Marlon Carlos França

Mid- and late-Holocene sedimentary process and palaeovegetation changes near the mouth of the Amazon River

The integration of sedimentary facies, pollen, spores, carbon and nitrogen isotopes records, C/N ratio and radiocarbon dates allowed the identification of changes in vegetation and the sources of organic matter accumulated on tidal flats near the mouth of the Amazon River during the mid and late Holocene. Data from the margin of Amazon River indicate marine influence related to mangrove presence over a tidal mud flat between 5560–5470 cal. yr BP and 5290–5150 cal. yr BP. Afterward, the mangrove area shrank following the return of more humid conditions and increase of Amazon River discharge. A common reworking process of the tidal flat through the lateral migration of a meandering creek occurred in the study site, with later development of transitional vegetation under freshwater influence. Following the natural vegetation succession under stable climate and hydrological conditions, the expansion of ‘várzea’ (flooded freshwater vegetation) forests occurred since 600–560 cal. yr BP until the present. Furthermore, regarding the tidal flats located west of the mouth of Amazon River, these stable conditions also allowed the mangrove maintenance over mudflats with deposition of marine organic matter during at least the last 2350–2300 cal. yr BP.

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

Os tipos de vegetacao atual, sequencias sedimentares, dados de polen e datacoes por radiocarbono obtidas em tres testemunhos de sedimento da planicie costeira de Calcoene foram utilizados para estabelecer uma historia paleoecologica durante o Holoceno superior das zonas umidas costeiras do Amapa conforme as mudancas no regime de inundacao, nivel do mar e clima. Baseado nestes tres registros, quatro fases de desenvolvimento da vegetacao sao apresentadas e provavelmente refletem a interacao entre o fluxo de energia na acumulacao do sedimento e a influencia das aguas salobras e doces na vegetacao. Este trabalho sugere alternâncias entre periodos caracterizados por influencias marinha e fluvial. O perfil longitudinal nao revelou a ocorrencia de manguezais nos sedimentos depositados por volta de 2100 anos A.P. Durante a segunda fase, a lama preencheu progressivamente as depressoes e canais de mare. Provavelmente, os manguezais iniciaram seu desenvolvimento nas margens dos canais, e os campos herbaceos nos setores elevados. A terceira fase e caracterizada por uma interrupcao no desenvolvimento dos manguezais e a expansao da vegetacao de varzea devido a uma diminuicao na influencia das aguas marinhas. A ultima fase e representada pela expansao de manguezais e varzeas. A correlacao entre os padroes atuais de distribuicao das unidades geobotânicas e a paleovegetacao indica que os manguezais e as florestas de varzea estao migrando sobre os campos herbaceos nos setores topograficamente mais elevados do litoral em estudo, o que pode estar relacionado a um aumento do nivel relativo do mar.

Morphological and vegetation changes on tidal flats of the Amazon Coast during the last 5000 cal. yr BP

The analysis of morphology, sedimentary facies, palynology, carbon and nitrogen isotopes, C/N ratio and radiocarbon data from tidal flats sediments influenced by the Amazon River indicates that vegetation development during the last 5000 cal. yr BP was controlled by morphological changes associated with marine and fluvial process. The proximal portion of the tidal flat corresponds to abandoned channels surrounded by terrestrial vegetation since 5280–5160 cal. yr BP. During the last 2840–2750 cal. yr BP, autochthonous organic material became prevalent as well as the increase in contribution of terrestrial organic matter mainly from ‘várzea’ vegetation. Herbaceous plants already colonized the tidal flat before 3170–2970 cal. yr BP, and after 2630–2310 cal. yr BP and 1350–1290 cal. yr BP they were replaced by mangrove vegetation following the development of secondary channels connected to the sea with brackish water influence. Furthermore, the erosion of the herbaceous field to form chenier ridges/tidal mixed flat after 3170–2970 cal. yr BP and before 220–140 cal. yr BP in the distal portion of the tidal flat suggests an overall interpretation of a retrogradation cycle. This process was driven by a relative sea-level rise influenced by the increase of Amazon discharge during the late Holocene.

