Amazon Estuary Research Articles

Effect of environmental factors on microbiological quality of oyster farming in Amazon estuaries

The objective of this study was to assess the effect of environmental factors on the microbiological quality of water and oyster flesh (Crassostrea gasar) farmed in two Amazon estuaries in Pará, Brazil. The estuaries were located in the Nova Olinda community in Augusto Corrêa (site 1) and the Lauro Sodré community in Curuçá (site 2). Physicochemical water parameters (the rainfall, salinity, temperature and pH) were evaluated over a one-year period. A total of six liters of water and 720 oyster samples from oyster farms were used to analyze coliforms, Escherichia coli, coagulase-positive staphylococci, molds, yeasts and Salmonella spp. The rainfall and salinity were the environmental factors that most strongly influenced the microbiological quality of the water and oyster flesh. The mean total and thermotolerant coliforms were higher in the farming water from site 2 (Curuçá) than from site 1. The oyster flesh from site 1 (Augusto Corrêa) had higher mean levels of total and thermotolerant coliforms, coagulase-positive staphylococci and molds and yeasts than that from site 2. E. coli was absent from the water and oyster flesh of both sites. Salmonella spp. was found in 38.33 % of oyster flesh with no significant differences across sites and seasonal periods. The water quality was considered good for farming bivalve mollusks. However, the presence of Salmonella spp. in the oyster flesh compromised the sanitary quality and represents a threat to public health. Therefore, depuration facilities and microbiological monitoring are required.

The Amazonian dwarf cichlid Apistogramma agassizii (Steindachner, 1875) is a geographic mosaic of potentially tens of species: Conservation implications

Abstract Assessing biodiversity and understanding how it works is a prerequisite for species conservation. The Amazon basin is one of the main biodiversity hotspots where fish are heavily exploited for ornamental purposes. The ornamental trade heavily exploits the genus Apistogramma, which is one of the most species‐rich among Neotropical cichlids with 94 formally described species. This number is certainly underestimated owing to the limitations of conventional taxonomy, which is still too often based solely on morphological criteria and sometimes on few individuals. Most species of this genus have a high degree of endemism and are highly prized on the ornamental market, which could put them at risk. A few species are supposed to have extensive distributions, and in particular Apistogramma agassizii, present from the Amazon estuary up to the Ucayali and Marañon rivers in Peru. This study assessed the taxonomic status of 1,151 specimens of A. agassizii collected from 35 sites around Iquitos in the Peruvian Amazon. On the basis of molecular analyses (nuclear and mitochondrial DNA) and mate choice experiments, at least three biological species within the nominal A. agassizii were evidenced in the sampling area, which is extremely small compared with the known distribution of the species as initially described. According to the molecular calibrations, these three species would have diverged during the Plio‐Pleistocene. Two of them seem to be endemic from small sub‐basins, one from the Nanay River and the other from the Apayacu/Ampiyacu systems. A possible scenario that may explain the evolutionary history of these species is proposed. The conservation implications of these results on the estimation of the diversity of A. agassizii, of Apistogramma species in general, and of other Amazonian cichlids are discussed.

Vulnerability of the Açaí Palm to Climate Change

Acai fruit is vital for rural food security and livelihoods in the Amazonian Estuary. Local enrichment of forests to enhance acai palm densities and climatic warming are subjecting palms to higher temperatures, and local people have reported large falls in acai fruit production during hot years. Here we investigate this local perception, using over 400 interviews with acai producers. Most producers reported a fall in acai production in hot years, due to low initial production and failure of developing fruit. There was a widespread perception that intensively enriched groves (high acai palm densities) produce more fruit, but that fruit loss was greater in these same areas during hot years - presenting a potential management paradox. Our study provides initial evidence of the prevalence, mechanisms, and management implications of acai fruit production loss due to climate change. Further multidisciplinary research is needed to better understand this problem, and to minimize potential socioeconomic impacts.

