Amazon Coast Research Articles

Microbiological quality of oysters and water in macromarine mangrove swamps of the Amazon coast (Island of São Luís, MA), Brazil

Resumo Com o objetivo de avaliar a qualidade microbiológica de águas e ostras de bancos naturais e ostreiculturas localizados na ilha de São Luís (MA), foram analisadas no período de setembro de 2020 a fevereiro de 2021 60 amostras, sendo 30 de água e 30 de ostras (Crassostrea sp.), coletadas diretamente com os marisqueiros e proprietários de cultivos nos municípios da ilha de São Luís. Para a determinação de coliformes totais e Escherichia coli nas amostras de água, foi utilizado o método rápido Colilert®. A contagem de coliformes totais e termotolerantes em ostras foi realizada pelo método do número mais provável (NMP) e de E. coli por testes bioquímicos (Indol, VM, VP, Citrato). A enumeração de Staphylococcus coagulase positiva ocorreu pelo meio Baird Parker para isolamento e identificação, assim como por testes bioquímicos. A média geométrica do resultado da contagem de E. coli nas amostras de água variou entre 604,3 e 1.130,8 NMP/100 mL, indicando qualidade microbiológica insatisfatória. Quanto às amostras de ostras, oito (26,7%) das 30 amostras estavam impróprias para consumo, sendo quatro (13,3%) contaminadas por Salmonella sp. e E. coli, respectivamente. Segundo a Resolução da Diretoria Colegiada nº 331/19 e a Instrução Normativa nº 60 da Agência Nacional de Vigilância Sanitária, os resultados são preocupantes para a saúde pública, e recomendam-se ações mitigadoras, como o monitoramento regular da qualidade microbiológica da água.

Taphonomic feedback, paleoecology, and ostracod biostratigraphy of the Oligocene-Miocene carbonate deposits in the onshore Pará-Maranhão Basin, Northern Brazil

The Oligocene-Miocene carbonates of the Bragantina Platform are represented by densely fossiliferous rocks, which overlay the basement of the Northern Brazilian coast. Outcrop-based stratigraphy analysis combined with petrography, taphonomy, paleoecology, and ostracod biostratigraphy was carried out in the eight (8) m-thick of the Neogene mixed carbonate-siliciclastic succession exposed mainly in the Atalaia Beach. This outcrop is the classical exposure of the Pirabas Formation, generally overlaid by the siliciclastic deposits of the middle Miocene Barreiras Formation. The taphonomic signature in the last carbonate beds of this sedimentary succession indicates intense storms as autogenic processes succeeded by rapid allogenic burial by Barreiras’ deposits. These processes caused death, disarticulation, and accumulation of the benthic communities in the shallow platform, forming a coquina substrate (Taphofacies 1). During a low-energy period, shell-gravel-dwelling individuals represented mainly by Turbinella tuberculata and Mercenaria prototypa colonized this carbonate hardground (Taphofacies 2). Forced regression of Barreiras’ siliciclastics caused a fast shift of continental facies over coastal carbonate zones. The rapid burial culminated in the death of benthic communities creating a geochemical environment propitious for the pyritization of shells, leaves, and trunks (Taphofacies 3). The ostracod biozonation formed by the Cytherella stainforthi biozone and by the Quadracythere brachypygaia, Jugosocythereis pannosa, and Neocaudites macertus sub-biozones support the paleoenvironmental interpretation, chronocorrelation with the Caribbean units and confirm the Miocene age for this carbonate succession. Although taphonomic, paleoecologic, and biostratigraphic studies were carried out in a unique occurrence of the Pirabas Formation. These high-resolution stratigraphy analysis allowed the discovery of the details of this burial event that led to the shutdown of carbonate fabric on the Eastern Amazon Coast.

