Zsolt Berner

Arsenic enrichment in groundwater of West Bengal, India: geochemical evidence for mobilization of As under reducing conditions

Abstract The mechanism of As release and source(s) of As has been investigated in a small part of a watershed in the Murshidabad district of West Bengal. Analyses include major ion and trace element concentrations, as well as O, H and S isotope ratios of groundwater, surface water and a thermal spring. The results indicate that all water samples belong to the Ca–HCO 3 type, except for the thermal spring which is of the Na–HCO 3 type. Shallow and deeper groundwaters have distinct hydrochemical features. High As contents were registered only in the deeper groundwater horizon. Factor analysis and the distribution pattern of major and trace elements indicate that As is present in the aquifer as a scavenged phase by Fe(III) and to a lesser extent by Mn(IV) phases. The release of As into the groundwater occurs gradually in successive stages, corresponding to the actual redox state in the aquifer. The main stage of As release is related to the bacterial reduction of Fe(III) to Fe(II) (i.e. to the simultaneous dissolution of Fe oxyhydroxides). Low redox conditions in highly polluted areas are indicated by low SO 4 concentration and high δ 34 S values. During bacterial SO 4 reduction, residual SO 4 in groundwater is depleted in the lighter S isotope ( 32 S). However, the cause of the gradual decrease of the redox state in the groundwater is still not well understood.

Phosphorus and the roles of productivity and nutrient recycling during oceanic anoxic event 2

Four sections documenting the impact of the late Cenomanian oceanic anoxic event (OAE 2) were studied in basins with different paleoenvironmental regimes. Accumulation rates of phosphorus (P) bound to iron, organic matter, and authigenic phosphate are shown to rise and arrive at a distinct maximum at the onset of OAE 2, with an associated increase in δ 13 C values. Accumulation rates of P return to preexcursion values in the interval where the δ 13 C record reaches its fi rst maximum. An offset in time between the maximum in P accumulation and peaks in organic carbon burial, hydrogen indices, and Corg/Preact molar ratios is explained by the evolution of OAE 2 in the following steps. (1) An increase in productivity increased the fl ux of organic matter and P into the sediments; the preservation of organic matter was low and its oxidation released P, which was predominantly mineralized. (2) Enhanced productivity and oxidation of organic matter created dysoxic bottom waters; the preservation potential for organic matter increased, whereas the sediment retention potential for P decreased. (3) The latter effect sustained high primary productivity, which led to an increase in the abundance of free oxygen in the ocean and atmosphere system. After the sequestration of CO 2 in the form of black shales, this oxygen helped push the ocean back into equilibrium, terminating black shale deposition and removing bioavailable P from the water column.

Characterization of late Campanian and Maastrichtian planktonic foraminiferal depth habitats and vital activities based on stable isotopes

Abstract Depth habitats of 56 late Cretaceous planktonic foraminiferal species from cool and warm climate modes were determined based on stable isotope analyses of deep-sea samples from the equatorial Pacific DSDP Sites 577A and 463, and South Atlantic DSDP Site 525A. The following conclusions can be reached: Planoglobulina multicamerata (De Klasz) and Heterohelix rajagopalani (Govindan) occupied the deepest plankton habitats, followed by Abathomphalus mayaroensis (Bolli), Globotruncanella havanensis (Voorwijk), Gublerina cuvillieri Kikoine, and Laeviheterohelix glabrans (Cushman) also at subthermocline depth. Most keeled globotruncanids, and possibly Globigerinelliodes and Racemiguembelina species, lived at or within the thermocline layer. Heterohelix globulosa (Ehrenberg) and Rugoglobigerina, Pseudotextularia and Planoglobulina occupied the subsurface depth of the mixed layer, and Pseudoguembelina species inhabited the surface mixed layer. However, depth ranking of some species varied depending on warm or cool climate modes, and late Campanian or Maastrichtian age. For example, most keeled globotruncanids occupied similar shallow subsurface habitats as Rugoglobigerina during the warm late Campanian, but occupied the deeper thermocline layer during cool climatic intervals. Two distinct types of ‘vital effect’ mechanisms reflecting photosymbiosis and respiration effects can be recognized by the exceptional δ13C signals of some species. (1) Photosymbiosis is implied by the repetitive pattern of relatively enriched δ13C values of Racemiguembelina (strongest), Planoglobulina, Rosita and Rugoglobigerina species, Pseudoguembelina excolata (weakest). (2) Enriched respiration 12C products are recognized in A. mayaroensis, Gublerina acuta De Klasz, and Heterohelix planata (Cushman). Isotopic trends between samples suggest that photosymbiotic activities varied between localities or during different climate modes, and may have ceased under certain environmental conditions. The appearance of most photosymbiotic species in the late Maastrichtian suggests oligotrophic conditions associated with increased water-mass stratification.

