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Projections of the impacts of modern Relative Sea Level (RSL) rise on estuarine mangroves should be supported by coastal topographic data and records of mangrove dynamics under past RSL change. This work identified inland and seaward mangrove migrations along the Jucuruçu River (Bahia, Northeastern Brazil), during the Holocene based on sedimentary features, palynological and geochemical (δ13C, δ15N, C/N) data integrated with digital elevation models. During the Middle Holocene, in response to RSL rise, the estuary saw mangrove forest establish up to ~37 km inland. RSL stood between ‐1.4 (+0.36/‐2.2 m) and +1 (2.19/0.2 m) around 7400 cal yr BP, and rose to a highest position of +3.25 (4.22/2.45 m) reached around 5350 cal yr BP. That marine incursion caused the inland replacement of freshwater vegetation by mangroves on tidal flats. Since then, the estuary experienced RSL fall, reducing inland tidal water salinity towards the Late Holocene, making that the mangroves were replaced by freshwater floodplain vegetation. Today, in the seaward part of the estuary near its mouth, mangroves occupy an area of ~10 km2 along tidal channels. Considering a RSL rise of 98 cm up to the end of the 21st century, at a rate significantly higher than that of Middle Holocene RSL rise (1.5 mm/yr) and fall (0.6 mm/yr), the current mangrove substrates are expected to drown and/or eroded near the coast, while new mangroves may establish inland, at topographically higher tidal flats in nowadays freshwater‐tidal zones. Mangrove area could expand over 13 km2 of coastal and flood plain. Following the same interaction between RSL/climate changes and Holocene mangrove dynamics, such upstream mangrove migration may be attenuated or intensified by changes in fluvial discharge. © 2019 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

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 recent 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) database 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 km2 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 the topographically highest tidal flats. Assuming 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 km2, respectively, by the end of this century. The combination of photogrammetry with theodolite/hydrotopographic surveying proved to be an efficient and innovative process for monitoring and evaluating the impacts of global changes on mangroves. © 2018 John Wiley & Sons, Ltd. Surface Data Models obtained by photogrammetry (drone surveying) and theodolite/hydrotopographic surveying. [ABSTRACT FROM AUTHOR]

The Atlantic Forest and mangrove dynamics along the Brazilian coast have been affected by climate, relative sea-level (RSL), and anthropogenic forces. Individualizing the effects of these drivers on paleoecological records is a challenge. This was addressed by pollen analysis along three cores sampled from lakes on a coastal plateau, primarily influenced by rainfall, and from a fluvial valley, influenced by sea-level and fluvial discharge, in northeastern Brazil. Pollen records from the fluvial valley indicated the presence of mangroves along an estuary in the mid-Holocene. During the past ~5800 cal yr BP, mangroves, adapted to brackish water, were replaced by herbaceous vegetation adapted to freshwater in the fluvial valley. Concurrently (~5680–240 cal yr BP), expansion of Atlantic Forest and contraction of herbaceous vegetation occurred on the coastal plateau. This divergence of pollen records between two distinct sedimentary environments (lakes on a coastal plateau and fluvial valleys) was attributed to RSL and climate effects. The combination of RSL fall and higher fluvial discharge favored seaward mangrove migration and expansion of herbaceous vegetation along the fluvial valley during the mid-late Holocene. However, the increase in rainfall on the coastal plateau favored the expansion of arboreal vegetation and contraction of herbaceous vegetation. At ~1700 CE, an abrupt shift from arboreal to herbaceous vegetation occurred on the coastal plateau. This vegetation change is likely attributed to European colonization on the southern coast of the state of Bahia, which was colonized by Portuguese navigators ~1500 CE. Part of the Atlantic Forest has naturally regenerated and was preserved as a national park in recent decades. This study showed that although the sampling sites are close, pollen assemblages can differ considerably depending on the depositional environment. Therefore, pollen analyses in different depositional environments are necessary to assess individually driving forces impacts on coastal vegetation dynamics during the Holocene. • Atlantic Forest and mangrove in the Brazilian coast were studied by pollen analysis. • Mangroves along fluvial valley were replaced by herbs after 5800 cal yr BP. • Atlantic Forest expanded and herbs area shrank on coastal plateau (5700–240 cal yr BP). • Abrupt shift from arboreal to herbs occurred on coastal plateau at ~1700 CE. • Climate, sea-level, and European colonization effects on vegetation were identified. [ABSTRACT FROM AUTHOR]

Mangrove creeks are considered important routes between terrestrial and adjacent coastal waters regarding the transport of dissolved material to oceans. The present study assessed if Amazonian seasonal rainfall patterns affect the pore water biogeochemistry and the intensity and direction of nutrient (NH 4 + and PO 4 3−) and metal (Fe2+ and Mn2+) exchanges from intertidal creek mudflats fringed by pristine mangroves. The results indicate that mangrove-fringed mudflats are effective in retaining iron and nutrients in solid sediment phases compared to export to coastal waters, also potentially comprising a significant manganese contributor to coastal waters. However, nutrient and metal retention are lower during the wet season, as intense rainfall periods reduce pore water salinity and promote increased reducing sediment conditions. Such conditions enhance organic matter degradation and pore water NH 4 +, PO 4 3−, Fe2+ and Mn2+ concentrations just below the sediment-water interface, generating higher effluxes during this period. Our findings demonstrate that seasonal variabilities drive substantial physicochemical property and pore water biogeochemistry changes, affecting the efficiency of mudflat sediments retaining and exporting nutrients and metals. • Rainfall promoted vertical oscillations in redox status. • Rainfall favored pore water exchange of Fe2+, Mn2+, PO 4 3− and NH 4 +. • PO 4 3− and NH 4 + mobilization is predominantly regulated by sulfate reduction. • Marapanim creek mudflats are quite effective in retaining nutrients and iron. [ABSTRACT FROM AUTHOR]

The Marapanim River estuary (MRE) is part of the Amazon estuarine system located in northern Brazil, which is characterized as having extensive mangrove forests. Given that previous studies reported CO 2 and CH 4 fluxes from mangrove creeks in this region, here we investigate the potential organic carbon sequestration of the creek mudflats to get a better understanding of the carbon cycling through these systems. Sediment accumulation rates derived from 210Pb dating indicated that sampled cores represent the previous 24 (± 4) yr. The approximately 24-year total organic carbon (TOC), total nitrogen (TN) and total phosphorus (TP) burial rates were estimated to be 192.5 (± 43.5), 15.3 (± 4.1) and 3.2 (± 0.8) g m−2 yr−1, respectively. A binary source mixing model based on carbon stable isotopes (δ13C) revealed that the sedimentary organic matter (OM) is mainly influenced by marine phytoplankton input (49% to 95%). Furthermore, the TOC accumulation rates found here were slightly higher than the global averages estimated for within mangrove forests, suggesting that these unaccounted carbon sinks along creek mudflat environments are relevant for carbon budgets in mangrove-colonized coastal zones. The highest contents, stocks and accumulation rates were found in the tidal creek sediments that are most influenced by nearby mangroves and are more protected than sediments from major river margins. Our results indicate that the creek mudflats play a major role in carbon and nutrients sequestration, directly related to grain size and OM sources. • Organic matter (OM) source was mainly influenced by marine OM input (49% to 95%). • Amazon mangrove creeks accumulate large amounts of carbon and nutrients. • OC, N and P contents, stocks and burial depend on the grain size and OM sources. • The capacity to sequester OC increased with increases in TN and TP burial rates. [ABSTRACT FROM AUTHOR]