Iron-rich Groundwater Research Articles

New insights on the hydrochemistry, geothermometry, and isotopic characteristics of the hydrothermal groundwater of the SASS basin: case study of the Jérid geothermal field, Southern Tunisia.

Chemical and isotopic indicators were used to recognize the origin of hydrothermal groundwater, to assess the mineralization processes and groundwater quality, to identify the source of solutes and the likely mixing with cold, and elucidate the fluid geothermometry in the Jérid field of Southern Tunisia. The results show that the geothermal groundwater is neutral to slightly alkaline. They are characterized by SO4-Cl-Na-Ca water type. The dissolution of evaporates and pyrite-bearing rocks is the dominant mineralization process. The groundwater quality index indicates that the majority of samples are very hard and belong to poor to unsuitable for drinking classes. Applications and calculations of hydrogeochemical parameters, including SAR, %Na, PI, Kr, and MAR, showed that the majority of samples are unsuitable for agricultural practices. The human health risk was assessed based on hazard quotient and total hazard index through ingestion and dermal contact with iron-rich groundwater. The consumption of CI groundwaters does not present non-carcinogenic risk to adults and children. The δ18 O and δ2H signatures indicate that the geothermal groundwater was recharged by ocean precipitation during cold and wet paleoclimatic periods. The slight enrichment of oxygen-18 and deuterium contents suggests a limited mixing effect between geothermal water and cold groundwater within the same aquifer. This mixing effect is confirmed by the Na-K-Mg and the chloride-enthalpy diagrams. The K-Mg and SiO2 geothermometers provided fairly reliable reservoir temperature values, ranging between 69.6 and 99°C. Calculated geothermal potential values, varying between 469 and 16987 kWth, which allow several applications such as domestic and agricultural heating.

Iron-rich sandstones in medieval churches in the Cambridge region, UK: distribution, sources and significance

ABSTRACT England’s 13,000 medieval churches are a distinctive landscape feature, not least because they were mostly constructed of local building materials. Especially prominent are churches incorporating iron-rich (ferruginous) stone, in a range of yellow-brown colours. This study investigates churches in an 1,800 km2 area centred on south Cambridgeshire, and interprets the distribution of three iron-rich building stones in space and time. Over 120 churches have been studied in the field, and a further sixty churches provisionally assessed using only photographs. The study confirms existing views that two iron-rich walling stones — the Ely and Gamlingay sandstones — were quarried from the bedrock Woburn Sands Formation (Lower Cretaceous). However, a third walling stone — the Cottenham Sandstone — is re-interpreted as a ferricrete (ironpan) formed by cementation of Quaternary river sediments by iron-rich ground-water. The churches containing ferricrete are shown to lie on the relict floodplains of the ancestral River Cam, rather than following the Woburn Sands outcrop. Cottenham ferricrete was used most commonly during the twelfth to fourteenth centuries with some reuse in the fifteenth and sixteenth centuries. This result conflicts with a hypothesis based on churches in the London Basin that ferricrete walling indicates a twelfth-century or earlier date. There is no evidence in the Romanesque and later churches of the study area that iron-rich and iron-poor building stones were used to create patterned rubble walling as a visual feature. The lack of patterning supports the view that such walls were not meant to be seen and were usually rendered or lime-washed.

Speciation of inorganic arsenic with mixed mode HPLC-ESI-MS and Arsenite Oxidation

It has been challenging to analyze inorganic arsenic (iAs) with anion exchange HPLC-Electrospray Ionization-Mass spectrometry (HPLC-ESI-MS), because arsenite (As(III)) is difficult to retain on column and the salts in mobile phase causes ionization suppression of iAs. To address these issues, a method has been developed involving the determination of arsenate (As(V)) with mixed mode HPLC-ESI-MS and the conversion of As(III) to As(V) for total iAs. As(V) was separated from other chemicals on Newcrom B, a bi-modal HPLC column involving anion exchange and reverse phase interaction. The elution employed a two-dimensional gradient, including a formic acid gradient to elute As(V) and a concurrent alcohol gradient to elute organic anions used in sample preparations. As(V) was detected by Selected Ion Recording (SIR) in negative mode at m/z = 141 with a QDa (single quad) detector. As(III) was quantitatively converted to As(V) by mCPBA oxidation and measured for total iAs. By replacing salt with formic acid in elution, the ionization efficiency for As(V) was greatly enhanced in ESI interface. The limit of detection (LOD) for As(V) and As(III) were 0.0263 μM (1.97 ppb) and 0.0398 μM (2.99 ppb), respectively. The linear range was 0.05–1 μM.The method has been used to characterize iAs speciation change in the solution and precipitation in a simulated iron-rich groundwater caused by air exposure.

