Total Hg and methylmercury dynamics in a river-floodplain system in the Western Amazon: Influence of seasonality, organic matter and physical and chemical parameters.
Sci Total Environ
; 656: 388-399, 2019 Mar 15.
Article
en En
| MEDLINE
| ID: mdl-30513429
ABSTRACT
Total mercury (Hg) and methylmercury (MeHg) circulation in a connected river-floodplain system composed of two black water (a small forest river, igarapé, and Cuniã Lake) and a white water body (Madeira River), located in the Madeira River Basin were evaluated during the rising-water, early and late falling-water periods. We assessed organic matter (C and N composition, (CN)a; and δ13C isotopic signature), and physical and chemical influences (pH, dissolved O2, electric conductivity) in relationship to Hg and MeHg concentrations. Hg and MeHg concentrations in a sediment profile and three aquatic macrophytes (E. crassipes, E. azuera and Oryza sp.) were measured. Igarapé and Cuniã Lake showed higher Hg and MeHg concentrations (115-709; 10-25â¯ngâ¯g-1) in the suspended particulate matter compared (SPM) compared to the Madeira River (Hg 5-16; MeHg 0.2-0.3â¯ngâ¯g-1), partially independent of seasonality (pâ¯=â¯0.06). Total Hg had higher affinity for the SPM (1.75 times) than for dissolved organic matter. Organic matter characteristics correlated with MeHg concentrations (δ13C and (CN)a; r2â¯=â¯0.79; pâ¯<â¯0.0001), as well as physical and chemical parameters of the water column (dissolved O2 and pH; r2â¯=â¯0.80; pâ¯<â¯0.0001), demonstrating that physical and chemical changes between the river-floodplain system affect MeHg circulation and production. The inverse correlation of MeHg and SO42- concentrations (r2â¯=â¯0.73; pâ¯<â¯0.0001) suggests the action of sulfate-reducing bacteria. Total Hg and MeHg concentrations as well as %MeHg were detected in the sediment profile (Hg 24-51; MeHg 0.6-3.2â¯ngâ¯g-1; %MeHg 1.8-6.2) and aquatic macrophytes (Hg 1-30; MeHg 0.3-7.5â¯ngâ¯g-1; %MeHg 1.6-33.7). We conclude that the highest Hg and MeHg concentrations in Cuniã Lake, compared to the Madeira River, are due to the physical and chemical differences between these environments.
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MEDLINE
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En
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Sci Total Environ
Año:
2019
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Article