Ok Tedi copper mine, Papua New Guinea, stimulates algal growth in the Fly River

Fish populations utilised by riparian populations along the Fly River, Papua New Guinea (PNG), downstream of the Ok Tedi gold and copper mine have markedly declined in species richness (between 21 and 90%) and biomass (between 57 and 87%) during the operation of the mine (Storey et al., The Fly River Papua New Guinea. Environmental studies in an impacted tropical river system. Developments in Earth and Environmental Sciences, vol 9. Elsevier, Amsterdam, pp 427–462, 2009). A concern was that copper in wastes from the mine were negatively impacting algae in the river, thus altering the food web supporting the fish populations. This investigation found that the mining discharge to the Fly River increased, rather than decreased algal biomass in the Fly River, and did not appear to impact algae in associated off-river water bodies. It appears that nitrogenous explosives used in the mine have a fertilizing impact on the Fly River. There was no apparent impact of mine discharges on phytoplankton in the floodplain off-river water bodies, which was often concentrated in a prominent sub-surface maximum, and was not the main source of riverine plankton.