Dinâmica espacial e sazonal de mercúrio no reservatório hidrelétrico de Curuáuna, Amazônia

Abstract

The objective of this thesis is to investigate the spatiotemporal dynamics of total mercury (HgT) in the reservoir of the Curuá-Una Hydroelectric dam, Santarém, Pará, in the Amazon. The concentrations of HgT in filtered water, aquatic macrophytes, plankton and fish were evaluated on the influence of the river regime (low-water, rising-water, high-water, and falling-water), hydrosystem (riverine, transition and lacustrine zone) and trophic level of fish species downstream and upstream of the Curuá-Una reservoir dam, Santarém, Pará, Brazil. The sampling campaigns were carried out in four seasonal periods: Dec/2021 (low-water), Mar/2022 (falling-water), Jun/2022 (high-water) and Sep/2022 (low-water). The [HgT] levels were determined by Cold Atomic Vapor Florescence (CVAFS). The longitudinal gradient of the reservoir hydrosystem influenced the HgT concentrations in the water and plankton during seasonal periods. The HgT concentrations varied according to the river regime, demonstrating the importance of hydrological and hydrometric processes in the dynamics of HgT in the reservoir. In the plankton, the HgT concentrations varied according to the mesh diameter of the net used, with higher concentrations in the 60μm net, where there is the presence of mixed and organo-mineral material composed of plankton, amorphous seston and fine mineral particles. The present study shows that seasonality and the longitudinal gradient of the hydrosystem influence the dynamics of Hg in the water and plankton of the Curuá-Una reservoir. THg concentration in filtered water was higher (5.3–11.2 ng L−1) during the low-water period. THg concentration in fish ranged from 0.075 to 1.160 μg g−1 in specimens caught downstream and from 0.014 to 1.036 μg g−1 in specimens caught upstream of the dam. The highest THg concentrations were detected in specimens of the piscivorous species Acestrorhynchus falcirostris (1.161 μg g−1) caught at downstream sites. There were significant correlations of THg concentration with the trophic level (Analysis of Variance; p ≤ 0.001) of fish species and fluvial regime (Analysis of Variance; p ≤ 0.001). The macrophyte Utricularia foliosa contained the highest THg levels in leaf tissues in the low-water period (71.4 μg g−1). It is concluded that THg concentration varies between fish trophic levels and fluvial regimes. Macrophytes contribute to enhancing mercury transfer and availability along the aquatic trophic chain.