Retention of metals originating from an abandoned lead-zinc mine by a wetland at Glendalough, Co Wicklow

Wetlands are effective filters for metal-containing water owing to the high metal-binding affinity of their soils. At Glendalough, Co. Wicklow, drainage from abandoned zinc/lead mines is still acting as a source of metals. Part of the mine drainage flows into a nearby marsh. The accumulation of metals ill the marsh was investigated. A similar marsh without metal inflow at Lough Dan, Co. Wicklow, was included in the study as an unpolluted control. Porewater and soil samples were taken throughout the marsh. Analyses were carried out for pH and dissolved organic carbon (DOG) in porewater, and for zinc, arsenic, iron, lead and cadmium in porewater and soil. Results showed a decrease in concentrations of zinc, arsenic, lead and cadmium with increasing distance from the source, indicating an accumulation of these elements in the marsh. Iron does not show this trend but concentrations in porewater correlate with DOG, suggesting that DOC affects the mobility of iron. The results further indicate that the longevity of wetlands used as so-called helophyte filters is in the order of centuries rather than decades.