Comparison of UAS and Sentinel-2 Multispectral Imagery for Water Quality Monitoring: A Case Study for Acid Mine Drainage Affected Areas (SW Spain)

Uncrewed Aerial Systems (UAS) and satellites are used for monitoring and assessing the quality of surface waters. Combining both sensors in a joint tool may scale local water quality retrieval models to regional and global scales by translating UAS-based models to satellite imagery. The main objective of this study is to examine whether Sentinel-2 (S2) data can complement UAS data, specifically from the MicaSense RedEdge MX-Dual sensor, for inland water quality monitoring in mining environments affected by acid mine drainage (AMD). For this purpose, a comparison between UAS reflectance maps and atmospherically corrected S2 imagery was performed. S2 data were processed with Case 2 Regional Coast Colour (C2RCC) and Case 2 Regional Coast Colour for Complex waters (C2X) atmospheric correction (AC) processors. The correlation between the UAS data and the atmospherically corrected S2 data was evaluated on a band-by-band and a pixel-by-pixel basis, and the compatibility of the spectral data was analyzed through statistical methods. The results showed C2RCC and C2X performed better for acidic greenish-blue and non-acidic greenish-brown water bodies concerning the UAS data than for acidic dark reddish-brown waters. However, significant differences in reflectance between the UAS sensor and both S2 AC processors have been detected. The poor agreement between sensors should be considered when combining data from both instruments since these could have further consequences in developing multi-scale modelsThis study was supported in part by the Erasmus Mundus Joint Master Degree (EMJMD) in Water and Coastal Management (WACOMA) with the contribution of the Erasmus+ Programme of the European Union. This work was also supported by Plan Andaluz de Investigación RNM 166 Environmental radioactivity research group (LB) and partially by the FEDER UHU2020-21 Project. UAS equipment from University of Cádiz Drone Service was supported by MINECO infrastructure projects (EQC2018-00446-P and UNCA-2013-1969). MDB thanks the Spanish Ministry of Science and Innovation for the Postdoctoral Fellowship granted under application reference IJC2018-035056-I. This research was also funded by the Spanish Ministry of Science and Innovation, the Spanish State Research Agency, the European Regional Development Fund MCIN/AEI/10.13039/501100011033 (Sen2Coast Project; RTI 2018-098784-J-I00), and the Consejería de Transformación Económica, Industria, Conocimiento y Universidades from Andalusian Government through the Andalusian FEDER operational program 2014-2020 (A1123060E0_PYC20 RE 032 UHU) and the call 2020 for collaborative interest projects in the field of the Innovation Ecosystems of the International Excellence Centers). We thank to Tharsis Mining & Metallurgy for allowing us to collect the samples in the abandoned mining areas that belong to the company since 2018. The authors also gratefully acknowledge the support of the Guest Editor, the Assistant Editor and the three anonymous reviewers for their comments and positive criticisms, which notably improved the quality of the original pape

Metal partitioning and speciation in a mining-impacted estuary by traditional and passive sampling methods

