Elemental gaseous mercury flux at the water/air interface over the Negro River basin, Amazon, Brazil

The amount of dissolved gaseous mercury (DGM) released annually into the atmosphere by water bodies in each of the 18 major sub-basins of the Negro River tributaries has been estimated for the wet season and adopted for the entire year. Using Remote Sensors (RS) and the Geographic Information System (GIS), an estimate was made for the total flooded area during the period of the wet season (May–July), which corresponds to around 10% of the total basin area. The estimates of DGM evasive flux values were made during four scientific campaigns and ranged from 0.09 to 14 μg m−2 y−1. Mercury wet deposition to the same area was estimated using average values of the metal concentration in the rainwater (9.8 ng L−1), which varies from 17 to 27 μg m−2 year−1. Considering the flooded area of the Negro River Basin as 69000 km2, the total amount of mercury emitted by all bodies of water reaches nearly 0.26 ton year−1, which represents not more than 2% of the total mercury found in wet deposition in this same area.