Hydrogeological and biogeochemical constrains of arsenic mobilization in shallow aquifers from the Hetao basin, Inner Mongolia.

Little is known about the importance of drainage/irrigation channels and biogeochemical processes in arsenic distribution of shallow groundwaters from the Hetao basin. This investigation shows that although As concentrations are primarily dependent on reducing conditions, evaporation increases As concentration in the centre of palaeo-lake sedimentation. Near drainage channels, groundwater As concentrations are the lowest in suboxic-weakly reducing conditions. Results demonstrate that both drainage and irrigation channels produce oxygen-rich water that recharges shallow groundwaters and therefore immobilize As. Groundwater As concentration increases with a progressive decrease in redox potential along the flow path in an alluvial fan. A negative correlation between SO₄²⁻ concentrations and δ³⁴S values indicates that bacterial reduction of SO₄²⁻ occurs in reducing aquifers. Due to high concentrations of Fe (> 0.5 mg L⁻¹), reductive dissolution of Fe oxides is believed to cause As release from aquifer sediments. Target aquifers for safe drinking water resources are available in alluvial fans and near irrigation channels.

Age and paleoenvironment of the Maastrichtian to Paleocene of the Mahajanga Basin, Madagascar: a multidisciplinary approach

Abstract Lithology, geochemistry, stable isotopes and integrated high-resolution biostratigraphy of the Berivotra and Amboanio sections provide new insights into the age, faunal turnovers, climate, sea level and environmental changes of the Maastrichtian to early Paleocene of the Mahajanga Basin of Madagascar. In the Berivotra type area, the dinosaur-rich fluvial lowland sediments of the Anembalemba Member prevailed into the earliest Maastrichtian. These are overlain by marginal marine and near-shore clastics that deepen upwards to hemipelagic middle neritic marls by 69.6 Ma, accompanied by arid to seasonally cool temperate climates through the early and late Maastrichtian. An unconformity between the Berivotra Formation and Betsiboka limestone marks the K–T boundary, and juxtaposes early Danian (zone Plc? or Pld) and latest Maastrichtian (zones CF2–CF1, Micula prinsii ) sediments. Seasonally humid warm climates began near the end of the Maastrichtian and prevailed into the early Danian, accompanied by increased volcanic activity. During the late Danian (zones P1d–P2), a change to seasonally arid climates was accompanied by deepening from middle to outer neritic depths.

The cretaceous-tertiary transition on the shallow Saharan Platform of southern tunisia

