Abstract: A system of planted and implanted small-scale SSF (subsurface flow) and SF (surface flow) constructed wetlands together with HP (hydroponic systems) were installed to compare the removal efficiencies of Fe and Zn from AMD (acid mine drainage) under long-term field conditions. Maximum removal of 94 % – 97 % (116 mg/m(exp 2)/d – 142 mg/m(exp 2)/d) for Fe and 69 % – 77 % (6.2 mg/m(exp 2)/d – 7.9 mg/m(exp 2)/d) for Zn was calculated for the planted soil systems. The planted SSF was most sensitive to heavy rain fall. Short-term increases of the metal concentration in the outflows, short-term breakdowns of the Fe removal and continual long-term breakdowns of the Zn removal were observed. In contrast to Zn removal, all wetland types are applicable for Fe removal with maximum removal in the range of 60 % – 98 %. Most of the removed Fe and Zn was transformed and deposited inside the soil bed. The amount absorbed by the plants (0.03 % to 0.3 %) and gravel-associated soil beds (0.03 % to 1.7 %) of the total input were low for both metals. The response of the planted SSF to rainfall suggests a remobilisation of metals accumulated inside the rhizosphere and the importance of buffering effects of the surface water layers of SF systems. The importance of plants for metal removal was shown.

Abstract: Seven kilometres of the River Pelenna in South Wales were impacted for approximately 30 years by discharges from abandoned coal mines. Elevated iron and low pH caused significant ochreous staining and had detrimental effects on the river ecology. The River Pelenna Mine water 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 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 mine waters. In the rivers downstream, 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 mine water 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 those found in 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.