Millennial to secular time-scale impacts of climate and sea-level changes on mangroves from the Doce River delta, Southeastern Brazil

This work integrates geomorphological, sedimentological, and palynological data with radiocarbon dating, as well as δ13C, δ15N, and C/N from sedimentary organic matter to provide a model of mangrove dynamics during the evolution of a wave-dominated delta in Southeastern Brazil. Mangrove dynamics are analyzed within the context of millennial and secular climatic and sea-level changes. Tidal flats, positioned at highest limit of the intertidal zone along the edge of a lagoon sheltered by beach ridges, were occupied by wetlands represented by mangrove and herbaceous vegetation during the mid-Holocene high sea level. After considering the relative sea-level fall and relatively higher fluvial sediment discharge, during the last ~6350 years, progradation took place along this shoreline, resulting in extensive beach ridge deposits that overlie transgressive muds. This process led to loss of mangrove area. Similar dynamics were repeated at ~3043 cal. yr BP, although in a relatively more distal (i.e. seaward) position. Between ~1337 and ~900 cal. yr BP, a tidal flat attached to the edge of a lagoon near the modern coastline was colonized by herbaceous vegetation (C4 plants). The next phase, which occurred between ~900 and ~400 or ~100 cal. yr BP, is marked by the transition from herbaceous to mangrove tidal flats with an increased trend of terrestrial organic matter. During the recent centuries, a mangrove vegetation became established, and there was an increased trend of estuarine-derived organic matter. This mangrove phase, recorded during the last century(ies), may be due to a relative sea-level rise. Under this scenario, erosion of beach ridges and expansion of lagoons and mangroves are expected along the littoral of the State of Espírito Santo in Southeastern Brazil.

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

Com base em dados sedimentologicos e geoquimicos, este trabalho relaciona medicoes espectrofotometricas com a composicao do sedimento, e sua aplicacao em estudos paleoecologicos das areas alagaveis da Amazonia. Os dados CIELAB estao diretamente relacionados a composicao mineralogica e quimica dos sedimentos, especialmente quartzo, oxihidroxidos e sulfetos de ferro, e carbono orgânico total. Conteudos de carbono orgânico total entre 0,4-1%, 1-2%, 3-5% e 15-40% foram relacionados a dados de L* (luminosidade) de 27, 26-15, 7-10 e 7 ou menos, respectivamente. Os valores CIELAB de um deposito com turfa em Maraba, Para, foram proporcionais a variacoes no conteudo de quartzo e carbono orgânico total, mas mudancas nas zonas de cores similares, principalmente nos valores de +a* (vermelho) e +b* (amarelo), ao longo de outros depositos em Calcoene, Amapa e Soure, Para, indicam uma relacao muito proxima entre os conteudos de carbono orgânico total, oxihidroxidos e sulfetos de ferro. Alem disso, o diagrama Q7/4 (razao entre valores percentuais de refletância em 700 nm e 400 nm, juntamente com dados de L*) indicou sedimentos ricos em ferro para a facies lama bioturbada no deposito do Amapa, facies lama bioturbada e areia bioturbada do deposito de Soure, e das facies areia com laminacao cruzada e areia macica do deposito de Maraba. Ainda, sedimentos ricos em carbono orgânico foram encontrados na lama bioturbada no deposito do Amapa, facies heterolitica lenticular e lama bioturbada do deposito de Soure, e das facies lama laminado e turfa do deposito de Maraba. Na area de Maraba, os dados sugerem uma influencia autoctone com formacao de turfa. As areas de zonas umidas costeiras no Marajo e Amapa representam o desenvolvimento tipico de planicies de mare com formacao de sulfetos e oxihidroxidos de ferro durante alternâncias entre inundacao e exposicao.