Change lost: Corrosion of Roman copper alloy coins in changing and variable burial environments

We studied the corrosion of Roman copper alloy coins that experienced alternations or progressive changes in their burial environment. We used coins that were still embedded in soil or in a concretion selectedfrom three professional excataved sites - Berlicum and Krommenie in the Netherlands and Kempraten in Switserland. mCT scanning and neutron scanning were used to record the 3-D properties of these coins prior to (destructive) analyses. It proved possible to tentatively identify the coins. Microscope observations and SEM-EDX analyses revealed complex corrosion processes, related to changing burial environments. In soil horizon with fluctuating groundwater levels in a region with upwelling reducing, iron-rich groundwater, the copper in a gunmetal coin is essentially replaced by iron oxides while tin remains and forms tin-oxide bands. Fluctuating redox conditions in marine-influenced environments was shown to transform a copper-alloy coin into strongly laminated copper sulphides with embedded gypsum crystals, with an outer surface of copper and copper-iron sulphides. Burial of bronze in a charcoal rich layer probably caused temporary highly alkaline soil conditions. This caused most of the copper to leach from this coin, leaving behind a laminated tin-dominated mass, with only a limited amount of (malachite) corrosion products remaining in the surrounding groundmass. In all three cases, corrosion processes tend to be anisotropic, probably because of cold-hammering of the coins during their manufacture. Such corrosion processes on massive copper alloy coins may produce features that may lead to their incorrect classification as subferrati, i.e. copper alloy coins with an iron core. Our results may help in future to distinguish strongly corroded massive coins from subferrati.

A sharp contrasting occurrence of iron-rich groundwater in the Pearl River Delta during the past dozen years (2006–2018): The genesis and mitigation effect

Fe-rich (>0.3 mg/L) groundwater is generally present in areas where organic matter-rich fluvial, lacustrine, or marine sedimentary environments occur. The Pearl River Delta (PRD) that marine sediments is common, where a large scale of Fe-rich groundwater was distributed but disappearing in recent decade. This study aims to investigate the change of Fe-rich groundwater in the PRD, and to discuss the genesis controlling Fe-rich groundwater in the PRD during the past dozen years. A total of 399 and 155 groundwater samples were collected and analyzed at 2006 and 2018, respectively. Results showed that Fe-rich groundwater of the PRD was from 19.3% at 2006 dropped to 1.3% at 2018. Fe-rich groundwater in coastal-alluvial aquifers was more than 2 times that in other aquifers at 2006. Both of anthropogenic and geogenic sources were contributed to the widely distribution of Fe-rich groundwater in the PRD at 2006. The infiltration of industrial wastewater and the irrigation of Fe-rich surface water were the major anthropogenic driving forces for the occurrence of Fe-rich groundwater in the PRD at 2006. The reductive dissolution of Fe minerals in aquifer sediments, associated with the degradation of organic matter in marine sediments and the sewage infiltration, was the main driving force for the enrichment of groundwater Fe in coastal-alluvial aquifers at 2006. The intrusion of sewage triggering the reductive dissolution of Fe minerals in terrestrial sediments and the reductive dissolution of Fe minerals in carbon-rich rocks induced by sewage leakages were the major driving forces for the occurrence of Fe-rich groundwater in alluvial-proluvial and fissured aquifers at 2006. All these driving forces were weaker or even not work at 2018 because of the large decrease of untreated wastewater discharge in the PRD during 2006–2018. Therefore, limiting untreated wastewater discharge is the first choice to improve the groundwater quality in urbanized areas.

