Name: Cybelle Menolli Longhini
Type: PhD thesis
Publication date: 03/02/2020

Namesort descending Role
Renato Rodrigues Neto Advisor *

Examining board:

Namesort descending Role
Ana Teresa Macas Lima Internal Examiner *
Gilberto Fonseca Barroso Internal Examiner *
Maristela de Araujo Vicente External Examiner *
Renato Rodrigues Neto Advisor *

Summary: Iron and other trace metal biogeochemistry have been largely discussed because of their ecological role as micronutrients and consequent control on phytoplankton growth in the ocean. Experimental studies have shown that Fe fertilization in marine areas favours specific algae groups, mainly diatoms and flagellates, even though the effects of metal contamination from mining tailings have not been addressed until the moment. The present study describes the processes controlling dissolved Fe (dFe) stability in the water column and the effects of this metal and other nutrients on phytoplankton community in the continental shelf impacted by the Fundão dam mining tailings. The review study indicated that the inputs of dFe from mining activities can be more representative than the fluxes from natural sources in coastal areas vulnerable to this kind of contamination. Regarding to the impacts of those activities, can be predicted changes on Fe chemical speciation and bioavailability, changes on biochemical uptake mechanisms by phytoplankton and also shifts on its community structure, including harmful algae growth. The distribution of Fe in different size-fractions and their relation to humic substances (HS) showed that Fe concentrations remain very high even three years after the disaster, reaching up to 2.8 µM (dFe, < 0.45 µm), 700 nM (dFe, < 0.22 µm) e 40 nM (Soluble Fe - sFe, < 0.02 µm). HS levels control only the binding of 2% and 10% (median values) of dFe (0.22 µm) and sFe concentrations, respectively. This is an unexpected result as HS is the main Fe binding agent in unaffected coastal areas. These results suggest the presence of other organic compounds to bind Fe (possibly amine compounds widely used in the ore extraction process) and/or the occurrence of sFe as colloidal nanoparticulate Fe(III) oxy-hydroxides, both acting to maintain the stability of dFe in solution. The interrelations analyses among metals/micronutrients (Fe, Mn, Zn, Cu, Co e V), major nutrients (Dissolved Inorganic Nirogen - DIN, phosphate and silicate) and phytoplankton composition revealed the influence of Zn, Cu and V in particulate fraction (pZn, pCu e pV) and a lesser contribution of particulate Fe (pFe) and dFe controlling the algae densities. Cyanophyceae was the most frequent group and their density was determined by pFe concentrations that remained high during all sampling surveys. Furthermore, diatoms growth was modulated by pZn levels and restricted to high Doce River discharge and specific metals enrichment conditions (7pFe, 5pV, 4pCu, 8pZn), suggesting a control related to physiological mechanisms of silic acid uptake. These results demonstrated an unexpected behaviour of phytoplankton community in response to metals enrichment and these differences are probably driven by the form of metals from the tailings. Therefore, it has been hypothesized that cyanobacteria species obtained competitive advantages compared to other groups due to their versatile strategies to assimilate metals from a wide range of forms. Considering the continuing metals contamination in the study area during time, it is recommended the integrated analyses between the metals pointed by this study and the possibility of toxic microalgae growth.

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