Sulphur isotopes as tracers of the influence of a coal-fired power plant on a Scots pine forest in Catalonia (NE Spain)

Stable sulphur isotopes and major ionic composition were analysed in precipitation and throughfall samples from a Scots pine (Pinus sylvestris, L.) forest near the Cercs coal-fired power plant (Catalonia, NE Spain). The purpose of the study was to determine the main sources of sulphur deposition on this pine forest. Sulphur isotope measurements from the SO2 power plant stack emissions were used to identify the isotopic signature of this source. Net throughfall fluxes of sulphur (26.1 kg S ha 1 yr−1) and nitrogen (16.3 kg N ha−1 yr−1) were higher 5-25 times higher for S and 5-15 times for N at this site than in other forests in Catalonia. Sulphur isotope analysis confirmed that the net throughfall fluxes of sulphur were mostly due to the dry deposition of the SO2 power plant emissions onto the pine canopies. Two potential atmospheric end-members were distinguished: regional background rainwater (δ34S=+7.2 ) and power plant emissions (δ34S=−2.8 ). By applying a two-component sulphur isotope mixing model, we found that during periods of low power plant activity (⩽10 emission h day−1), 62% of the throughfall sulphate could be attributed to the power plant emissions. At higher activity periods (⩾14 emission h day−1), this contribution rose to 73%. Although power plant contribution to bulk deposition was lower in both cases (34% and 45%), the possible influence of sulphate coming with long-range transport events from the polluted areas in the Mediterranean basin (δ34S≈0 ) was not discarded

Compound-specific carbon isotope analysis of volatile organic compounds in water using solid-phase microextraction.

The compound-specific isotope analysis technique in conjunction with solid-phase microextraction using a Carboxen-polydimethylsiloxane fiber was tested and implemented for isotopes analysis of organic compounds aiming for environmental application in contaminated groundwater. δ13C values of several chlorinated methanes and ethenes, toluene and chlorobenzene were determined using a gas chromatograph coupled to an isotope ratio mass spectrometer through a combustion interface. Direct and headspace solid-phase microextraction (D-SPME, HS-SPME) methods were tested in order to determine the optimum conditions to obtain reproducible δ13C values at very low concentration (ug/L range) and, to elucidate the carbon isotopic effects associated with the competitive extraction. For D-SPME higher accuracy and precision of δ13C results were obtained with no salted aqueous standards. Despite that the δ13C of those compounds analyzed with both methods showed similar precision (< 0.5 ¿) and accuracy, the highest sensitivity was reached with HS-SPME. Furthermore, the δ13C values of cis-1,2-dichloroethylene, chorinated methanes and aromatic compounds obtained using HS-SPME showed measurable deviations respect to the isotopic composition of pure phase compounds, however, these deviations are constant according to the analytical uncertainties, indicating that they are not affected by competitive extraction and, they could be corrected using standard correction technique based on internal calibrated standards

Groundwater-Gossan interaction and the genesis of the secondarysiderite rock at Las Cruces ore deposit (SW Spain)

Part of the Las Cruces secondary siderite deposit has sparked an interest in the scientific communitybecause of its unique mineralogy. The original gossan formed by goethite and hematite has been replacedby a siderite and galena rock. We postulate that this rock can be formed by the interaction of iron oxideswith groundwater similar in composition to that of the present day. Hydrochemical and isotopic charac-teristics of groundwater support this hypothesis. The negative Eh values, the existence of H2S and the ten-dency toward high sulfate isotope values indicate a reducing groundwater condition. The highammonium, boron and iodine concentrations as well as the low d13C values of dissolved inorganic carbon(DIC) confirm the organic matter oxidation. The reductive dissolution of Pb-bearing goethite at theexpense of Dissolved Organic Carbon (DOC) leads to the precipitation of Fe-sulfides, galena and siderite.The formation of siderite from this process is confirmed by the low amount of dissolved Fe in groundwa-ter (<10 ppb), its low d13C values and thermodynamic calculations. One-dimensional reactive transportmodeling demonstrated that the present-day groundwater flux and chemical composition could formthe siderite rock in less than 1 Ma with no external supply of reactants. Sensitivity analyses revealed thatthe time of formation depends on the structure of the groundwater flux (spaced fractures or pervasive),the flow rate and especially the DOC concentration. In fact, calculations with the highest DOC measuredconcentration resulted in a mineral zonation: one zone formed by Fe-sulfides and other zone formed bysiderite, with galena in both zones. Reactive transport calculations and the similarity of its high d34S val-ues indicate that the sulfur of galena came from the current groundwater. Reactive transport calculationsand the similarity of its high d34S values indicate that the sulfur of galena came from the currentgroundwater

