Tereza Nováková

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.

Distinguishing regional and local sources of pollution by trace metals and magnetic particles in fluvial sediments of the Morava River, Czech Republic

PurposeRegional contamination of southern Moravia (SE part of the Czech Republic) by trace metals and magnetic particles during the twentieth century was quantified in fluvial sediments of the Morava River. The influence of local pollution sources on regional contamination of the river sediments and the effect of sampling site heterogeneity were studied in sediment profiles with different lithologies.Materials and methodsHundreds of sediment samples were obtained from regulated channel banks and naturally inundated floodplains and proxy elemental analyses were carried out by energy dispersive X-ray fluorescence spectroscopy (ED XRF) and further calibrated by inductively coupled plasma mass spectrometry (ICP MS). Magnetic susceptibility was determined as a proxy for industrial contamination. The age model for the floodplain sediments was established from 137Cs and 210Pb dating. Trace metal contamination was assessed by establishing the lithological background values from floodplain profiles and calculating enrichment factors (EF) of trace metals (i.e. Pb, Zn, Cu) and magnetic susceptibility for the entire study area.Results and discussionChannel sediments are unsuitable for the reconstruction of historical regional contamination due to their lithological heterogeneity and the “chaotic” influence of local sources of contamination, as well as the possibility of geochemical mobility of pollutants. On the other hand, sediments from regulated river banks qualitatively reflected the actual, local contamination of the river system.ConclusionsThis approach allowed us to distinguish the influence of local sources of contamination by comparison with more spatially averaged contamination signals from distal floodplain profiles. The studied area is weakly contaminated (EF ∼1–2), while individual sediment strata from regulated channel banks reflect local sources of contamination and contain up to several times higher concentrations of trace metals.

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.

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).

Pollution assessment using local enrichment factors: the Berounka River (Czech Republic)

PurposeThe Berounka River is considered a relatively clean river, but recent studies have reported various levels of pollution. The purpose of this work is to identify anthropogenic pollution by metals (i.e. Pb, Zn, Cu) and magnetic particles in the sediments of that river and its tributaries.Materials and methodsSamples were obtained from hand-drilled cores taken from representative areas within the fluvial system; in distal floodplains (overbank fines) and closer to the channel (laterally deposited sediments). Samples were subjected to analysis using mass magnetic susceptibility (MS), X-ray fluorescence spectrometry (XRF) and also by inductively coupled plasma mass spectrometer (ICP MS) which allowed for a determination of 206Pb/207Pb isotope ratios. Macroelement ratios (K/Ti and Ti/Al) were used to distinguish variegated sediment provenance in the Berounka system. Normalization of trace elements by Ti (in the case of trace elements) and by Fe (magnetic susceptibility) allowed us to establish lithogenic background functions of trace elements and magnetic susceptibility within these two geologically different areas. A pollution assessment of the study area was performed using magnetic susceptibility and local enrichment factors (LEFs) for the risk elements. By comparing 1/(LEF Pb) and Pb isotopic composition, the origins of Pb within the catchment were determined. This unique method was able to distinguish Pb from various origins.Results and discussionThe upper parts of the floodplain cores contained higher levels of trace elements and magnetic particles (anthropogenically polluted), but samples taken from the cores in the active channel belt exhibited considerably higher concentrations of trace elements and magnetic particles than the upper parts of the floodplain cores and to much greater depths. We interpreted the deeper parts of the floodplain cores as a local lithogenic background. The upper parts of floodplain sediments hence showed moderate pollution (LEF of Pb and Zn ∼2, MS ∼2.5); whereas laterally deposited sediments showed significantly higher LEF values (LEF of Pb ∼6, Zn ∼9, MS ∼8).ConclusionsThe analysis of the sediments confirmed that the Berounka River system contains higher concentrations of trace elements and magnetic particles than can be accounted for by natural geological processes. Our pollution assessment of the Berounka River and its tributaries demonstrated that their sediments are moderately polluted from sources situated on its tributaries: Ag–Pb mining near the city of Stříbro in the Mže catchment; Pb–Zn mining in the Příbram ore district in the Litavka catchment and Fe ore processing and smelting in the Klabava catchment.

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.

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.

Larch Tree Rings as a Tool for Reconstructing 20th Century Central European Atmospheric Mercury Trends

We propose the tree rings of European Larch ( Larix decidua) as a widely available and reliable geochemical archive of local and regional changes in atmospheric mercury (Hg). Mean Hg concentrations in larch tree rings from 8 background sites across the Czech Republic ranged from 2.2 to 4.8 μg kg-1; the maximum concentrations occurred in the period 1951-1970. At 3 sites impacted by Hg-emission sources [gold amalgamation processing, caustic soda production, and lead (Pb) ore smelting] mean larch tree ring Hg concentrations were significantly elevated relative to background sites. Changes in larch tree ring Hg concentrations were temporally coherent with known activities at the sites that would alter Hg emissions; the nearly simultaneous response in tree rings indicated little or no translocation of Hg within the larch bole. Based on the present-day atmospheric Hg concentration of 1.63 ng m-3 at the intensively monitored Czech Global Mercury Observation System site and the most recent mean tree ring Hg concentration of 2.8 μg kg-1 in co-located larch trees, we developed a simple distribution model of Hg between the atmosphere and larch tree rings. We applied the model using observed changes of Hg in larch tree rings from the countrywide background sites to reconstruct past atmospheric Hg concentrations in central Europe. Modeled Hg concentrations were in agreement with annual means from the European Monitoring and Evaluation Programme observatories.

Stability of mercury concentration measurements in archived soil and peat samples

Archived soil samples can provide important information on the history of environmental contamination and by comparison with recently collected samples, temporal trends can be inferred. Little previous work has addressed whether mercury (Hg) concentrations in soil samples are stable with long-term storage under standard laboratory conditions. In this study, we have re-analyzed using cold vapor atomic absorption spectroscopy a set of archived soil samples that ranged from relatively pristine mountainous sites to a polluted site near a non-ferrous metal smelter with a wide range of Hg concentrations (6.7-6485 μg kg-1). Samples included organic and mineral soils and peats with a carbon content that ranged from 0.2 to 47.7%. Soil samples were stored in polyethylene bags or bottles and held in laboratory rooms where temperature was not kept to a constant value. Mercury concentrations in four subsets of samples were originally measured in 2000, 2005, 2006 and 2007, and re-analyzed in 2017, i.e. after 17, 12, 11 and 10 years of storage. Statistical analyses of either separated or lumped data yielded no significant differences between the original and current Hg concentrations. Based on these analyses, we show that archived soil and peat samples can be used to evaluate historical soil mercury contamination.