Trace metals distribution pattern in floodplain sediments of a lowland river in relation to contemporary valley bottom morphodynamics

Abstract

The distribution of trace metals in alluvial sediments depends on their natural background concentrations, and on the dynamics of contemporary depositional and erosional (mainly flood-induced) processes. Geological and geochemical investigations were carried out in the valley of Vistula River near Magnuszew (central Poland). Sediment samples were collected from a depth of 35 cm and comprise sediments of all defined geomorphological features. Identification and geological interpretation of the morphodynamic sediment features was supported by aerial photographs and high-resolution satellite images. These studies revealed that the distribution of trace metals is closely linked to the morphogenesis of the alluvial floodplain. The highest concentrations of Cu, Co, Zn, V, Cr and Ni were observed in crevasse-splays deposits. By contrast, Sr, Pb and As were concentrated in deposits which fill oxbow lakes (partly infilled with organic deposits). The lowest concentrations of trace metals were detected in flood sediments deposited within erosional troughs. The geomorphological and sedimentological history of the fluvial features explains the pattern of heavy metal distribution on the current floodplain surface.

Floodplain morphodynamics and distribution of trace elements in overbank deposits, Vistula River Valley Gorge near Solec nad Wisłą, Poland

“…This phenomenon also occurred after the construction of flood banks as a result of failures in these embankments. Sediments deposited in the place of eroded older deposits are often characterised by a much greater variability in grain size and mineral composition than deposits from the period of the meandering river (Falkowski 2007;Falkowska and Falkowski 2015). Contemporary flood flows reworked also the oxbow lakes from the period of the meandering river, filling them, often completely, with mineral sediment.…”

“…However, despite a direct relationship between the content of anthropogenically introduced elements in river water and alluvial sediments, their concentrations in the individual grain-size fractions often show significant differences (Martin 2004). Changes in the supply of trace elements in the history of the drainage basin in the particular section of the river valley can also show a completely different record in the individual morphodynamic zones of its floodplain (Falkowska and Falkowski 2015). This stems from the fact that the amount of transported elements depends on both the geochemical and mineralogical characteristics of the sediment, as well as on the chemical and dynamic properties of the water environment (Förstner and Wittman 1983;Miller 1997;Ciszewski et al 2004).…”

“…Various mineral components of the suspension bind trace elements to a different extent. Therefore, their concentrations in sediments are affected by its mineral composition, the clay fraction content, and the contents of organic matter, CaCO 3 , iron oxides and hydroxides (Velde 1995;Miller and Orbock-Miller 2007;Falkowska and Falkowski 2015). The sedimentary conditions of individual minerals in the river bedload, that bind various trace elements within the fluvial environment, vary and depend on both the geomorphological conditions of the flow and hydrological regime of the river (Miller 1997;Miller et al 1998;Walling et al 2003;Ciszewski et al 2004;Galán et al 2008;Conde Bueno et al 2009).…”

“…The second of these parameters characterises the dynamics of discharge across a vast floodplain (Wyżga and Ciszewski 2010). Various geomorphological features of the floodplain along the lowland river's mature valley contain characteristic trace elements (Falkowska and Falkowski 2015).…”

“…These have been reworking the floodplain surface before man-made levees were constructed, and later as a result of failure in these structures (Wierzbicki et al 2013). These events have left clear signs not only in the lithology and textures of surface deposits (Gębica and Sokołowski 2001), but also in the microrelief of the valley floor (Falkowska and Falkowski 2015). Morphodynamic analysis of the floodplain surface should therefore be a key to identify the diversity of sedimentary environments, affecting the specific contents of trace metals in contemporary overbank sediments, especially in zones of narrowing of the floodplain belt.…”