Impact of the introduction of stingless bee colonies (Scaptotrigona aff. postica) on the productivity of acai (Euterpe oleracea)

O açaí é uma palmeira típica do estuário amazônico, especialmente importante na alimentação e economia da agricultura extrativista da Amazônia Oriental. Sua produtividade de frutos é altamente dependente da polinização cruzada. A meliponicultura avançou muito nas últimas décadas, porém o uso de meliponineos para a polinização de fruteiras tropicais é pouco usual. Neste trabalho, em uma cultura irrigada de Euterpe oleracea, a produtividade dos frutos foi avaliada após a introdução de colônias de Scaptotrigona aff. postica (Latreille, 1807). Três gradientes, 0-50, 65-115 e 130-180 metros, foram utilizados como metodologia para avaliar o aumento de produtividade, a partir do ponto central onde foram instaladas 30 colônias. A produtividade foi avaliada pelo peso do fruto por cacho, número de frutos por rachilla, diâmetro médio do fruto e peso de cem frutos amostrados. Pôde-se observar um aumento significativo na produtividade, chegando a 2,5 vezes mais, dependendo da distância da planta às colônias de abelhas. O maior intervalo de produtividade foi o mais próximo, de 0-50 metros.

Use of biochemical markers to quantify the toxicological effects of metals on the fish Sciades herzbergii: potential use to assess the environmental status of Amazon estuaries.

Enzymatic biomarkers, especially oxidative-stress enzymes, are useful for assessing the status of aquatic environments. The present study used biochemical markers determined in nervous, gill, and liver tissues of Sciades herzbergii, concomitantly with analyses of trace metals in the tissues and bottom sediment, to evaluate environmental quality in Amazon estuaries. The study was conducted from March 2014 to February 2016 in two areas: Caeté estuary in Bragança, state of Pará, which is relatively unimpacted; and São Marcos Bay, next to a harbor in São Luís, state of Maranhão. In the laboratory, the fish were weighed (g) and measured (cm). Fragments of the gills, the brain, and the liver were biochemically analyzed, and the metal contents in the brain, the liver, and the muscle tissues were determined. Turbidity was significantly higher (p < 0.05) in São Marcos than in Bragança. Specimens of S. herzbergii were smaller in São Marcos, and aluminum, iron, nickel, copper, cadmium, and mercury levels were higher in bottom sediment (p < 0.05) collected at this location. Fish from São Marcos contained significantly higher (p < 0.05) concentrations of aluminum, iron, and cadmium in the muscle tissue than fish from Bragança. In addition, fish from São Marcos had significantly higher concentrations of nickel in both the nervous and hepatic tissues. Only fish from São Marcos contained measurable concentrations of mercury in the liver and muscle. Fish from Bragança had copper concentrations in the liver significantly different from those captured at São Marcos (p < 0.05). The activities of gill glutathione S-transferases (GSTs) (F = 6.62; df = 1, 16; p < 0.05) and liver CAT (F = 10.22; df = 1, 16; p < 0.05) were higher in fish from São Marcos. However, ChE in brain tissues and lipid peroxidation (LPO) in the gills and liver did not differ significantly between fish from both areas. The physico-chemical conditions of the water and the concentrations of metals found in sediment and biological tissues, together with the biochemical responses of S. herzbergii in the study areas, indicate that this species is still tolerant to adverse environmental conditions, but the presence of metals is a risk to the health of fish, mainly to fish from São Marcos, especially if chronically exposed.

Modern pollen signatures of Amazonian rivers and new insights for environmental reconstructions

