Fracionamento do fósforo em sedimentos da plataforma continental adjacente à foz do rio Doce (Espírito Santo) após o desastre de Fundão

Abstract

Phosphorus (P) is an essential element for life and limits biological productivity in marine ecosystems. The biogeochemical cycle of phosphorus in the oceans involves external inputs, mainly from fluvial and estuarine sources, as well as internal recycling and sediment-water column interactions. In the sediment, this element can occur associated with different chemical fractions, and the interactions with iron oxides-hydroxides (Fe) are recognized for forming strong complexes with P. After the collapse of the Fundão dam, in the city of Mariana/MG, inputs of Fe ore tailings into the coastal area significantly affected the quantities and chemical species of phosphorus in the sediment of the estuary with expected impacts on the marine region. Therefore, the present work aims to evaluate the spatiotemporal variation of phosphorus mobility in the different fractions of sediment and interstitial water on the continental shelf adjacent to the mouth of the Doce river, affected by the Fundão disaster. For this, surface sediment samples were collected in nine stations distributed in the Central, North and South portions of the mouth of the Doce River, during four years of sampling (from November 2018 to September 2021), contemplating dry and rainy periods. The different phosphorus fractions bound to the sediment were analyzed from sequential extraction and quantified by spectrophotometry. The results showed a greater mobility of phosphorus in the sediment due to the hydrodynamic processes of the shelf, and an increase in the total P content in the interstitial water, especially in the southern portion. In addition, in the initial years, the content of the fraction bound to crystalline Fe oxide and the subsequent predominance of the amorphous fraction were observed. A negative correlation was also observed between exchangeable P and amorphous Fe. Thus, the sediment input triggered by the Fundão disaster altered the behavior and dynamics of phosphorus in the region of the mouth of the Doce River.