Sedimentary PAH and oxidative stress biomarkers responses on Namalycastis abiuma (Polychaeta: Nereididae) from an urbanized Amazon estuary

Contamination by polycyclic aromatic hydrocarbons (PAH) in sediments and oxidative stress biomarkers responses (glutathione-S-transferase activity—GST and lipoperoxidation—LPO) on the polychaetes Namalycastis abiuma were screened along the urbanized margin of the Guajará Estuary, Brazilian Amazon coast, during dry and rainy seasons. Total 16 priority PAH concentrations ranged from 17 to 386 ng g−1 dry sediment, with higher values during the dry season. High molecular weight PAHs predominated during dry season and were probably originated from fossil fuel burning. Increased naphthalene and anthracene concentrations were noted when the maximum river flow was recorded and suggest diffuse sources from drainage of contaminated surfaces. Ecotoxicological PAH risks were low according to international sediment quality indices. Nevertheless, PAH toxicity equivalency was around 10-fold higher nearer the oil terminal than alongside the estuary. Highest GST activities at the oil terminal and industrial sites coincided with the rainy season, and combined with hydrochemical and sedimentary conditions thought to promote PAH bioavailability and a prolonged toxicant exposure. LPO approached similar levels in both seasons, suggesting that enzymatic activities were sufficient to uphold the prooxidants exposure. This result indicates that the overall estuarine condition exerts subtle oxidative stress on a keystone species and matches the low PAH ecotoxicological risks. Depositional margins within the mangrove areas and port operation are susceptible to an enhanced PAH accumulation and need special surveillance.

Study of Ancient Pottery from the Brazilian Amazon Coast by EDXRF, PIXE, XRD, Mössbauer Spectroscopy and Computed Radiography

This paper presents the application of five analytical methods to analyze ceramic fragments excavated in the archaeological sites of Sambaqui do Bacanga (SB), Sambaqui da Panaquatira (SP), and Rabo de Porco (RP) located on the Brazilian Amazon coast. It is a region that presents evidence of one of the oldest ceramic productions in the Americas. Characterization of ceramics from the three sites led to the identification of the production processes, technological acquisition and choices, and the origin of the raw materials. The analytical methods employed in this study were EDXRF, PIXE, Mössbauer spectroscopy, XRD, and computed radiography. It was concluded through the Mössbauer and XRD Spectroscopy analyses that the firing temperature range used on the ceramics was 750–900 °C, performed in an oxidizing environment. Fragments from the three archaeological sites were grouped into two groups through multivariate statistical analysis. The first group was composed of SB and SP samples, and the second of RP samples, indicating that different groups were manufactured with different clays. The result of the cluster analysis indicates that the clay used in the manufacture of the RP site fragments came from the bank of the Bacanga River. The ceramic fragments’ internal structures, observed by computed radiography, revealed the presence of various sizes and types of temper in the fragments, showing different production technologies.

Biostratigraphy and paleoenvironment correlation based on benthic foraminifera from the cenozoic Marajó and Pirabas formations, Eastern Amazon Coast, Brazil

The Oligocene-Miocene foraminifera biostratigraphy correlation has been applied successfully as a geological tool for establishing the paleoenvironmental conditions during the deposition of siliciclastic and carbonate strata in the Eastern Amazon coastal basins. In this region, previously interpreted tectonic compartments represented by the Marajó Basin and Bragantina Platform were the main sites of siliciclastic and carbonate sedimentation influenced by Late Paleogene-Neogene transgressive–regressive events. In the subsident Marajó basin, a siliciclastic estuary was developed, supplied by the Cratonic Amazon River. The transcontinental river did not influence the Bragantina region to the East, allowing the implantation of a shallow carbonate platform. These Neogene segments require further sedimentological, stratigraphic, and paleontological studies to define these limits. The use of foraminifera content has been considered an important tool to assist in this differentiation, providing a paleoenvironmental and paleoecological reconstruction model. This work used qualitative and quantitative analyses integrating several diversity indices, complementing the R-mode cluster and the correlation of planktonic and benthic (P/B) ratios. The similarity in faunal diversity indicated that these siliciclastic and carbonate units represented by the Marajó and Pirabas formations are chronocorrelated. Marajó Formation is interpreted as a restricted, suboxic, marginal marine environment (lagoons/mangroves) with variable salinity and abundance of the species as Cribroelphidium williamsoni, Ammonia tepida, and A. beccari. In contrast, the Pirabas Formation was deposited in a brackish, oxic, and carbonate platform characterized by Cibicidoides subhaidingerii, Cibicides pachyderma A. beccarii, and Cassidulina laevigata species. These foraminifera assemblages confirm the previous stratigraphic and paleoenvironmental interpretations providing new insights into understanding the Late Paleogene-Neogene evolution of the Eastern Amazonia Coast.