Paleoenvironmental reconstructions based on Amazonian fluvial and marine pollen data are often hindered due to the scarcity of modern calibration data. In Amazonia, rivers are the main pathways for pollen from upland and flooded forests to continental and marine sediment sinks. Linking pollen assemblages transported by rivers to watershed vegetation is crucial to interpret palynological archives. In order to constrain the interpretation of palynological archives, we analysed the pollen content of 36 riverbed sediment samples distributed from the mouth of the Içá River (ca. 68oW) to the Amazon estuary (ca. 49oW) with support of grain size and major element analyses of the inorganic sedimentary content. The palynological analysis shows a strong imprint of the lowland floodplain vegetation as the main source of the riverborne pollen. The upper reaches of the Amazon River present abundant Cecropia, reflecting early-successional stages induced by intense floodplain disturbance. The middle and lower reaches of the Amazon River exhibit a progressive increase in herbs mainly represented by Poaceae and Cyperaceae, related to wider floodplains covered by seasonally inundated vegetation. Floodplain forests of whitewater rivers (várzeas) are palynologically characterized by Iriartea, Mauritia, Ilex, Pseudobombax, Acalypha, and Luehea/Laetia, with high frequency of Cecropia or herbs, and montane taxa. At the black- and clearwater rivers, the igapó floodplain forests provide high percentages of Symmeria, Myrtaceae, and Alchornea, and can be distinguished by Sapium/Sebastiana, Piranhea, Amanoa, Pouteria, Ferdinandusa/Genipa, Attalea/Astrocaryum, and Eschweilera which suggest conditions of higher stability and mature forests. Contribution from the non-flooded uplands, Andean Mountains, and savannas/Cerrado occur, but their signals are blurred by the high pollen production of the lowland floodplains. Our data provide a calibration set for environmental reconstructions of river-influenced deposits across the Amazon including offshore areas of the most iconic riverine dominated landscape in the world.

Pharmaceuticals and personal care products in a Brazilian wetland of international importance: Occurrence and environmental risk assessment

Despite the fact that the occurrence of emerging contaminants in the environment has become frequent in recent decades, the seasonal dynamics of contaminants in different environmental compartments are little studied in protected areas influenced by effluent discharges. In this study, the seasonal and spatial occurrence of 33 pharmaceuticals and personal care products (PPCPs) was investigated in surface waters and sediments from Anil and Bacanga rivers (northeast of Brazil). The studied area is located within a Wetland of International Importance by Ramsar Convention (Amazon Estuary and its Mangroves). Sample preparation was carried out using solid-phase extraction and QuEChERS, for water and sediment samples, respectively and all determinations were performed by liquid chromatography tandem mass spectrometry. Eleven PPCPs were detected in water samples and 14 in sediments. In aqueous samples, caffeine was the most occurring compound reaching 13,798 ng L−1. In addition, high levels of acetaminophen, ibuprofen, sulfamethoxazole, carbamazepine and diclofenac were also observed. In the sediment samples, triclocarban, benzophenone-3, ketoconazole and methylparaben were also detected. The spatial and temporal distribution of the assessed molecules indicates urbanization and anthropic activities as relevant sources of PPCPs in the region. Moreover, the levels of acetaminophen, caffeine, diclofenac, ibuprofen, benzophenone-3, triclosan and triclocarban measured within the Ramsar site pose a high risk to aquatic and terrestrial organisms. These findings indicate potential threats to the allegedly protected biodiversity and, therefore, urgent actions are needed to effectively protect this unique and vulnerable area.

Determination of background geochemistry of an Amazon estuary: The Cuñaní Estuary – Amapá

This study aims to determinate the background geochemistry values for 23 chemical elements on the Amapá coastline. To do so, 8 cores were sampled (≤70 cm) along the Cuñaní Estuary. The metal concentrations were measured by means of inductively coupled plasma mass spectrometry. In mg.kg-1, the background values for Ba, Sr, Y, Sc, V, Cr2O3, Co, Ni, Cu, Zn, Ga, As, Rb, Nb, Sn, Cs, Ta, W, Hg, Pb, Bi, Th, and U were, respectively, 392.41, 133.29, 29.22, 12.80, 109.13, 0.008, 13.82, 22.69, 19.73, 75.09, 19.50, 14.77, 94.81, 15.62, 3.38, 6.59, 1.05, 1.82, 0.04, 19.02, 0.27, 13.25, and 3.57. The background geochemistry values for the region are an important tool for monitoring the metal concentrations and serve as a baseline for comparison with possible incidents of contamination with these elements on the Amapá coast.

