Feedbacks between the formation of secondary minerals and the infiltration of fluids into the regolith of granitic rocks in different climatic zones (Chilean Coastal Cordillera)

Subsurface fluid pathways and the climate-dependent infiltration of fluids into the subsurface jointly control the intensity and depth of mineral weathering reactions. The products of these weathering reactions (secondary minerals), such as Fe(III) oxyhydroxides and clay minerals, in turn exert a control on the subsurface fluid flow and hence on the development of weathering profiles. We explored the dependence of mineral transformations on climate during the weathering of granitic rocks in two 6 m deep weathering profiles in Mediterranean and humid climate zones along the Chilean Coastal Cordillera. We used geochemical and mineralogical methods such as (micro ) X-ray fluorescence, oxalate/dithionite extractions, X-ray diffraction and electron microprobe mapping to elucidate the transformations involved during weathering. In the profile of the Mediterranean climate zone, we found a low weathering intensity affecting the profile down to 6 m depth. In the profile of the humid climate zone, we found a high weathering intensity. Based on our results, we propose mechanisms that can intensify the progression of weathering to depth. The most important is weathering-induced fracturing (WIF) by Fe(II) oxidation in biotite and precipitation of Fe(III) oxyhydroxides, and by swelling of interstratified smectitic clay minerals that promotes the formation of fluid pathways. We also propose mechanisms that mitigate the development of a deep weathering zone, like the precipitation of secondary minerals (e.g., clay minerals) and amorphous phases that can impede the subsurface fluid flow. We conclude that the depth and intensity of primary mineral weathering in the profile of the Mediterranean climate zone is significantly controlled by WIF. It generates a surface-subsurface connectivity that allows fluid infiltration to great depth and hence promotes a deep weathering zone. Moreover, the water supply to the subsurface is limited in the Mediterranean climate and thus most of the weathering profile is generally characterized by a low weathering intensity. The depth and intensity of weathering processes in the profile of the humid climate zone, on the other hand, are controlled by an intense formation of secondary minerals in the upper section of the weathering profile. This intense formation arises from pronounced dissolution of primary minerals due to the high water infiltration (high precipitation rate) into the subsurface. The secondary minerals, in turn, impede the infiltration of fluids to great depth and thus mitigate the intensity of primary mineral weathering at depth. These two settings illustrate that the depth and intensity of primary mineral weathering in the upper regolith are controlled by positive and negative feedbacks between the formation of secondary minerals and the infiltration of fluids.</p

Transport und Attenuation partikularer Substanzen zusammen mit organischen Spurenstoffen in Karstgrundwasserleitern

