Impact of Land Use on the Mobility of Hg Species in Different Compartments of a Tropical Watershed in Brazil.

Abstract

This study evaluated the levels of total Hg and CH3Hg+ from a comprehensive perspective, considering the retention, leaching, and deposition of these contaminants in the main compartments (soil, plant litter, and sediment) of three landscapes (Atlantic Forest, pasture, and agricultural area) in a watershed in northern Rio de Janeiro State, Brazil. Variables analyzed were total Hg, CH3Hg+, organic carbon, total nitrogen, grain size, and surface area. In soil samples, total Hg levels were the highest in agricultural soil followed by forest soil and pasture (97.3, 87.6, and 77.1ngg-1, respectively), and CH3Hg+ was lower than 1.7%. Total Hg levels in leaf litter varied between 22.6 and 34.2ngg-1, and CH3Hg+ was 4.37%. In sediment, Hg (60-180ngg-1) and CH3Hg+ (<1%) indicate the transport of these contaminants from soils to this compartment and may be associated with soil use and cover. Multiple regressions were used to understand the dispersion of Hg species, and the effect of each variable varied with the landscape, showing that plant cover should not be ignored in investigations related to Hg species retention in a watershed. The landscapes surveyed in the present study clearly influence the quantitative and qualitative distribution of Hg species. On the other hand, anthropic processes associated with changes in soil use did not have any critical effects on the absolute levels of total Hg and CH3Hg+, meaning that the landscapes evaluated seem to represent the background concentration of these chemical species for the evaluated watershed.