Sorption of Monothioarsenate to the Natural Sediments and Its Competition with Arsenite and Arsenate

Monothioarsenate (MTAsV) is one of the major arsenic species in sulfur- or iron-rich groundwater, and the sediment adsorption of MTAsV plays an important role in arsenic cycling in the subsurface environment. In this study, batch experiments and characterization are conducted to investigate the sorption characteristic and mechanism of MTAsV on natural sediments and the influences of arsenite and arsenate. Results show that MTAsV adsorption on natural sediments is similar to arsenate and arsenite, manifested by a rapid early increasing stage, a slowly increasing stage at an intermediate time until 8 h, before finally approaching an asymptote. The sediment sorption for MTAsV mainly occurs on localized sites with high contents of Fe and Al, where MTAsV forms a monolayer on the surface of natural sediments via a chemisorption mechanism and meanwhile the adsorbed MTAsV mainly transforms into other As species, such as AlAs, Al-As-O, and Fe-As-O compounds. At low concentration, MTAsV sorption isotherm by natural sediments becomes the Freundlich isotherm model, while at high concentration of MTAsV, its sorption isotherm becomes the Langmuir isotherm model. The best-fitted maximum adsorption capacity for MTAsV adsorption is about 362.22 μg/g. Furthermore, there is a competitive effect between MTAsV and arsenate adsorption, and MTAsV and arsenite adsorption on natural sediments. More specifically, the presence of arsenite greatly decreases MTAsV sorption, while the presence of MTAsV causes a certain degree of reduction of arsenite adsorption on the sediments before 4 h, and this effect becomes weaker when approaching the equilibrium state. The presence of arsenate greatly decreases MTAsV sorption and the presence of MTAsV also greatly decreases arsenate sorption. These competitive effects may greatly affect MTAsV transport in groundwater systems and need more attention in the future.

Quantifying Preservation Potential: Lipid Degradation in a Mars-Analog Circumneutral Iron Deposit.

Comparisons between the preservation potential of Mars-analog environments have historically been qualitative rather than quantitative. Recently, however, laboratory-based artificial maturation combined with kinetic modeling techniques have emerged as a potential means by which the preservation potential of solvent-soluble organic matter can be quantified in various Mars-analog environments. These methods consider how elevated temperatures, pressures, and organic-inorganic interactions influence the degradation of organic biomarkers post-burial. We used these techniques to investigate the preservation potential of deposits from a circumneutral iron-rich groundwater system. These deposits are composed of ferrihydrite (Fe5HO8 · 4H2O), an amorphous iron hydroxide mineral that is a common constituent of rocks found in ancient lacustrine environments on Mars, such as those observed in Gale Crater. Both natural and synthetic ferrihydrite samples were subjected to hydrous pyrolysis to observe the effects of long-term burial on the mineralogy and organic content of the samples. Our experiments revealed that organic-inorganic interactions in the samples are dominated by the transformation of iron minerals. As amorphous ferrihydrite transforms into more crystalline species, the decrease in surface area results in the desorption of organic matter, potentially rendering them more susceptible to degradation. We also find that circumneutral iron-rich deposits provide unfavorable conditions for the preservation of solvent-soluble organic matter. Quantitative comparisons between preservation potentials as calculated when using kinetic parameters show that circumneutral iron-rich deposits are ∼25 times less likely to preserve solvent-soluble organic matter compared with acidic, iron-rich environments. Our results suggest that circumneutral iron-rich deposits should be deprioritized in favor of acidic iron- and sulfur-rich deposits when searching for evidence of life with solvent extraction techniques.

