Arsenic in shallow groundwater of Bangladesh: investigations from three different physiographic settings

Occurrences of arsenic (As) in the Bengal Basin of Bangladesh show close relationships with depositional environments and sediment textures. Hydrochemical data from three sites with varying physiography and sedimentation history show marked variations in redox status and dissolved As concentrations. Arsenic concentration in groundwater of the Ganges Flood Plain (GFP) is characteristically low, where high Mn concentrations indicate redox buffering by reduction of Mn(IV)-oxyhydroxides. Low DOC, \( {\text{HCO}}^{ - }_{3} \), \( {\text{NH}}^{ + }_{4} \) and high \( {\text{NO}}^{ - }_{3} \) and \( {\text{SO}}^{{2 - }}_{4} \) concentrations reflect an elevated redox status in GFP aquifers. In contrast, As concentration in the Ganges Delta Plain (GDP) is very high along with high Fe and low Mn. In the Meghna Flood Plain (MFP), moderate to high As and Fe concentrations and low Mn are detected. Degradation of organic matter probably drives redox reactions in the aquifers, particularly in MFP and GDP, thereby mobilising dissolved As. Speciation calculations indicate supersaturation with respect to siderite and vivianite in the groundwater samples at MFP and GDP, but groundwater in the GFP wells is generally supersaturated with respect to rhodochrosite. Values of log P_CO2 at MFP and GDP sites are generally higher than at the GFP site. This is consistent with Mn(IV)-redox buffering suggested at the GFP site compared to Fe(III)-redox buffering at MFP and GDP sites.     

A comparison of the sedimentary records of the 1960 and 2010 great Chilean earthquakes in 17 lakes: Implications for quantitative lacustrine palaeoseismology

Seismically‐induced event deposits embedded in the sedimentary infill of lacustrine basins are highly useful for palaeoseismic reconstructions. Recent, well‐documented, great megathrust earthquakes provide an ideal opportunity to calibrate seismically‐induced event deposits for lakes with different characteristics and located in different settings. This study used 107 short sediment cores to investigate the sedimentary impact of the 1960 M_w 9·5 Valdivia and the 2010 M_w 8·8 Maule earthquakes in 17 lakes in South‐Central Chile (i.e. lakes Negra, Lo Encañado, Aculeo, Vichuquén, Laja, Villarrica, Calafquén, Pullinque, Pellaifa, Panguipulli, Neltume, Riñihue, Ranco, Maihue, Puyehue, Rupanco and Llanquihue). A combination of image analysis, magnetic susceptibility and grain‐size analysis allows identification of five types of seismically‐induced event deposits: (i) mass‐transport deposits; (ii) in situ deformations; (iii) lacustrine turbidites with a composition similar to the hemipelagic background sediments (lacustrine turbidites type 1); (iv) lacustrine turbidites with a composition different from the background sediments (lacustrine turbidites type 2) and (v) megaturbidites. These seismically‐induced event deposits were compared to local seismic intensities of the causative earthquakes, eyewitness reports, post‐earthquake observations, and vegetation and geomorphology of the catchment and the lake. Megaturbidites occur where lake seiches took place. Lacustrine turbidites type 2 can be the result of: (i) local near‐shore mass wasting; (ii) delta collapse; (iii) onshore landslides; (iv) debris flows or mudflows; or (v) fluvial reworking of landslide debris. On the contrary, lacustrine turbidites type 1 are the result of shallow mass wasting on sublacustrine slopes covered by hemipelagic sediments. Due to their more constrained origin, lacustrine turbidites type 1 are the most reliable type of seismically‐induced event deposits in quantitative palaeoseismology, because they are almost exclusively triggered by earthquake shaking. Moreover, they most sensitively record varying seismic shaking intensities. The number of lacustrine turbidites type 1 linearly increases with increasing seismic intensity, starting with no lacustrine turbidites type 1 at intensities between V½ and VI and reaching 100% when intensities are higher than VII½. Combining different types of seismically‐induced event deposits allows the reconstruction of the complete impact of an earthquake.     