Hydrodynamic Modeling and Simulation of Water Residence Time in the Estuary of the Lower Amazon River

Studies about the hydrodynamic behavior in the lower Amazon River remain scarce, despite their relevance and complexity, and the Water Residence Time (Rt) of this Amazonian estuary remains poorly unknown. Therefore, the present study aims to numerically simulate three seasonal Rt scenarios based on a calibrated hydrodynamic numerical model (SisbaHiA) applied to a representative stretch of the lower Amazon River. The following methodological steps were performed: (a) establishing experimental water flow in natural channels; (b) statistically test numerical predictions (tidal range cycles for different hydrologic periods); and (c) simulating velocity fields and water discharge associated with Rt numerical outputs of the hydrodynamic model varied from 14 ≤ Rt ≤ 22 days among different seasonal periods. This change has shown the significant influence of hydrologic period and geomorphological features on Rt. Rt, in its turn, has shown significant spatial heterogeneity, depending on location and stretch of the channels. Comparative analyses between simulated and experimental parameters evidenced statistical correlations higher than 0.9. We conclude that the generated Rt scenarios were consistent with other similar studies in the literature. Therefore, they depicted the applicability of the hydrodynamics to the conservation of the Amazonian aquatic ecosystem, as well as its relevance for biochemical and pollutant dispersion studies, which still remain scarce in the literature.

Distribution of brachyuran larvae in an Amazonian estuary as evidence for retention and export

AbstractBrachyuran crabs, like other decapod crustaceans, adopt a number of different strategies for larval dispersal. We verified the influence of variations in temperature, salinity, and pH on the abundance and taxonomic composition of brachyuran larvae in an Amazonian estuary and found evidence of both retention and export dispersal strategies. We identified larvae of 20 different taxa belonging to the families Grapsidae, Ocypodidae, Panopeidae, Pinnotheridae, and Sesarmidae. Ucides cordatus (Linnaeus, 1763) (Ocypodidae), Pachygrapsus gracilis (Saussure, 1857) (Grapsidae), Leptuca cumulanta (Crane, 1943) (Ocypodidae), and Armases rubripes (Rathbun, 1897) (Sesarmidae) were the most abundant species. Most of the taxa present in the study area were at the zoea I stage but later larval stages were found in some species, indicating retention and export. Results were supported by canonical correspondence analysis and general linear model, which related larval community structure and reproduction patterns to variations in salinity, influenced primarily by the enormous discharge of the Amazon River and the high rainfall levels in the region. Further investigations of the distribution of larvae on the continental shelf are necessary to confirm the identified dispersal patterns. The study also presents novel data on the composition, abundance, and dispersal of brachyuran larvae in the tropical estuaries of the Amazon River.

Integrated models show a transient opportunity for sustainable management by tropical forest dwellers

Nearly 25% of world’s poor are dependent on forests, with 0.5–1 billion smallholders managing trees. This extensive human use of forests points to the need for sustainable timber management (STM) at smallholder scales. Similar to other tropical regions, households in the Amazon Estuary have harvested timber informally with minimal management for decades. This research provides a comprehensive look at the ecological and economic sustainability of forest use by local smallholders by integrating detailed plant demography, microeconomic, management and land use models at a whole watershed and community scale.In terms of conservation outcomes, resulting models show that forest management results in extensive harvests that allow for faster tree population recovery. In terms of economic outcomes, management also improves the long-term viability of the local timber industry in all scenarios considered. However, with respect to harvest regulations, given the costs of legalizing these small informal operations, legalization may indirectly lead to heavier ecological impacts as households need to harvest more to keep economic returns similar to the predominant alternative land use in the region (açaí palm fruit agroforestry).Despite a fast-growing and resource-rich forest, an increasing extent of degraded forest area reduces the ecological and economic prospects for long-term management. Consequently, for this and other similar tropical forests, the viability of STM should not be evaluated as a binary and static yes or no response but instead as a moving window of opportunity that occurs when ecological, economic and policy conditions are met. Integrated model projections show that regionally-derived and ecologically-based sustainable management guidelines widen this window of opportunity by delivering the best ecological and economic outcomes under a range of scenarios considered.

