STABLE ISOTOPES AND 137CS DATING OF SEDIMENT CORES FROM THE WESTERN BASIN OF LAKE EIRE: PRELIMINARY RESULTS

Stable isotopes (oxygen, carbon, deuterium), physiochemical parameters and ¹³⁷Cs isotopes were determined for water and sediment samples from several cores from the Western Basin of Lake Eire. These analyses were carried out to investigate lake isotopic chemistry and productivity, sedimentation history, and the consequent effect on the historical contaminant input in the basin. ¹³⁷Cs isotope analyses from 145 sediment samples provided an excellent record about the sedimentation rate of the Western Basin of Lake Eire. Sedimentation rate from four locations within the basin show values varying between 0.297 cm/yr and 0.493 cm/yr. These variations reflect proximity to the shipping channel or areas affected by bioturbation caused by the presence of mayfly in the sediment. The sediment chronology is based on the assumption that the peak Cs activity registered in the investigated cores correspond to the global fallout of radiocesium during the atmospheric nuclear bomb testing in 1963, and taking into consideration atmospheric flux and sediment density.

Oxygen and deuterium isotopes in porewater do not show a significant vertical variation in any of the four cores investigated. However, deuterium isotope values show a slight departure from the regional meteoric water line (MWL) of southwest Ontario and southwest Michigan. The carbon isotopic composition of the water column of the Western Basin of Lake Eire is fairly consistent between the surface layer and the bottom layer. In contrast, the carbon isotopic composition of the porewaters shows a significant variation down core (varies between –13.7 to +7.5 per mil VPDB). These variations reflect changes in water productivity and changes in redox conditions with time.