Fecundity and reproductive patterns of the fiddler crab Uca maracoani Latreille 1802-1803 in an Amazonian estuary in northern Brazil

ABSTRACT In this study, aspects of the reproductive biology of a Uca maracoani population from northern Brazil were examined. Ovigerous females monthly captured from December 2013 to November 2015 were measured and dissected to count, collect morphometric data, and classify the eggs. Ovigerous females were encountered throughout the two-year period but were absent during the months with the highest rainfall and lowest salinity, which indicates a seasonal–continuous reproductive pattern. The fecundity varied from of 12,233 to 85,000 eggs per female, and mean was 36,840 ± 3,361 eggs. The egg size increased progressively and significantly over the course of embryonic development. We found a direct relationship between the size of the females and their fecundity, and a clear trend was seen in which the larger females produced more eggs with larger sizes, which increased less in size during embryonic development. The presence of early- and late-stage eggs together in the same ovigerous mass in a considerable number of the ovigerous females suggests multiple spawning. The fecundity of U. maracoani is greater than that of other Atlantic fiddler crab species, and its reproductive strategy ensures its survival in the estuaries of the Amazon coast, which are subject to considerable fluctuations in salinity.

Brachyuran crab diversity and the population biology of Panopeus americanus on a tropical Sabellariidae (Polychaeta: Annelida) reef

This paper describes the species composition, abundance, and diversity of brachyuran crabs and the population structure of Panopeus americanus on a Sabellaria wilsoni reef on Caixa D’Água beach, a macrotidal sandy beach on the Amazon coast. Samples were collected monthly throughout a single natural growth–destruction cycle of the reef. Ten crab species were recorded, of which the most abundant were Panopeus americanus (83% of the individuals collected), Panopeus occidentalis (6.8%), and Menippe nodifrons (5.3%). The highest crab species richness was recorded during the eroded reef phase, reflecting the increase in habitat complexity, whereas the highest crab density was recorded during the reef recuperation period, reflecting an intense recruitment process. Juveniles and adults (including ovigerous females) of P. americanus and P. occidentalis were found at certain times on the reef, while for M. nodifrons, the largest species, most of the captured individuals were juveniles, and no ovigerous females were captured. These findings reflect the importance of the biogenic substrate provided by the S. wilsoni reef to the population biology of the crabs on the Amazon coast, with some species using the reef more permanently, including as breeding and nursery grounds. The results also showed that the structural cycle of bioconstructions determines changes in the crab assemblages.

When are mangrove crabs fat? Seasonal and sexual variation in the fatty acid composition of edible crab species Ucides cordatus from the Brazilian Amazon coast

Fatty acids play important role in several biological processes taking place in crustaceans, such as reproduction and molting. The aim of the current study is to evaluate the seasonal variation in fatty acid concentration and profile in crab species Ucides cordatus exploited in Brazilian mangroves. Eight samplings were performed throughout one year and 30 adult specimens - 15 males and 15 females - were selected - it totaled 240 individuals. Muscle and hepatopancreas were freeze-dried and had their fatty acid profiles analyzed through gas chromatography. Analysis of variance, principal component analysis and cluster analysis were carried out in order to find patterns among sample groups. Sixteen fatty acids were found in hepatopancreas; palmitic acid presented the highest concentration in male (22.25–33.72%) and female individuals (24.97–31.74%). On the other hand, five fatty acids were identified in muscle tissues - linoleic acid was the fatty acid recording the highest concentration in male (20.51–27.49%) and female individuals (21.62–28.05%). Based on multivariate analysis, fatty acid concentrations played major role in group formation. With respect to the hepatopancreas, reproduction and pre-ecdysis phases were more clearly distinguished for female than for male individuals. Higher fatty acid concentrations were found in the muscles of the pos-ecdysis group. Overall, fatty acid concentrations have shown different behaviors for both tissues and for both sexes - the main variations were observed during the breeding and intermolt phases.

