Inputs and fate of contaminants in a reservoir with circumneutral water affected by acid mine drainage

doi:10.1016/j.scitotenv.2020.143614

Science of The Total Environment

Volume 762, 25 March 2021, 143614

https://doi.org/10.1016/j.scitotenv.2020.143614 Get rights and content

Highlights

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Metal fluxes were obtained from relationships between flow rate and other variables
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The sources of acid mine drainage pollution into the reservoir were characterized
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Main factors controlling metal contents in the reservoir are dilution/precipitation
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However, Zn and Cd concentrations in the reservoir exceed environmental standards
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The results will allow the optimization of remediation efforts in the watershed

Abstract

The Olivargas River drains materials from the Iberian Pyrite Belt with a large number of abandoned sulphide mining complexes that produce highly contaminated acid mine drainages (AMD). The Olivargas River is regulated by a reservoir that receives these acid leachates through its three main tributaries. In this study, the chemical composition of the waters from the reservoir and the water courses in its watershed are investigated based on samples taken throughout a hydrological year. We calculated the contaminant load for Al, Cd, Co, Cu, Fe, Mn, Ni, Pb, Zn, SO₄ and other elements entering the reservoir by two methods, establishing the relations of the dissolved element concentrations with 1) the water flow and 2) the specific conductance. The most extreme conditions were found in the tributary Los Peces Creek, with a mean pH value of 2.8 and concentrations of up to 736 mg/L of Zn and 291 mg/L of Al, making it the main source of metals in the reservoir (up to 65 t/year of Zn). Given that the volume of acid mine water pouring into the reservoir is relatively low, the water pH in the reservoir remains neutral. Under these conditions, most of the mine-derived metals (especially Al and Fe) form precipitates that accumulate in the bottom sediments, while dissolved concentrations are low (0.2 mg/L of Al and <0.1 mg/L of Fe). However, some potentially toxic elements, such as Zn and Cd, remain dissolved, exceeding the limiting concentrations set by environmental legislation. These results are of interest to understand the behaviour of trace elements in other reservoirs affected by AMD and to study the effectiveness of possible remediation measures.

Graphical abstract

Introduction

Contamination of the natural environment by trace elements poses a serious global environmental problem for aquatic systems (Carman et al., 2007; Chon et al., 2010; Palma et al., 2015; Lopes-Rocha et al., 2017). One of the most important sources of trace elements in the environment is acid mine drainage (AMD), generated by the oxidation of pyrite and other sulphides in contact with the atmosphere (Nordstrom et al., 2015; Skousen et al., 2019). AMD is characterized by a low pH and high content of sulphates, iron and other metals and metalloids (Nordstrom et al., 2015).

The Odiel River drains materials from the Iberian Pyrite Belt, one of the most important metallogenic sulphide provinces worldwide, where mining dates back to the Third Millennium B.C. (Nocete et al., 2005). The intensive mining of massive sulphide ore bodies has resulted in the generation of sulphide-rich wastes, affecting most of the watercourses of the Odiel River (Sánchez España et al., 2005; Sarmiento et al., 2009a). The Odiel, together with the adjacent Tinto River, constitutes an extreme case of contamination by AMD because of the numerous sulphide deposits that have been intensively mined, together with the low neutralization capacity of the Iberian Pyrite Belt materials. The main water bodies of the basin are the Olivargas Reservoir (with a capacity of 28 million m³) and the Sancho Reservoir (58 million m³). The Sancho Reservoir has a pH close to 3.5 and high concentrations of toxic elements (Sarmiento et al., 2009b; Torres et al., 2013; Santisteban et al., 2014; Cánovas et al., 2016). In contrast, the waters of the Olivargas Reservoir are of neutral pH despite receiving acidic waters. The studies carried out on this reservoir have mainly focused on analysing the concentration of metals in the bottom sediments (Sarmiento et al., 2009b; Torres et al., 2014). To increase the water resources available in the area, mainly for irrigation, the Spanish Hydrological Plans foresee two new reservoirs in the Odiel River: Alcolea (246 million m³), which is currently being built, and La Coronada (800 million m³). The water quality of these reservoirs is thus a cause of concern due to the acidity and high concentration of metals from the Odiel River and its tributaries (Olías et al., 2011).