Use of environmental isotopes (13C, 15N, and 18O) for evaluating sources and fate of nitrate and tetrachloroethene in an alluvial aquifer

Environmental isotopes and geochemical parameters were used to evaluate the sources and fate of nitrate (NO3-) and tetrachloroethene (PCE) in an alluvial contaminated aquifer. Isotope data and redox parameters data indicated that biodegradation does not play any role in the attenuation of these compounds along the groundwater flow system. Furthermore, nitrate isotopes and concentration data allowed the authors to distinguish two nitrate inputs and relate them to their possible sources. The primary source originates from septic waste and the secondary source is associated with nitrogenous fertilizer application. Regarding PCE, the δ13C values do not change for almost 1000 m along the groundwater flow system despite large decreases of PCE concentration, thus confirming that physical processes do not alter the isotopic composition of organic compounds; this finding has a significant implication for the use of carbon isotope ratios for fingerprinting sources of PCE in VOC plumes. This study has shown that combined use of environmental isotopes and geochemical parameters is an efficient approach for water resource management studies in sites polluted by various types of contaminants

Evaluating the potential use of a dairy industry residue to induce denitrification in polluted water bodies: a flow-through experiment

Improving the effectiveness and economics of strategies to remediate groundwater nitrate pollution is a matter of concern. In this context, the addition of whey into aquifers could provide a feasible solution to attenuate nitrate contamination by inducing heterotrophic denitrification, while recycling an industry residue. Before its application, the efficacy of the treatment must be studied at laboratory-scale to optimize the application strategy in order to avoid the generation of harmful intermediate compounds. To do this, a flow-through denitrification experiment using whey as organic C source was performed, and different C/N ratios and injection periodicities were tested. The collected samples were analyzed to determine the chemical and isotopic composition of N and C compounds. The results proved that whey could promote denitrification. Nitrate was completely removed when using either a 3.0 or 2.0 C/N ratio. However, daily injection with C/N ratios from 1.25 to 1.5 seemed advantageous, since this strategy decreased nitrate concentration to values below the threshold for water consumption while avoiding nitrite accumulation and whey release with the outflow. The isotopic results confirmed that nitrate attenuation was due to denitrification and that the production of DIC was related to bacterial whey oxidation. Furthermore, the isotopic data suggested that when denitrification was not complete, the outflow could present a mix of denitrified and nondenitrified water. The calculated isotopic fractionation values (ε15NNO3/N2 and ε18ONO3/N2) might be applied in the future to quantify the efficiency of the bioremediation treatments by whey application at field-scale

Tracing the role of endogenous carbon in denitrification using wine industry by-product as an external electron donor: coupling isotopic tools with mathematical modeling

Nitrate removal through enhanced biological denitrification (EBD), consisting of the inoculation of an external electron donor, is a feasible solution for the recovery of groundwater quality. In this context, liquid waste from wine industries (wine industry by-products, WIB) may be feasible for use as a reactant to enhance heterotrophic denitrification. To address the feasibility of WIB as electron donor to promote denitrification, as well as to evaluate the role of biomass as a secondary organic C source, a flow-through experiment was carried out. Chemical and isotopic characterization was performed and coupled with mathematical modeling. Complete nitrate attenuation with no nitrite accumulation was successfully achieved after 10 days. Four different C/N molar ratios (7.0, 2.0, 1.0 and 0) were tested. Progressive decrease of the C/N ratio reduced the remaining C in the outflow and favored biomass migration, producing significant changes in dispersivity in the reactor, which favored efficient nitrate degradation. The applied mathematical model described the general trends for nitrate, ethanol, dissolved organic carbon (DOC) and dissolved inorganic carbon (DIC) concentrations. This model shows how the biomass present in the system is degraded to dissolved organic C (DOCen) and becomes the main source of DOC for a C/N ratio between 1.0 and 0. The isotopic model developed for organic and inorganic carbon also describes the general trends of δ13C of ethanol, DOC and DIC in the outflow water. The study of the evolution of the isotopic fractionation of organic C using a Rayleigh distillation model shows the shift in the organic carbon source from the WIB to the biomass and is in agreement with the isotopic fractionation values used to calibrate the model. Isotopic fractionations (ε) of C-ethanol and C-DOCen were −1¿ and −5¿ (model) and −3.3¿ and −4.8¿ (Rayleigh), respectively. In addition, an inverse isotopic fractionation of +10¿ was observed for biomass degradation to DOCen. Overall, WIB can efficiently promote nitrate reduction in EBD treatments. The conceptual model of the organic C cycle and the developed mathematical model accurately described the chemical and isotopic transformations that occur during this induced denitrification

