Variação espaço-temporal dos parâmetros físicos e químicos e do fluxo de elementos-traço como indicadores basais no Arquipélago Fluvial de Anavilhanas – AM

Abstract

The Amazon biome has a great variety of natural environments with specific characteristics. The main source of nutrient renewal in floodable areas is caused by the hydrological cycle and plays an important role in the variation of the physical and chemical characteristics of Amazo-nian waters. Nutrients, both dissolved and suspended, are incorporated or disintegrated into the aquatic environment. In this study, carried out around the Anavilhanas National Park on the Rio Negro and with upstream observation since the contribution of the Rio Branco, 24 collection points were used grouped into 8 sample stations, through five collections in different hydrological periods: flood (March), flood (May and July) and dry (October and November) in 2017. The parameters evaluated were: pH, EH, CE, Temp, COD, OD and STS in surface water; trace elements (Cd, Cr, Cu, Fe, Mn, Ni, Pb, Sb, Se, V, Zn) in surface water, suspended solids and bottom sediment by ICP-OES. The data obtained were submitted to statistical tests of normality (Shapiro-Wilk) and conducted to appropriate tests in order to establish the analysis of the spatial variation between the parameters analyzed in the different hydrological phases. All physical-chemical variables showed no similarity between the flood, flood and dry periods (ANOVA and Friedman; p < 0.05), even in the campaigns performed in the same hydrological period, as observed in flood (May-July) and dry (October-November). In Anavilhanas, the Rio Negro presented mean pH values at 4.86 ± 0.41; EH 103.39 ± 26.49 mV; CE 12.04 ± 1.41 μS cm-1; Temperature 29.71 ± 1.24 ºC; COD 9.71 ± 1.22 mg L-1; OD 7.22 ± 1.57 mg L-1; STS 4.43± 1.62 mg L-1, which are characteristic values for rivers with natural black waters. Multivariateanalyses of PCA and HCA showed that the Rio Branco, during the flood period, had a greaterinfluence on the stations in Anavilhanas due to the difference in the physical-chemical charac-teristics of its white/clear waters and the greater flow in this period (11,055 m3 s-1), which cor-responded to 22.5% of the flow in Rio Negro, influencing mainly the left margin of the PARNAof Anavilhanas. All trace elements exhibited variation between hydrological periods in all analy-zed compartments (ANOVA and Friedman, p < 0.05), except Cr and Pb in surface water thatshowed no modification. The predominance of these trace elements in surface water was es-tablished in Fe > Mn > Pb > Zn > Cu > Ni > V > Cr > Cd; suspended solids in Fe > Mn > Zn >Cu > Pb > Cr > V > Ni > Cd; bottom sediment in Fe > Mn > Zn > Pb > V > Cr > Cu > Ni > Cd.High concentrations of metals in background sediment were observed in the drought (Novem-ber), due to trace elements present in suspended solids transported by the Rio Branco anddeposited downstream in the Rio Negro, but they did not exceed the limit values establishedby environmental agencies. The flow of dissolved trace elements followed the same flow pat-tern of the rivers (Negro and Branco), with the largest predominant flows in the flood (July), inthe upstream stations of PARNA, near the mouth of the Rio Branco. The average mass ba-lance values at PARNA of Anavilhanas showed a retention of the transported material of 22.0%in the flood (July) and 65.5% in the dry (November); and release of 24.1% in the dry (Novem-ber) during the passage through PARNA for all trace elements, except Fe, which had releasein all hydrological periods, with 32.9%, 0.5%, 3.7% and 16.7% in March, July, October andNovember, respectively. The difference in the behavior of the trace elements during the hydro-logic cycle consists in the mobility of the trace elements by deposition/sorption and leaching/re-solubilization processes in natural aquatic environments. The data presented in this study canbe visualized as a natural background for Amazonian environments of natural black water,becoming a support for further studies regarding the spatio-temporal variation of physical-che-mical parameters and the behavior of trace elements in different compartments for environ-mental impact diagnosis.