Ondřej Bábek

Robust assessment of moderate heavy metal contamination levels in floodplain sediments: a case study on the Jizera River, Czech Republic.

Enrichment factors for Cr, Cu, Ni, Pb and Zn in floodplain fines from the middle and the lower courses of the Jizera River (a tributary of the Elbe River in the Czech Republic) were evaluated to compare the original contamination profiles with post-depositional and pedogenic changes. Background concentrations of heavy metals were assessed from uncontaminated sediments (soils) in the study area that belong to the same sedimentary facies and were not affected by reductimorphic processes. Facies assignment is accessible by geophysical imaging combined with core analysis. Sediments from point bars and channel banks in direct contact with riverine water are more heavily polluted than overbank fines from the distal floodplain. The point pollution source, a century-old battery and car production facility in the city of Mladá Boleslav, has certainly been responsible for Ni and Cr pollution, contributed substantially to Cu and Pb pollution, and had a less significant effect on the Zn enrichment factor. Although the use of soil enrichment factors has been criticized, these factors help to manage hydraulic sorting and recognition of post-depositional migration in soil profiles of floodplain sediments. When moderate pollution (enrichment factor about 1.5 for Cu, Pb and Zn) is found, background concentrations must be carefully evaluated and natural enrichment must be taken into account. Studies of such small enrichment factors contribute to the understanding of the dispersal and fates of pollutants in floodplains.

Regional Contamination of Moravia (South-Eastern Czech Republic): Temporal Shift of Pb and Zn Loading in Fluvial Sediments

Regional contamination by Pb and Zn in southern Moravia (south-east part of the Czech Republic) in the twentieth century was analysed in Brno Dam lake sediments and in floodplain sediments of the Morava River near Strážnice. The age model for the Brno Dam lake sediments has been obtained by 137Cs (maxima corresponding to the nuclear tests in atmosphere and the 1986 Chernobyl accident) and the construction of the dam (1940); the time constraints for the Morava River sediments was the erection of flood defences (1930s) and 210Pb dating. In the case of floodplain sediments, profiles exhibiting post-depositional mobilisation of heavy metals by pedogenic processes (gleying) must be excluded to reconstruct the history of contamination. There was a relatively fast joint onset of Pb and Zn load since the early stages of industrialisation in the first half of the twentieth century, but then the concentrations of these two metals developed in a different manner. Pb load only slightly increased till its peak in 1960s and 1970s. The increase of Zn load was rather stepwise: Soon before 1930s (Morava River floodplain) and in 1940s and 1950s (in Brno Lake), the relative contamination by Zn was much lower than during its peak in the 1970s to the present days. The offset of Pb and Zn contamination curves could have been caused by three different artificial sources of these heavy metals. The temporal shift of Pb and Zn loads can be used for dating sediments.

A high-resolution, multiproxy stratigraphic analysis of the Devonian–Carboniferous boundary sections in the Moravian Karst (Czech Republic) and a correlation with the Carnic Alps (Austria)

A multidisciplinary correlation of the Devonian–Carboniferous (D–C) boundary sections from the Moravian Karst (Czech Republic) and the Carnic Alps (Austria), based on conodont and foraminifer biostratigraphy, microfacies analysis, field gamma-ray spectroscopy (GRS), carbon isotopes and element geochemistry, is presented in this paper. The study is focused on the interval from the Middle Palmatolepis gracilis expansa Zone (Late Famennian) to the Siphonodella sandbergi Zone (Early Tournaisian). In Lesni lom (Moravian Karst), a positive δ 13 C excursion in the Bisphatodus costatus – Protognathodus kockeli Interregnum from a distinct laminated carbonate horizon is correlated with a carbon isotope excursion from the Grune Schneid section of the Carnic Alps and is interpreted as the equivalent of the Hangenberg black shales and a local expression of the global Hangenberg Event sensu stricto . Higher up at both sections, a significant increase in the terrigenous input, which is inferred from the GRS signal and elevated concentrations of terrigenous elements (Si, Ti, Zr, Rb, Al, etc.), provides another correlation tieline and is interpreted as the equivalent of the Hangenberg sandstone. Both horizons are discussed in terms of relative sea-level fluctuations and palaeoceanographic changes. Recent studies show that conodont biostratigraphy is facing serious problems associated with the taxonomy of the first siphonodellids, their dependence on facies and discontinuous occurrences of protognathodids at the D–C boundary. Therefore, the correlative potential of geochemical and petrophysical signatures is high and offers an alternative for the refining of the problematic biostratigraphic division of the D–C boundary.

