The Pará River estuary is a complex and special system in amazon continental shelf, with micro and mesoscale physical processes generated by forces of different sources (e.g., astronomical tides and river discharge). In this study, the main semidiurnal (M2) and the overtide (M4) components were analyzed by quantifying distortions degrees and identifying tidal asymmetries in the Pará River estuary. Two submersible tidal gauges were moored to measure the water level. One on the right margin (point #RG) and another on the left margin (#LF) recorded measurements 6 months (from September 2014 to March 2015). Furthermore, we used harmonic charts from Marine Studies Foundation (FEMAR, Fundação de Estudos do Mar). Lateral variations were also identified between #RG and #LF points from the amplitude and phase cotidal charts, with about 10 minutes delay and variation of 2 cm in tidal amplitude. We verified that the tidal wave enters in system by the right margin (#RF). The results show distortion degrees higher than 10% and positive asymmetry of the tidal wave in the Pará River, and the tidal attenuation in the estuary may be greater than 400 km upstream along the drainage basin.Keywords: Tidal distortion, Tidal asymmetry, Tidal components, Lateral variations.

A análise de variações na linha de costa através de imagens multitemporais permite a identificação de processos erosivos e acrecionais em uma escala evolutiva. O objetivo desse trabalho foi avaliar as mudanças na linha de costa de praias estuarinas do litoral amazônico (município de Marapanim), entre os anos de 1988 a 2016, por meio de imagens do satélite Landsat. A partir da digitalização de linhas de costa das praias de Santa Maria, Marudá e Crispim, nos referentes anos e, utilizado a extensão Digital Shoreline Analysis (DSAS) no software ArcGis, foi possível realizar cálculos estatísticos de amplitude espacial (m) e taxa de variação anual (m/ano) do posicionamento da linha de costa. Os resultados indicaram que a praia de Santa Maria está em estado de equilíbrio sedimentar a acresção, apresentando variações de 3,89 a -1,23 m/ano ao longo da linha de costa. As praias de Marudá e Crispim estão em processo predominante de acreção costeira, apresentando linearmente variações de 8,87 a -1,61 m/ano, 40,91 a -9,82 m/ano; respectivamente. Contudo, fenômenos climáticos, físicos e impactos antrópicos podem ter sido responsáveis pela diminuição da taxa acrecional da linha de costa em determinados períodos (1994-2008), em setores distintos das praias.

This paper describes the influence of tidal currents on sediment transport on Amazonian equatorial beaches during extreme events. The study area (Salinópolis city) was divided into two sectors: western (Sampaio tidal channel) and eastern (Atalaia Island). Field surveys were conducted in 2013 during two periods of highest tides: April (the rainy season) and October (the less rainy season and Spring Equinox). The optical backscatter sensors (tide, turbidity, and wave data) and current meter sensors (velocity field data) were programmed to collect data every 0.1 and 60 seconds, respectively. They operated together for 24/12 hours on the upper shoreface (surf zone). Wave heights were higher in the Atalaia Island (up to 1 meter during the less rainy season). The currents were stronger, reaching 1.2 m.s-1, during ebb tide in the rainy season (Sampaio tidal channel). Higher turbidity values (maximum 1,200 FTU) occurred at the Atalaia Island during the less rainy season. The coastal dynamics in the area derives mostly from the Amazonian continental shelf, where intense tidal currents interact with a high volume of particulate debris, especially fine sand in Salinópolis. Nevertheless, estuaries and tidal channels are also largely responsible for sediment supply and play a key role in shoreline stability and coastal transport, especially during extreme tide events.

Este artigo tem como objetivo identificar e quantifi-car as áreas em erosão e/ou em acreção com intui-to de compreender a dinâmica da linha de costa (LC) dos municípios de Vigia e de São Caetano de Odivelas (margem leste) no trecho inferior do Estu-ário do Rio Pará, utilizando uma análise multitem-poral através de emprego de imagens de satélite Landsat (1987 a 2019) da USGS, como auxílio do Digital Shoreline Analysis System (DSAS). A maior tendência de acreção ocorreu em Vigia, com taxas, média de 1,26 m/ano e máxima de 10,06 m/ano no EPR. Em São Caetano de Odivelas, a taxa média de variação nos parâmetros EPR, LRR e NSM foram respectivamente de 0,40 m/ano 0,25 m/ano e 13,09 m/ano, confirmando o predomínio da acre-ção nesta área.

Context Understanding how different biological groups respond to multiple drivers is essential for advancing freshwater ecology and improving biodiversity conservation. Objectives Here, we investigated the relative importance of local habitat conditions, spatial structure, and landscape composition in shaping species richness and composition across four aquatic biological groups (zooplankton, macrophytes, adult odonates, and fish) in streams and ponds on Marajó Island (eastern Amazonia). Methods We sampled lotic and lentic water bodies and used generalized linear mixed models, permutational analyses, and distance-based regressions to disentangle multiscale controls on biodiversity patterns. Results Zooplankton richness was primarily driven by local physicochemical variables, whereas macrophyte, odonate, and fish richness were more strongly associated with landscape composition and spatial structure. System type (lentic vs. lotic) influenced richness and composition only for specific groups. Landscape elements, including forests, flooded areas, grasslands, pastures, and urbanization, exerted context- and scale-dependent effects on community structure, with some forms of landscape modification increasing compositional heterogeneity or favoring particular taxa. Weak covariation among biological groups further indicated low cross-taxon congruence in biodiversity patterns. Conclusions Our findings demonstrate that freshwater biodiversity responses to environmental change are multidimensional, taxon-specific, and scale-dependent. These results highlight the need for integrated, multi-taxon, and multi-scale approaches that account for context-dependent landscape effects to improve biodiversity assessment, monitoring, and conservation in highly heterogeneous tropical systems.

Lagrangian Coherent Structures (LCSs) in the mesoscale circulation of the Western Equatorial Atlantic (WEA), a region governed by the North Brazil Current (NBC) and its retroflection, are analyzed. Observations from 63 surface drifters deployed between 2018 and 2019 were combined with ocean analysis/forecast fields. The Finite-Time Lyapunov Exponent (FTLE) was computed using 15- and 90-day integrations to identify transport barriers and persistent structures. FTLE ridges showed strong seasonal correspondence with drifter trajectories, with 34–74% of drifter positions lying within 0.25° of attracting or repelling LCSs. Characteristic FTLE magnitudes reached ~0.3 d⁻¹, implying particle separation e-folding times of approximately 3.3 days. Spatial agreement between drifter-derived and model-based FTLE fields exhibited similar variability across seasons, with the highest correspondence during periods of intensified frontal activity. These results indicate that a substantial portion of the observed drifter motion follows or remains close to FTLE-defined pathways, supporting the robustness of the Lagrangian structures identified in the WEA. Overall, the study provides the first quantitative LCS-based characterization of mesoscale transport in this region, revealing recurrent eddies, instability zones, and flow boundaries associated with the NBC system and its interaction with the North Equatorial Countercurrent.