Abstract A multidisciplinary approach to the study of a K/T boundary section on the Saharan Platform based on planktic and benthic foraminifera, calcareous nannofossils, lithology, stable isotopes, mineralogy and geochemistry reveals a biota stressed by fluctuating hyposaline, hypoxic littoral and nearshore environments, productivity changes, and a paleoclimate altering between seasonal warm to temperate and warm/humid conditions. Benthic formaminifera indicate that during the last 300 kyr of the Maastrichtian (CF1, Micula prinsii) deposition occurred in a inner neritic (littoral) environment that shallowed to a near-shore hyposaline and hypoxic environment during the last 100–200 kyr of the Maastrichtian. These conditions were accompanied by a seasonal warm to temperate climate that changed to warm/humid conditions with high rainfall, by decreasing surface productivity, and significantly decreasing planktic and benthic foraminiferal species richness. The K/T boundary is marked by an undulating erosional contact overlain by a 10 cm thick sandstone layer which is devoid of any exotic minerals or spherules. Their absence may be due to a short hiatus and the fact that the characteristic clay and red layer (zone P0) are missing. During the earliest Danian (Pla), low sea-levels prevailed with continued low oxygen, low salinity, high rainfall, high erosion and terrigenous sediment influx, accompanied by low diversity, low oxygen and low salinity tolerant species. These environmental conditions abruptly ended with erosion followed by deposition of a phosphatic siltstone layer that represents condensed sedimentation in an open (transgressive) marine environment. Above this layer, low sealevels and a return to near-shore, hyposaline and hypoxic conditions prevailed for a short interval [(base of Plc(2)] and are followed by the re-establishment of normal open marine conditions (inner neritic) comparable to the late Maastrichtian. This marine transgression is accompanied by increased productivity, and the first diversified Danian foraminiferal assemblages after the K/T boundary event and represents the return to normal biotic marine conditions. Though the K/T Seldja section represents one of the most shallow marginal sea environments studied to date for this interval, it does not represent isolated or atypical conditions. This is suggested by the similar global trends observed in sea-level fluctuations, hiatuses, as well as faunal assemblages. We conclude that on the Saharan platform of southern Tunisia, longterm environmental stresses beginning 100–200 kyr before the K/T boundary and related to climate, sea-level, nutrient, oxygen and salinity fluctuations, were the primary causes for the eventual demise of the Cretaceous fauna in the early Danian. The K/T boundary bolide impact appears to have had a relatively incidental short-term effect on this marine biota.

Characterization of aquifers conducting groundwaters with low and high arsenic concentrations: a comparative case study from West Bengal, India

Abstract Possible relationships between groundwater arsenic concentration and alluvial sediment characteristics in a ~19 km2 area in West Bengal have been investigated using a combination of hydrogeochemical, lithogeochemical and geophysical techniques. Arsenic hotspots, typically associated with elevated groundwater Fe and Mn, were found to be correlated to some extent with old river channels (abandoned meanders, oxbow lakes), where sandy aquifers included intercalated fine-grained overbank deposits, rich in As, Fe, Mn and Corg. Otherwise no demonstrably significant overall differences in any of lithology, grain-size distribution, mineral composition or Fe, Mn and organic C content of the sediments were found between two representative sites with contrastingly low (<50 μg 1-1) and high (>200 μg 1-1) As groundwater contents. Our results are consistent with microbially mediated redox reactions controlled by the presence of natural organic matter within the aquifer and the occurrence of As-bearing redox traps, primarily formed by Fb and Mn oxides/hydroxides, being the most important factors which control the release of As into shallow groundwaters at the study site.

Verteilung verkehrsbedingter Edelmetallimmissionen in Böden

ZusammenfassungDie Verteilung verkehrsbedingter Platingruppenelemente (PGE) aus Kfz-Abgaskatalysatoren in straßennahen Böden wurde an verschiedenen Standorten untersucht. Entlang senkrecht zur Fahrbahn verlaufender Traversen (0,1–10 m) wurden Bodenproben aus drei unterschiedlichen Bodentiefen entnommen. Die Bestimmung der Gehalte an Platin, Rhodium und Palladium erfolgte nach Abtrennung und Anreicherung durch Nickelsulfid-Dokimasie und naßchemischem Aufschluß (HCl/H2O2) mittels ICP-MS. Die Platinkonzentrationen im straßennahen Boden liegen zwischen 250 μg/kg und den geogenen Hintergrundwerten. Die Platin/Rhodium-Verhältnisse in Straßensedimenten und kontaminierten Oberböden liegen bei 6∶1 und entsprechen somit weitgehend den langjährig in der Katalysatorproduktion eingesetzten Mengenverhältnissen. Deutliche Abhängigkeiten der Immissionen von der Entfernung zur Fahrbahn, der Bodentiefe und Standortmerkmalen, wie Hauptwindrichtung, Barrieren durch Vegetation oder Morphologie sowie der Verkehrsdichte und Stauhäufigkeit zeichnen sich anhand der gemessenen Konzentrationsprofile ab.AbstractContents and distribution of platinum-group-elements (PGE) in soils caused by automobile emissions were investigated at three transects perpendicular to the road at various depths. Concentrations of platinum, rhodium and palladium were determined by ICP-MS after separation and preconcentration by nickel-sulphide fire-assay. Platinum contents in roadside soils range from 250 μg/kg to the local background values which are below 0.5–0.8 μg/kg. Ratios of platinum and rhodium (about 6∶1) are similar to the ratios in catalytic converters. There is evidence for a significant correlation of PGE input and local parameters such as traffic-conditions, distance from the trafficlane, prevailing wind direction, and barriers such as vegetation or morphology.