Human risk assessment of toxic elements (As, Cd, Hg, Pb) in marine fish from the Amazon

The present study evaluated As, Hg, Pb and Cd burdens in both ecologically and commercially important 314 marine fishes belonging to 47 species sampled along the Amazon Coast. We specifically investigated variations in these four elements among different habitats and their relationships with trophic position and estimated potential human health risk by calculating the hazard quotient (HQ), hazard index (HI), and target cancer risk (TR). Our analyses revealed that Hg concentrations in reef-associated fish were over 2-fold those recorded in demersal fish (p < 0.001). A stable isotope analysis indicated that most of the fish species analyzed herein are secondary consumers (i.e., TP > 2.9) and their trophic positions exhibited a significant negative correlation to As, Pb and Cd. Positive significant relationships were noted between As–Cd, As–Pb, As–Hg, Hg–Cd and Cd–Pb, suggesting that these elements exhibit similar dispersion properties and bioaccumulation homology, probably arising from natural fluvial inputs from the Amazon basin system. Detected As concentrations were higher than established guidelines and legal limits in 63.8% of the examined species (n = 30), whereas Cd, Hg and Pb levels were generally very low. Estimated daily intake (EDI) of iAs, Hg and Pb were above reference dose (RfD) in more almost half of species analyzed and HQ values were each found to pose potential non-carcinogenic health risks if high amounts are consumed over time. HI indicates that the determined elements attained levels considered as potential human health hazards trough consumption of eight cartilaginous fish. The TR values of iAs and Pb were higher than the guideline value and given this, individuals who continuously consume cartilaginous fish contaminated with the toxic elements determined here will likely be under increased cancer risks in the long term.

Drivers of phytoplankton biomass and diversity in a macrotidal bay of the Amazon Mangrove Coast, a Ramsar site

Biodiversity maintenance is a main goal in ecology. Hence, phytoplankton diversity and biomass were analyzed in a coastal bay (Cumã Bay) of the Amazon Macrotidal Mangrove Coast, which has been designated as an international hotspot for conservation (Ramsar site) with high biological productivity and diversity that provides crucial ecosystem services and elevated fish production. An ecohydrology-based approach was applied to identify the main factors that drive the patterns of phytoplankton diversity and biomass, considering spatio-temporal analyses of physical, chemical, and biological variables from May 2019 to June 2020. Phytoplankton dynamics were investigated using multivariate analyses, correlations, and generalized additive models. Seven indices were tested to select the most efficient biodiversity metric. The hydrological conditions of Cumã Bay were governed primarily by elevated precipitation and macrotidal dynamics, resulting in two different functional zones based on environmental variability: the freshwater influence zone and marine influence zone. Seasonally, the maximum freshwater discharge, low salinity and light availability promoted cell abundance and biomass increase, with blooms of Skeletonema costatum, which reduced the taxonomic diversity of the community in the rainy season. During the dry season, turbid waters resulting from macrotidal dynamics and wind speed limited light penetration and phytoplankton photosynthesis, leading to a higher uniformity in the species distribution. Shannon index was the most sensitive biodiversity metric to environmental changes. This study found that deterministic processes governed the community, which rainfall on the Amazon coast, along with wind speed, salinity, light availability and nutrients were the main controlling factors for phytoplankton diversity and richness.

