Abstract
An innovative remote sensing approach that combines land-use change and water quality information is proposed in order to investigate if Artisanal and Small-scale Gold Mining (ASGM) area extension is associated with water siltation in the Tapajós River Basin (Brazil), containing the largest small-scale gold mining district in the world. Taking advantage of a 40-year period of the multi-satellite imagery archive, the objective of this paper is to build a normalized time-series in order to evaluate the influence of temporal mining expansion on the water siltation data (TSS, Total Suspended Solids concentration) derived from previous research. The methodological approach was set to deliver a full characterization of the ASGM expansion from its initial stages in the early 1970s to the present. First, based on IRS/LISSIII images acquired in 2012, the historical Landsat image database (1973–2001) was corrected for radiometric and atmospheric effects using dark vegetation as reference to create a normalized time-series. Next, a complete update of the mining areas distribution in 2012 derived from the TerraClass Project (an official land-use classification for the Brazilian Amazon) was conducted having IRS/LISSIII as the base map with the support of auxiliary data and vector editing. Once the ASGM in 2012 was quantified (261.7 km2) and validated with photos, a reverse classification of ASGM in 2001 (171.7 km2), 1993 (166.3 km2), 1984 (47.5 km2), and 1973 (15.4 km2) with the use of Landsat archives was applied. This procedure relies on the assumption that ASGM changes in the land cover are severe and remain detectable from satellite sensors for decades. The mining expansion area over time was then combined with the (TSS) data retrieved from the same atmospherically corrected satellite imagery based on the literature. In terms of gold mining expansion and water siltation effects, four main periods of ASGM activities were identified in the study area: (i) 1958–1977, first occurrence of mining activities and low water impacts; (ii) 1978–1993, introduction of low-budget mechanization associated with very high gold prices resulting in large mining area expansion and high water siltation levels; (iii) 1994–2003, general recession of ASGM activities and exhaustion of easy-access gold deposits, resulting in decreased TSS; (iv) 2004 to present, intensification of ASGM encouraged by high gold prices, resulting in an increase of TSS.
Highlights
Artisanal and Small-scale Gold Mining (ASGM) refers to the mining practiced using rudimentary technology by individuals, groups, or communities
We considered the use of TerraClass-2012 as a starting point in identifying and mapping ASGM distribution in 2012 as it use of TerraClass-2012 as a starting point in identifying and mapping ASGM distribution in 2012 as is an official classification that is freely available, and provides land use validated with field works
This research paper presents an innovative remote sensing approach that combines land-use change and water quality information in order to investigate whether ASGM area extension is associated with water siltation
Summary
Artisanal and Small-scale Gold Mining (ASGM) refers to the mining practiced using rudimentary technology by individuals, groups, or communities. This practice is primarily found in developing countries of South America, Asia, and Africa [1,2,3]. The ASGM local practice results in high water siltation due to the discharge of sediment from the margins of the rivers, where exploitation of alluvial deposits usually takes place [4]. As the miners exploit a particular area of the alluvial plain, new pits are opened, and the mine tailings (water + sediment) are usually discharged back into the river drainage, or to adjacent small ponds/lakes. The discharge of sediment into the water results in severe impacts on the water quality, such as decreasing light availability for primary production [9], and changing benthic [10] and fish communities [11]
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