Investigation into the Cause of Iron-Related Clogging of Groundwater Bores Used for Viticulture in the Limestone Coast, South Australia

Iron-related clogging of boreholes, pumps and dripper lines is a significant and costly problem for irrigators worldwide. The primary cause of iron-related clogging is still debated. Previous studies have described complex interactions between biological clogging and inorganic iron/manganese oxide precipitation. This case study examined groundwater bores used for viticulture irrigation in the Limestone Coast region, a highly productive wine growing area in the SE of South Australia. Iron clogging of bore screens, pumps and dripper systems has been a persistent problem in the region and the issue is perceived to be growing, with irrigators suggesting the widespread introduction of iron-related bacteria (IRB) through drilling equipment to be the root cause of the problem. Analysis of the groundwater microbiology and inorganic chemistry found no apparent correlation between the presence of IRB and the clogging status of wells. In fact, IRB proved to be widespread throughout the limestone aquifer. However, a clear correlation could be found between clogging affected bores and the redox potential of the groundwater with the most severely affected bores strongly oversaturated in respect to iron oxide minerals. Elevated dissolved concentrations of Fe(II) thereby tended to be found in deeper bores, which also were generally more recently drilled. Following decades of less than average rainfall, a tendency to deepen bores in response to widespread declines in water levels has been documented for the SE of South Australia. The gradually widening clogging problem in the region is postulated to be related to the changes in climate in the region, with irrigators increasingly driven to rely on deeper, anoxic iron-rich groundwater resources.

Effect of low-iron micronutrient powder (MNP) on the composition of gut microbiota of Bangladeshi children in a high-iron groundwater setting: a randomized controlled trial

PurposeAdverse effects of iron fortification/supplements such as Micronutrient Powder (MNP) on gut microbiota have previously been found in infection-prone African settings. This study examined the adversaries of a low-iron MNP compared with the standard MNP on the composition of gut microbiota in Bangladeshi children exposed to a high concentration of iron from potable groundwater.MethodsA randomized controlled trial was conducted in 2- to 5-year-old children, drinking groundwater with a high concentration of iron (≥ 2 mg/L). Children were randomized to receive one sachet per day of either standard MNP (12.5 mg iron) or low-iron MNP (5 mg iron), for 2 months. A sub-sample of 53 children was considered for paired assessment of the gut microbiome by 16S rRNA amplicon sequencing.ResultsAt baseline, the gut microbiota consisted of Bifidobacteriaceae (15.6%), Prevotellaceae (12.2%), Lactobacillaceae (3.6%), Clostridiaceae (4.1%) and Enterobacteriaceae (2.8%). Overall, there was no significant treatment effect of the low-iron MNP compared to the standard MNP. However, an apparent treatment effect was observed in children with a relative adult-like microbiota, with a higher relative abundance of potentially pathogenic Enterobacteriaceae after receiving the standard MNP compared to the low-iron MNP. This effect, however, was statistically non-significant (p = 0.07).ConclusionIn Bangladeshi children drinking iron-rich groundwater, a low-iron MNP supplementation did not have a significant impact on their gut microbiota profile/composition compared to the standard MNP.The trial registration number is ISRCTN60058115; Date of registration 03/07/2019; retrospectively registered.

Ferruginous banding in Sydney sandstone

Spectacular ferruginous (goethite-rich) banding is a common feature of Triassic sandstone in the Sydney Basin, southeast Australia. The banding is of two broad types: (1) intersecting sets (implying water composition in which goethite is stable) and (2) trough-like sets that truncate and obliterate previously formed banding (implying water composition destabilising goethite, probably owing to increased acidity and/or reductive power). The following two mechanisms could be responsible for the formation of banding during or after permeation of sandstone by water. The pre-nucleation (Ostwald) model involves a supersaturation–nucleation–depletion cycle, during which meteoric water reacts with siderite cement and takes iron into solution, until becoming sufficiently supersaturated to precipitate a goethite-rich band; then the water permeates further into the sandstone, dissolving more iron until the supersaturation is large enough for another episode of precipitation. The post-nucleation (self-organisation) model involves the development of bands from randomly dispersed nuclei, small particles dissolving and large particles growing, to minimise the total surface free energy. The trough-type of banding cannot be explained by either of these processes, because ferruginous bands are inferred to be dissolved, not deposited, during advance of the water. An alternative mechanism is the evaporation–precipitation model, which involves precipitation caused by evaporation of retreating water, rather than precipitation from advancing water. The festoon patterns of trough-type band sets resemble strand line patterns in sand left by backwash and could be the result of spasmodic reduction in the volume of rainwater. The typical iron-rich margins of the troughs could reflect evaporation during prolonged stagnation, but transitions from iron-rich borders to transgressive veins, as well as later-thickened borders, suggest continued penetration of iron-rich groundwater after formation of the banding. KEY POINTS Some bands intersect (implying water composition in which goethite is stable). Trough-type bands obliterate previously formed banding (implying water composition destabilising goethite, owing to increased acidity and/or reductive power). Possible banding processes are the pre-nucleation (Ostwald) model and the post-nucleation (self-organisation) model, each with some problems. Banding (especially trough-type) can also be formed by evaporation–precipitation during water retreat.

