摘要：The 38.5 m deep Lake Accesa is a sinkhole located in southern Tuscany (Italy) that shows a peculiar water composition, being characterized by relatively high total dissolved solids (TDS) values (2 g L -1 ) and a Ca(Mg)-SO 4 geochemical facies.The presence of significant amounts of extra-atmospheric gases (CO 2 and CH 4 ), which increase their concentrations with depth, is also recognized.These chemical features, mimicking those commonly shown by volcanic lakes fed by hydrothermal-magmatic reservoirs, are consistent with those of mineral springs emerging in the study area whose chemistry is produced by the interaction of meteoric-derived waters with Mesozoic carbonates and Triassic evaporites.Although the lake has a pronounced thermocline, water chemistry does not show significant changes along the vertical profile.Lake water balance calculations demonstrate that Lake Accesa has >90% of its water supply from sublacustrine springs whose subterranean pathways are controlled by the local structural assessment that likely determined the sinking event, the resulting funnel-shape being then filled by the Accesa waters.Such a huge water inflow from the lake bottom (~9·10 6 m 3 yr -1 ) feeds the lake effluent (Bruna River) and promotes the formation of water currents, which are able to prevent the establishment of a vertical density gradient.Consequently, a continuous mixing along the whole vertical water column is established.Changes of the drainage system by the deep-originated waters in the nearby former mining district have strongly affected the outflow rates of the local mineral springs; thus, future intervention associated with the ongoing remediation activities should carefully be evaluated to preserve the peculiar chemical features of Lake Accesa.
关键词：Central Italy;lake chemistry;Lake Accesa;sinkholes;lake water balance;structural geology setting.