Late Holocene mangrove dynamics dominated by autogenic processes

Generally, palaeoenvironmental interpretations consider only allogenic processes, when autogenic factors may have a strong influence on proxies of stratigraphic sequences. For instance, the Holocene history of the vegetation along the southern littoral of the State of Bahia in north-eastern Brazil is characterized by mangrove dynamics controlled by allogenic processes. However, over smaller timescales (~700 years), autogenic processes may have controlled vegetation dynamics and hence observed pollen distribution. This work proposes tidal channel dynamics as one of the main cause for changes in pollen assemblage along the studied stratigraphic profiles during the last centuries, based on sedimentology, pollen and elemental analysis (δ13C, δ15N and C/N) and radiocarbon dating of sedimentary organic matter from two cores sampled from an abandoned meander and a tidal flat at the mouth of the Jucurucu River. One core was sampled from a mangrove formed during the past ~550 cal yr bp. Another core recorded sediments in a varzea forest (swamp seasonally and permanently inundated by freshwater) located ~2.7 km from the current shoreline, which displayed a maximum age of ~680 cal yr bp. Two facies associations were identified: tidal channel (A) and tidal flat/oxbow lake (B). This work proposes allogenic processes as the main driving forces controlling the wetlands dynamics at the studied site during the Holocene. However, our data also reveal that part of the changes in vegetation over the last ~700 years reflect tidal channels and tidal flats development, which represent autogenic processes. The change in timescale analysis from the Holocene to recent centuries may have weakened the influence of allogenic factors. However, this needs interpretation with reference to the spatial scale of the depositional environment as the larger the depositional system analyzed, the stronger the influence of autogenic processes on stratigraphic sequences over longer timescales. Copyright

Allogenic and autogenic effects on mangrove dynamics from the Ceará Mirim River, north-eastern Brazil, during the middle and late Holocene: Allogenic and autogenic effects on mangrove dynamics

been through the copyediting, typesetting, pagination and proofreading process which may lead to differences between this version and the Version of Record. Please cite this article as doi: 10.1002/esp.4342 This article is protected by copyright. All rights reserved. Allogenic and autogenic effects on mangrove dynamics from the Ceará Mirim River, Northeastern Brazil, during the middle and late Holocene

Decadal-scale dynamics of an Amazonian mangrove caused by climate and sea level changes: Inferences from spatial-temporal analysis and digital elevation models: Decadal-scale dynamics of an Amazonian mangrove

Sea level rise and climate change are major forces driving wetland dynamics. The northern Brazilian coast has one of the largest continuous mangrove areas on Earth, with the mangroves from the Bragança Peninsula, in eastern Amazonia, being the most representative ones. These mangroves have migrated into higher tidal flats over the last years. We analyzed spatial-temporal changes of vegetation units adapted to different physical-chemical conditions along the Bragança Peninsula in order to decipher possible causes responsible for such recent mangrove dynamics. The investigation was based on time series analysis of a 33-year (1984-2017) data base consisting of satellite and drone images. These data were combined with digital elevation models based on topographical data obtained by photogrammetry, theodolite and hydrotopographic devices. During this time frame, mangroves invaded 2.7 km of inner tidal flats, which is compatible with a rise in relative sea level (RSL) and with a rainfall decreasing. Such topography-dependent dynamic suggests that an increased frequency of tidal inundation decreased porewater salinity and caused mangroves to expand into topographically higher grounds. However, the study area contains small basins, that are less affected by tidal inundation, and Avicennia trees are dying in these locations due to increased porewater salinity, probably caused by a decreased rainfall. We propose that climate and RSL are responsible for driving the death of mangroves in the study area, and their migration into topographically highest tidal flats. Considering the hypothesis of a RSL rise of 5 mm/yr under stable rainfall, or a RSL rise of 3 mm/yr accompanied by decreased rainfall, it is projected that mangrove areas will expand by 2.93 or 1.35 km, respectively, by the end of this century. The mangrove expansion rates have decreased from 0.136 km/yr to 0.081 km/yr, with projection of 0.036 km/yr (2017-2100). It is caused by the steeper topographic gradients nowadays occupied by herbaceous and Terra Firme vegetation and the effects of decrease trend of rainfall rates in the central depression. The combination of time series analysis based on satellite and drone images associated with photogrammetry techniques, based on interpolated dense points cloud and ground control topographic data, proved to be an efficient and innovative process for monitoring and evaluating the impacts of global changes on coastal wetlands.