Application of biogenic iron precipitation by strain H117 for tetracycline removal: mechanism of adsorption and activation.

To date, biogenic metals have opened up a window for new applications in adsorption of contaminants. But there is still little attention to be paid in the removal of tetracycline (TC) by biogenic iron precipitation (BIP). In this paper, the BIP, from iron-based mixotrophic denitrification batch reactor, was estimated for its adsorption property of TC under various parameters to simulate the behavior in aquatic environment. The maximum adsorption capacity for TC was 195.336mgg-1. Analyses of spectrum verified the existence of Fe3O4 and FeOOH in BIP, which was the main reason for the removal of TC. The adsorption kinetic and isotherm of TC were well fitted to Elovich and Langmuir isotherm models, respectively, indicating that the adsorption process was mainly controlled by chemical adsorption. Furthermore, we proposed a potential mechanism of adsorption: a combination of cation-π, hydrogen bonding (H-bonding), and electrostatic interaction. Additionally, the activation experiment showed that BIP could enhance the degradation of TC (more than 98.00% removal within 1.0h) by advanced oxidation process (AOP), due to the existence of FeOOH and Fe3O4. Considering its effectiveness in both adsorption and activation performance, BIP is highlighted as an economical and eco-friendly material for TC removal and offers a promising method to resolve sludge disposal in biological treatment of iron-rich groundwater.

Hydrogeological Characterization of the Thyspunt Area, Eastern Cape Province, South Africa

This paper presents a comprehensive hydrogeological investigation that involves field work, aquifer test, hydrogeochemical analysis, environmental isotope analysis, and interpretations around a proposed nuclear power facility in South Africa. The study was undertaken to test the complementarity of the various methods in the coastal aquifer and to verify the hydrogeological conditions within and around the site. The study revealed the presence of two types of aquifers: an upper primary aquifer made up of the Cenozoic deposits of the Algoa Group, and a deeper fractured aquifer made of the Palaezoic Table Mountain Group (TMG) metasedimentary rocks. Owing to ductile deformation in the form of folding, the fractured quartzite and shale aquifers resulted in an artesian condition, often characterized by slightly acidic (pH ≤ 6) and iron-rich groundwater. The most important hydrogeochemical processes responsible for the observed changes in the hydrochemical composition and facies are mineral dissolution, ion exchange and mixing. The environmental isotope results suggest that all groundwater samples are characterized by a depleted δ18O and δ2H signal, indicating high latitude moisture source (southern polar region) and recharge from rainfall, with no or minimal evaporation before and during infiltration. Similarities in the stable isotope signatures between the deeper and shallow aquifer confirm the presence of a strong hydraulic link. The residence time of groundwater in the aquifers underlying the proposed nuclear power plant is estimated using tritium (3H) and 14C, and the results indicate that in the shallow aquifer it ranges from recent recharge to 50 years, and in the deeper aquifer, it ranges from 430 ± 5 years to 1000 ± 10 years, which exists in a quasi-pristine condition.

