Modificações nas propriedades físico-químicas de sedimentos de manguezais submetidos ao clima amazônico

Abstract

A contínua e progressiva maturação dos sedimentos de manguezal distribuídos ao longo do estuário do rio Marapanim, costa nordeste do estado do Pará, foi descrita com base nas propriedades físico-químicas (pH, Eh e salinidade intersticial), com o objetivo de demonstrar a influência das curtas, porém marcantes, oscilações do clima nesse setor da costa paraense. Os padrões de salinidade resultaram de fluxos superficiais, concentrados por processos de evapotranspiração, diluídos pelas marés e pelas fortes e prolongadas chuvas da região. Condições redutoras (-200 < Eh < -400 mV) estabeleceram-se em terrenos mais baixos, argilosos e ricos em matéria orgânica. Em contraposição, os períodos de estiagem promoveram a oxidação e a dessecação dos sedimentos topograficamente mais elevados, originando a diminuição do pH (3,5 a 4,5) e relações inversas entre o Eh e o pH. As variações dos gradientes físico-químicos estão em estreita associação com o clima, com os ciclos das marés e com a circulação das águas intersticiais, determinando o grau de desenvolvimento e de diferenciação vertical e lateral dos sedimentos e a distribuição da vegetação no estuário.

Seasonal changes in metal and nutrient fluxes across the sediment-water interface in tropical mangrove creeks in the Amazon region

“…Fe 2+ , Mn 2+ , NH4 + , and PO4 Marchand et al, (2004) and at the Marapanim mangrove by Berrêdo et al, (2016). The seasonal effects controlled the conservative Cland salinity values, especially in the upper sediment intervals (< 15 cm).…”

“…Therefore, the biogeochemistry of these waters alter at both the temporal (seasonal, tidal, diel) and spatial scales, due to seasonal fluvial discharge and organic matter (OM) input from different sources (mainly mangroves and phytoplankton). Previous assessments have reported that the documented seasonal rainfall patterns can lead to seasonal changes in sedimentary physical and chemical properties (Alongi et al, 2004;Berrêdo et al, 2016;Marchand et al, 2004) pore water chemistry (Lee et al, 2008;Taillardat et al, 2019;Thanh-Nho et al, 2020;Wu et al, 2015) and nutrient and metals fluxes to coastal waters (Adame et al, 2010;Alongi et al, 2001;Rao et al, 2018;Yasui et al, 2016). Therefore, local weather conditions in the estimation and management of nutrient and metal budgets, especially in small mangrove rivers (Terada et al, 2017), must be considered.…”

Spatiotemporal Variability in Soil Properties and Composition in Mangrove Forests in Baía de Todos os Santos (NE Brazil)

“…3), which promotes soil aeration. Additionally, the more sandy texture observed in PT soils, together with the higher relief related to the riverbed, promotes faster drainage and higher levels of soil aeration, with the subsequent oxidation of Fe sulfates according to reactions 3 and 4, leading to proton release and decreased pH [32,33]. Moreover, the small size observed for many isolated pyrite crystals (<1 µm, Fig.…”

Spatiotemporal Variability in Soil Properties and Composition in Mangrove Forests in Baía de Todos os Santos (NE Brazil)

“…The higher acidity and Eh in PT soils are consistent with their lower water saturation (Figure 3), which promotes soil aeration. Additionally, the more sandy texture observed in PT soils, together with the higher relief related to the riverbed, promotes faster drainage and higher levels of soil aeration, with the subsequent oxidation of Fe sulfides according to Reactions 3 and 4, leading to proton release and decreased pH [9,13]. Moreover, the small size observed for many isolated pyrite crystals (<1 µm, Figure 7) provides them with a large specific surface area and a high reactivity, promoting their rapid oxidization.…”

“…Intertidal soils often show water saturation, high organic matter contents, fine textures, near-neutral pH, and redox conditions varying from suboxic to anoxic [6][7][8]. However, small variations in topography and in hydrological conditions lead to complex spatial variability in terms of the composition and properties of soils and sediments in these environments [9,10]. Additionally, these properties and compositions show significant seasonal changes in these environments, sometimes affecting soil and water quality, since these changes can increase the bioavailability of potentially toxic elements and substances [11,12].…”