Denitrification of groundwater with pyrite and Thiobacillus denitrificans

Anaerobic batch and flow-through experiments were performed to confirm the role of pyrite as electron donor in bacterial denitrification and to look into the feasibility of pyrite-driven denitrification of nitrate- contaminated groundwater. Nitrate reduction was satisfactorily accomplished in experiments with pyrite as the sole electron donor, in presence of the autotrophic denitrifying bacterium Thiobacillus denitrificans and at nitrate concentrations comparable to those observed in contaminated groundwater. The experimental results corroborated field studies in which the reaction occurred in aquifers. Nitrate reduction rates and nitrate removal efficiencies were dependent on pyrite grain size, initial nitrate concentration, nitrate-loading rate and pH. The N and O isotopic enrichment factors (εN and εO) obtained experimentally for pyrite-driven nitrate reduction by T. denitrificans ranged from − 13.5¿ to − 15.0¿ and from − 19.0¿ to − 22.9¿, respectively. These values indicated the magnitude of the isotope fractionation that occurs in nitrate- contaminated aquifers dominated by autotrophic denitrification

FEM DE CONSULTORS! La geoquímica des d'un punt de vista pràctic

Es tracta d'un projecte de millora i innovació docent centrat en canviar la metodologia d'una part de les classes per a que l'estudiant assoleixi els coneixements d'una manera més eficaç i efectiva, reduint la seva sensació de sobrecàrrega de treball, sense passar per una reducció dels continguts de l'assignatura. Es proposa la resolució d'un cas concret, com faria en una consultoria del món professional real, combinant aprenentatge col·laboratiu i aula invers

Fem de Consultors!. La geoquímica des d’un punt de vista pràctic.

Projecte: 2017PID-UB039Aquest PMID ha estat dissenyat per a l’assignatura de Mineralogia Ambiental, assignatura optativa de 3 crèdits de 4rt curs del Grau de Geologia, que s’imparteix durant el segon quadrimestre. L’assignatura combina classes magistrals on es promou la interrelació entre conceptes ja explicats en anteriors assignatures i conceptes nous amb classes pràctiques amb ordinadors on s’introdueix als alumnes en l’ús de dos programaris lliures molt utilitzats a nivell professional. Com que durant el mes de maig hi ha moltes sortides i campaments de camp obligatoris, des de la facultat s’ha promogut la compactació del curs, de manera que les classes presencials acaben a finals d’abril, principis de maig. Com a conseqüència, els estudiants tenen pics amb molt volum de feina i no poden assimilar bé els continguts. Aquest PMID està centrat en canviar la metodologia d'una part de les classes per a que l'estudiant assoleixi els coneixements d'una manera més eficaç i efectiva, reduint la seva sensació de sobrecàrrega de treball, sense passar per una reducció dels continguts de l'assignatura. Es proposa la resolució d'un cas concret, com faria en una consultoria del món professional real, combinant aprenentatge col·laboratiu i aula inversa

Sulphur isotopes as tracers of the influence of a coal-fired power plant on a Scots pine forest in Catalonia (NE Spain)

Stable sulphur isotopes and major ionic composition were analysed in precipitation and throughfall samples from a Scots pine (Pinus sylvestris, L.) forest near the Cercs coal-fired power plant (Catalonia, NE Spain). The purpose of the study was to determine the main sources of sulphur deposition on this pine forest. Sulphur isotope measurements from the SO₂ power plant stack emissions were used to identify the isotopic signature of this source. Net throughfall fluxes of sulphur (26.1 kg S ha¹ yr־¹) and nitrogen (16.3 kg N ha־¹ yr־¹) were higher-5-25 times higher for S and 5-15 times for N-at this site than in other forests in Catalonia. Sulphur isotope analysis confirmed that the net throughfall fluxes of sulphur were mostly due to the dry deposition of the SO2 power plant emissions onto the pine canopies. Two potential atmospheric end-members were distinguished: regional background rainwater (δ³⁴S=+7.2‰) and power plant emissions (δ³⁴S=−2.8‰). By applying a two-component sulphur isotope mixing model, we found that during periods of low power plant activity (⩽10 emission h day¹) 62% of the throughfall sulphate could be attributed to the power plant emissions. At higher activity periods (⩾14 emission h day־¹), this contribution rose to 73%. Although power plant contribution to bulk deposition was lower in both cases (34% and 45%), the possible influence of sulphate coming with long-range transport events from the polluted areas in the Mediterranean basin (δ34S≈0‰) was not discarded