ASSESSING BEST PRACTICES FOR REFORESTATION OF AREAS DEGRADED BY ARTISANAL AND SMALL-SCALE GOLD MINING IN THE PERUVIAN AMAZONIAN REGION OF MADRE DE DIOS

Abstract

Artisanal and Small-Scale Gold Mining (ASGM) have pressured the Peruvian Southern Amazon rainforest, causing deforestation, soil degradation, and mercury (Hg) emissions in large areas. The Peruvian government and NGOs have performed reforestation projects in areas degraded by ASGM in this region using native plant species with an economic value. Previous research has studied the restoration of areas degraded by ASGM in this region. However, there is lack of information about the Hg's distribution, accumulation, and the effects of Hg exposure in native plants in this region. Additionally, few studies have investigated the recovery of soil fertility in these degraded areas during restoration.In this dissertation, the distribution and predictors of Hg accumulation in soil and native plant species from artisanal mining sites and the primary forest near these sites were studied. The highest Hg concentrations in soil were found in the intact primary forest topsoil and the plant rhizosphere area. The highest Hg levels in plants were found in the foliage of the intact primary forests. The Hg levels found in the plant leaves of the primary forest are the highest ever recorded in this region, exceeding values found in forests impacted by Hg pollution worldwide and raising concerns about the extent of the ASGM impact in this ecosystem. The effects of Hg exposure on the survival, growth, health, and rhizosphere microbial communities of three Amazonian agricultural plant species, aji dulce (Capsicum Chinense), sacha culantro (Eryngium foetidum), and uncucha (Xanthosoma sagittifolium L. Schott) were also investigated. The lowest observable concentration of Hg affecting the plant’s health was 2 mg kg-1 dw. This Hg concentration was three times lower than the soil screening level (SSL) for Hg in agricultural soil established in the Peruvian regulation. This suggests that a review of this SSL may be necessary before developing restoration projects in Amazonian areas impacted by ASGM. The soil physic-chemical characteristics, such as soil organic matter (SOM), electrical conductivity (EC), pH, nutrients, and bacterial communities, in the rhizosphere soil of plant species growing in naturally regenerated and reforested areas impacted by ASGM and in the primary forest near these areas were assessed. The results suggest that the plant species Acacia loretensis and Inga sp. (Inga sp. when planted with biochar as a soil amendment) might be good candidates for restoring areas degraded by ASGM, due to the level of nutrients and SOM in their rhizosphere. Finally, the integration of Indigenous and scientific knowledge to monitor and manage land degradation in regions impacted by ASGM was also studied. The findings emphasize the need to use the Indigenous communities’ knowledge of their territory for the early detection of soil degradation and facilitate a dialogue about land degradation and restoration of areas affected by ASGM between local communities, researchers, and policymakers to develop more sustainable and successful restoration projects in Indigenous communities affected by ASGM.