Edited by Andrea Rinaldo, École Polytechnique Fédérale de Lausanne, Lausanne, Switzerland, and approved October 6, 2019 (received for review May 6, 2019)
Artisanal-scale gold mining (ASGM) operations are expanding across the planet, leading to widespread riparian deforestation and excavation, and hastening sediment transport into nearby rivers. Here, we show that ASGM operations have led to major increases in river suspended-sediment concentrations across a wide region of the Peruvian Amazon. The magnitude of suspended-sediment increase we detect implies detrimental and long-lasting impacts on aquatic biota, particularly behavior and community structure of fish populations, and increased riverine transport of ASGM-contributed, mercury-laden sediments. Our data document that ASGM has rapidly decreased water quality in this large region since the 1980s, indicating a pressing need for biogeochemical and ecological evaluations of ASGM-affected rivers worldwide in order to quantify indirect consequences on aquatic species and human health.
In recent years, rising gold prices have exacerbated the global proliferation of artisanal-scale gold mining (ASGM), with catastrophic consequences for human and ecological health. Much of this burgeoning industry has occurred in biodiversity hot spots, notably in the tropical forests of South America. While the loss of tropical forests and floodplains as a result of ASGM has been well characterized, ASGM impacts on riverine hydrological properties are less understood. Previous fieldwork on ASGM-affected and gully-eroded tropical streams and rivers has demonstrated that increases in suspended-sediment concentration (SSC) can substantially impact fish diversity and aquatic community structure, yet our understanding of the timing and scope of impacts of such increases is limited by the lack of long-term records of SSC. To address this challenge, we present a 34-y analysis of the direct effect of ASGM on 32 river reaches in the Madre de Dios region of Peru, which has been heavily impacted by ASGM since the 1980s. We evaluate spatial and temporal patterns of impacts using estimated SSC derived from Landsat satellite imagery. We find that 16 of 18 stretches of river impacted by ASGM show significant increasing trends in SSC (P < 0.05), while only 5 of 14 unaffected sites do so. Additionally, ASGM appears to reverse natural seasonal cycles of SSC, which may imperil aquatic species. Overall, our findings indicate that ASGM is fundamentally altering optical water quality dynamics of a critical tropical biodiversity hot spot and provide guidance for future regulation of these activities.
Author contributions: E.N.D., S.L.S., and D.A.L. designed research; E.N.D. and S.L.S. performed research; E.N.D. contributed new reagents/analytic tools; E.N.D., S.L.S., and D.A.L. analyzed data; and E.N.D., S.L.S., and D.A.L. wrote the paper.
The authors declare no competing interest.
This article is a PNAS Direct Submission.
Data deposition: The data used in this analysis have been deposited at HydroShare, http://www.hydroshare.org/resource/0efe95f8326d497eb427e97a58b1b577/. Appropriate metadata are also included.
This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1907842116/-/DCSupplemental.
Published under the PNAS license.
