Publication details
Record of river contamination in modern oxbow lake deposits (Czech Republic): Depositional architecture and sediment contamination
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| Year of publication | 2007 |
| Type | Conference abstract |
| MU Faculty or unit | |
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| Description | Most of the toxic compounds transported by rivers are bound to fine-grained solid particles, which are deposited as contaminated fluvial sediments. Much of this contamination is likely to be redistributed, constituting potential serious environmental hazards. Stratigraphic record of sediment contamination is usually incomplete in the highly dynamic systems such as river channels but it can be more complete in floodplains or oxbow lakes. We studied sediments and stratigraphic architecture of an artificial oxbow lake, a former meander separated by river realignment in 1930s. The lake has been connected to the active channel via a water-gate allowing contaminated fine-grained sediments to enter and settle in the lake. Facies analysis of four cores up to 4m long, supported by ground penetration radar (GPR) profiling allowed us to recognise two major depositional phases. The basal fluvial succession (more than 255 cm depth) is composed of light-grey, parallel-laminated, occasionally graded or cross-laminated silts and sandy silts (sand fraction: 8.5 to 30.0 %; silt: 65.4 % to 84.6 %; clay: 4.6 to 6.8 %). In GPR sections, this succession consists of several convex-upward bodies composed of lateral and vertical accretion units. The upper, oxbow-lake succession (0 to 255 cm depths) is composed of horizontally stratified layers of light-coloured silts alternating with dark-coloured silts and sandy silts (sand fraction: 8.4 to 20.1 %; silt: 76.4 to 86.9 %; clay: 3.5 to 6.3 %) rich in organic matter and plant remains. In GPR sections, this succession consists of horizontal reflectors that seal the hummocky upper surface of the underlying succession. Dating of the lake deposits based on the Chernobyl 137Cs anomaly, and the historical records of river realignment indicate relatively high sedimentation rates of ~4 to ~5 cm per year. Contamination in the oxbow lake deposits (Pb: 25.5 to 54.5; As: 8 to 17.3; Cd: 0.6 to 4.8; Suma PAH(16): 6.7 to 29.0 microgram/g; Suma PCB(7): 11.1 to 24.8 ng/g) is much higher than in the underlying fluvial deposits (Pb: 14 to 17.4; As: 5.6 to 7.1; Cd: 0.1 to 0.2; Suma PAH(16): 0.07 to 0.4 microgram/kg; Suma PCB(7): 0.7 to 2.6 ng/g), reaching its maximum approximately 25 to 30 years ago. For the last ~25 years, the contents of toxic organic compounds and heavy metals in the oxbow-lake sediments have decreased by the factor of 2 to 2.5. Unravelling the stratigraphy of the oxbow-lake deposits seems to have great potential in making estimates of the total contamination being transported by rivers, its history and distribution. |
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