Waste Ochre for Control of Phosphates and Sulfides in Digesters at Wastewater Treatment Plants with Enhanced Biological Phosphorus Removal

Ochre, waste iron sludge from the treatment of iron rich groundwater for potable use, makes up a significant waste problem. Furthermore, wastewater treatment plants with enhanced biological phosphorus removal and the digestion of sludge are in lack of iron for the prevention of hydrogen sulfide production and the release of phosphorous during anaerobic digestion. Thus, the addition of ochre to anaerobic digestion is a potential beneficial reuse of ochre. Sludge from wastewater treatment plants with enhanced biological phosphorus removal was used for the experiments. Batch and continuous pilot-scale tests were performed for the mesophilic digestion of primary and waste-activated sludge with different doses of ochre. Two different doses of ochre corresponding to molar ratios of 1 and 2 moles Fe3+/mole P released in the batch test resulted in 29% and 57% reductions of phosphates respectively in the sludge liquor compared to the control sludge without inhibiting the digestion process. In the pilot experiment, the dosing of ochre at both a high and low dose (molar ratios of 1.6 and 0.8 Fe3+/S2−, respectively) resulted in an immediate drop in the H2S concentration (from >2000 ppm down to 570 ppm), while the control reactor still produced biogas with a high hydrogen sulfide concentration. The inhibition of the digestion process was observed (accumulation of acetate) at the higher dose. In a second pilot scale experiment, lower doses of ochre were tested continuously (1.5 and 0.75 mole Fe3+/mole Preleased) to avoid any inhibition, while evaluating the phosphate precipitation. A reduction of phosphates in sludge liquor (33% and 66% for the low and high doses respectively) was obtained.

Synthesis of zerovalent iron from water treatment residue as a conjugate with kaolin and its application for vanadium removal.

This study was aimed at examining the possible utilization of iron-rich groundwater treatment sludge in the synthesis of zerovalent iron (ZVI) as a conjugate with kaolin clay (Slu-KZVI), and its application for vanadium adsorption from aqueous solutions. Iron was extracted from the sludge using 1 M HCl and was used in ZVI synthesis by the sodium borohydride reduction method. The characteristics and performance of Slu-KZVI were compared to a kaolin modified with synthetic iron (FeCl3·6H2O) (Syn-KZVI). Adsorption results showed a competitive performance by both classes of KZVI, with Syn-KZVI slightly outperforming Slu-KZVI. X-ray photoelectron spectroscopy, X-ray diffraction and transmission electron microscopy confirmed the formation of Fe0 on the core-shell structure of both modified adsorbents. In addition, the surface analysis of Slu-KZVI indicated the presence of P and Ca to a small extent, originating from the sludge. Both classes of sorbents performed better in solutions with acidic and neutral pH values (3-7). Surface complexation was thought to be the primary mechanism whereas simultaneous V(V) reduction and Fe oxidation (redox) reactions may also have taken place to some extent. A sorption test with groundwater confirmed that adsorbents were able to reduce vanadium to a very low concentration.

An overview of fault zone permeabilities and groundwater level steps in the Roer Valley Rift System

AbstractFaults in the Roer Valley Rift System (RVRS) act as barriers to horizontal groundwater flow. This causes steep cross-fault groundwater level steps (hydraulic head differences). An overview of the size and distribution of fault-related groundwater level steps and associated fault zone permeabilities is thus far lacking. Such an overview would provide useful insights for nature restoration projects in areas with shallow groundwater levels (wijstgronden) on the foot wall of fault zones. In this review study, data on fault zone permeabilities and cross-fault hydraulic head differences were compiled from 39 sources of information, consisting of literature (starting from 1948), internal reports (e.g. from research institutes and drinking water companies), groundwater models, a geological database and new fieldwork. The data are unevenly distributed across the RVRS. Three-quarters of the data sources are related to the Peel Boundary Fault zone (PBFZ). This bias is probably caused by the visibility of fault scarps and fault-adjacent wet areas for the PBFZ, with the characteristic iron-rich groundwater seepage. Most data demonstrate a cross-fault phreatic groundwater level step of 1.0 to 2.5 m. Data for the Feldbiss Fault zone (FFZ) show phreatic cross-fault hydraulic head differences of 1.0 to 2.0 m.In situmeasured hydraulic conductivity data (K) are scarce. Values vary over three orders of magnitude, from 0.013 to 22.1 m d−1, are non-directional and do not take into account heterogeneity caused by fault zones. The hydraulic conductivity (and hydraulic resistance) values used in three different groundwater models are obtained by calibration using field measurements. They also cover a large range, from 0.001 to 32 m d−1and from 5 to 100,000 days. Heterogeneity is also not taken into account in these models. The overview only revealed locations with a clear cross-fault groundwater level step, and at many locations the faults are visible on aerial photographs as cropmarks or as soil moisture contrasts at the surface. Therefore, it seems likely that all faults have a reduced permeability, which determines the size of the groundwater level steps. In addition, our results show that cross-fault hydraulic head gradients also correlate with topographic, fault-induced offsets, for both the Peel Boundary and the Feldbiss fault zone.