Benthic species as mud patrol - modelled effects of bioturbators and biofilms on large-scale estuarine mud and morphology

Sediment-stabilizing and -destabilizing organisms, i.e. microphytobenthos (biofilms) and macrozoobenthos (bioturbators), affect the erodibility of muddy sediments, potentially altering large-scale estuarine morphology. Using a novel eco-morphodynamic model of an idealized estuary, we investigate eco-engineering effects of microphytobenthos and two macrozoobenthic bioturbators. Local mud erodibility is based on species pattern predicted through hydrodynamics, soil mud content, competition and grazing. Mud resuspension and export is enhanced under bioturbation and prevented under biostabilization through respective exposure and protection of the supra- and intertidal. Bioturbation decreases mud thickness and bed elevations, which increases net mud fluxes. Microphytobenthos reduces erosion, leading to a local mud increase of intertidal sediments. In multi-species scenarios, an effective mud-prone bioturbator strongly alters morphology, exceeding that of a more abundant sand-prone moderate species, showing that morphological change depends on species traits as opposed to abundance. Altering their habitat, the effective mud-prone bioturbator facilitates expansion of the sand-prone moderate bioturbator. Grazing and species competition favor species distributions of dominant bioturbators. Consequently, eco-engineering affects habitat conditions while species interactions determine species dominance. Our results show that eco-engineering species determine the mud content of the estuary, which suggests large effects on the morphology of estuaries with aggravating habitat degradation.     

Scientists' warning on extreme wildfire risks to water supply

2020 is the year of wildfire records. California experienced its three largest fires early in its fire season. The Pantanal, the largest wetland on the planet, burned over 20% of its surface. More than 18 million hectares of forest and bushland burned during the 2019–2020 fire season in Australia, killing 33 people, destroying nearly 2500 homes, and endangering many endemic species. The direct cost of damages is being counted in dozens of billion dollars, but the indirect costs on water-related ecosystem services and benefits could be equally expensive, with impacts lasting for decades. In Australia, the extreme precipitation (“200 mm day −1 in several location”) that interrupted the catastrophic wildfire season triggered a series of watershed effects from headwaters to areas downstream. The increased runoff and erosion from burned areas disrupted water supplies in several locations. These post-fire watershed hazards via source water contamination, flash floods, and mudslides can represent substantial, systemic long-term risks to drinking water production, aquatic life, and socio-economic activity. Scenarios similar to the recent event in Australia are now predicted to unfold in the Western USA. This is a new reality that societies will have to live with as uncharted fire activity, water crises, and widespread human footprint collide all-around of the world. Therefore, we advocate for a more proactive approach to wildfire-watershed risk governance in an effort to advance and protect water security. We also argue that there is no easy solution to reducing this risk and that investments in both green (i.e., natural) and grey (i.e., built) infrastructure will be necessary. Further, we propose strategies to combine modern data analytics with existing tools for use by water and land managers worldwide to leverage several decades worth of data and knowledge on post-fire hydrology.     

Environmental controls on the Late Holocene carbonate sedimentation of a karstic lake in the Middle‐Atlas Mountains (Lake Afourgagh,Morocco)

The Lake Afourgagh sediment record and facies successions provide an outstanding example of environmentally controlled carbonate sedimentation. Afourgagh is a small, shallow permanent lake located in the Middle‐Atlas Mountains in Morocco in a karstic context. It is fed by ground waters that are relatively enriched in Mg resulting from the leaching of the Jurassic dolomitic bedrock of the catchment. This eutrophic lake is episodically restricted and characterized by alkaline waters with a fluctuating high Mg/Ca ratio. The maximum extension of the Holocene shoreline coincides with evidence of a lake stabilization level corresponding to the outflow of the lake through a wadi. Lakeshore terrace sediments deposited on an alluvial fan siltstone during the past ca 2500 cal yr bp comprise four main facies: a littoral crust, palaeosols, palustrine silts and charophyte tufas, which reflect different environments from the shoreline toward the deeper water. In the more distal parts, the charophyte tufas display a well‐expressed lamination punctuated by the development of microstromatolites on algae thalli. The mineralogical composition of the carbonates is linked to the facies. While the charophyte tufas are characterized by a relatively high content in aragonite, in addition to low‐Mg calcite, the littoral crust is mainly composed of magnesite. This pattern is related to the evolving chemistry of water due to the influence of charophyte proliferation during dry summers. Calcium‐carbonate precipitation on algae thalli (both bioinduced and microbially mediated) progressively induces an increase in the Mg/Ca ratio of the lake water, while the capillary evaporation of shallow ground waters causes precipitation of a magnesite precursor on the shoreline, producing magnesite during early diagenesis. This effect is characteristic of two episodes: part of the Roman Warm Period and the beginning of the Dark Age Cold Period. The carbonate mineralogy of the different depositional sequences at Afourgagh indicates lake‐level and water‐chemistry fluctuations under a climatic influence. Therefore, among other regional records, the Lake Afourgagh sedimentary record provides useful evidence for reconstructing these environmental changes.     