Worldwide, there are numerous examples of lakes and mine pits affected by AMD, but relatively few are related to large reservoirs. Exceptions include the Spring Creek Reservoir (capacity of 7.2 million m³) and Keswick Reservoir (capacity of 29.3 million m³) on the Sacramento River. These reservoirs receive acid mine waters from the Iron Mountain Superfund Site (California, EEUU), where the acidic waters of the mines are neutralized when they mix with neutral pH water, producing precipitates of metals that accumulate in the sediment (Nordstrom et al., 1999). Igarashi and Oyama (1999) reported a reservoir in central Japan (capacity of 1 million m³), where rocks excavated from a rhyolitic formation were dumped. Due to the oxidation of the pyrite contained in these rocks, the reservoir water became acidified, with a pH of 4.5 and an increase in the concentration of Al from 1 to 2 mg/L. Munk and Faure (2004) studied the Dillon Reservoir in Colorado (USA), with a capacity of 310 million m³, that receives acid leachates from abandoned mines. The pH of this reservoir remains near neutral, while trace elements accumulate in the sediments, and the concentration of contaminants in the water column is not high (25 μg/L for Zn and 1.5 μg/L for Ni).

When AMD acidic waters enter a reservoir with circumneutral pH, some toxic elements will precipitate/coprecipitate and be removed from the water column, accumulating in the sediments, while others show more conservative behaviour and remain dissolved. The main objectives of this study were 1) to assess the loads of trace elements that reach the Olivargas Reservoir coming from three abandoned sulphide mines and 2) to investigate how these elements behave in the reservoir.

Section snippets

Study zone

The Olivargas River has a total drainage basin of 182 km² (Fig. 1). It runs mainly north-south, and its drainage basin lies in a landscape containing numerous gorges with steep banks, as evidenced by its varying altitude, ranging from 93 to 913 m above sea level, with a mean of 364 m (Galván et al., 2016). Climatologically, it is located in a sub-humid Mediterranean climate with Atlantic influence, characterized by high intra- and inter-annual variability in rainfall, which produces an

Sampling and analytical methods

Several samplings were performed during the hydrological year 2009/10 to take into account the seasonal variations in the 3 main tributaries to the reservoir affected by AMD (Fig. 1). Current conditions at the reservoir and the tributaries have not changed since then, as seen in the periodic analyses carried out by the regional water authorities. The number of samples collected at each point ranged from 9 to 16. The lowest number corresponds to Herrerito Creek, which was totally dry during the

Flow rate data and analytical results

Regarding the water flow data, the Olivargas River provides 67% of the water that reaches the reservoir, while only 4% comes from Los Peces Creek and 3% from Herrerito Creek, which becomes completely dry in the summer. The rest (26%) comes from streams not affected by AMD that enter directly into the reservoir.

Table 1, Table 2, Table 3 summarise the statistics for the main physical and chemical parameters for the Olivargas River and Los Peces and Herrerito Creeks. Data for As and K were not

Conclusions

The three watercourses that drain into the Olivargas Reservoir are contaminated by AMD from abandoned mines. The concentrations of contaminating elements in the Olivargas River, which is the main water contribution to the reservoir, are much lower than in the other two streams, which have acidic pH values throughout the year and high concentrations of contaminants (up to 291 mg/L of Al and 150 mg/L of Fe). The concentrations of contaminants in the rivers showed a wide range of variation due to

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

This work was financed by the Spanish Ministry of Science and Innovation through the project EMPATIA (Ref. CGL2013-48460-C2-1-R). We are grateful to three anonymous reviewers for their valuable comments which allowed us to improve the original manuscript.

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Inputs and fate of contaminants in a reservoir with circumneutral water affected by acid mine drainage

Highlights

Abstract

Graphical abstract

Introduction

Section snippets

Study zone

Sampling and analytical methods

Flow rate data and analytical results

Conclusions

Declaration of competing interest

Acknowledgements

Sci. Total Environ.

Sci. Total Environ.

Appl. Geochem.

J. Hydrol.

J. Hydrol.

J. Geochem. Explor.

Sci. Total Environ.

Appl. Geochem.

Environ. Int.

J. Anthropol. Archaeol.

Geochim. Cosmochim. Acta

Appl. Geochem.

Appl. Geochem.

Catena

J. Hydrol.

Appl. Geochem.

Appl. Geochem.