Prawn larvae of Macrobrachium amazonicum (Decapoda, Palaemonidae) in contaminated oligohaline creeks on the Amazon estuary

ABSTRACTThe objective of this study was to assess larval stage densities of Macrobrachium amazonicum in two highly contaminated amazonian creeks (Tucunduba and Mata Fome) and in one creek less impacted by human activities (Combu). The hypothesis tested is that larvae are more abundant in protected areas, independently of their development stage. Zooplankton was collected once every 3 months by conducting horizontal hauls at the sub-surface of the water column using a 300 µm mesh size plankton net during flood and ebb tides. Temperature, pH, conductivity, salinity, dissolved oxygen, water hardness, biochemical oxygen demand, chemical oxygen demand, Cl, N-NO, NO, NH3, NH4, PO4, SO4, Fe, Mg, Li, K and Na values or concentrations were estimated for each creek in order to determine whether these factors influence larval stage densities. Zoea stages I, V, VIII, X and XI were recorded: zoea stage I was present all along Combu creek and downstream of Tucunduba and Mata Fome creeks; the other stages were encountered only in the uncontaminated creek. Larval stage zoea XI was considered ‘occasional’. Densities were statistically different between months. It was concluded that spawning ground of M. amazonicum was close to the three creeks because the first larval stage was found indiscriminately at all downstream sampling stations. The more advanced stages (zoea V or higher) were found mid-downstream but only in the most preserved creek (Combu); no other larval stage beside zoea I was encountered in the creeks with greater anthropic influence. Further, not only is the adult population affected by water contamination, but also the occurrence of larval stages is associated with more protected waters. The high concentration of coliforms was associated with nitrates, and the low larval density of the Amazonian prawn was a clear response to this contamination of the water.

Intertidal Biogeographic Subprovinces: Local and Regional Factors Shaping Fish Assemblages

Intertidal zones shelter a wealth of species and natural resources, provide important ecological services, and sustain several economic activities in coastal communities. However, the tidepool fish species that inhabit the intertidal zone are subject to a wide array of impacts due to the human presence and their accessibility, creating a challenge for the mitigation of habitat loss, in particular in tropical regions where the ecology and distribution of species are poorly known. In this study, we investigated tidepool fish species distribution patterns systematically across ca. 4,900 km of tropical Brazilian coastline (00–21° latitude) in order to verify the latitudinal trends and environmental variables influencing tidepool communities. A total of 5,113 fish specimens belonging to 67 taxa were collected at the 19 sites, revealing four distinct biogeographic subprovinces: Amazon Estuary (AE), Northern Mangrove (NM), Northeastern Semiarid (NS), and Tropical Warm (TW). Distance-based linear modeling evidenced in sequence water salinity, tidal range, shape of rocky shore formation, algae cover, distance to subtidal zone, latitude and rainfall as the most important environmental variables to shape biogeographic subprovinces. Fish species such as Bathygobius soporator, Bathygobius geminatus, Labrisomus nuchipinnis, and Scartella cristata presented wide distribution, occupying more than one subprovince. The trophic structure of the tidepool fishes also varied among subprovinces, with carnivores being associated with the AE subprovince, omnivores with the NM, and herbivores dominating the NS and TW. These findings reinforce the determining role of local and regional factors in the geographic distribution of fish and, in particular, highlight a new arrangement for the intertidal subprovinces of the tropical Brazilian shoreline, which may provide a valuable tool for the more effective management and conservation of this vulnerable ecosystem at the land-ocean interface.

METAIS PESADOS EM ÁREAS DE CULTIVO DE OSTRAS NA AMAZÔNIA

Análises de contaminantes nos sedimentos, como os elementos traços são fundamentais para caracterizar normalidade ou alterações nos ambientes aquáticos. Estas são informações importantes para avaliar áreas usadas para aquicultura, em especial aquelas onde há uma interação mais próxima entre os sedimentos e organismos cultivados, como ocorrem na prática da ostreicultura. Foram avaliadas as concentrações de elementos traços (Al, Cd, Co, Cr, Cu, Fe, Ni, Mg) nos sedimentos de seis áreas de cultivos de ostras no estuário Amazônico. As amostragens de sedimentos foram realizadas nos meses de novembro de 2013 (seco) e abril de 2014 (chuvoso) e priorizaram pontos centrais nestas. Os ní­­veis de elementos traços foram quantificados por espectrometria de emissão ótica com plasma induzido (ICP- MS). Possí­­veis efeitos sobre a biota aquática foram avaliados a partir da comparação dos ní­­veis de metais nos sedimentos com os valores de referência proposto nos protocolos TEL e o PEL. As concentrações dos elementos traços nos sedimentos em todas as áreas avaliadas foram superiores no perí­­odo chuvoso, com exceção do cobre. Seguindo a ordem de concentração, na maioria das localidades Al &gt; Fe &gt; Mg &gt; Cr &gt; Ni &gt; Co &gt; Cu &gt; Cd. Apenas para Cd os ní­­veis foram superiores em referência aos de TEL e PEL.