Riverbank filtration in Cairo, Egypt: part II—detailed investigation of a new riverbank filtration site with a focus on manganese

A 5-day detailed field investigation at a new RBF test well gallery in Embaba, Cairo, was conducted to evaluate the hydraulic setting and the behavior of iron and manganese. The well gallery consists of six vertical wells placed along a straight line parallel to the Nile riverbank. A low anisotropy factor for the aquifer (kf,h:kf,v) of 1.7 was determined by evaluation of a multi-step pumping test. Travel times between 11 days from the river toward the central wells and 22 days toward the outermost wells were estimated by groundwater flow modeling and particle tracking. The riverbed is rich in fine suspended sediments that have elevated iron and nitrogen concentrations. Depth-dependent water sampling during regular well operation indicates that the thick organic-, Fe- and Mn-rich riverbed is the primary source for ammonium, iron and manganese in the bank filtrate. Iron-rich groundwater flow from the opposite riverbank was identified as a secondary source of iron in the pumped water. The vertical position of the filter screen affects total travel times but would not reduce the portion of Mn-rich bank filtrate. The authors recommend continuous well operation for achieving stable water quality and lowering the risk of well clogging.

Iron Regulation of Wetland Vegetation Performance Through Synchronous Effects on Phosphorus Acquisition Efficiency

Iron-rich groundwater flowing into wetlands is a worldwide environmental pollution phenomenon that is closely associated with the stability of wetland ecosystems. Combined with high phosphorus (P) loading from agricultural runoff, the prediction of the evolution of wetland vegetation affected by compound contamination is particularly urgent. We tested the effects of anaerobic iron-rich groundwater discharge in a freshwater marsh by simulating the effect of three levels of eutrophic water on native plants (Glyceria spiculosa (Fr. Schmidt.) Rosh.). The management of wetland vegetation with 1–20 mg/L Fe input is an efficient method to promote the growth of plants, which showed an optimum response under a 0.10 mg/L P surface water environment. Iron-rich groundwater strongly affects the changes in ecological niches of some wetland plant species and the dominant species. In addition, when the P concentration in a natural body of water is too high, the governance effect of eutrophication might not be as expected. Under iron-rich groundwater conditions, the δ13C values of organs were more depleted, which can partially explain the differences in δ13C in the soil profile. Conversely, the carbon isotope composition of soil organic carbon is indicative of past changes in vegetation. The results of our experiments confirm that iron-rich groundwater discharge has the potential to affect vegetation composition through toxicity modification in eutrophic environments.

Performance of Iron Plaque of Wetland Plants for Regulating Iron, Manganese, and Phosphorus from Agricultural Drainage Water

Agricultural drainage water continues to impact watersheds and their receiving water bodies. One approach to mitigate this problem is to use surrounding natural wetlands. Our objectives were to determine the effect of iron (Fe)-rich groundwater on phosphorus (P) removal and nutrient absorption by the utilization of the iron plaque on the root surface of Glyceria spiculosa (Fr. Schmidt.) Rosh. The experiment was comprised of two main factors with three regimes: Fe2+ (0, 1, 20, 100, 500 mg·L−1) and P (0.01, 0.1, 0.5 mg·L−1). The deposition and structure of iron plaque was examined through a scanning electron microscope and energy-dispersive X-ray analyzer. Iron could, however, also impose toxic effects on the biota. We therefore provide the scanning electron microscopy (SEM) on iron plaques, showing the essential elements were iron (Fe), oxygen (O), aluminum (Al), manganese (Mn), P, and sulphur (S). Results showed that (1) Iron plaque increased with increasing Fe2+ supply, and P-deficiency promoted its formation; (2) Depending on the amount of iron plaque on roots, nutrient uptake was enhanced at low levels, but at higher levels, it inhibited element accumulation and translocation; (3) The absorption of manganese was particularly affected by iron plague, which also enhanced phosphorus uptake until the external iron concentration exceeded 100 mg·L−1. Therefore, the presence of iron plaque on the root surface would increase the uptake of P, which depends on the concentration of iron-rich groundwater.

