Floodplain sediments of the 2002 catastrophic flood at the Vltava (Moldau) River and its tributaries: mineralogy, chemical composition, and post-sedimentary evolution

Fine-grained floodplain sediments of the catastrophic 2002 flood deposited along the lower reaches of the Berounka and Vltava Rivers, Czech Republic, were not highly contaminated with heavy metals and other toxic elements. This is due to the dominantly mineral character of the sediments (C-tot in the range 3.97-5.01%, relatively low content of clay minerals), and due to the very high degree of contamination dilution by eroded pre-industrial non-contaminated floodplain sediments. Despite this high degree of dilution, the influence of the small Litavka River, draining the historical Pb-Zn-Ag Pribram ore region, is well visible. The Litavka River is one of important sources of Pb and Zn contamination in the whole Berounka-Vltava-Labe river system. The 2002 flood sediments deposited in the floodplain of the Berounka and Vltava Rivers show poor vertical chemical zoning, except for some components enriched in the uppermost layer by precipitation from evaporated pore-water contained in the mud, i.e. secondary carbonate. The content of C-carb of the sediments (0.05-0.15%) is partly represented by this secondary carbonate, which is later leached by rainwater, and partly by fragments of river mollusk shells. A majority of the heavy metals contained in sediments can be readily leached by diluted acids, and to a much smaller degree by rainwater.