Natural analogues: a potential approach for developing reliable monitoring methods to understand subsurface CO2 migration processes

One possible way of mitigating carbon dioxide (CO₂) emissions from fossil fuel combustion is using carbon dioxide capture and storage (CCS) technology. However, public perception concerning CO₂ storage in the geosphere is generally negative, being particularly motivated by perceived leakage risks. Therefore, a main issue when attempting to gain public acceptance is ensuring provision of appropriate monitoring practices, aimed at providing health, safety and environmental risk assessment, so that potential risks from CO₂ storage are minimized. Naturally occurring CO₂ deposits provide unique natural analogues for evaluating and validating methods used for the detection and monitoring of CO₂ spreading and degassing into the atmosphere. Geological and hydrological structures of the Cheb Basin (NW Bohemia, Czech Republic) represent such a natural analogue for investigating CO₂ leakage and offer a perfect location at which to verify monitoring tools used for direct investigation of processes along preferential migration paths. This shallow basin dating from the Tertiary age is characterized by up to 300?m thick Neogene sediment deposits and several tectonically active faults. The objectives of this paper are to introduce the CO₂ analogues concept to present the Eger Rift as a suitable location for a natural CO₂ analogue site and to demonstrate to what extent such an analogue site should be used (with a case study). The case study presents the results obtained from a joint application of geoelectrical measurements in combination with soil CO₂ concentration and flux determination methods, for the detection and characterization of natural CO₂ releases at gas seeps (as part of a hierarchic monitoring concept). To highlight discharge-controlling structural near surface features was the initial motivation for the application of geoelectrical measurements. Soil-gas concentration and flux measurement techniques are relatively simple to employ and are valuable methods that can be used to monitor seeping CO₂ along preferential pathways. Joint interpretation of both approaches yields a first insight into fluid paths and reveals that the thickness and permeability of site-specific near surface sedimentary deposits have a great influence upon the spatial distribution of the CO₂ degassing pattern at surface level.     

Iridium enrichment and poor fractionation from gold, platinum and palladium in clausthalite (PbSe), Tilkerode, eastern Harz, Germany

Enrichments in platinum-group elements were found in clausthalite, PbSe, which occurs in carbonate–hematite veins hosted in black shale of Upper Wenlockian age in the eastern Harz, Germany. Spot measurements by laser ablation–quadrupole inductively coupled plasma mass spectrometry (LA–QICPMS) show that the clausthalite has Pt contents that average 0.459?ppm and range from 0.003 to 2.83?ppm. Other noble metals quantified in the present work include Au (0.226?ppm, 0.109–0.451?ppm), Ru (0.061?ppm, 0.006–0.264?ppm), Ir (0.071?ppm, 0.010–0.185?ppm), Pd (0.046?ppm, 0.017–0.107?ppm) and Os (0.010?ppm, <0.003–0.024?ppm). Elemental ratios of Au/Ir, Pd/Ir and Pt/Ir, the average values of which are respectively 4.6, 0.8, and 4.9, suggest that Au, Pd and Pt are poorly fractionated from Ir. The resulting Ir enrichment is unusual and should reflect a particularly soluble (and stable) aqueous complex of Ir in a highly oxidizing, low-temperature, Se-rich solution.     