This study deals with the metal partitioning and bioavailability of metal/loids in the estuary Ria of Huelva (SW Spain) which is strongly affected by historical mining and industrial activities. To address this issue, traditional (i.e., grab samples) and passive sampling (i.e., diffusive gradient in thin films, DGTs) was carried out in the outer part of the estuary during different tidal cycles in order to determine the dissolved and particulate metal/loid concentrations. The dissolved concentrations exceeded, by several orders of magnitude, those reported in other estuaries worldwide that are affected by anthropogenic activities. A spatial pattern was observed in the metal distribution; a decrease seaward was recorded for some of the elements associated with mining (e.g., Cu, Zn, and Cd), the opposite tendency is observed for others associated with harbor emissions (e.g., Sn, Ni, or Pb). A different metal/loid partitioning pattern was also observed; Fe, and to a lesser extent Pb and Sn, were chiefly found in the particulate matter, while the rest of the elements were mainly found in the dissolved form. The bioavailability of the metal/loids was studied by speciation using both geochemical modeling and DGTs; while concentrations in DGTs supported metal/loid speciation for Zn, Cd, Mn, Co, As, and Sb according to their affinity to form strong or weak complexes, some discrepancies were observed for other elements such as Cu, V, Fe, and Pb, which are prone to forming strong complexes. The main reason behind the unexpectedly high Fe and Pb DGTs concentrations may be associated with their presence in the colloidal particles passing through the DGT. There was a strong positive correlation between dissolved and DGT concentrations for Cd and Mn, and to a lesser extent for Fe and Cu, highlighting the direct relationship between the concentrations in water and availability to living organisms in the estuary.This work was supported by the Spanish Ministry of Economy and Competitiveness through the research project CAPOTE (CGL2017-86050-R) and by the CEIMAR Excellence Research Campus through the project CEIMAR-CEIJ-005. M.D. Basallote thanks the Spanish Ministry of Science and Innovation for the Postdoctoral Fellowship granted under application reference IJC2018-035056-I. The authors would also like to thank to the Co Editor-in-Chief Dr. Damiá Barceló and two anonymous reviewers for the support and comments that notably improved the quality of the original paper.Departamento de Geologí

Valorization of wastes from the fertilizer industry: current status and future trends.

Based on a systematic literature search (Number of initial publications = 1571; Number of in-depth publications = 97), this paper reviews the different potential applications for phosphogypsum, the main unwanted by-product of the fertilizer industry, providing some insights into the new valorization routes, and critically describing the advantages and drawbacks of each one. Industry and policy makers face the challenge to manage the increasing loads of phosphogypsum generated worldwide, especially on reasons of cost, safety and environmental impact. The recycling of this material could be an environmentally friendly, safe and cost-effective solution for this quandary. Different phosphogypsum valorization routes were developed in the last years in agriculture, building, and environmental and energy sectors, and these topics are described along this review. The first barrier to be overcome is the shift of paradigm needed to consider phosphogypsum not as a waste but as a raw material and the harmonization of classification rules of this material worldwide. Another issue to be faced is the heterogeneity of phosphogypsum reported worldwide, which could make unfeasible certain applications due to chemical and physical differences. On the one hand, while technical and economic constraints are increasingly lifted, many applications of phosphogypsum valorization consume low amounts of waste, and thus cannot satisfy the purpose of mass consumption. In addition, the different valorization routes may cause a secondary pollution which must be evaluated and compared with that caused by traditional disposal options. In order to provide a solution to this waste management, a better social and political awareness is needed. Economic and technical constraints must be lifted by a higher economic investment on research and development. However, site by site studies and assessment of secondary pollution using suitable tools (e.g. life cycle analysis) must be performed in order to assure the success of each valorization route.This work was supported by the Regional Government of Andalusia through the research project FOREVER (P12-RNM-2260) and the Spanish Ministry of Economic and Competitiveness through the research projects ERAMIN (PCIN2015-242-256), and SCYRE (CGL2016-78783-C2-1-R). The authors are also very grateful to the funding support for the Committee of Experts on “The environmental diagnosis and the proposal of measures of restoration of the phosphogypsum stacks of Huelva”, appointed by the City Hall of Huelva. MD Basallote also thanks the Spanish Ministry of Economy and Competitiveness for the Postdoctoral Fellowship granted under application references FJCI-2015-24765. We would also thank to Cecília Maria Villas Bôas de Almeida (co-Editor in chief) and three anonymous reviewers that notably improved the quality of the original manuscript.Departamento de Geologí

Metal bioaccumulation in spontaneously grown aquatic macrophytes in Fe-rich substrates of a passive treatment plant for acid mine drainage

