Oxygen and hydrogen isotopic composition of waters in a past-mining area of southern Apuan Alps (Italy): Hydrogeological characterization and implications on the fate of potentially toxic elements

https://doi.org/10.1016/j.gexplo.2019.106338Get rights and content

Highlights

  • The oxygen and hydrogen isotopic signature of rainwater traces groundwater recharge.

  • Acid mine drainage impacted waters show hydrogen isotopic fractionation.

  • Osingle bondH isotopes allow interconnections between groundwater pathways to be established.

Abstract

The oxygen and hydrogen isotopic composition of stream water, springs, groundwater tapped from irrigation wells and acid mine drainages were determined during two different surveys in 2015 in an area highly impacted by past-mining activity of Apuan Alps (Italy), as a guidance on good practices for water management. The isotopic local meteoric water line (LMWL) was built by monthly collecting rainwater between 2014 and 2018, given by δD = 7.02 ± 0.35 × δ18O + 8.54 ± 2.89. The obtained results indicate that acid mine drainages (AMD) are supplied by freshwater from karst systems which flow throughout the post-mining workings. Such waters contaminate by interactions with sulfides (pyrite) that remained unmined in the ore-bodies. During rainstorms, infiltration rainwater displaces water ponding within mine, sharply increasing the outflow rate of highly-contaminated AMD. Acidic drippings in tunnels show an isotopic shift in both δ18O and δD values attributable to pyrite oxidation and Fe hydrolysis. The data reveal that karst-springs represents the primary supply for the stream. The isotopic data also reveal that waters flowing in the bedrock carbonate aquifer represent the main feeding component for the overlying alluvial aquifer tapped by wells. The prevailing transfer of clean freshwaters from the carbonate aquifer towards the alluvial aquifer system mitigates the possible influence of contaminated water from stream seepage. However, these observations require a monitoring program on water quality to be established.

Introduction

In past mining areas, the major environmental impact is represented by potentially toxic elements (PTE) leaching and acid rock drainage (AMD) produced by sulfide oxidation and their by-products (Fields, 2003; Nordstrom, 2011; Nordstrom et al., 2015). In these settings, the contaminant migration through the aqueous routes is a growing concern (Hajalilou et al., 2011; Sun et al., 2014; Ghezzi et al., 2019). The oxidative reaction pathways of sulfide minerals and the fate of PTE are impacted by the meteorological drivers governing the hydrological regime (Morton and Merkek, 1993; Schaider et al., 2014) throughout variations in the infiltration rate of oxygenated meteoric waters and the dynamics of mine-tunnels flooding (e.g. Cidu et al., 2011). Indeed, within the hydrologic system of post-mining workings, AMDs are generated continuously during the groundwater flow in channels and open voids, and the quantity and quality of acid water that targets the aquatic environment is dependent on the recharge of the aquifer that is hydrologically connected to the mine. In this scenario, the interconnections between acidic water outflows and the recharge of groundwater systems can represent a major environmental hazard.

Oxygen and hydrogen that form the water molecule have Damköhler number ≪1, indicating negligible effects of fluid-rock interaction in most low-temperature environments (Blattner and Lassey, 1989). Indeed, the 18O/16O and D/H ratios in water, expressed through the δ18O and δD values (Clark and Fritz, 1997), generally act as conservative tracers. This implies that changes in stable oxygen and hydrogen isotopic abundances reflect the variation in time and space in precipitations at recharge areas and the physical processes that occur during the fluid flow (Gat, 2010). It has however to be noted that a study on AMD-impacted waters Sun et al. (2014) reported isotopic shifts in the δD of the water molecule due to pyrite oxidation and Fe hydrolysis.

The southern sector of the Apuan Alps chain (Tuscany Region, Italy) is characterized by the occurrence of sulfide-bearing mineral deposits (Lattanzi et al., 1994) since long exploited (the Valdicastello Carducci mining area). Mine closure occurred at the beginning of 1990's, leaving the legacy of abandoned tunnels and mine waste residuals that introduce a variety of PTE into the environment, in a densely-populated and high tourist vocation area (Perotti et al., 2017). Indeed, the acid mine drainages produced by the oxidation of the fine-grained pyrite and other base metal-sulfide minerals that characterize the mining area represent a source for As, Al, Fe, Ni, Zn, Cd, Sb, Tl released into the surface waters of the Baccatoio stream, crossing the mining area and the Valdicastello Carducci village. Previous studies (Perotti et al., 2017) showed highly variable concentration of PTE in the acidic plumes outflowing from tunnels and attenuation processes downstream. Flow rate measurements demonstrated that the outflow rate may change on order of magnitude and it is related to the rainfall amount (Giannecchini et al., 2016a). However, the interconnections between the water recharge, the mine tunnels flows, the groundwater-dependent ecosystem and the seepage infiltration from the Baccatoio stream are still unexplored.