Distribution of Heavy-Metal Contamination in Regulated River-Channel Deposits: a Magnetic Susceptibility and Grain-Size Approach; River Morava, Czech Republic

Anthropogenic contamination by heavy metals in fluvial systems is mostly bound to fine-grained clay minerals and organic substances, which accumulate by vertical accretion in sediment traps along river courses (oxbow lakes, dams and floodplains). These environmental settings are considered as good archives of historical changes in contamination. Much less attention, however, is paid to deposits of river channels, which act as sourcing transport paths for these archives and/or build archives of their own. In order to provide a better insight into the spatio-temporal distribution of pollutants in channel deposits, we investigated contamination levels of Cu, Pb and Zn in a series of sediment cores along the River Morava, a left-hand tributary of the Danube River, Czech Republic. In particular, the relationships between metal concentrations, sediment lithology (facies), grain size, magnetic susceptibility and mineralogy and chemistry of fly-ash particles were investigated. Element chemistry and lithology of channel deposits were compared with those of the nearby floodplain deposits in the same catchment. Four river-channel facies were defined, ranging from sandy gravels to clayey silts, and confronted with the floodplain sediments. Al/Si ratios were found to be useful proxies of grain size, and Al was utilized as an excellent normalizing element for heavy metals, which filters out much of the grain size effects on contamination. The floodplain deposits are significantly less contaminated than their river-channel counterparts. Heavy-metal contamination of river bed sediments (expressed as enrichment factors, EFs) is not simply bound to fine-grained particles, and much of the contamination was found in coarse-grained, sandy facies. Elevated EFs of Zn, Cu and Pb in several sediment layers, which show high magnetic susceptibility (MS), high values of MS normalized to Fe and a high proportion of magnetic fly-ash spherules and their chemistry suggest that significant part of the heavy-metal contamination can be carried by magnetic fly-ash spherules. A part of this contamination is bound to coarse-grained fluvial facies, indicating that the magnetic spherules can be transported as bed load sediments. Magnetic pollution and heavy-metal pollution can therefore coincide in river bed deposits. It is suggested that most of this contamination can be related to local point sources of pollutants (fly-ash deposit spills).

Sedimentary record and anthropogenic pollution of a complex, multiple source fed dam reservoirs: An example from the Nové Mlýny reservoir, Czech Republic.

While numerous studies of dam reservoirs contamination are reported world-wide, we present a missing link in the study of reservoirs sourced from multiple river catchments. In such reservoirs, different point sources of contaminants and variable composition of their sedimentary matrices add to extremely complex geochemical patterns. We studied a unique, step-wise filled Nové Mlýny dam reservoir, Czech Republic, which consists of three interconnected sub-basins. Their source areas are located in units with contrasting geology and different levels and sources of contamination. The aim of this study is to provide an insight into the provenance of the sediment, including lithogenic elements and anthropogenic pollutants, to investigate the sediment dispersal across the reservoir, and to assess the heavy metal pollution in each basin. The study is based on multi-proxy stratigraphic analysis and geochemistry of sediment cores. There is a considerable gradient in the sediment grain size, brightness, MS and geochemistry, which reflects changing hydrodynamic energy conditions and primary pelagic production of CaCO3. The thickness of sediments generally decreases from proximal to distal parts, but underwater currents can accumulate higher amounts of sediments in distal parts near the thalweg line. Average sedimentation rates vary over a wide range from 0.58cm/yr to 2.33cm/yr. In addition, the petrophysical patterns, concentrations of lithogenic elements and their ratios made it possible to identify two main provenance areas, the Dyje River catchment (upper basin) and the Svratka and Jihlava River catchments (middle and lower basin). Enrichment factors (EF) were used for distinguishing the anthropogenic element contribution from the local background levels. We found moderate Zn and Cu pollution (EF ~2 to 5) in the upper basin and Zn, Cu and Pb (EF ~2 to 4.5) in the middle basin with the peak contamination in the late 1980s, indicating that the two basins have different contamination histories.

Late Chadian–early Arundian high-resolution biostratigraphy in the Ogmore-by-Sea section (South Wales–Mendip shelf) and the mid-Avonian unconformity

The study of the foraminiferal fauna in the Ogmore section in south Wales produced a detailed late Chadian–early Arundian biostratigraphy and sequence stratigraphy with a higher resolution than in the Arundian stratotype in Hobbyhorse Bay. The earliest Visean (late Chadian) pedogenic horizon close to the Gully Oolite and Caswell Bay Mudstone boundary (MFZ9) corresponds to the mid-Avonian unconformity. The entry of primitive archaediscids of MFZ10 within the Caswell Bay Mudstone is followed by more advanced archaediscids of MFZ11 at the base of the High Tor Limestone. The mid-Avonian unconformity at the Chadian–Arundian boundary is not confined to the London–Brabant Massif, but is also present in central Europe, the East European Platform, the Urals, west Siberia and probably also in Kuzbass and North America. The global extent of the the mid-Avonian unconformity suggests that it is a consequence of early to mid-Visean glacioeustacy.

