Influence of environmental conditions on the mercury levels of the sediment along the Balbina Reservoir, Brazilian Amazon

Mercury dynamics in hydroelectric reservoirs have been studied worldwide. In tropical reservoirs, especially in those of the Amazon, the influence of geochemistry on Hg levels along this aquatic system is not well understood. The main objective of the present study was to assess the influence of environmental conditions (physical and chemical water parameters, trace element concentrations of sediment and sediment geochemistry) on mercury levels of sediment along the Balbina Reservoir (Amazon basin, Brazil). Sediment was collected along the reservoir and in the main tributaries in May 2015 (n = 10). These samples were assessed for labile iron (LFe), manganese (LMn), aluminum (LAl) and mercury (LHg) concentrations, total mercury (THg) concentrations, organic matter (OM) content, and granulometry. Concentrations in the sediment were 4-212 (LFe), 2-460 (LAl), 180-613 (LMn), < detection limit-256 (LHg), and 12-307 μg kg^-1 dry weight (THg). In general, these concentrations decreased along the reservoir from upstream to downstream, reaching the lowest concentrations in the middle of the lake, and they increased in the sampling points near the dam. The lability and concentrations of mercury were influenced by the concentrations of LFe, LMn, LAl, and the granulometry and OM content of the sediment. Altogether, THg concentrations of sediments of the Balbina Reservoir encompass the range of concentrations of other reservoirs or natural lakes in the Amazon basin (from ten to a few hundred μg kg^-1 dry weight).

BIOGEOQUIMICA ESPAÇO-TEMPORAL DA LITEIRA EM AMBIENTE DE FLORESTA NATURAL NA AMAZÔNIA CENTRAL

SPACE-TEMPORAL BIOGEOCHEMISTRY OF THE LITTER IN A NATURAL FOREST ENVIRONMENT IN THE CENTRAL AMAZON. This research was aimed to evaluate the concentration of 15 chemical elements as a reference base for the quality of the litter in a forest in the central region of the Amazon. The sampling of the litter was performed monthly in two topographic positions for one year. For the quantification of the elements, digestion by nitroperchloric solution and reading by ICP OES were performed. The mean of macronutrient contents in the litter in decreasing order were Ca>K>Mg>Na. For micronutrients, the order was Al>Mn>Fe>Sr>Zn>Cu>Ba>Cr>Ni>Co>Cd for the Plateau and Al>Mn>Fe Sr>Zn>Cu>Ba>Cr>Ni>Cd>Co for the Baixio. Among the fractions, calcium had its highest concentration in the woody material, potassium in the reproductive material, while magnesium, sodium, and aluminum showed higher concentrations in the leaf fraction. Also, it was observed that the return of the elements to the soil by litter was greater in the dry period of the region, due to the greater fall in plant material. Calcium differed significantly within the same area, obtaining the highest concentrations compared to the other elements, while aluminum and zinc differed significantly between the areas studied, with a higher return for both elements on the Plateau.

Potential of Bacterial Isolates from a Stream in Manaus-Amazon to Bioremediate Chromium-Contaminated Environments

Igarapé do Quarenta (IgQ), a stream located in the Manaus-AM, BR, has directly experienced the impacts of urban expansion over the last five decades, which contributed for its contamination. As an affluent of Rio Negro, IgQ also affects the water quality of this important river that bathes Manaus. However, the stress caused by the prolonged exposition to chemical agents may have selected microorganisms that exhibit great bioremediation potential. In the present study, bacteria isolated from four distinct sites of the IgQ were identified, and their potential to degrade hexavalent chromium (Cr(VI)) was investigated using the s-diphenylcarbazide method. Among the investigated isolates, 14 exhibited resistance against Cr(VI) at a concentration of 300 mg/L and eight isolates reduced over 50% (53.5-97.4%) chromium ratios after 72 h of incubation. Those isolates were identified by gene sequencing and classified in 10 genera (Acidovorax sp., Acinetobacter sp., Alicycliphilus sp., Bacillus sp., Comamonas sp., Enterobacter sp., Micrococcus sp., Proteus sp., Serratia sp., and Vagococcus sp.). Under control conditions, the isolate of Vagococcus sp. genus, in only 24 h of incubation, reduced 96.8% of the rate of Cr(VI) added to the culture medium at the concentration of 10 mg/L. Obtained results indicate that the Vagococcus sp. exhibits a great potential to be used in the bioremediation of areas contaminated with chromium. The mechanisms of action of microorganisms should be investigated for more specific applications in the decontamination of effluents and direct use of its by-products to bioremediate polluted environments.