GOLA DI LAGO, A MINEROTROPHIC PEATLAND AND ITS NATURAL ENRICHMENT OF ARSENIC

Peat is an unconsolidated soil material consisting of more than 65 percent organic matter and which is largely accumulated under conditions of excessive moisture. Arsenic (As) is commonly enriched in peat and coal (Valkovic, 1983; Swaine, 1990), the potential mobility and forms of As in peat are largely unknown. In Gola di Lago (GdL), Canton Ticino, Switzerland, there is a small minerotrophic peatland (29 375 m2) formed in the last 13000 years (Zoller and Kleiber, 1971) where intermittent stream waters entering this peatland contain up to 400 ppb As, but the permanent waters leaving the peatland contain less than 2 ppb (Gonzalez et al., 2005). Chemical analyses of peat show remarkable concentrations of As. Coring at regular intervals revealed several zones of pronounced accumulation, with As concentrations up to 500 ppm. Using Ti as a conservative, lithogenic reference element, this represents an enrichment, relative to crustal rocks, of 1100 times. Both Fe and S are also enriched in this zone, suggesting that redox-related transformations have affected all three elements. XRD analyses showed the presence of pyrite and SEM photomicrographs revealed pyrite framboids, but failed to identify arsenopyrite. The goal of this study is to explain the mechanism of As removal from the water by the peat.