Some plants may thrive in polluted environments, accumulating high concentrations of metal/loids in their organs. This study investigates for the first time the bioaccumulation and translocation of metal/loids in Typha domingensis spontaneously grown in extremely Fe-rich substrates (38–44% of Fe2O3) from different components of an acid mine drainage disperse alkaline substrate passive treatment. Most metal/loids were predominantly accumulated in the roots over the aerial parts of the plant, with concentrations of 0.66–9.5% of Fe, 0.02%–0.18% of Al, 55–2589 mg kg-1 of Mg, 51–116 mg kg-1 of Zn, 17–173 mg kg-1 of Cu, and 5.2–50 mg kg-1 of Pb. Bioconcentration factors were mostly below 1 for metal/loids in the studied aneas (e.g. 0.03–0.47 for Cu, 0.10–0.73 for Zn, 0.04–0.28 for As, 0.07–0.55 for Pb, 0.27–055 for Cd, 0.24–0.80 for Ni), which evidences that T. domingensis behaves as an excluder species in these substrates. Translocation factors were below 1 for most elements (e.g. 0.01–0.42 for As, 0.06–0.50 for Pb, 0.24–0.65 for Cd, and 0.10–0.56 for Sb), except for Mn, Ni and in some cases for Tl, Cu and Zn, which indicates limited transfer of metals between plant tissues. Mineralogical and geochemical substrate properties are pointed out as the main factors responsible for the lower bioconcentration and translocation of potentially toxic elements. In addition, the oxidizing conditions existent in the pore water-root system may also limit the mobility of metals from Fe oxides and hydroxysulfates, the main component of the substrate. The formation of a Fe plaque inside the roots may also limit the transfer of metals to the aerial parts. The spontaneous occurrence of T. domingensis in the substrates of the acid mine drainage passive treatments is an environmental indicator of the efficiency of the system and could be used as a complementary polishing step, given the strong tolerance of this plants to high concentrations of metal/loids.Funding for open access charge: Universidad de Huelva / CBUA M.D. Basallote thanks the Spanish Ministry of Science and Innovation for the Postdoctoral Fellowship granted under application reference IJC2018-035056-I. C.R C´anovas thanks the Spanish Ministry of Science and Innovation for the Postdoctoral Fellowship granted under application reference RYC2019-027949-I

Thallium in environmental compartments affected by acid mine drainage (AMD) from the Iberian Pyrite Belt (IPB): From rocks to the ocean

This works investigates the origin, behavior and fate of Tl in acid mine drainage (AMD) affected areas at catchment scale, following the path from rocks to the ocean. To address this issue, comprehensive data set of Tl in rocks, waters, secondary minerals, plants and other environmental compartments is presented, using the Iberian Pyrite Belt (SW Spain) as representative example. The content of Tl in host rocks (mean of 0.51 mg/kg) exhibits moderate positive correlations with elements such as K and Rb, whereas no correlations were observed in sulfides (27 mg/kg) between Tl, Fe and other metal/loids commonly found in these minerals, such as As, Pb, Cd, Cu or Zn. During sulfide oxidation processes, Tl is mobilized from sulfides, as evidenced by the depletion of Tl in gossans (1.8 mg/kg), and host rock minerals, leading to a Tl enrichment in AMD leachates (mean of 242 μg/L), with concentrations of up to 8.3 mg/L, several orders of magnitude higher than those reported in natural waters. The precipitation of secondary minerals, with large surface areas, may be a sink for Tl, especially in jarosite minerals (8.4 mg/kg). Thallium can be also removed during the treatment of AMD in alkaline passive treatment systems due mainly to sorption processes onto Fe and Al secondary minerals (i.e., schwertmannite and basaluminite, respectively). Mean Tl contents of 13 mg/kg have been observed in wastes dumped in abandoned mines of the IPB, mainly spoil heaps, slags, roasted pyrite, heap leaching wastes and tailings. However, there is no clear relationship between Tl content and the type of mining wastes. These wastes can suffer weathering, leading to an enrichment of Tl in soils. Previous studies reported that <25% of total Tl is easily extractable, being mainly adsorbed to crystalline Fe oxides in acidic soils and Al oxides in neutral-alkaline soils. Despite this, Tl may be translocated by plants. The translocation of Tl in plants of the IPB has not been properly addressed, however previous studies in other areas showed a low phytoavailability of Tl compared to Cd and Zn, although Tl translocation appears to be strongly controlled by plant species or by differences in Tl speciation. The weathering of rocks, mine wastes and soils may lead to the release of notable amounts of both dissolved and particulate Tl to the hydrosphere. In acidic conditions, Tl seems to be mainly transported by the dissolved phase in AMD-affected streams and rivers, with <15% being transported by the particulate matter. This latter Tl transport may be associated to its incorporation into diatoms and Fe minerals such as jarosite after replacement of Tl+ by H+ in their structure. Subsequent release by desorption processes from jarosite and diatoms in acidic conditions can occur. This process has also been observed in estuaries affected by AMD, thus, Tl transported by jarosite minerals in the particulate matter and diatoms are released back to the estuarine waters across the salinity gradient due to the increasing proportion of unreactive TlCl0 and K+ ions, which compete for adsorption sites in jarosite with Tl+. Thus, enhanced transport of Tl to the oceans is observed in AMD-affected systems.This work was supported by the Spanish Ministry of Economy and Competitiveness under the research project TRAMPA (MINECO; PID2020-119196RB-C21) and the Andalusian Regional Government under the AIHODIEL project (PYC20 RE 032 UHU) within the FEDER program. C.R Canovas thanks the Spanish Ministry of Science and Innovation for the Postdoctoral Fellowship granted under application reference RYC2019-027949-I. M.D. Basallote thanks the Spanish Ministry of Science and Innovation for the Postdoctoral Fellowship granted under application reference IJC2018-035056-I. Funding for open access charge: Universidad de Huelva /CBU