Karst aquifers are intensively used for drinking water production around the world. In some European countries karst water contributes to about 50% of the drinking water supply. In contrast to porous aquifers, particulate matter like clay particles or bacteria is transported over long distances in these aquifers, which results in three main problems and questions related to the transport of particulate matter that are specific for karst aquifers. (1) Microorganisms like bacteria, virus and protozoa, that present a serious health risk are mobile in karst aquifers and are detected frequently and in high concentrations. Factors that influence their transport have rarely been investigated in the field. (2) Turbidity is a cumulative parameter for particulate matter in water and is used as proxy parameter for water quality deterioration of karst springs. Still, there is a lack in a mechanistic understanding of relationships in the occurrence of turbidity and contaminants. Especially the differentiation of different origins of turbidity is of high relevance and great interest. (3) Due to high sediment fluxes in karst aquifers there is a high potential for particle facilitated transport of contaminants like heavy metals, organic chemicals or microorganisms – which, in addition, have a higher survival probability when attached to sediments. The aim of this thesis was to contribute to a process based understanding of the relationship of the occurrence of particulate matter and contaminants at karst springs. Therefore, existing methodical and analytical tools were applied and further developed at a well investigated karst spring in south-west Germany (Gallusquelle, Swabian Alb). In the beginning there was a focus on a detailed investigation of suspended matter at the karst spring shortly after precipitation events. Turbidity is a cumulative parameter and measures a broad spectrum of particle sizes. A previous studiy at a other location has shown, that the particle size distribution (PSD) can be used to differentiate between turbidity originating from the surface and the aquifer and can therefore be used to predict bacterial contamination. However, that study lacks in comparability for its qualitative approach. In this thesis the single parameter b that allows for comparison of PSDs at different times and between different locations is proposed and calculated for about 150 samples. The parameter allows for characterizing and quantifying PSD using a single value, which facilitates, for example, the use of PSDs in multivariate statistical approaches. In our studies the PSD that was determined for a particle size range of 0.5 to 60 mm was not able to differentiate suspended matter of different origin and could therefore not be used to predict bacterial contamination. Yet, validation of the b-value might be worth studying at other karst springs for predicting bacterial contamination. Additional methods that were promising in determining the origin of particulate matter and processes involved in its transport using easy-to-measure parameters were investigated. A method of plotting changes in turbidity and electrical conductivity to observe their hysteresis was therefore applied and further developed. The method was used to derive and differentiate hydro-sedimentary processes like remobilization, sedimentation and direct transport of particles. Source indicating organic micropollutants and hydro-sedimentary processes have, to date, only been studied separately. In this thesis we combined features of both – using a set of more than 50 organic micropollutants – to derive a systematic relationship that allows for predicting potential contamination of karst spring water. The method can easily be adapted to other sites. A basis for establishing and applying proxy parameters that predict the occurrence of microorganisms in karst springs is to examine important factors for their transport and attenuation. Although there are numerous laboratory studies on the transport of colloids and particles, field studies are rare. To determine and evaluate factors that influence the transport and attenuation of particles with different density (latex and silica) and surface charge (neutral and negative) a particle tracer test was conducted at the test site using a set of four 1 mm sized particles. It was shown that the surface charge has significant influence on the attenuation of particles. Differences in particle density had no effect on transport or attenuation. Interestingly, particles have shown higher mean transport velocities than the simultaneously applied fluorescence tracer uranine – their retardation was calculated to 0.98 assuming a ideal transport of uranine.Weltweit haben Karstgrundwasserleiter eine große Bedeutung für die Trinkwassergewinnung. Einige europäische Staaten beziehen bis zu 50% ihres Trinkwassers aus Karstgrundwasserleitern. Im Gegensatz zur Porengrundwasserleitern sind in diesen Grundwasserleitern