Marine and fluvial effects on flooding environments dynamics of the Pará River Upper Estuary, Northern Brazil

Abstract

In coastal regions, floodplain environments occur in the lower course of rivers and their tributaries, where the daily flooding cycle controlled by tides results in hydrodynamic conditions of considerable complexity. On the north coast of Brazil, close to the Tocantins-Maratauíra System (STM), in the Pará River Estuary, the flooding environments present physical characteristics such as insular geography in a sheltered continental sector, an intense fluvial discharge, and a tidal range up to 6 m. In order to understand how the floodplain environments of this estuary are affected by tides, this study performed a multi-proxy approach (hydrodynamics, topography, vegetation, morphology, superficial sedimentary cover) for the delimitation of the Pará River Estuary in zones and for the investigation of the floodplain environments of the STM, correlating them to the corresponding estuarine zone. From the results achieved, three floodplain environments and a non-floodable one were recognized. These environments integrate the Pará River Upper Estuary, and have their flooding cycle controlled by tides with a mesotidal range. On the other hand, due to the high fluvial discharge, the ecological landscape essentially consists of freshwater ecosystems. It can be concluded from the results that the environments most vulnerable to flooding are in the interval between 0 and 3 m and represent 39% of the insular region. However, the highest occurrence of those environments is found in the southern sector (40.6%), landward-directed, which highlighted the dynamic and more unstable nature of this area when compared to the northern sector (21.1%), seaward-directed. It can be observed that the tide is one of the major forcings of local hydrodynamics, leading to the conceptual definition of the courses integrated into the STM drainage network compatible as tidal rivers. The results provide a better understanding of the morphodynamics of the modern landscape and expose its vulnerability, taking into account its human occupation.