Stream-pit lake interactions in an abandoned mining area affected by acid drainage

Opencast mining of sulfide ore deposits may lead to the formation of anthropogenic acidic lakes with highly polluted waters. In these systems, it is crucial to understand the hydrological connections between surface and groundwater and their contribution to the pollutant load delivered to the downgradient streams. This study characterizes the interactions between surface and groundwater in an acidic pit lake using different geochemical tracers (i.e., REE and other trace metals). The San Telmo pit lake, located in one of the most pollutant sources of the Iberian Pyrite Belt (IPB), can be considered as a flow-through pit lake except during dry periods, when it behaves as a terminal lake due to lower inputs by surface waters and higher outputs by evaporation. Results based on geochemical tracers indicate that the main inputs to the pit lake come from surface waters, with minor groundwater inputs rich in As, Cr, Cu, Fe and Pb. The contaminant load released from the mining area is very high (e.g., median values of 520 kg/day of Fe and 38 kg/day of Zn), causing the degradation of the fluvial network downstream. Most of released pollutants come from waste dumps located at the W of the mining zone (~50–70% of Al, Cd, Mg, Mn, Ni, SO4 and Zn and > 70% for Cu, Cr, Fe and, V), while the contribution of the water coming out the pit lake and other dumps is much lower. Thus, remediation efforts to improve the area and fluvial courses downstream must focus on the W waste dumps.This work was supported by the Spanish Ministry of Economic and Competitiveness through the projects CGL2016-78783-C2-1-R (SCYRE) and by H2020 European Institute of Innovation and Technology (EIT RawMaterials) through the projects Modular Recovery Process Services for Hydrometallurgy and Water Treatment (MORECOVERY). C.R Cánovas thanks the Spanish Ministry of Science and Innovation for the Postdoctoral Fellowship granted under application reference RYC2019-027949-I. F. Macias was funded by the R&D FEDER Andalucía 2014–2020 call through the project RENOVAME (FEDER;UHU-1255729).The commentsand helpful criticisms of two anonymous reviewers and the support of Dr. Jose Virgilio Cruz (Associate Editor) have considerably improved the original manuscript and are also gratefully acknowledged. Funding for open access charge: Universidad de Huelva / CBUA

Metal(loid) release from sulfide-rich wastes to the environment: The case of the Iberian Pyrite Belt (SW Spain)

