The impacts of land use changes in the mercury flux in the Madeira River, Western Amazon

Abstract

Changes in hydrochemistry and Hg distribution in the Madeira River from Porto Velho to the confluence with the Amazon River were studied in two cruises in 1997 and 2002. Water conductivity was similar in both periods, but the pH was significantly higher in 2002, in particular along the middle reaches of the river. Total suspended matter concentrations also increased from 1997 to 2002 along the same river portion, which is a result of forest conversion to other land uses, in particular pastures and agriculture accelerated during the interval between the cruises. Dissolved Hg concentrations were similar along the river in both cruises, but particulate Hg concentrations increased significantly along the middle portion of the river, although the suspended matter from 2002 was relatively poorer in Hg compared to that from 1997. Since particulate Hg represents more than 90% of the total Hg present in the river water, there was a significant increase in the total Hg transport in the Madeira River. Although gold mining has nearly ceased to exist in the region, the remobilization of Hg from forest soils through conversion to other land uses is responsible for maintaining relatively high Hg content in the Madeira River environment.

Mercury speciation and safety of fish from important fishing locations in the Czech Republic

“…Our findings regarding mercury concentrations in tissues of different fish species in fish from the studied locations correspond to data reported in the literature (Lacerda et al 1994;MarrugoNegrete et al 2008). It means that the highest THg concentrations were found in the muscle of predatory fish species, i.e.…”

Toward an Assessment of the Global Inventory of Present-Day Mercury Releases to Freshwater Environments

“…Studies have estimated these soils may release up to 3000 µg Hg m −2 per cm of soil eroded [72]. Consistent with this assumption, Lacerda et al [74] concluded that the remobilization of Hg naturally present in forest soils during conversion of forest to other land uses, and not historic ASGM mining, was responsible for relatively high Hg levels in these rivers. Globally, deforestation is enhanced across the pan-tropical regions, where 9.5 million km 2 of tropical forest was converted to agricultural land [75].…”

Flood pulse and spatial dynamics of mercury in sediments in Puruzinho lake, Brazilian Amazon

“…Alluvial gold mining on the Madeira river reached its peak between 1980 and 1990. It is estimated that from 1979 to 1985, about 100 tons of Hg (12.4 t yr -1 ) were discharged into the Madeira river basin (Lacerda et al1989) and this amount remained constant through the early 1990's, decreasing to less than 0.5 t yr -1 after 1995 (Lacerda et al 2012). In recent years, gold mining in the Madeira river has declined, however the activity still contributes significantly to the amount of mercury discharged into this ecosystem, mostly from gold mining on the Beni and Madre de Dios rivers ).…”