The impact of the Ada Tepe gold mine on the ecological status of Krumovitsa River, Bulgaria

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Ada Tepe is a gold mine in the area of the Eastern Rhodope Mountains near Krumovgrad in Bulgaria, which officially began operation in August 2019. Ada Tepe is the one out of six sections of the gold mining field Khan Krum. Dundee Precious Metals owns a 30-year concession for the Khan Krum mining field, and the Ada Tepe mine was financed by the EBRD. It impacts the Natura 2000 Habitats Directive site Rodopi-Iztochni and the Natura 2000 Birds Directive site Krumovitsa. Bulgarian state authorities only approved the project after the investor significantly reduced the project’s exploitation area and minimised their expected usage of pollutants. The investor was further obliged to prevent environmental degradation and pollution through strict management of waste water and mining waste. An independent hydrobiological study on the impact of the mine’s operation on a 12 kilometre section of the Krumovitsa River was conducted in October 202029. Discharge conditions were not suitable for proper ecological assessment because some river sections were dry, without any surface water flow. However, the visit took place during a rainy period and erosional flows coming from the mining area were registered and observed to be the cause of the blanketing and colmatation (clogging) of the Krumovitsa River bed. Such an impact disrupts water exchange between the surface and hyporheic zones and negatively affects the macroinvertebrate community, which is highly dependent on the conditions in the interstitial microhabitats and hyporheic zone during periods of drought. The affected section was 2 kilometres long. These conditions differed significantly from those upstream of the mining area, where the river was in excellent ecological status. The presence of fish and otters along the whole investigated section of Krumovitsa River is a positive sign, however, indicating that the river ecosystem is not heavily affected.