INTRODUCTION
Gold industry in the world has experienced a surge over recent years
with the record mine production of 4,490t (World Gold Council, 2018a)
and reaching great international price of 1,456.85$ OZ
TR-1 (World Gold Council, 2019). Peru occupies
1st place in Latinoamerica and the
6th place in the world gold production, which
represents 4.4% overall world gold production (Ministerio de Energía y
Minas, 2019). Gold is an extremely scarce element (World Gold Council,
2018b), which in the Amazon need the extraction of thousands tons of
sediments to get goldbearing gravel, leading to a large scale
deforestation and Hg pollution (Alvarez, Solano, Brack, & Ipenza,
2011). In Madre de Dios Region, also known as the “Peruvian Capital of
Biodiversity”, artisanal and small gold production accounts for 7% of
the total annual gold production in Peru of approximately 144 metric
tonnes (Ministerio de Minas y Energía, 2019).
Deforestation caused by gold mining industry has become a major threat
to some of the most remote and better-conserved old-growth forests in
tropical South America. Between 2001 and 2013, there was a loss of
1680,000 ha of forest at 177 gold mining sites (Alvarez-Berríos &
Mitchell Aide, 2015). Here the Peruvian Amazon constitutes part of the
highest biodiversity region in the global tropics (Myers, Mittermeier,
Mittermeier, da Fonseca, & Kent, 2000). Unfortunately, gold mining
activities in Madre de Dios has resulted in the deforestation of 95,750
ha (Caballero Espejo et al., 2018), annual deforestation rates have
fluctuated between 6,000 ha (Asner, Llactayo, Tupayachi, & Luna, 2013)
leading to an estimated topsoil loss of 1.3 t ha-1year (Gomez, 2013). Moreover, It was reported that gold market prices
were close correlated with mining rates on interannual timescales (R2
=0.43; p < 0.05) (Asner & Tupayachi, 2017). This pattern of
mining in tropical forested regions continues to rise globally with
similar consequences as observed in Madre de Dios (Alvarez-Berríos &
Mitchell Aide, 2015).
Alluvial gold mining in Madre de Dios old growth forest generally
involves slash and burn deforestation, sediment extraction, amalgamation
of gold with Hg, burning, Hg evaporation and gold recovery (Alvarez et
al., 2011; Salinas, 2007). All these stages of gold production are
typically carried out on site, hence generating an importance source of
Hg pollution in the local environment. It is estimated that between at
least 1 and 2 grams of Hg is lost to the environment for every gram of
produced gold (Mallas & Benedicto, 1986; Veiga & Baker, 2004).
Sediment extraction is accomplished through the use of highly mechanized
mining and minimally mechanized technology level. Highly mechanized
mining uses heavy machinery such as excavators, front loaders, and dump
trucks, and minimally mechanized mining uses suction pumps, high
pressure water cannons to liquify stream-side sediments which are
transported to sluice boxes via diesel-powered water/sediment pumps
(Caballero Espejo et al., 2018). During this process the topsoil,
characterized by a fine texture, is scattered and coarse gravel, stones
and boulders from deeper soil layers become to predominate at the
surface (Salinas, 2007).
In spite of the degraded conditions of mine spoils, natural succession
also happens in most of them resulting in the formation of secondary
forests in different stages of development, and with it the formation of
new soil profiles with different physical and chemical characteristics.
However, limited information exists in the Amazon about the composition
of such new soil profiles, hampering decision making on how to best
reclaim, rehabilitate or restore the ecosystem in these areas. Our aim
was to support further effective restoration experiences by classifying
these soils in Madre de Dios according to the Soil Taxonomy (Soil Survey
Staff, 2014) and World Reference base (Working Group WRB, 2015) to
verify how they differ from soils under undisturbed old-growth forest.
We primarily focused on a local area, such as Fortuna Community, which
is the most characteristic model of Artisanal and Small Scale Gold
Mining (ASGM) in the Peruvian Amazon.