The history of the sedimentation processes and heavy metal pollution in the Central Danube Delta (Romania)

The aim of this study was to investigate the effects of the Iron Gates (IG) hydroelectric power station on the Danube Delta sediment dynamics, and to assess the heavy metal concentrations and pollution in a typical Central Danube Deltaic lake.

Eight sediment cores were analysed. The total ²¹⁰Pb content was measured with ²¹⁰Po using alpha spectrometry, and the supported ²¹⁰Pb (²²⁶Ra) and ¹³⁷Cs were measured by gamma spectrometry. The age depth model was derived by applying the ²¹⁰Pb dating method, and for the calculation of the ages and the sedimentation rates the CRS model was used.

The sedimentation rates can be divided into four periods:1940–1972, 1972–1980, 1972–1989 and 1989–2013. In the case of Lake Iacob in the first period, the average sedimentation rate was 0.418 g/cm²y, while in the second it slowly decreased to 0.376 g/cm²y. In the third period, the sedimentation fell to 0.209 g/cm²y, which means the retention of 27.3% of the sediment by the IG dam. In the case of Lake Isac the changes were more visible: in the first period the average sedimentation rate was 0.446 g/cm²y, while in the second it decreased to 0.197 g/cm²y, which means a 42.35% retention of sediment. In the last period, in both cases, a high increase in the sedimentation rate is shown: 0.677 g/cm²y for Lake Iacob and 0.715 g/cm²y for Lake Isac. The heavy-metal concentrations for As, Co, Cr and Ni show decreasing and Hg increasing tendencies, while Cd and Pb show constant values of 310 ± 12 ppb and 9 ± 1 ppm respectively.