Distribution of physical and chemical variables in the water column and characterization of the bottom sediment in a macrotidal estuary on the Amazon coast of the state of Maranhão, Brazil

The objective of this research was to characterize the distribution of dissolved nutrients at six sampling stations in the estuary of the Anil River (ARE) and characterize the bottom sediment. The study area is influenced by a tropical climate and semidiurnal macrotidal regime. Sampling of the surface water and sediment was performed in the main channel at six sampling stations distributed along the estuary in the rainy period (May 9th) and dry period (October 5th) during the spring. Physical variables were collected with the aid of a HANNA HI-8424 multi-parameter probe (water temperature, salinity, pH, dissolved oxygen, and turbidity) and YSI CTD (conductivity, temperature, and depth) probe. A van Veen dredge was used for the collection of bottom sediment from the main channel. The sedimentological results were heterogeneous. Grain size ranged from very fine to medium sand. Dissolved nutrients in the ARE had different sources depending on the season. Continental and fluvial inputs, evidenced by salinity values, governed the distribution of nutrients in the rainy period (January to June), whereas nutrient concentrations were related to the recycling of organic material in the estuary in the dry season (July to December). The considerable presence of sand in the main channel indicates that the sediments available in ARE are exposed to intense hydrodynamics. The distribution of nutrients and the grain size revealed the occurrence of different sources in the estuary according to the rainfall regime and the intense hydrodynamics of tidal currents (semidiurnal macrotidal).&#x0D; Keywords: dissolved nutrients, estuarine environment, sedimentology.

Effects of Extreme Climatic Events on the Hydrological Parameters of the Estuarine Waters of the Amazon Coast

Oscillations in rainfall levels are one of the principal factors that determine seasonal shifts in physicochemical and hydrobiological variables, and exceptional climate events can have an enormous effect on the characteristics of small tropical estuaries. Given this, the present study investigated the responses of the physiochemical and hydrobiological variables of a small, shallow, and well-mixed Amazonian estuary with absence of any direct fluvial discharge to different climatic scenarios (typical conditions, and drier events). The study was based on 21 field campaigns conducted between April 2012 and April 2017. During rainy seasons of typical condition, when rainfall levels were higher and salinity lower than 7 (just after a weak La Niña), phytoplankton biomass was affected by increased turbidity (> 400 NTU) of the water, even when nitrogenous compounds were readily available (ammonium: 3.39 ± 1.71 µmol L−1, nitrite 0.90 ± 0.80 µmol L−1, and nitrate (3.91 ± 1.86 µmol L−1). In addition, the absence of any direct fluvial discharge appearance has contributed to the cumulation of phytoplankton biomass (chlorophyll-a > 20 mg m−3) into the estuary during the rainy season of the drier events and typical conditions, when turbidity was lower (< 200 NTU). Conversely, during the dry seasons of the drier events, when rainfall levels were lower, and extremes of salinity were recorded (> 38), phytoplankton biomass (chlorophyll-a < 10 mg m−3) was affected by the lower levels of nitrogenous compounds, even when phosphorous compounds were largely available. Overall, the present study has shown that extreme oscillations in rainfall levels cause abrupt shifts in the physicochemical parameters of the estuary, and affected the phytoplankton biomass, although high turbidity appeared to limit the buildup of this biomass. These effects are manifested immediately in the study area, given that the Taperaçu is a small estuary with a limited freshwater input, and it would seem reasonable to expect similar processes in other minor Amazonian estuaries when subjected to extreme fluctuations in rainfall levels.

FIRST OCCURRENCE OF Sphenia fragilis (H. Adams &amp; A. Adams, 1854) (BIVALVIA: MYIDAE) ON THE AMAZON COAST

Sphenia fragilis is a bivalve mollusk, belonging to the family Myidae, which has a habit of digging unconsolidated or consolidated substrates. Its estimated distribution indicates the presence of the species in the eastern Pacific and western Atlantic oceans. The present study indicates the first occurrence of S. fragilis on the Amazon coast (Urindeua River, Salinópolis, State of Pará). Additionally, it presents updated data on the species biogeography on the Brazilian coast. Altogether, 309 specimens of S. fragilis were found between the years 2013 and 2016, at depths between 1 and 4 meters, always associated with the surface of oysters. Based on these occurrences, added to the records made available on the Global Biodiversity Information Facility - GBIF platforms and the speciesLink network, it indicates an expansion of the biogeography of S. fragilis on the Brazilian coast, extending between the state of Pará and Rio Grande do Sul

