Gold mining significantly limits the regrowth of Amazon forests and thus their ability to accumulate carbon, according to a new study.
The researchers report that forest recovery rates on abandoned mining pits and tailing ponds are amongst the lowest ever recorded for tropical forests, with no tree regeneration at some sites even three to four years after mining has stopped.
They estimate that mining-related deforestation results in the annual loss of over two million tonnes of forest carbon across the Amazon.
The research was led by the University of Leeds, UK, and the findings are published in the Journal of Applied Ecology.
“Our results clearly show the extraction process has stripped nitrogen from the soil, a critical component to forest recovery, and in many cases directly contributed to the presence of mercury within neighbouring forests and rivers,” says lead author Michelle Kalamandeen.
“Active mining sites had on average 250 times more mercury concentrations than abandoned sites.”
Gold mining has rapidly increased across the Amazon in recent years, especially along the Guiana Shield, where it is responsible for as much as 90% of total deforestation, the researchers say.
The Shield encompasses Guyana, Suriname, French Guiana, Venezuela and small parts of Colombia and northern Brazil, and its forests hold roughly 20 billion tonnes of aboveground carbon in its trees.
Kalamandeen and colleagues used forest inventory plots installed on recently abandoned mines in two major mining regions in Guyana, then re-assessed them 18 months later.
The study analysed soil samples and determined a tree’s above-ground biomass – its living plant material – to determine recovery and chemical changes caused by mining.
Their results suggest, they say, that forest recovery is more strongly limited by severe mining-induced depletion of soil nutrients, especially nitrogen, rather than by mercury contamination.
The high rate of mercury does however have serious implications for negative impacts on food security, water supply and local biodiversity.
One positive finding, Kalamandeen says, is that “overburden sites” – areas where topsoil is deposited during the mining process – recorded similar recovery rates as secondary tropical forests in Central and South America abandoned after agriculture or pasture.
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