auch partikuläre Substanzen wie Tonpartikel oder Bakterien über große Entfernungen mobil. Daraus ergeben sich drei wesentliche, Karst-spezifische Probleme und damit verbundene Fragestellungen. (1) Partikuläre Substanzen wie Bakterien, Viren und Protozoen, deren Auftreten im Wasser ein hohes gesundheitliches Risko darstellt, sind mobil in Karstgrundwasserleitern und werden häufig und in hohen Konzentrationen in Karstquellen detektiert. Einflussgrößen auf deren Transport und Attenuation in Karstgrundwasserleitern sind kaum untersucht. (2) Die Trübe als Summenparameter für die Menge partikulärer Substanzen im Wasser wird in der Praxis oft als Leitparameter für die Verschmutzung von Karstquellen verwendet. Bisher fehlt allerdings ein mechanistisches Verständis zwischen den Zusammenhängen von Trübe und dem Auftreten von Kontaminanten. Insbesondere die Unterscheidung verschiedener Quellen der Trübe ist dafür von großer Bedeutung. (3) Aufgrund der hohen Sedimentströme in Karstaquiferen existiert ein großes Potential für den partikulär gebundenen Transport von Schadstoffen wie Schwermetallen, organischen Chemikalien oder auch Mikroorganismen – letztere weisen zusätzlich erhöhte Überlebensraten auf, wenn sie am Sediment adsorbiert sind. Ziel der vorliegenden Arbeit war es, einen Beitrag zum Prozessverständis der Assoziation partikulärer Substanzen mit Kontaminanten an Karstquellen zu leisten. Dafür wurden bestehende methodische und analytische Methoden an einer gut untersuchten Karstquellen in Süddeutschland (Gallusquelle, Schäbische Alb) eingesetzt und weiter entwickelt. Zu Beginn der Arbeit wurde der Fokus auf eine detaillierte Untersuchung der Trübe gelegt. Diese umfasst als Summenparameter einen breiten Umfang von Partikeln unterschiedlicher Größe. In vorhergehenden Studien an anderen Standorten konnte gezeigt werden, dass sich die Partikelgrößenverteilung nutzen lässt, um zwischen Einträgen der Trübe aus dem Aquifer und von der Oberfläche zu differenzieren. Zum Zweck der Vergleichbarkeit unterschiedlicher Partikelgrößenverteilung an einem aber auch zwischen unterschiedlichen Standorten wurde in dieser Arbeit der b-Wert vorgeschlagen und für etwa 150 Proben berechnet. Dieser Parameter erlaubt es, die Größenverteilung mit nur einem Wert zur charakterisieren und zu quantifizieren, was beispielsweise die Verwendung der Partikelgrößenverteilung in der multivariaten Statistik erlaubt. In der vorliegenden Arbeit konnte letztendlich gezeigt werden, dass die Verwendung der Partikelgrößenverteilung, die für eine Größenbereich von 0.5 bis 60 mm bestimmt wurde, als Leitparameter allerdings nicht von allgemeiner Gültigkeit ist, sondern es einer Überprüfung der Methode für den jeweiligen Standort bedarf. Eine Validierung des b-Wertes als Möglichkeit der Prognose des Auftretens bakterieller Verunreinigungen von Karstquellen ist weitere Untersuchungen wert. Es wurden weitere Methoden untersucht, die vielversprechend schienen, die Quellen und die im Transport von partikulären Substanzem involvierten Prozesse mittels einfach zu messender Parameter zu beschreiben. Die Methode der Hysterese-Darstellung von Trübe und elektrischer Leitfähigkeit erwies sich dafür als vielversprechend. Sie wurde verwendet, um hydrosedimentäre Prozesse abzuleiten. Damit konnte zwischen einer Remobilisierung, der Ablagerung und dem direkten Transport von Partikeln unterschieden werden. Die Kombination mit organischen Spurenstoffen als Quellindikatoren – hier wurde eine Palette von mehr als 50 Stoffen analysiert – erlaubte es, diese Prozesse mit dem Eintrag von Stoffen aus verschiedenen potentiellen Kontaminationsquellen zu vergleichen und zu systematisieren. Die Methode kann mit nur geringem Aufwand an anderen Lokationen eingesetzt werden. Die Etablierung und Anwendung von Leitparametern und die Prognose des Auftretens von Mikroogranismen erfordert es, Einflussgrößen auf ihr Transportverhalten und ihre Attenuation zu kennen. Zwar existiert eine große Anzahl von Laborexperimenten zum Transportverhalten von Kolloiden und Partikeln, Feldexperimente sind dagegen kaum durchgeführt worden. Mit der Durchführung eines Markierungsversuchs mit Mikrosphären unterschiedlicher Dichte (Latex und Silikat) und Oberflächenladung (ungeladen und negativ geladen) sollte der Einfluss dieser Größen auf den Transport und die Attenuation von vier Partikelarten mit einer Größe von 1 mm untersucht werden. Es wurde gezeigt, dass die Oberflächenladung einen maßgeblichen Einfluss auf das Attenuationsverhalten hat. Die Dichteunterschiede machten sich weder im Transport noch in der Attenuation bemerkbar. Interessanterweise hatten die Partikel höhere Fließgeschwindigkeiten als der zeitgleich eingesetzte Fluoreszensfarbstoff Uranin – ihre Retardation wurde mit 0.98 berechnet unter der Annahme, dass sich Uranin ideal-konservativ verhält.BMBF, 02WRS1277A/B, Risikomanagement von Spurenstoffen und Krankheitserregern in ländlichen Karsteinzugsgebieten / AGR

