Land Use Change and Mercury Mobilization in the Amazon: The Madeira River Basin Case Study
L.D. Lacerda and W.R. Bastos
from: Bioremediation of Mercury: Current Research and Industrial Applications (Edited by: Irene Wagner-Döbler). Caister Academic Press, U.K. (2013)
Mercury is an ubiquitously presence in large areas of the Amazon, resultant form the gold rush which occurred in the region during the past century and from emissions of colonial mining operations, which used Hg amalgamation as major mining procedure. High Hg environmental levels are also favored by the capacity of most Amazon soils to accumulate and immobilize atmospheric Hg deposition over millennia. The immobilization of Hg, however, depends on the integrity of the ecosystems functioning, directly influenced by the recent development of the region. The effect of land use change on Hg mobilization from Amazon soils and sediments to the atmosphere and waterways is discussed, based on decadal data on Hg distribution in soil profiles under different land use categories; primary tropical forest, slashed forest prior to burning, silviculture and pastures. Degassing rates from these soils were monitored under different sampling periods, as well as air Hg concentrations over them. Comparisons of the Hg distribution in water, suspended solids and bottom sediments along a 1,600 km stretch of the Madeira River obtained in 5-years interval cruises are also discussed in view of large scale changes in the basin. All the results suggest strong mobilization of deposited Hg, both to the atmosphere and waterways. This process is suggested as responsible for the maintenance of elevated Hg concentrations in top carnivorous fish and riverside human populations reported recently, even after a decade of the cessation of Hg emission from gold mining in the region read more ...