Ecological Recovery of the River Pelenna (South Wales) Following the Passive Treatment of Abandoned Mine Drainage

Abstract

Abstract. From the 1960s to the late 1990s, the River Pelenna in South Wales was impacted for a distance of 7 km by five significant discharges from abandoned coal mines. Elevated iron and low pH caused significant orange staining and had detrimental effects on the river ecology. The River Pelenna Minewater Project constructed a series of passive wetland treatment systems to treat these discharges. Monitoring of the performance and environmental benefits of these has been undertaken as part of an ongoing Environment Agency R&D project. This project has assessed the changes in water quality as well as monitoring populations of invertebrates, fish and birds between 1993 and 2001.Performance data from the wetlands show that on average the three systems are removing between 82 and 95% of the iron loading from the minewaters. Downstream in the rivers the dissolved iron concentration has dropped to below the Environmental Quality Standard (EQS) of 1 mg/l for the majority of the time. Increases in pH downstream of the discharges have also been demonstrated.Trout (Salmo trutta) recovered quickly following minewater treatment, returning the next year to areas that previously had no fish. Intermittent problems with overflows from the treatment systems temporarily depleted the numbers, but the latest data indicate a thriving population. The overflow problems and also background episodes of acidity have affected the recovery of the riverine invertebrates. However there have been gradual improvements in the catchment, and in the summer of 2001 most sites held faunas, which approached unpolluted controls. Recovery of the invertebrate fauna is reflected in marked increases in the breeding success of riverine birds between 1996 and 2001.This study has shown that constructed wetlands can be an effective, low cost and sustainable solution to ecological damage caused by abandoned mine drainage. ___________________