Mutual Effects of pH and Competing Cations on the Mobility of Metoprolol in Saturated Quartz Sand: Parameter Estimation and Mobility Prediction Using Retardation Modeling

Predicting the fate of organic compounds in the aquatic environment remains a challenge due to the complexity of natural systems and diverse interactions with surfaces. In this study, the transport behavior of the β-blocker metoprolol (MTP) was studied in water-saturated columns filled with quartz sand (pH 3–11; [NaCl] of 1, 10, and 100 mmol L–1). A significant dependence of MTP retardation on pH and [NaCl] was observed ranging from a 10-fold retardation at pH 6 and 1 mmol L–1 NaCl to virtually none at pH 11. A retardation model was implicated considering (1) the speciation of MTP, (2) the surface reactions of MTPH+, and Na+ with charged surface silanol groups SiO– of quartz, and (3) the protolysis reaction between SiO– and SiOH. Modeling was performed using the complete dataset of 43 retardation values at once (R2 = 0.998). Exemplary predictions were performed for three aquifer settings to illustrate general trends in mobility. This comprehensive approach is an important basis for environmental fate prediction of organic contaminants in the future

Transport and Attenuation of Particles of Different Density and Surface Charge: A Karst Aquifer Field Study

Although karst aquifers are far more susceptible to contamination than porous aquifers, with the transport of particulate matter being an important factor, little is known about the attenuation of solutes within karst aquifers and even less about the attenuation of particulate matter. These in situ investigations have therefore aimed to systematically identify the processes that influence the transport and attenuation of particles within a karst aquifer through multitracer testing, using four different types of 1 μm fluorescent particles and the fluorescent dye uranine. Each of the types of particles used were detected at the observed spring, which drains the investigated aquifer. However, the transport behavior varied significantly between the various particles and the uranine dye, with the breakthrough of particles occurring slightly earlier than that of uranine. Attenuation was determined from the tracer recovery and attributed to filtration processes. These processes were affected by the hydrophobicity and surface charge of the particles. Carboxylated polystyrene particles with a density and surface charge comparable to pathogenic microorganisms were found to be mobile in groundwater over a distance of about 3 km. No attenuation was observed for plain silica particles. Particles with these characteristics thus pose a major threat to karst spring water as they might occur as contaminants themselves or facilitate the transport of other contaminants

Sorption of the β‑Blocker Metoprolol on Montmorillonite Colloids as a Function of pH and Concentration of Competing Sodium Ions

Understanding and predicting the mobility of charged organic contaminants in groundwater is complex, given limited investigations on the sorption of organic cations to pure aquifer constituents using equilibrium models. Clay minerals, with their substantial sorption capacity and widespread presence in aquifer matrices and mobile fluid phases, are of particular importance as sorbents. This study investigates the sorption of metoprolol (MTP), a cationic β-blocker, on montmorillonite colloids, under various physicochemical conditions (pH 3–11; 1, 10 & 100 mmol L–1 Na as NaCl; ∼100 μmmol L–1 MTP). Results show that sorption is highest at intermediate pH and low ionic strength with Na+ and H+ competing for sorption sites with MTPH+. Additionally, as the pH approaches the pKa of MTP sorption decreases due to the transformation of MTPH+ to its uncharged MTP0 species. Sorption was attributed to the incorporation of MTP into clay interlayers, evidenced by the widening of d-spacing in X-ray diffraction data. This study deciphered the number of sorption sites and their affinities towards MTPH+, Na+, and H+ using a multisite sorption model. The resulting model facilitates the prediction of MTP sorption at varying pH and Na-concentrations and provides a fundamental basis for quantitative environmental risk assessment and groundwater resource protection

