Muddy rivers and toxic flows : risks and impacts of artisanal gold-mining in the riverine catchments of Bombana, Southeast Sulawesi (Indonesia)

Artisanal mining in the Bombana district of Southeast Sulawesi and its downstream effects are strikingly evident in the quality of water and sediments examined in this study. Through targeted water and sediment sampling at different locations in the river systems, we can see what is being added to the system over time. We can also see how these impacts are modified by their dynamic interaction within the riverine systems. Test results reveal how and where mercury-contaminated particulates are trapped or removed from a stream. The pattern of mining intensity also influences how the contaminant concentration varies over time and space within waterways (for instance, during the Ramadhan fasting month), as does the seasonal pattern of monsoon rainfall, where the onset of the wet season has a flushing effect on river sediments and the mercury load that they carry. Identifying hotspots of contamination provides insight into the risks of exposure, for both people and aquatic ecosystems. Preliminary results drawn from this study suggest that the risks of mercury suspended in river water downstream of mining activity occur at a whole-of-river scale. The transport of mercury within the water column, mainly adsorbed into particulate matter, creates risks for biota (especially catfish, freshwater shrimp, etc.) to take up mercury along the river course. The long-term direct and cascading effects of mercury ingestion within these catchments remain unclear without further research. The results of the sampling survey thus illustrate the need for active and longer-term monitoring of river and sediment quality as an important environmental and public health initiative by local government. Continuing efforts of the research partners to promote and support policy initiatives directed to these ends form an integral part of the action research objectives of the present project. Finally, the complementary social mapping survey into human–water interactions along the mining-affected river systems has highlighted a series of adverse environmental and ecological impacts from the massively increased sediment flows due to unregulated hydraulic mining of riverbeds and banks. In particular, damage and destruction to the river amenity and its associated high-value, downstream benefits for local communities and rural livelihoods is a major and unfortunate legacy of artisanal mining. It is by no means evident that the short-term and limited economic benefits of the Bombana gold rush offset the long-term environmental costs that are borne by the majority of residents.