Sulfide-mining wastes may lead to severe environmental and human health risks, especially challenging in abandoned mines without environmental regulation. This work is aimed at discussing the environmental problems associated with this type of wastes, the risks posed by metal(loid) exposure to living organisms, as well as the measures available to mitigate such risks, taking the case of the Iberian Pyrite Belt (SW Iberian Peninsula), as an example, worldwide. The release of metal(loid)s from these wastes upon weathering is strongly controlled by mineral assemblage, processing technique, grain size distribution, and occurrence of highly reactive secondary minerals. Exposure to these wastes may pose a severe risk for humans and animals, and thus, remediation measures must be adopted in abandoned mines. Among these measures, recovery of valuable metals from sulfide wastes could be a promising environmentally friendly solution; however, grade and mineralogical siting of valuable metals, as well as selective recovery methods, must be site-by-site investigated.This work was supported by the Spanish Ministry of Economy and Competitiveness through the research projects SCYRE (CGL2016-78783- C2-1-R) and CAPOTE (CGL2017-86050-R). C.R Ca ́novas and M.D. Basallote thank the Spanish Ministry of Science and Innovation for the Postdoctoral Fellowships granted under application references RYC2019- 027949-I and IJC2018-035056-I, respectively. F. Macı ́as was funded by the R&D FEDER Andalucı ́a 2014e2020 call through the project RENOVAME (FEDER; UHU-1255729). The authors would like to thank to the Guest Editor Dr. Georgios Bartzas and two anonymous reviewers for their helpful comments that notably improved the quality of the original manuscript.Funding for open access charge: Universidad de Huelva / CBU

Hydrogeochemical model of an acid mine drainage affected watershed (Odiel River Basin): current state and possible remediations actions

El estado actual de la cuenca del río Odiel, gravemente conta-minada por drenaje ácido de mina (AMD), requiere del desarrollo de un modelo hidrogeoquímico predictivo que refleje las condiciones hidroquímicas actuales a lo largo de la cuenca. El modelo permite evaluar de forma individual y conjunta los numerosos cursos fluvia-les que conforman la cuenca, determinando el grado de contamina-ción de cada uno, el aporte de acidez y metales de los lixiviados y los resultados de su mezcla en las confluencias. Ante las incertidumbres de la futura construcción del embalse de Alcolea y las presiones que ejerce la Directiva Marco del Agua, el modelo puede ser muy útil para simular actuaciones de remediación en la cuenca y cómo éstas afectarían a la calidad del agua. De este modo, se han modelizado reducciones del 50% y 100% de la carga contaminante que las mi-nas de Riotinto, Tharsis y San Telmo aportan a la cuenca. Se estima que las concentraciones Al, Fe y SO4 disminuirían notablemente en la parte baja del Odiel donde está planificada la obra de la futura presaThe current situation of the Odiel River basin, severely polluted by acid mine drainage (AMD), calls for the design of a hydrogeo-chemical predictive model which matches the actual hydrochemical conditions along the watershed. The model allows an individual or combined evaluation of the different river courses within the basin, assessing the pollution grade of each one, the acid and metal load contribution of the leachates and the results of their mixing within the watershed confluences. Given the uncertainties associated to the future construction of the Alcolea reservoir and the pressures exerted by the European Water Framework Directive, the model could be a useful tool for simulating remediation actions in the basin and eva-luate their impact on the water quality. Therefore, reduction of 50% and 100% of the pollutant load delivered by the Riotinto, Tharsis and San Telmo mines has been modeled. It is estimated that the concen-tration of Al, Fe, SO4 would decrease significantly in the lower part of the Odiel basin, where the future dam will be locate

Effects of estuarine water mixing on the mobility of trace elements in acid mine drainage leachates

