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

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.

Mangrove vegetation changes on Holocene terraces of the Doce River, southeastern Brazil

“…Although the rates are nonlinear between the dated points, they are same magnitude order with the vertical accretion range of 0.1 to 10 mm/yr of mangrove forests reported by other authors (e.g. Behling et al, 2004;Bird, 1980;Cahoon and Lynch, 1997;Cohen et al, 2005aCohen et al, , 2008Cohen et al, , 2009Guimarães et al, 2010;Spenceley, 1982;Vedel et al, 2006).…”

Relative sea-level and climatic changes in the Amazon littoral during the last 500 years

“…Although the rates are nonlinear between the dated layers, they are the same magnitude order with the vertical accretion range of 0.1 to 10 mm yr − 1 of mangrove forests reported by other authors (e.g. Cahoon and Lynch, 1997;Bird, 1980;Spenceley, 1982;Behling et al, 2004;Cohen et al, 2005aCohen et al, , 2008Cohen et al, , 2009Guimarães et al, 2010;Vedel et al, 2006).…”

Mineralogical and geochemical influences on sediment color of Amazon wetlands analyzed by visible spectrophotometry

“…The Amapá site presents extensive Holocene tidal flats, influenced by a semi-diurnal macrotidal regime (5-6 m amplitude) and the Amazon River's discharge (Meade et al 1985;Gallo and Vinzon 2005), and is mainly colonized by herbaceous vegetation (Guimarães et al 2010, Figure 1B). The herbaceous plain sampled is only flooded by a water column of 10 cm during overbank flow at higher spring tides of the rainy season (supratidal), and is characterized by an elevation between approximately 2 and 4 m and low drainage density due to the siltation of the tidal channels (Guimarães et al 2012).…”