Practical Aspects of Log-ratio Coordinate Representations in Regression with Compositional Response

Abstract Regression analysis with compositional response, observations carrying relative information, is an appropriate tool for statistical modelling in many scientific areas (e.g. medicine, geochemistry, geology, economics). Even though this technique has been recently intensively studied, there are still some practical aspects that deserve to be further analysed. Here we discuss the issue related to the coordinate representation of compositional data. It is shown that linear relation between particular orthonormal coordinates and centred log-ratio coordinates can be utilized to simplify the computation concerning regression parameters estimation and hypothesis testing. To enhance interpretation of regression parameters, the orthogonal coordinates and their relation with orthonormal and centred log-ratio coordinates are presented. Further we discuss the quality of prediction in different coordinate system. It is shown that the mean squared error (MSE) for orthonormal coordinates is less or equal to the MSE for log-transformed data. Finally, an illustrative real-world example from geology is presented.

Dam reservoirs as an efficient trap for historical pollution: the passage of Hg and Pb through the Ohře River, Czech Republic

The concentration of Hg and Pb pollutants was examined in sediments of a central European lowland river, the Ohře River. The pollution originated from several sources that were active mainly between the thirteenth and twentieth centuries. Its passage through the river system has been altered by two dam reservoirs built in the 1960s. The pre-dam pollution levels were evaluated from historical floodplain and dam reservoir sediments. We evaluated influence of damming on pollution status of sediments using the concept of ambient background concentrations based on the examination of polymodality in the distribution of concentrations and identification of breaks between the concentration modes. The Skalka Dam Reservoir has suppressed the transport of Hg pollution from a chemical factory in Marktredwitz, Germany (nineteenth and twentieth centuries): the dam has decreased the Hg concentrations in the downstream channel sediments by an order of magnitude compared to pre-dam conditions. The concentration of Hg in suspended particulate matter in the outflow from the Skalka Reservoir varies between 10 and 60% of the inflow concentrations depending on the discharge. The Nechranice Dam Reservoir has suppressed the passage of Pb pollution originating from historical metal mining, which has led Pb concentrations in sediments downstream to decrease to the levels of average topsoil pollution in the sub-catchments without ore mining. Both reservoirs act as sediment traps and thus play a beneficial role for the quality of the Ohře River downstream environment.

Assessing provenance of Upper Cretaceous siliciclastics using spectral γ-ray record

Abstract The relationship between contents of clay minerals/grain size and spectral γ-ray record (concentrations of K, U and Th) in sediments is used for interpretation of sedimentary facies in wire-line logs. However, this approach is often complicated by the multi-component nature of mineralogically immature siliciclastics. As mineralogy of the source material and grain-size sorting during transport both contribute to the detrital composition of the final sediment, a joint study of facies and outcrop γ-ray spectra can potentially make the latter an effective tool in provenance studies. This paper provides comparison of outcrop γ-ray data and detailed facies mapping with mineral and chemical composition of the rocks (modal composition; transparent heavy mineral assemblages; WDX SEM chemistry of minerals) and interprets them in terms of provenance changes. We studied the Upper Cretaceous, synorogenic siliciclastic sediments of the Mazák and Godula Formations (Silesian Unit of the Western Carpathians flysch belt). Decreasing mineral maturity of the studied sandstones is consistent with provenance change from craton interior – (Mazák Formation) to transitional continental and recycled orogen sources (Godula Formation). Two major phases of K, U and Th concentration shifts, which occurred close to the Mazák/Godula Formation and Middle/Upper Godula Members boundaries, are consistent with changes in main detrital modes. These trends indicate gradually accelerated influx of material derived from high-grade metamorphic and plutonic rocks during deposition of the Mazák and Godula Formations. These changes are interpreted as reflecting a gradual exhumation and erosion of deeper crustal levels of the source area, the Silesian ridge.

Identification of a Buried Late Cenozoic Maar-Diatreme Structure (North Moravia, Czech Republic)

Abstract The maar-diatreme volcanic structure in the vicinity of the village of Lomnice near the town of Bruntál (North Moravia, Czech Republic) has been investigated using a set of geophysical methods including ground magnetometry, gravimetry and electrical resistivity tomography. The structure was detected by an aerial magnetic survey in the second half of the 20th century. Since its discovery only limited information about this buried structure has been available. The coherence of the magnetic anomaly of 190 nT and Bouguer anomaly of -4.7 mGal indicates a volcanic origin of the structure. The funnel-shaped maar-diatreme structure is filled with lacustrine clay and colluvium of Car-boniferous greywacke, which forms the country rock. The surface diameter of the structure is about 600 m, the depth is more than 400 m. The spatial association with other volcanic centers in the surroundings of the town of Bruntál infers the relative dating of the Lomnice maar. The phreatic eruption and maar-diatreme formation could be an indirect conse-quence of effusive activity of the nearby Velký Roudný volcano. The Lomnice structure is the first Plio-Pleistocene maar-diatreme ever described in North Moravia and Silesia.