Increase in mercury contamination recorded
in lacustrine sediments following deforestation in
the central Amazon
Chemical Geology, Volume 165, Issues 3-4,
M. Roulet, M. Lucotte, R. Canuel, N. Farella, M. Courcelles, J. -R. D. Guimarães,
D. Mergler and M. Amorim
Summary of
Points:
·
The
article examined a geochemical study of surface
sediments (vertical profiles of 30¯80 cm) from lentic
ecosystems of the
·
The Arapiuns and Amazon Rivers were compared -
measurements of mercury, textural indicators (water content and dry density), mineralogic indicators (iron and aluminum associated with oxyhydroxides and aluminosilicates),
and organic indicators (carbon, nitrogen, atomic C/N ratio) were performed over
the full length of the cores.
·
The
results demonstrate that soil erosion is responsible for an increase in surficial sediment mercury concentrations in the different
aquatic systems of the Tapajós and Arapiuns rivers. This increase is the result of the
relative enrichment of the sedimentary deposits in fine particulates rich in aluminosilicates, oxyhydroxides and
mercury, transported in suspension in the water column.
·
The oxyhydroxides of iron and aluminum associated with fine,
claylike particles seem to control the accumulation of heavy metals in the
sediments of the Tapajós, Arapiuns
and
·
Overall,
the mercury levels in the sediments studied have the same relationship with the
aluminosilicates and the texture of the sediments.
·
The
activity of lead-210 measured in two cores suggests that the superficial
sediments originate from eroded soils. A preliminary dating using the constant
initial concentration model indicates that the environmental changes recorded
in the
·
The
results presented have important implications for the geochemical
interpretation of anthropogenic disturbances in the Amazon. They demonstrate
that the recent colonization of the drainage basins and the growing
exploitation of new parcels of land in the central Amazon disturb the mineral
and organic matter cycles, as well as that of mercury. The ensuing result is
increased exportation of fine particulate mercury from the surface of soils to
drainage waters that transport them to fluvio-lacustrine
systems where they finally settle out.
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