A gridded monthly upper-air data set from 1918 to 1957

Significant efforts have been devoted in recent years towards extending observation-based three-dimensional atmospheric data sets back in time. Such data sets form an important basis for a better understanding of the climate system. Here we present a new monthly three-dimensional global data set that is based on historical upper-air data and surface data. We use statistical reconstruction techniques, calibrated using ERA-40 data, to obtain gridded data from the numerous, but scattered and heterogeneous historical upper-air observations. In contrast to previous work, in which we used hemispheric principal components on both the predictor and the predictand side to reconstruct spatially complete fields back to 1880, we restrict the procedure to places and times where upper-air observations are available. Each grid column (consisting of four variables at six levels) is then reconstructed independently using only predictor variables in the vicinity (i.e., only local stationarity is required rather than stationary large-scale patterns). The product, termed REC2, is a gridded, global monthly data set of geopotential height, temperature, and u and v wind from 850 to 100?hPa back to 1918. The data set is sparse (i.e., many grid cells are empty), but provides an alternative to large-scale reconstructions as it allows for non-stationary teleconnections. We show the results of several validation experiments, compare our new data set with a number of existing data sets, and demonstrate that it is suitable for analysing large-scale climate variability on interannual time-scales.     

Fluid influence on mineral reactions in ultrahigh-pressure granulites: a case study in the Śnieżnik Mts. (West Sudetes, Poland)

Small tectonic slices of undeformed eclogites and ultrahigh-pressure granulites occur in three tectonic units of the Śnieżnik Mts. (SW Poland). Ultrahigh-pressure granulite/eclogite transitions with peak metamorphic conditions between 21 and 28 kbar at 800 to 1000 °C occur only in the Złote unit. Conventional U-Pb multigrain analyses of zircons from a mafic granulite provided ²⁰⁷Pb/²⁰⁶Pb ages between 360 to 369 Ma which are interpreted to approximate timing of original crystallisation from a melt. Diffusion kinetics and the restricted availability of a fluid phase mainly controlled the conversion from granulite to eclogite, although some bulk-chemical differences were also recognised. The ultrahigh-pressure granulites from the Złote unit exclusively contain H₂O-rich inclusions with variable salinities which distinguishes them from high-temperature (HT)-granulites world-wide. This is also in contrast to the fluid regime (H₂O-N₂-CO₂) recognised in the lower-temperature eclogites (600–800 °C) from the closely associated Międzygórze and Śnieżnik units. The variation in fluid composition between the lower-temperature eclogites and ultrahigh-pressure granulites on the one hand and ultrahigh-pressure granulites and HT-granulites on the other hand probably indicates contrasting P-T-t paths as a result of different tectonic environments. Received: 15 June 1998 / Accepted: 2 March 1999     

Life cycles of spots on Jupiter from Cassini images

Using the sequence of 70-day continuum-band (751 nm) images from the Cassini Imaging Science System (ISS), we record over 500 compact oval spots and study their relation to the large-scale motions. The ∼100 spots whose vorticity could be measured—the large spots in most cases—were all anticyclonic. We exclude cyclonic features (chaotic regions) because they do not have a compact oval shape, but we do record their interactions with spots. We distinguish probable convective storms from other spots because they appear suddenly, grow rapidly, and are much brighter than their surroundings. The distribution of lifetimes for spots that appeared and disappeared during the 70-day period follows a decaying exponential with time constant (mean lifetime) of 3.5 days for probable convective storms and 16.8 days for all other spots. Extrapolating the exponential beyond 70 days seriously underestimates the number of spots that existed for the entire 70-day period. This and other evidences (size, shape, distribution in latitude) suggest that these long-lived spots with lifetime larger than 70 days are from a separate population. The zonal wind profile obtained manually by tracking individual features (this study) agrees with that obtained automatically by correlating brightness variations in narrow latitude bands (Porco et al., 2003). Some westward jets have developed more curvature and some have developed less curvature since Voyager times, but the number of westward jets that violate the barotropic stability criterion is about the same. In the northern hemisphere the number of spots is greatest at the latitudes of the westward jets, which are the most unstable regions according to the barotropic stability criterion. During the 70-day observation period the Great Red Spot (GRS) absorbed nine westward-moving spots that originated in the South Equatorial Belt (SEB), where most of the probable convective storms originate. Although the probable convective storms do not directly transform themselves into westward-moving spots, their common origin in the SEB suggests that moist convection and the westward jet compose a system that has maintained the GRS over its long lifetime.