Model of wetland development of the Amapá coast during the late Holocene

José T.F Guimarães,Marlon C França,Rúben J Lara,Marcelo C.L Cohen,Hermann Behling

doi:10.1590/s0001-37652010000200021

José T.F Guimarães, Marlon C França + Show 3 more

Open Access

https://doi.org/10.1590/s0001-37652010000200021

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Abstract

The modern vegetation types, sedimentary sequences, pollen records and radiocarbon dating obtained from three sediment cores from Calçoene Coastal Plain were used to provide a palaeoecological history during the late Holocene of Amapá coastal wetland according to flood regime, sea-level and climatic changes. Based on these records, four phases of vegetation development are presented and they probably reflect the interaction between the flow energy to the sediment accumulation and the brackish/freshwater influence in the vegetation. This work suggests interchanges among time periods characterized by marine and fluvial influence. The longitudinal profile did not reveal the occurrence of mangrove in the sediment deposited around 2100 yr B.P. During the second phase, the mud progressively filled the depressions and tidal channels. The mangrove probably started its development on the channel edge, and the herbaceous field on the elevated sectors. The third phase is characterized by the interruption of mangrove development and the increase of "várzea" vegetation that may be due to the decrease in porewater salinity related to a decrease in marine water influence. The last phase is represented by the mangrove and "várzea" increase. The correlation between current patterns of geobotanical unit distribution and palaeovegetation indicates that mangrove and "várzea" forests are migrating over the herbaceous field on the topographically highest part of the studied coast, which can be related to a relative sea-level rise.

Highlights

Mangroves are the most favorable environment for palaeoclimatic studies during the Holocene because of their high sedimentation rates and susceptibility to climatic and sea-level changes (Gornitz 1991)
The modern vegetation types, sedimentary sequences, pollen records and radiocarbon dating obtained from three sediment cores from Calçoene Coastal Plain were used to provide a palaeoecological history during the late Holocene of Amapá coastal wetland according to flood regime, sea-level and climatic changes
The correlation between current patterns of geobotanical unit distribution and palaeovegetation indicates that mangrove and “várzea” forests are migrating over the herbaceous field on the topographically highest part of the studied coast, which can be related to a relative sea-level rise

Summary

Introduction

Mangroves are the most favorable environment for palaeoclimatic studies during the Holocene because of their high sedimentation rates and susceptibility to climatic and sea-level changes (Gornitz 1991). Regarding the Amapá coastal plain, the mangrove community presents a zonation parallel to the shoreline (Boaventura and Narita 1974). Ally the response of individual mangrove species to the gradients of flooding frequency (Cohen and Lara 2003), waterlogging (Hutchings and Saenger 1987), nutrient availability (Junk 1997), soil salinity across the intertidal area (Wolanski et al 1990) and volume of river water discharge, which depends of regional rainfall (Mörner 1999, Cohen et al 2005b). Interchanges between dry and wet periods may have significant impacts on coastal wetland, as they modify the soil salinity gradients and the soil moisture (Cohen et al 2005a)

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