New Rare Earth Elements Found In Amazon Estuary?

New Rare Earth Elements Found In Amazon Estuary?

Sotalia dolphins in their potential sympatry zone: searching for hybrids in the Amazonian estuary

The two Sotalia species (the marine S. guianensis and the freshwater S. fluviatilis) have only recently been recognized, and both face several conservation challenges. We investigated the existence of hybridization between the two species in their possible area of sympatry in the Amazon Estuary, in northern Brazil. A fast and cheap PCR-RFLP diagnostic method using nuclear DNA was developed to discriminate between the two species, while allowing the detection of hybrids. All samples that could be identified (N = 51) were identified as S. guianensis, and no hybrids were detected. Our results, coupled with previous mitochondrial data, suggest that S. fluviatilis is not present in the Amazon delta. Thus, sympatry with S. guianensis, if it does occur, may be restricted to upstream areas of the Amazon River.

First evidence of microplastic ingestion by fishes from the Amazon River estuary

This study investigated occurrence of microplastic particles in digestive tracts of fishes from the Amazon River estuary. A total of 189 fish specimens representing 46 species from 22 families was sampled from bycatch of the shrimp fishery. Microplastic particles removed from fish gastrointestinal tracts were identified using Attenuated Total Reflectance – Fourier Transform Infrared (ATR-FTIR). In total, 228 microplastic particles were removed from gastrointestinal tracts of 26 specimens representing 14 species (30% of those examined). Microplastic particles were categorized as pellets (97.4%), sheets (1.3%), fragments (0.4%) and threads (0.9%), with size ranging from 0.38 to 4.16 mm. There was a positive correlation between fish standard length and number of particles found in gastrointestinal tracts. The main polymers identified by ATR-FTIR were polyamide, rayon and polyethylene. These findings provide the first evidence of microplastic contamination of biota from the Amazon estuary and northern coast of Brazil.

Fish assemblage structure in a port region of the Amazonic coast

ABSTRACT: The fish assemblage structure in a port area in São Marcos Bay (Amazonic coast) was evaluated based on the spatial and temporal distributions to identify potential changes in response to anthropic pressure increases associated with industrial and port activities in region. The samples were taken between March 2011 and November 2015. The ichthyofauna was represented by a total of 56 species, distributed in 15 orders and 29 families. Captures were dominated by Genyatremus luteus (Bloch, 1790), but Sciades proops (Valenciennes, 1840) was the most representative in terms of biomass. Seasonal distributions of fish assemblage did not reveal significant differences. However, there was a difference between catch sites, abundance, biomass and Shannon diversity index was higher in the Site 1 and evenness in Site 4. The analysis NMDS and the test ANOSIM between months and between sampling sites, based on species composition, revealed a seasonal differentiation associated with the rainy and drought months, as well as spatial differentiation, in function of a depth gradient and hydrodynamics, resulting from greater distance from mangrove areas. The low diversity recorded may be a reflection of port activities that historically occur in the area investigated. However, there was still a maintenance of regional diversity throughout the period under analysis. Thus, temporal and spatial scales become important for the detection and understanding of fish biodiversity in an Amazonian estuary, reflecting, the importance of mangroves for the maintenance of the ichthyofaunistic diversity in the area. In this context, the present study may subsidize possible conservation projects in the area since information of this nature is almost non-existent for estuarine fish from the Maranhão Amazon.