Trace elements, stable isotopes, and clay mineralogy of the Elles II K–T boundary section in Tunisia: indications for sea level fluctuations and primary productivity

Abstract Trace elements and stable isotopes in bulk rocks and foraminifera, bulk rock and clay mineral compositions, are used as palaeoproxies to evaluate sea level fluctuations, climatic changes and variations in primary productivity across the K–T transition at Elles II in Tunisia from 1 m (∼33 kyr) below to 1 m (∼70 kyr) above the K–T boundary. Results on clay minerals, major and trace elements, stable isotopes in bulk rock samples (e.g. Ca, Cu, Zn, Rb, Sr, Zr, Ba, δ13C and δ18O), and in foraminifera (Sr/Ca, δ13C, δ18O) indicate that the latest Maastrichtian (last ∼33 kyr) in Tunisia was marked by a relatively warm, but humid climate and a rising sea level. The transgressive surface is marked by deposition of a foraminiferal packstone just below the K–T boundary followed by maximum flooding across the K–T boundary (red layer and black clay layer). Humid warm conditions accompanied the maximum flooding, along with increased total organic carbon values and rapidly decreasing primary productivity. At the K–T boundary, an impact event (Ir anomaly, Ni-rich spinels, spherules) exacerbated already stressed environmental conditions leading to the mass extinction of tropical planktic foraminifera. Increasingly more humid conditions prevailed within the lowermost Danian Zone P0 (∼50 kyr) culminating in a sea level lowstand near the top of P0. A slow recovery of the ecosystem in Zone P1a coincided with a rising sea level and gradually less humid climatic conditions.

S- and O-isotopic character of dissolved sulphate in the cover rock aquifers of a Zechstein salt dome

Abstract Sulfur and O isotope analyses of dissolved SO4 were used to constrain a hydrogeological model for the area overlying the Gorleben–Rambow Salt Structure, Northern Germany. Samples were collected from 80 wells screened at different depth-intervals. The study area consists of a set of two vertically stacked aquifer systems. Generally, the isotope data show a good spatial correlation, outlining well-defined groundwater zones containing SO4 of characteristic isotopic composition. Highly saline waters from deeper parts of the lower aquifer system are characterized by rather constant SO4 isotopic compositions, which are typical of Permian Zechstein evaporites (δ34S=9.6–11.9‰; δ18O=9.5–12.1‰). Above this is a transition zone containing ground waters of intermediate salinity and slightly higher isotopic values (average δ34S=16.6‰; δ18O=15.3‰). The confined groundwater horizon on the top of the lower aquifer system below the low permeable Hamburg Clays is low in total dissolved solids and is characterized by an extreme 34S enrichment (average δ34S=39.1‰; δ18O=18.4‰), suggesting that bacterially mediated SO4 reduction is a dominant geochemical process in this zone. Two areas of distinct isotopic composition can be identified in the shallow ground water horizons of the upper hydrogeological system. Sulfate in groundwaters adjacent to the river Elbe and Locknitz has a typical meteoric isotopic signature (δ34S=5.2‰; δ18O=8.2‰), whereas the central part of the area is characterized by more elevated isotopic ratios (δ34S=12.7‰; δ18O=15.6‰). The two major SO4 pools in the area are represented by Permian seawater SO4 and a SO4 of meteoric origin that has been mixed with SO4 resulting from the oxidation of pyrite. It is suggested that the S-isotope compositions observed reflect the nature of the SO4 source that have been modified to various extent by bacterial SO4 reduction. Groundwaters with transitional salinity have resulted from mixing between brines and low-mineralized waters affected by bacterial SO4 reduction.