Artisanal and small-scale gold mining is a lifeline for many people living in the Madre de Dios region of southeastern Peru. However, economic development in this part of the Amazon Basin comes at a cost, as it causes deforestation, sediment accumulation in rivers and mercury contamination of nearby watersheds, threatening public health, indigenous peoples and the future of this biodiversity hotspot. And much of the mining activity is unauthorized.
An old mining camp in Peru's Madre de Dios La Pampa region shows shallow mining pools that have flooded the original river system. Image source: Photo by Jason Houston (iLCPRedsecker Response Fund/CEES/CINCIA)
Government intervention: Operation Mercury
In order to eliminate illegal artisanal and small-scale gold mining activities and the many negative impacts it brings, the Peruvian government deployed "Operation Mercurio" (Operation Mercurio) in the La Pampa region in February 2019. Gold mining is prohibited in most parts of the region. La Pampa straddles the Interoceanic Highway. North of the highway, mining is mostly done legally within mining concessions. But south of the highway, mining is strictly prohibited within the buffer zone of the Tambopata National Reserve.
Through Operation Mercury, armed forces and national police were sent to the area and remained there until March 2020. Miners were expelled and mining equipment destroyed. Interventions successfully stopped illegal gold mining in La Pampa, but mining in legal areas surged, raising many of the same environmental concerns, according to a Dartmouth-led study. The findings were recently published in Conservation Letters, a journal of the Society for Conservation Biology.
Mining equipment and shallow mining pools show where forests have been left to waste in the La Pampa region of Madre de Dios, Peru. Image source: Photo by Jason Houston (iLCPRedsecker Response Fund/CEES/CINCIA)
Lead author Evan Dethier, an assistant professor of geology at Occidental College, conducted the research while a postdoctoral fellow at Dartmouth.
After the operation, mining volumes were reduced by 70% to 90%. Excavated pits ("pools") in illegal mining areas have decreased by up to 5% per year, compared with annual increases of 33% to 90% before the intervention. While deforested areas are revegetating at a rate of 1 to 3 square kilometers per year, this progress is offset by increases in deforestation at a rate of 3 to 5 square kilometers per year in legal mining areas north of the Interoceanic Highway. Most revegetation occurs at the edges of deforested areas, with the highest rates in southern La Pampa. Vegetation in mining pool areas outside the intervention area also increased by 42% to 83%.
"The spillover effects in areas adjacent to the intervention area indicate that increased regulation is also needed in legal gold mining areas to help mitigate environmental impacts," Desier said. "But the intervention did have some of the intended effects, continuing to limit mining activities within the protected area."
Map of the main mining areas of Madre de Dios, Peru. Delta and Vepetuche are dominated by highly mechanized mining using bulldozers, while La Pampa relies almost entirely on low-mechanized mining with suction pumps and manpower. In February 2019, Operation Mercury targeted the area south of the La Pampa Interoceanic Highway. Image source: Compiled by Evan Dethier, Image: NASA/US Geological Survey via Landsat 8 in 2019
To assess the impact of Operation Mercury on mining activity, the team used satellite data from 2016 to 2021 provided by the European Space Agency's Sentinel-1 and Sentinel-2. Data came from nine mining areas: four illegal mining areas targeted by the intervention, two legal mining areas on the other side of the interoceanic highway to the north, and three distant sites not involved in law enforcement as study controls. Using radar and multispectral data, the researchers quantified changes in water quantity, water quality, mining pool area and deforestation in La Pampa after Operation Mercury by comparing data before, during and after the intervention.
As part of the analysis, the team studied the spectral properties of mining ponds and changes in pond color. Mining pools often appear yellow, a sign of gold mining activity. According to previous research led by Dethier, the pond's "yellow" color is associated with an increase in suspended sediment in the water.
During gold mining, sediments are stirred up from the land, creating turbid water with lower reflectivity, and clearer water with higher reflectivity. Reflectivity in mining ponds south of La Pampa increased after Operation Mercury, but has since stabilized.
After the end of Operation Mercury and the suspension of mining activities in all areas of La Pampa except the northern area, the yellowness of the ponds decreased rapidly. Northwest of La Pampa, where mining activity surged, pond yellowness increased by 43% compared to before the intervention. In the northeast of La Pampa, yellowness remains stable due to continued mining activity.
"Peru, like many other countries around the world with precious natural resources, has rich gold deposits, and it must determine who will control this exploitable resource and how this particular mining sector will emerge," said co-author David A. Lutz, an assistant professor in Dartmouth's Department of Environmental Studies.
By January 2023, when this paper was under journal review, illegal gold mining in protected areas had resumed, as law enforcement and anti-corruption activities by the military and national police had been halted as they were redeployed to focus on the COVID-19 pandemic.
"Our findings suggest that federal-level intervention can be effective in stopping illegal mining in Peru," Desier said. "But this is only one aspect of the problem, as a multifaceted approach must be taken to address the long-term impacts of illegal and legal gold mining on humans, wildlife and the environment in the Madre de Dios watershed."
"Conserving this tropical biodiversity hotspot will require strong governance, conservation and remediation strategies," Dethier said. "And, as our related work continues to show, this challenge is a global phenomenon."
Dethier, Lutz and others have just published a study showing an increase in similar mining operations in 49 countries in tropical regions around the world. Their research shows that up to 7% of large tropical rivers have been degraded by these expanding mining operations.