The Influence Of Seasonality On Haline Zones In An Amazonian Estuary

Valentim, M.M.; Monteiro, S.M., and Rollnic, M., 2018. The influence of seasonality on haline zones in an Amazonian estuary. In: Shim, J.-S.; Chun, I., and Lim, H.S. (eds.), Proceedings from the International Coastal Symposium (ICS) 2018 (Busan, Republic of Korea). Journal of Coastal Research, Special Issue No. 85, pp. 76–80. Coconut Creek (Florida), ISSN 0749-0208.This study relates salinity fluctuations throughout Mojuim estuary, dominated by macrotides and situated in the humid tropical region between the Para River mouth and the Atlantic ocean (−0.72° and −48.00°), Northeastern Para, Brazil. Water salinity in situ were measured, on the surface and at the bottom, with a multiparameter probe (Horiba U-50) for six months, corresponding to the intermediate season (July and August, 2016), dry season (November and December, 2016), and rainy season (January and February, 2017) during spring tide. Sampling stations comprehended 50 km throughout the estuary and were divided in five 10-km sectors. The sectors were classified according to the Venice System. Significant variations salinity (p>0.5) in water column were not observed, as it is a well-mixed estuary. During rainy season, were observed the lowest mean salinity (8.5±0.8 PSU), which increased to 15.99±0.37 PSU during the intermediate season, and to 22.38±0.61 PSU during dry season. Saline intrusion reached sector 5 (50 km upstream of the mouth) during dry season and was restricted to sector 3 (30 km) during rainy season. The latter showed the highest variation in haline zones in all seasons, and they varied from oligohaline during rainy season, to mesohaline during intermediate season, and polyhaline during dry season. During rainy and intermediate seasons, river domain limits tidal progression, and it is why sector 5 shows no haline variations, remaining as a freshwater zone, as opposed to dry season, when this sector shows a oligohaline zone, due to the higher tide reach and to the higher dispersion of salts in the estuary. These haline limits might vary interannually, which indicates the influence of climatological anomalies on estuary dynamics over the last years.

Tide Influence on Suspended Matter Transport in an Amazonian Estuary

Rollnic, M.; Costa, M.S.; Medeiros, P.R.L., and Monteiro, S.M., 2018. Tide Influence on Suspended Matter in an Amazonian Estuary. In: Shim, J.-S.; Chun, I., and Lim, H.S. (eds.), Proceedings from the International Coastal Symposium (ICS) 2018 (Busan, Republic of Korea). Journal of Coastal Research, Special Issue No. 85, pp. 121–125. Coconut Creek (Florida), ISSN 0749-0208.The aim of this study is to check which tidal component (dispersive or diffuse) dominates suspended particulate matter transport (SPM) in the Mojuim River estuary. This estuary comprises the eastern sector of the Amazon coast, characterized by mangrove-vegetated tidal flats. Measurements of current intensity and direction, SPM, and tide level over a tidal cycle (13 h) were performed in a section of the lower estuary. Samplings were conducted in March (wet season) and September (dry season), 2014, during spring tide. The resulting transport and relative contribution of advective transport (SPM diffusion and dispersion) were calculated. Mojuim estuary has a macrotidal regime, with mean height of 4.9 m during spring tide and 3.2 m during neap tide. As it is a shallow environment, the water column is homogeneous, and hydrological parameters do not significantly vary along the water column. SPM ranged from 12 to 92 mg.L−1 during dry season and from 20.4 to 94.8 mg.L−1 during wet season. The highest SPM concentrations occurred during ebb tide, and this determined the maximum instantaneous transport, both during wet season (127.8 kg.s−1) and dry season (159 kg.s−1). This estuary is characterized as an exporter environment. During dry season, it had a residual transport of 4.1 kg.s−1 and a total transport of 191.9 tons downstream of the estuary. However, during wet season, it showed an inversion in advective transport due to equinoctial tidal influence, which caused a higher tidal prism thus resulting in a residual transport of 1.92 kg.s−1 and a total transport of 90 tons upstream of the estuary. The dominant SPM transport component downstream of the estuary was river discharge, whereas SPM transport upstream of the estuary was dominated by Stokes Transport.