Assessing the impacts of the main river and anthropogenic use on the degree of metal contamination of oxbow lake sediments (Tisza River Valley, Hungary)

Abstract

Purpose: Oxbow lakes, reaches that were cut off from a river during river straightening works, can accumulate during flooding metal-rich suspended sediments transported by a river from mining-impacted source areas and other anthropogenic sources. Additionally, the anthropogenic use of oxbow lakes may significantly impact the sediment-bound metal concentrations. The aim was to determine the dominating effect in the sediments’ enrichment in heavy metals. Materials and methods: We collected surface sediments (< 10-cm depth) from seven oxbow lakes once connected to the Tisza River (a transboundary river in Central and Eastern Europe). Four of the oxbows were located on the active floodplain, while three oxbows were at the reclaimed side (i.e., outside the flood defense levee). The sediment samples were subjected to total metal analyses (Cd, Co, Cr, Cu, Ni, Pb, and Zn) and sequential chemical extractions. Results and discussion: Contamination indices (geoaccumulation index (Igeo) and pollution load index (PLI)) show a moderate but significant metal pollution of oxbow lakes situated on the active floodplain (Igeo (Pb) 0.95–1.25, PLI 2.1–2.8) and an overall unpolluted to slightly polluted status of those at the reclaimed side (Igeo (Pb) − 0.36–0.51, PLI 1.3–1.7). Additionally, the geochemical fractionation of the target metals showed that Cd and Zn were the most labile (Cd 29–48%, Zn 18–37% of non-residual proportions), indicating their environmental significance. Conclusions: Canonical discriminant analysis of the sediment-bound metal concentrations revealed the prevalent role of the river connection over the anthropogenic use in controlling the metal enrichment of oxbow sediments.