Environmental factors associated with southern brown shrimp (Penaeus subtilis) yield at Brazilian Amazon coast

We evaluated the relationship between southern brown shrimp Penaeus subtilis (Pérez Farfante, 1967) yield and environmental parameters on the Amazon continental shelf. We analysed monthly fishing effort data (number of days spent at sea) and yield (kg of tails) collected between 1978 and 2009. A causal relationship had been expected between Amazon River discharge during the main period of shrimp occurrence in estuarine waters (considering post larval settlement and juvenile recruitment in second semester of each year) and adult abundance (represented by fishery yield in the first semester of the following year). We detected significant correlations between monthly river discharge and yield with a negative lag of four months, and between river discharge during the dry season (June to November) and yield in the following year. In general, low and high discharges during a given year were associated with high and low fishery yields, respectively, during the following year.

Temporal dynamics of a Sabellaria wilsoni (Sabellariidae: Polychaeta) reef on the Brazilian Amazon Coast

Polychaetes of the family Sabellariidae build extensive reefs in many coastal regions worldwide. These structures are dynamic systems that undergo a natural cycle of growth and destruction provoked by fluctuations in hydrodynamic conditions and biological factors. Here, we monitored a Sabellaria wilsoni reef over an annual cycle on Algodoal-Maiandeua Island on the Brazilian Amazon coast. We studied the impact of temporal variations in local environmental characteristics on the structure of the reef and the reef-building polychaete population. Metrics included the local climate (temperature, rainfall, and winds), hydrological variables (suspended particulate matter and salinity), and the output of a numerical model of the local hydrodynamics. There was increased hydrodynamic stress in the dry season due to changes in the direction and intensity of the wind and stronger waves. This in turn led to an accentuated decrease in sabellariid density, and the eventual erosion of the reef, which lost &gt;80% of its original area. The reduction in the hydrodynamic energy at the end of the rainy season favoured the mass recruitment of sabellariids as well as the subsequent growth and recuperation of the reef. Oligohaline conditions also contributed to a reduction in worm density, but not to any loss in reef structure. These findings provide important insights into the thresholds of energy and salinity tolerated by the reef-building polychaete S. wilsoni and offer a useful baseline for future research on the ecology of this species and the monitoring of this important marine habitat.

Histological (Gill and Liver) and Enzymatic (Glutathione S-Transferase and Catalase) Biomarkers in Sciades Herzbergii from Estuaries Near a Port Complex on the Brazilian Amazon Coast

Histological (Gill and Liver) and Enzymatic (Glutathione S-Transferase and Catalase) Biomarkers in Sciades Herzbergii from Estuaries Near a Port Complex on the Brazilian Amazon Coast

Foraminifera from the Marajó Basin and Bragantina Platform: Biostratigraphy and Paleoecological Correlation of Cenozoic Deposits in the Eastern Amazon Coast

Foraminifera from the Marajó Basin and Bragantina Platform: Biostratigraphy and Paleoecological Correlation of Cenozoic Deposits in the Eastern Amazon Coast

Phytoplankton of the shipping sector of São Marcos Bay (Amazon Coast): A potential risk area for the establishment of non-indigenous species

