP, has been decisive for increasing sediment transport by the rivers to the delta plain, resulting in a coastline increase, leading coastal progradation, which resulted in replace process between mangroves and herbaceous vegetation.