This work was supported by the Spanish Ministry of Science and Innovation under the research project TRAMPA (PID2020-119196RB- C21). C.R. C´anovas, A. Parviainen and M.D. Basallote also acknowledge the Spanish Ministry of Science and Innovation for the Postdoctoral Fellowships granted under application references RYC2019-027949-I, IJCI-2016-27412 and IJC2018-035056-I, respectively. We would also like to thank Dr. Geoff MacFarlane for the editorial handling and two anonymous reviewers for the support and comments that significantly improved the quality of the original paper. Funding for open access charge: Universidad de Huelva/CBUA.This research reports the effects of pH increase on contaminant mobility in acid mine drainage from the Iberian Pyrite Belt by seawater mixing in the laboratory, simulating the processes occurring in the Estuary of Huelva (SW Iberian Peninsula). Concentrations of Al, Fe, As, Cu and REY in mixing solutions significantly decreased with increasing pH. Schwertmannite precipitation at pH 2.5–4.0 led to the total removal of Fe(III) and As. Subsequently, iron-depleted solutions began to be controlled by precipitation of basaluminite at pH 4.5–6.0, which acted as a sink for Al, Cu and REY. Nevertheless, as the pH rises, schwertmannite becomes unstable and releases back to solution the previously retained As. Moreover, other elements (S, Zn, Cd, Ni and Co) behaved conservatively in mixing solutions with no participation in precipitation processes. Some toxic elements finally end up to the Atlantic Ocean contributing to the total pollutant loads and environmentally threatening the coastal areas

Metal mobility and bioaccessibility from cyanide leaching heaps in a historical mine site

Unlike acidic sulfide mine wastes, where metal/loid mobility and bioaccessibility has been widely studied, less attention has been paid to alkaline cyanide heap leaching wastes. Thus, the main goal of this study is to evaluate the mobility and bioaccessibility of metal/loids in Fe-rich (up to 55%) mine wastes resulting from historical cyanide leaching activities. Wastes are mainly composed of oxides/oxyhydroxides (i.e. goethite and hematite), oxyhydroxisulfates (i.e. jarosite), sulfates (i.e., gypsum, evaporitic sulfate salts), carbonates (i.e., calcite, siderite) and quartz, with noticeable concentrations of metal/loids (e.g., 1453–6943 mg/kg of As, 5216–15,672 mg/kg; of Pb, 308–1094 mg/kg of Sb, 181–1174 mg/kg of Cu, or 97–1517 mg/kg of Zn). The wastes displayed a high reactivity upon rainfall contact associated to the dissolution of secondary minerals such as carbonates, gypsum, and other sulfates, exceeding the threshold values for hazardous wastes in some heap levels for Se, Cu, Zn, As, and sulfate leading to potential significant risks for aquatic life. High concentrations of Fe, Pb, and Al were released during the simulation of digestive ingestion of waste particles, with average values of 4825 mg/kg of Fe, 1672 mg/kg of Pb, and 807 mg/kg of Al. Mineralogy may control the mobility and bioaccessibility of metal/loids under rainfall events. However, in the case of the bioaccessible fractions different associations may be observed: i) the dissolution of gypsum, jarosite and hematite would mainly release Fe, As, Pb, Cu, Se, Sb and Tl; ii) the dissolution of an un-identified mineral (e.g., aluminosilicate or Mn oxide) would lead to the release of Ni, Co, Al and Mn and iii) the acid attack of silicate materials and goethite would enhance the bioaccessibility of V and Cr. This study highlights the hazardousness of wastes from cyanide heap leaching, and the need to adopt restoration measures in historical mine sites.This work was supported by the Spanish Ministry of Economic and Competitiveness through the projects TRAMPA (PID2020–119196RBC21) and by H2020 European Institute of Innovation and Technology (EIT RawMaterials) through the project Modular recovery process services for hydrometallurgy and water treatment (MORECOVERY). This work was partially supported by FCT (Portugal) through contract UID/ Multi/04349/2019. C.R C´anovas thanks the Spanish Ministry of Science and Innovation for the Postdoctoral Fellowship granted under application reference RYC2019–027949-I. M.D. Basallote thanks the Spanish Ministry of Science and Innovation for the Postdoctoral Fellowship granted under application reference IJC 2018–035056-I. The authors would also like to thank to Prof. Edward D. Burton, Ph.D (Editor) and three anonymous reviewers for the support and comments that notably improved the quality of the original paper