The coastal zone of the Brazilian state of Maranhão is an area characterized by diverse human activities and services, in particular in the “Ponta da Madeira” shipping terminal. The present study evaluated the structure and spatiotemporal dynamics of the phytoplankton community of the shipping sector of São Marcos Bay. Additionally, the study also investigates the evidence of the presence of allochthonous phytoplankton species. Data were collected at three sampling stations during four months in the dry season and four months in the rainy season. The phytoplankton community structure and abiotic variables varied between seasons. Mean salinity was significantly higher in the dry season (33.6 ± 3.6), while water temperature (29.0±0.3°C) and turbidity (274.2 ± 11.9 NTU) were significantly higher during the rainy season. A total of 179 phytoplankton taxa were recorded, with the highest phytoplankton biomass (chlorophyll-a) observed during the rainy months (11.6±7.8μg L−1) reflecting the availability of dissolved nutrients, as well as the intense local hydrodynamics, which contribute to the re-suspension of benthic microalgae. The occurrence of species such as Chaetoceros danicus, Coscinodiscus cf. wailesii and Planctonema lauterbornii reported for the first time on the coast of Maranhão, as well as a number of potentially harmful species of microalgae reinforces the need for the continuous monitoring of the phytoplankton community of this shipping sector, in addition to the adoption of new approaches, such as toxicological studies, which may contribute to the prediction and prevention of the proliferation of harmful algae in the region.

A Holocene record of floodplain development in the northernmost portion of the Araguaia Belt, southeastern Amazonia

This work aimed to understand the drivers of landscape evolution and floodplain formation in a Precambrian Shield area of southeastern Amazonia. This area evolved during the Quaternary into a denudational system with strong structural control, which produced valley side slopes between the Araguaia Belt (AB) and the topmost Parnaíba basin and narrow floodplains in the lower Vermelho River. These floodplains developed at approximately 11215–11410 cal yr BP with the deposition of muds on the weathered basement rocks of the Couto Magalhães Formation in the Ab (CMF) long before sea-level stabilization on the Amazon coast. The chondrite- and upper continental crust-normalized patterns, along with Al/Ti and La/Th ratios, clearly indicate that muds were derived from the CMF-AB. The strong positive correlation of most of the trace elements and rare earth elements (REEs) with Al and Ti indicates their control by aluminous clay phases and a similar transport process. Overbank flows of the Vermelho River resulted in the deposition and vertical accretion of sands from the fluvial channel over the floodplain, forming discontinuous marginal levees after 4520–4710 cal yr BP. The accreted sands with the predominance of Si, Zr, and Hf and the depletion of most of the major and trace elements are likely associated with quartz enrichment and a strong sorting of heavy minerals, which is also supported by Al2O3/SiO2 vs Fe2O3/SiO2. The tributaries of the lower Vermelho River were active until 3890–4095 cal yr BP, and subsequently, the channel was abandoned as a result of the filling process. At approximately 3440–3560 cal yr BP, the floodplain was influenced by prolonged and severe droughts that fully exposed the muddy deposits and caused the enrichment of Fe-Mnoxyoxide phases. The affinity of most of the potentially toxic elements with Al signifies that these floodplain deposits are a natural record for geochemical background studies.

Shoreline Variation and Identification of Local Erosion Geoindicators on the Brazilian Amazon Coast

Teixeira, S.G.; Bandeira, I.C.N., and Dantas, M.E., 2021. Shoreline variation and identification of local erosion geoindicators on the Brazilian Amazon coast. Journal of Coastal Research, 37(6), 1088–1098. Coconut Creek (Florida), ISSN 0749-0208. An analysis was conducted of the change in the shoreline in the northern part of Para (Amazonian coast, Brazil) over a medium-term period. The analysis of the variation of the shoreline was carried out by tracing the spring high tide level in LANDSAT images from 1988 to 2019. With this tracing, it was possible to verify the behavior of the processes of erosion and accretion in the different morphological units (mangroves, beaches, cliffs, and rocky shores). The results show that changes in the shoreline occurred differently in the four morphological units, both in spatial and temporal scales. Regionally, the northern coast of Para showed a trend of stability between losses and gains in areas, but with a slight predominance of the accretion process. The mangroves and beaches showed periods of alternation of predominance between the processes, while in the stretches with cliffs, the smallest areas of retreat were detected. The stretches of shoreline with a rocky shore remained stable throughout the study period. The study allowed the identification of local geoindicators for diagnosis and identification of the erosion process in coastal macrotidal regions. These results can assist in the identification of areas at risk of coastal erosion, as well as in coastal management in Para State and related areas.