Assessing mercury contamiantion in the Amazon
3.4. Anthropogenic sources of mercury in the Amazon
I will comment on 3 important mercury sources arising directly or indirectly from anthropogenic activities in the Amazon. The sources are forest burning, gold mining and soil erosion.
3.4.1. Forest burning
Viega et al. (1994) estimated that the burning of forest biomass in the Amazon released 90 tons Hg / year into the atmosphere and suggested that the burning of forest biomass was the major source of atmospheric mercury emissions in the Amazon. This was disputed by Lacerda (1995) who calculated atmospheric mercury emissions from forest burning in the Amazon to be 17 tons Hg / year. However, both these estimates are based on assumed Hg concentrations, and not on actual values observed in the various compartments of the Amazonian forest. Roulet et al. (1998a) measured mercury concentrations in forest biomass from three forests situated in French Guyana and Brazil. The average emission factor from forest combustion for burning of primary forest is 273 g Hg / km2 and 370 g Hg / km2 for when the cumulative impact of slash and burn agriculture (cycles of 3 fires over 10 years) was accounted for. Annual deforestation rates for the Amazon region ranged from 22000 km2 / year to 34000 km2 / year (Fearnside, 1991 and Myers, 1991, respectively). Based on the data for initial burning of primary forest and annual deforestation rates it is estimated that forest burning releases 6 to 9 tons of Hg / year (Roulet et al. 1998a).