Trees may represent useful long-term monitors of historical trends of atmospheric pollution due to the trace elements stored along the tree rings caused by modifications in the environment during a tree’s life. Chestnut (Castanea sativa Mill.) tree trunk sections were used to document the yearly evolution of atmospheric Hg in the world-class mining district of Monte Amiata (MAMD; Central Italy) and were exploited until 1982. An additional source of Hg emissions in the area have been the active geothermal power plants. A marked decrease (from >200 µg/kg to <100 µg/kg) in Hg contents in heartwood tree rings is recorded, likely because of mine closure; the average contents (tens of µg/kg) in recent years remain higher than in a reference area ~150 km away from the district (average 4.6 µg/kg). Chestnut barks, recording present-day Hg pollution, systematically show higher Hg concentrations than sapwood (up to 394 µg/kg in the mining area). This study shows that tree rings may be a good record of the atmospheric Hg changes in areas affected by mining activity and geothermal plants and can be used as a low-cost biomonitoring method for impact minimization and optimal resource and land management.

During the last 40 years, extensive research has characterized the hydrogeology of many karst aquifers, as they are important water resources. Despite that, a systematic investigation on metamorphic karst aquifers is still lacking. The present study investigates the functioning of marble karst aquifers by means of spring hydrological monitoring, coupled with storm-hydrograph, thermograph, and chemograph (HTC) analysis and lag time analysis. Renara and Equi springs (Apuan Alps, Italy) were selected for this investigation. These springs drain catchments that have different degrees of structural complexity. Piston flow is the common hydrodynamic response of Renara spring to infiltration. Strong dilution effects were observed only during the heaviest rainfall events. Prolonged dry conditions after a sustained recharge phase showed the delayed arrival of infiltration water about a month later. Equi spring has a more complex behaviour due to its wider and more hydrologically heterogeneous catchment but the comparison of HTC graphs during the winter dry phase helped to recognize the differential contributions of proximal and distal sectors. Both springs show a rapid discharge increase in response to impulse infiltrative events. Conversely, water temperature and specific electrical conductivity increase only slightly during floods, indicating limited chemical and thermal exchanges between the rock and the water stored in these aquifers. The hydrodynamic behaviour of these karst springs suggests that the Apuan metamorphic aquifers are characterized by the predominance of conduit porosity over fissure and matrix porosities. This is explained by a reduced interstitial porosity and fracturing of the metamorphic carbonate rocks.

The Apuan Alps (Italy) are an internationally renowned karst region where several karst springs have a mean discharge exceeding 100 L/s, thus representing important water resources. One of the major springs, the Pollaccia, was monitored for approximately one year. This spring drains a structurally complex metamorphic karst aquifer that is characterized by multiple hydrologic sectors with variable recharge and infiltration styles. Spring discharge, water temperature, and electrical conductivity were compared to precipitation data, and time lag analysis was performed on 27 storm hydro/thermo/chemographs (HTC-graphs) that occurred in different hydrological phases. A marked seasonality was observed for all the monitored parameters and for the measured lags. The comparison of the storm HTC-graphs with no precipitation phases permitted recognition of the differential contribution of the various sectors. The Pollaccia’s hydrodynamic behavior was related to three different scenarios in the recharge area: (1) allogenic runoff recharge in the noncarbonate sectors; (2) autogenic recharge and runoff over the steeply dipping marble outcrops, characterized by fast epiphreatic flow through master conduits and low epikarst storage; (3) autogenic recharge through highly fractured, gently dipping marble outcrops, characterized by quick hydraulic pressure transfer to the phreatic zone and relevant epikarst storage.

Mining operations generate sediment erosion rates above those of natural landscapes, causing persistent contamination of floodplains. Riparian vegetation in mine-impacted river catchments plays a key role in the storage/remobilization of metal contaminants. Mercury (Hg) pollution from mining is a global environmental challenge. This study provides an integrative assessment of Hg storage in riparian trees and soils along the Paglia River (Italy) which drains the abandoned Monte Amiata Hg mining district, the 3rd former Hg producer worldwide, to characterize their role as potential secondary Hg source to the atmosphere in case of wildfire or upon anthropic utilization as biomass. In riparian trees and nearby soils Hg ranged between 0.7 and 59.9 μg/kg and 2.2 and 52.8 mg/kg respectively. In trees Hg concentrations were below 100 μg/kg, a recommended Hg limit for the quality of solid biofuels. Commercially, Hg contents in trees have little impact on the value of the locally harvested biomass and pose no risk to human health, although higher values (195-738 μg/kg) were occasionally found. In case of wildfire, up to 1.4*10^-3 kg Hg/ha could be released from trees and 27 kg Hg/ha from soil in the area, resulting in an environmentally significant Hg pollution source. Data constrained the contribution of riparian trees to the biogeochemical cycling of Hg highlighting their role in management and restoration plans of river catchments affected by not-remediable Hg contamination. In polluted river catchments worldwide riparian trees represent potential sustainable resources for the mitigation of dispersion of Hg in the ecosystem, considering i) their Hg storage capacity, ii) their potential to be used for local energy production (e.g. wood-chips) through the cultivation and harvesting of biomasses and, iii) their role in limiting soil erosion from riparian polluted riverbanks, probably representing the best pragmatic choice to minimize the transport of toxic elements to the sea.

The Apuan Alps (NW Tuscany) is an important area of Central Italy characterized by large karst systems mainly fed via direct and diffuse water infiltration (autogenic recharge). These waters usually transport a clastic sediment load, originated by natural, surface and subsurface rock erosion/weathering which, in part, is deposited underground. In the Apuan Alps, during extreme rain event, huge amounts of carbonate powder, produced as a waste resulting from the quarrying operations of the famous “Carrara” marble, mix up with meteoric waters forming a slurry that is transported through the karst openings into the caves, where the carbonate powder may be deposited along with natural sediments. Depending upon karst hydrology and water fluxes, the slurry may eventually reach karst springs heavily reducing water quality. Mineralogical composition of the sediments collected along karst waterways and springs shows variable proportions of calcite associated with dolomite and silicates particles whereas the marble powder samples from quarry areas are mainly composed by calcite grains. Cave deposits of natural origin have usually a fine-sand grain size whereas spring sediments have a more variable grain-size distribution. Marble powder mainly has a silt grain size and produces a sort of “granulometric and morphometric pollution” which influences the transport mechanism of solid load through the karst systems along both vadose and phreatic waterways.