Mineralogy and geochemistry of efflorescent minerals on mine tailings and their potential impact on water chemistry.

In the gold mining Witwatersrand Basin of South Africa, efflorescent mineral crusts are a common occurrence on and nearby tailings dumps during the dry season. The crusts are readily soluble and generate acidic, metal- and sulphate-rich solutions on dissolution. In this study, the metal content of efflorescent crusts at an abandoned gold mine tailings dump was used to characterise surface and groundwater discharges from the site. Geochemical modelling of the pH of the solution resulting from the dissolution of the crusts was used to better understand the crusts' potential impact on water chemistry. The study involved two approaches: (i) conducting leaching experiments on oxidised and unoxidised tailings using artificial rainwater and dilute sulphuric acid and correlating the composition of crusts to these leachates and (ii) modelling the dissolution of the crusts in order to gain insight into their mineralogy and their potential impact on receiving waters. The findings suggested that there were two chemically distinct discharges from the site, namely an aluminium- and magnesium-rich surface water plume and an iron-rich groundwater plume. The first plume was observed to originate from the oxidised tailings following leaching with rainwater while the second plume originated from the underlying unoxidised tailings with leaching by sulphuric acid. Both groups of minerals forming from the respective plumes were found to significantly lower the pH of the receiving water with simulations of their dissolution found to be within 0.2 pH units of experimental values. It was observed that metals in a low abundance within the crust (for example, iron) had a stronger influence on the pH of the resulting solutions than metals in a greater abundance (aluminium or magnesium). Techniques such as powder X-ray diffraction (PXRD) and in situ mineral determination techniques such as remote sensing can effectively determine the dominant mineralogy. However, the minerals or metals incorporated through solid solution into bulk mineralogy that dominates the chemistry of the solutions upon their dissolution may occur in minor quantities that can only be predicted using chemical analysis. Their mineralogy can be predicted using geochemical modelling and can provide a set of hypothetical minerals that upon dissolution yield a solution similar to that of the actual crusts. This realisation has a bearing on decision-making such as in risk assessment and designing pollutant mitigation strategies.

Quantitative analysis of biogeochemically controlled density stratification in an iron-meromictic lake

Abstract. Lake stratification controls the cycling of dissolved matter within the water body. This is of particular interest in the case of meromictic lakes, where permanent density stratification of the deep water limits vertical transport, and a chemically different (reducing) milieu can be established. As a consequence, the geochemical setting and the mixing regime of a lake can stabilize each other mutually. We attempt a quantitative approach to the contribution of chemical reactions sustaining the density stratification. As an example, we chose the prominent case of iron meromixis in Waldsee near Doebern, a small lake that originated from near-surface underground mining of lignite. From a data set covering 4 years of monthly measured electrical conductivity profiles, we calculated summed conductivity as a quantitative variable reflecting the amount of electro-active substances in the entire lake. Seasonal variations followed the changing of the chemocline height. Coinciding changes of electrical conductivities in the monimolimnion indicated that a considerable share of substances, precipitated by the advancing oxygenated epilimnion, re-dissolved in the remaining anoxic deep waters and contributed considerably to the density stratification. In addition, we designed a lab experiment, in which we removed iron compounds and organic material from monimolimnetic waters by introducing air bubbles. Precipitates could be identified by visual inspection. Eventually, the remaining solutes in the aerated water layer looked similar to mixolimnetic Waldsee water. Due to its reduced concentration of solutes, this water became less dense and remained floating on nearly unchanged monimolimnetic water. In conclusion, iron meromixis as seen in Waldsee did not require two different sources of incoming waters, but the inflow of iron-rich deep groundwater and the aeration through the lake surface were fully sufficient for the formation of iron meromixis.