Wetland dynamics of Marajó Island, northern Brazil, during the last 1000 years

The wetland dynamics in eastern Amazon region during the last thousand years were studied by pollen analysis and AMS radiocarbon date. Three sediment cores were sampled from the Marajó Island, which is located at the mouth of the Amazon River. Marajó Island is covered mainly by Amazon coastal forest, herbaceous and varzea vegetation. One core was obtained from Lake Arari, which is surrounded by herbaceous vegetation flooded by freshwater. Two cores were sampled from an herbaceous plain that lies 45 km southeast from the Lake Arari. The pollen records indicate that the herbaceous vegetation began its development approximately 800 cal yr B.P. The pollen percentages between 750 and 500 cal yr B.P. indicate the expansion of mangroves. The predominance of herbaceous and varzea pollen occurs between 500 and 200 cal yr B.P. and the varzea pollen percentage increased during the last 200 years. The vegetation changes proposed by the pollen records from the Lake Arari, probably, represent the regional vegetation dynamics of the Marajó Island, while the pollen profiles from herbaceous plain present a smaller spatial representativeness of the vegetation. The alternation between fresh and brackish water vegetation in the wetlands may indicate changes in the physicochemical characteristics of the sediment during the time interval studied.