Application of hydrologic-tracer techniques to the Casargiu adit and Rio Irvi (SW-Sardinia, Italy): Using enhanced natural attenuation to reduce extreme metal loads

Rio Irvi Zn load was extreme for a stream of this size and discharge. A comparison with two other mine-affected rivers in Sardinia indicated the loading in Rio Irvi was two to three orders of magnitude greater. This difference was attributed to different geochemical conditions, but also to a lack of a biogeochemical barrier like that seen to be acting along and below the riverbed in Rio San Giorgio. Several years of intense vegetation growth in the river bed of Rio San Giorgio created a biogeochemical barrier to metal loading, and the cumulative Zn load there was near 8 kg/day, despite being a drainage with a greater mass of mine wastes to contribute to the load.