To better understand some of the processes that take place in the Valdicastello Carducci mining area, and to ascertain how the hydrological regime behaves with time, oxygen and hydrogen isotopic data were obtained on acid effluents and acidic dripping waters inside tunnels, on stream water, springs and groundwater tapped from irrigation wells collected during different surveys in 2015. In addition, a local meteoric water line was built by collecting rainwater monthly between 2014 and 2018. Even if Osingle bondH stable isotopes represent a well-used tool in hydrology (Gat, 2010), these methods have been only occasionally applied to investigate mining areas (Seal, 2003; Parizi and Samani, 2014).

This approach assumes a particular interest in the study area, in view of the proximity of the mine site with springs providing drinking water supply and wells for domestic and irrigation uses.

Section snippets

Mine location, geological and hydrogeological outlines

The study mining area is located in the southern part of the Apuan Alps chain (Tuscany Region, Italy), in the Baccatoio stream catchment, a stream having its headwater in the Mt. Gabberi and Mt. Lieto reliefs (Fig. 1). The Baccatoio stream receives the AMD-impacted effluents from the mining districts of Mt. Arsiccio and Pollone (Fig. 1). The amount of AMD, averaged on annual basis, outflowing from Mt. Arsiccio and Pollone mine sites ranges between 0.3 and 3.0 L/s and 0.3 to 1.0 L/s (

Materials and methods

Rain water was collected monthly from 2014 to 2018 using a sampling device and prescriptions as specified by IAEA/GNIP (2014). The rain collector is designed with an anti-evaporation system as described in Gröning et al. (2012). It consists of a narrow polypropylene flexible tube, connecting the outlet of a 20 cmø polyethylene funnel to the bottom of a high quality high-density polyethylene (HDPE) reservoir tank of 10 L, a size suggested for rainy regions. This equipment minimizes the exposure

Results

The Osingle bondH isotopic composition and deuterium excess (d-excess ‰ = δD − 8 ∗ δ18O, Dansgaard, 1964 referred to the Global Meteoric Water Line GMWL: δD = 8 ∗ δ18O + 10, Craig, 1961) in precipitations are given in Table 1. Precipitations show quite large isotopic fluctuations, in the range from −10.11‰ to −2.01‰ and from −64.15‰ to −11.99‰ for δ18O and δD, respectively. The volume-weighted average annual isotopic composition of rain is: 2014: δ18O = −7.31 ± 0.69‰, δD = −45.73 ± 4.50‰,

Oxygen and hydrogen isotopic data of precipitation and the LMWL

The local meteoric water line (LMWL) is an important reference line for the quantitative understanding of hydrologic systems that are fed by meteoric water, as in the case of Baccatoio catchment response. In the present study, different regression techniques have been applied to the oxygen and hydrogen isotope composition of rain, including ordinary least squares regression (OLSR), reduced major axis regression (RMA; IAEA, 1992), major axis least squares (MA) and precipitation weighted

Conclusions

The karst aquifers in the Apuan Alps host a large portion of the freshwater reservoirs which are strategic for regional water availability. The Baccatoio stream catchment, in the southern sector of the Apuan Alps chain, is characterized by carbonate-hosted mineralizations that were extensively mined in the past. The mining practice promotes the pervasive flow of waters through the amount of pyrite that remained unmined in the ore-bodies, providing the conditions for pyrite oxidation and the

Acknowledgements

Critical comments and recommendations from two anonymous reviewers improved an early version of the MS and were greatly appreciated. M. D'Orazio is acknowledged for helpul discussions. E. Ferrari and S. Trifirò assisted throughout the study.

References (51)

  • D.K. Nordstrom

    Hydrogeochemical processes governing the origin, transport and fate of major and trace elements from mine wastes and mineralized rocks to surface waters

    Appl. Geochem.

    (2011)
  • D.K. Nordstrom et al.

