Martin Faměra

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).

Spatial distribution of organic pollutants (PAHs and polar pesticides) in the floodplain of the Ohře (Eger) River, Czech Republic

PurposeThe spatial distributions of organic pollutants, polycyclic aromatic hydrocarbons (PAHs), and polar pesticides were studied in the floodplain of a Middle European lowland river (the Ohře River, Czech Republic) to evaluate their possible use for pollution chemostratigraphy.Materials and methodsThe floodplain evolution and internal structure were evaluated from historical maps, a digital terrain model, and electric resistivity tomography (ERT) at sampling sites. The approximate age of the sediments was inferred from pollution by Cu, Pb, and Sn (sixteenth century and younger), as well as Hg and U (nineteenth to twentieth centuries), based on the known history of metal mining in the Ohře catchment.Results and discussionPolycyclic aromatic hydrocarbons, as non-polar persistent pollutants, have a stable stratigraphic distribution, with peak concentrations attributed to the local peak in the use of coal under low environmental concern from the middle nineteenth century to the late twentieth century as well as a minor peak due to more ancient charcoal production. Polar pesticides range from partially migrating (e.g. atrazine, simazine, and chloridazon) to very mobile ones with depth profiles that are not related to the sediment stratigraphy (e.g., chloroxuron and acetochlor). The post-depositional pollution maxima of the latter are near the contacts of more permeable channel sands and overlay finer, less permeable deposits near the accumulation of mobile elements (Ca, Mn) and minor secondary maxima for Hg and U pollutants.ConclusionsPolycyclic aromatic hydrocarbons can be used for pollution chemostratigraphy; the use of more mobile polar pesticides is limited. The occurrence of pesticides in the forested channel belt (not used for agriculture) and their seasonal variation document considerable dynamics of polar pollutants in fluvial systems.

Geochemical normalization of magnetic susceptibility for investigation of floodplain sediments

Magnetic susceptibility (MS) is commonly used as a proxy for industrial pollution in natural sediments or as a proxy for the percentage of detrital components in peat or carbonates. The MS may also reflect the geology of the sediment source and post-depositional processes in sediments, such as soil development. The aim of our research was to test the usefulness of Fe-normalized mass-specific MS (χ) and Ti-normalized Fe in a study of floodplain sediments. We sampled 27 floodplain sediment cores from several geologically different catchments throughout the Czech Republic, analysed their Fe and Ti concentrations using X-ray fluorescence spectroscopy, and determined their χ. To decipher sediment grain-size dependence and possible magnetic enrichment, background functions for χ were constructed using similar approach as that used for geochemical background functions of the risk element concentrations with Fe concentrations as an independent variable. It provides a mechanism to calculate χ of sediments as it would be “pristine”, i.e. without post-depositional changes and pollution. Sediments derived from “mafic” source rocks had χ/Fe larger by two orders of magnitude than sediments derived from “felsic” rocks. Sediments derived from “mafic” source rocks also exhibit lower mean Fe/Ti ratio in pristine sediment strata than the average upper continental crust. The magnetic carriers inherited from mafic rocks are stepwise destroyed by pedogenesis in the floodplains and thus slowly approach χ of sediments derived from felsic rocks. Gleying processes may change χ/Fe, Fe/Ti ratio allows identifying a past action of those post-depositional processes.

VYUŽITÍ ELEKTRICKÉ ODPOROVÉ TOMOGRAFIE K VIZUALIZACI VÝPLNÍ HISTORICKÝCH STEZEK

Electric resistivity tomography is suitaible method for geophysical survey of shallow subsurface subjects. We selected this method for identification of historical roads relicts. We choosed four localities for our study in the eastern part of Bohemia and north-western part of Moravia. Historical roads are detected by well defined vegetation features and the geoelectric cross sections were drawn across them. The relicts of historical roads are visible on cross resistivity sections. They manifest themselves as anomalous objects with diff erent resistivity. The resistivity is mostly higher than surroundings due to their higher compaction. They are located in depth about 1 m and create oval bodies.

GEOFYZIKÁLNÍ MAPOVÁNÍ KRASOVÝCH STRUKTUR METODOU MULTIELEKTRODOVÉHO ODPOROVÉHO PROFILOVÁNÍ: JESKYNĚ ZA HÁJOVNOU, JAVOŘÍČSKÝ KRAS

This paper investigates the scope and applicability of multielectrode resistivity surveying in the study of buried karst structures. Six resistivity sections, 62 to 117 m long, were measured above the well-documented cave system “Za hajovnou” in the Javořicko Karst, Bohemian Massif. Three domains of distinct resistivity values (27.6 to ~210 Ω.m; ~210 to ~1 300 Ω.m; ~1 300 to 26 112 Ω.m) were interpreted as clays and silts, carbonate-rich karstified zones, and massive carbonate, respectively. Most of the geophysically documented karstification manifests itself in planar zones of karstified carbonate, partly filled with fine-grained siliciclastics, which coincide with several cave corridors in plan view. Orientation of the karstified zones corresponds to the NNE–SSW trending axial plane cleavage and ESE–WNW trending fractures and faults in the underlying rocks. The resistivity surveying proves to be an excellent method for mapping of shallow cave structures.