Arsenic-poor fluids promote strong As partitioning into pyrite

Pyrite is a ubiquitous sulfide mineral found in diverse geological settings and holds great significance in the formation of Au deposits as well as the safe utilization of groundwater due to its remarkable ability to incorporate substantial amounts of As. However, despite its importance, there remains a dearth of fundamental data on the partitioning of As between pyrite and fluid, which is key for accurately modeling the As distribution in these environments. Here, we present new insights into the partitioning behavior of As between pyrite and fluid at conditions that mimic natural fluid systems. Pyrite was synthesized by replacement of natural siderite in hydrothermal experiments at 200 °C and pH 5 applying a wide range of fluid As concentrations, spanning from 0.001 to 100 µg/g. The As distribution and concentration in synthetic pyrite was analyzed by quantitative LA-ICP-MS mapping providing a high spatial resolution and sensitivity at 2–3 µm image pixel size at a detection limit of ∼1 µg/g at the single pixel scale. Pyrite-fluid partitioning coefficients (DAs(py/fluid)) between synthetic pyrite and experimental fluid agree with previously published data for high fluid As concentrations of 1 µg/g to 100 µg/g (DAs &lt; 2000). However, at low As concentrations in the experimental fluid (&lt;1 µg/g), a steep increase in the DAs(py/fluid) values of up to ∼30,000 was detected, demonstrating even stronger As partitioning into pyrite. This is confirmed by the analyses of natural pyrite that precipitated from As-poor fluids (0.3–0.4 ng/g) within a deep anoxic aquifer in SE Sweden. The discovery holds significant implications for the mobility and scavenging of As, which in turn is important for understanding the formation and fingerprinting of mineral deposits as well as for the secure utilization of groundwater resources

Mineralogical, geochemical and magnetic susceptibility data from a deep hydrothermally altered profile in a semi-arid region (Chilean Coastal Cordillera)

This data publication contains mineralogical, geochemical and magnetic susceptibility data of an 87.2 m deep profile of hydrothermally altered plutonic rock in a semi-arid region of the Chilean Coastal Cordillera (Santa Gracia). The profile was recovered during a drilling campaign (March and April 2019) as part of the German Science Foundation (DFG) priority research program SPP-1803 “EarthShape: Earth Surface Shaping by Biota” which aims at understanding weathering of plutonic rock in dependency on different climatic conditions. The goal of the drilling campaign was to recover the entire weathering profile spanning from the surface to the weathering front and to investigate the weathering processes at depth. To this end, we used rock samples obtained by drilling and soil/saprolite samples from a manually dug 2 m deep soil pit next to the borehole. To elucidate the role of iron-bearing minerals for the weathering, we measured the magnetic susceptibility, determined the mineral content and analysed the geochemistry as well as the composition of Fe-bearing minerals (Mössbauer spectroscopy) in selected samples

Mineralogical and geochemical data of two weathering profiles in a Mediterranean and a humid climate region of the Chilean Coastal Cordillera

This publication provides mineralogical and geochemical data of two 6-m-deep weathering profiles formed from granitic rock. They are located in different climate zones (Mediterranean and humid) and are close to the national parks of La Campana and Nahuelbuta in the Chilean Coastal Cordillera. Additional rock samples from adjacent boreholes were used to relate the regolith to the bedrock. The profiles were sampled in February and March 2020 as part of the German Science Foundation (DFG) priority research program SPP-1803 “EarthShape: Earth Surface Shaping by Biota”. The goal of this project is to obtain a holistic view on the interplay of the geosphere and the biosphere under different climatic conditions and to investigate weathering mechanisms. The aim of this publication is to provide the data basis for understanding the weathering processes that control the development of the profiles in relation to different climatic conditions. To this end, we measured the geochemistry with X-ray fluorescence, extracted Fe, Al and Si with oxalate/dithionite, determined the grain sizes by wet sieving and pipetting, measured the magnetic susceptibility, and analysed the mineral content of bulk samples and clay fractions with X-ray diffraction. The data are compiled in one Excel file and all results of the X-ray diffraction measurements are available as RAW- and TXT files