Morfodinâmica de praias estuarinas da vila de Jubim (ilha do Marajó-Pa)

Abstract

The Brazilian Amazon Coastal Zone (states of Amapá, Pará and Maranhão) has environmental characteristics such as a humid tropical climate (high temperatures, low thermal and rainfall variation) and important oceanographic conditions (hyper to mesotidal), in addition to extensive mangroves and sandy beaches, including estuarine beaches. These are vulnerable to seasonal changes in river discharge, in addition to current climate change, the consequent rise in sea level and the resulting coastal erosion, which causes negative consequences for the goods and services originating from this coastal ecosystem. The objective of this study was to analyze the changes in the morphology and sediment dynamics of the estuarine beaches of Jubim and adjacent areas, during a complete seasonal cycle (March 2023 to March 2024). Jubim is a district located in the municipality of Salvaterra, State of Pará, on the east bank of Marajó Island, under oceanographic conditions of the Pará River estuary. Data collection was carried out on four specific beaches, namely: Salazar Beach, Meninas Beach, Baleia Beach and Curuanã Beach. To characterize the morphodynamic state of the beaches, the slope (β) and relative tidal variation (RTR) parameters, derived from the treatment of physical and topographic data (beach profiles), were used as reference. For granulometric analysis, surface sediment samples were subjected to dry sieving in order to obtain the average size, grain selection and sedimentary balance of the beaches. The results showed that the beaches of the village of Jubim have sedimentation ranging from medium to fine sand 1 ɸ and 2 ɸ, with moderately well-sorted grains. The beaches presented quite varied morphometric parameters: topographic elevation from 5.6 m to 2.7 m, and beach width ranging from 79 m to 550 m, thus classifying them into dissipative to intermediate morphodynamic stages (beach slope from 0.2° to 2.6°), with tidal dominance (RTR = 44). The seasonal sedimentary variation was both positive and negative, indicating that the variability index alternate along the beaches and climatic seasons, showing both erosive and depositional tendencies. Erosive processes were observed mainly in the rainy season and greater sedimentary deposition in the dry season. The morphological behavior of the beaches studied on the eastern shore of Marajó Island is directly influenced by estuarine hydrodynamics, where the distinct sedimentary changes are due to the interation that hidrodynamics with the differentiated geology along the coast, and the respective material that constitutes the substrate of the beaches and backwaters.