    Hydrogeochemistry and microbiology of mine drainage: an update

    Appl. Geochem.

    (2015)
  • L.A. Schaider et al.

    Sources and fates of heavy metals in a mining-impacted stream: Temporal variability and the role of iron oxides

    Sci. Total Environ.

    (2014)
  • J. Sun et al.

    Hydrogen and oxygen isotopic composition of karst waters with and without acid mine drainage: Impacts at a SW China coalfield

    Sci. Total Environ.

    (2014)
  • R. Cidu et al.

    Drainage at abandoned mine sites: natural attenuation of contaminants in different seasons

    Mine Water Environ.

    (2011)
  • I.D. Clark et al.

    Environmental Isotopes in Hydrogeology

    (1997)
  • H. Craig

    Isotopic variations in meteoric water

    Science

    (1961)
  • H. Craig et al.

    Deuterium and oxygen 18 variations in the ocean and the marine atmosphere

  • W. Dansgaard

    Stable isotopes in precipitation

    Tellus

    (1964)
  • M. D'Orazio et al.

    Thallium-rich pyrite ores from the Apuan Alps, Tuscany, Italy: constraints for their origin and environmental concern

    Mineral. Deposita

    (2017)
  • E.C. Dos Santos et al.

    Pyrite oxidation mechanism by oxygen in aqueous medium

    J. Phys. Chem.

    (2016)
  • M. Doveri et al.

    Stable water isotopes as fundamental tool in karst aquifer studies: some results from isotopic applications in the Apuan Alps carbonatic complex (NW Tuscany)

    Italian Journal of Engineering Geology and Environment

    (2013)
  • M. Doveri et al.

    Hydrodynamic and geochemical features of metamorphic carbonate aquifers and implications for water management: the Apuan Alps (NW Tuscany, Italy) case study

  • S. Fields

    The Earth's open wounds: abandoned and orphaned mines

    Environ. Health Perspect.

    (2003)
  • J.R. Gat

    Atmospheric water balance – the isotopic perspective

    Hydrol. Process.

    (2000)
  • Cited by (13)

    • Is the deuterium excess in precipitation a reliable tracer of moisture sources and water resources fate in the western Mediterranean? New insights from Apuan Alps (Italy)

      2022, Journal of Hydrology
      Citation Excerpt :

      The proximity to the sea and the peculiar orography of the chain, characterized by steep slopes, induce the lifting of humid air masses and their rapid adiabatic cooling. This results in high precipitation of about 2500 mm/year with peaks up to 3000 mm/year in the areas close to the major ridges (Doveri et al., 2019a; Doveri et al., 2019b and references therein). The average rainfall regime is characterized by two peaks of precipitation: the main one in autumn and the secondary in late winter/spring (Bartolini et al., 2018; Rapetti and Vittorini, 1994).

    • Meteorological and geographical control on stable isotopic signature of precipitation in a western Mediterranean area (Tuscany, Italy): Disentangling a complex signal

      2021, Journal of Hydrology
      Citation Excerpt :

      The samples are not equally distributed among the various stations: P7 and P2 are the most represented sites (21.1% and 15.8%, respectively), followed by P6 (11.5%); P1 and P10 had the lowest number of samples (2.6% and 2.5%, respectively) (Table 1). The database includes both published data (Baneschi et al., 2015; Doveri et al., 2019; IAEA/WMO, 2020; Longinelli and Selmo, 2003; Magi et al., 2019) and unpublished measurements performed within three different projects. The first project was carried out between 2007 and 2015 in north-western Tuscany by the Institute of Geosciences and Earth Resources (IGG-CNR) of Pisa as complementary project of the palaeoclimatological researches performed by the University of Pisa and the University of Melbourne.

    • Carbonate aquifers threatened by legacy mining: hydrodynamics, hydrochemistry, and water isotopes integrated approach for spring water management

      2021, Journal of Hydrology
      Citation Excerpt :

      The O–H isotope data of water samples are reported in Table 4. According to Doveri et al. (2019b), precipitation collected in the Baccatoio catchment at 660 m a.s.L. showed large isotopic fluctuations (Fig. 5a) from −8.98‰ to −3.41‰ and from −57.9‰ to −19.5‰ for δ18O and δ2H, respectively. The amount-weighted average isotopic composition of rain was −6.40‰ for δ18O and −37.8‰ for δ2H.

    View all citing articles on Scopus
    View full text