Tropical Distress: Damage from the Contemporary Mining Surge’s Aquatic Destruction

In Peru’s Madre de Dios region, particularly in La Pampa, shallow mining ponds have replaced a once-vibrant river system. These ponds exhibit colors signifying suspended sediment and algae growth, subsequent to the halt in gold mining activities. Photo credits: Jason Houston (iLCP Redsecker Response Fund/CEES/CINCIA).

Mining, characterized by deforestation, erosion, and downstream sediment dissemination, is causing significant harm to the environment.

A research study led by Dartmouth, published in the journal Nature on August 23, has revealed the degradation of waterways in 49 countries, owing to gold and mineral mining in and near rivers across tropical regions. These findings are the inaugural documentation of the physical manifestation of river mining and its worldwide hydrological ramifications.

River mining typically entails extensive excavation, causing deforestation and elevated erosion. Much of the excavated material is released into rivers, affecting aquatic life in proximate and downstream ecosystems. The inorganic sediment, including clay, silt, and sand particles, is transported as “suspended sediment,” propagating the mining’s environmental consequences. Previous studies have reported that such sediment might also contain toxins like mercury, further deteriorating water quality and posing risks to human health and the environment.

Evan Dethier, an assistant professor at Occidental College and the study’s first author, emphasizes that though mining has occurred in the tropics for hundreds or even thousands of years, the recent two decades have witnessed an unprecedented scale. Dethier, who earned his PhD and MS in earth sciences from Dartmouth’s Guarini School of Graduate and Advanced Studies, calls the degradation from gold and river mining a “global crisis.”

You can find a timelapse gif of river mining’s impact in Myanmar between 1998 and 2022 on Dethier’s GitHub site.

In the La Pampa region of Madre de Dios, Peru, shallow mining ponds have taken over where streams once flowed through the rainforest. These degraded streams now transport waste sediment downstream from the mining ponds. Photo credits: Jason Houston (iLCP Redsecker Response Fund/CEES/CINCIA).

A Comprehensive Study of River Mining

For the study’s first phase, Dethier and his colleagues conducted an extensive analysis of tropical river mining from 1984 to 2021. Utilizing media information, literature, mining company reports, social media, satellite imagery from Landsat 5 and 7, NASA/United States Geological Survey Landsat program, Sentinel-2 data, and public aerial images, they logged over 7.5 million measurements to map mining areas, deforestation, and sediment impacts. Target minerals were also identified.

The research showed nearly 400 individual mining districts in 49 tropical countries, with over 80% situated within 20 degrees of the equator in South America, Africa, Asia, and Oceania.

They noted a substantial increase in mining during the 21st century, with 60% of sites emerging after 2000 and 46% after 2006, aligned with the global financial crisis. This trend persisted through the COVID-19 pandemic.

Image credits: Evan Dethier (Depicting rivers altered by mining boom in the 21st century).

Effects on River Systems

In the study’s second segment, the researchers evaluated mining’s influence on suspended sediment amounts in 173 impacted tropical rivers. They applied self-developed algorithms to Landsat data to detect suspended sediment transportation.

The data revealed that gold and mineral mining affect over 35,000 kilometers of tropical rivers. Of the world’s 500,000 kilometers of tropical rivers, approximately 6% are affected by such mining.

Moreover, mining led to a doubling of suspended sediment concentrations in 80% of the studied rivers compared to pre-mining conditions.

Dethier illustrates how tropical rivers that were once clear become muddied or clogged with sediment. He found that almost all mining areas transmitted sediment downstream, on average, 150 to 200 kilometers (93 to 124 miles) from the mining site, and in some cases, up to 1,200 kilometers (746 miles).

He compares this distance to the stretch between Bangor, Maine, and Richmond, Virginia.

In the 30 countries with active river mining operations and large tropical rivers wider than 50 meters, mining affects an average of 23% of the length of large rivers. In some nations, over 40% of these large rivers are altered, including in French Guiana (57%), Guyana (48%), and Cote d’Ivoire and Senegal (40%).

The study encompassed significant rivers like the Congo in Africa, the Irrawaddy in Asia, the Kapuas in Oceania, and the Amazon and Magdalena in South America.

Environmental Consequences and Future Directions

Senior author David Lutz, a research assistant professor of environmental studies at Dartmouth, points out the extreme biodiversity of many tropical river systems, despite being understudied. He raises concern about potential extinction of unknown species.

The team applied U.S. and global environmental management guidelines to assess the ecological impact. Since mining’s inception, they found that two-thirds of the studied rivers exceeded turbidity guidelines on 90% or more days, indicating higher cloudiness levels than recommended. Lutz explains that such high levels of suspended sediment can impair fish’s ability to see and may choke their gills, leading to disease or death.

Co-author Miles Silman emphasizes the societal cost of gold mining, particularly in the Peruvian Amazon, including environmental degradation, mercury pollution, corruption, and criminal networks. Although gold constitutes nearly 80% of mining sites, diamonds, nickel, and other precious minerals such as cobalt, coltan, tungsten, and tantalite are also mined, especially in regions like central and west-central Africa and Southeast Asia.

Dethier highlights the increasing necessity of these minerals in clean energy transition, making this an essential area to monitor.

The study’s authors urge government policymakers to collaborate with stakeholders to alleviate mining’s environmental and social consequences in tropical rivers, given its likely continuation in the foreseeable future.

Reference: “A global rise in alluvial mining increases sediment load in tropical rivers” by Evan N. Dethier, et al., 23 August 2023, Nature. DOI: 10.1038/s41586-023-06309-9

Contributors to the study also include Jimena Díaz Leiva at the Center for Environmental Health in Oakland, California; Sarra Alqahtani, Luis E. Fernandez, Paúl Pauca, and Seda Çamalan at Wake Forest University; Peter Tomhave at Bowdoin College; and Frank Magilligan and Carl Renshaw at Dartmouth.

The study received funding from NASA’s Land Cover Land Use Change Program under award 80NSSC21K0309, Dartmouth’s Neukom Institute for Computational Science, and NASA’s ROSES Program under award 80NSSC23K1293.

Frequently Asked Questions (FAQs) about river mining

More about river mining

• Dartmouth-led study on river mining
• Nature Journal – A global rise in alluvial mining increases sediment load in tropical rivers
• NASA’s Land Cover Land Use Change Program
• Wake Forest University’s Centro de Innovación Científica Amazónica (CINCIA)
• Dartmouth’s Neukom Institute for Computational Science