Analysis and dating of Pb, Cd, Cu, Zn sediment profiles from the Vitznau basin of Lake Lucerne (Switzerland) / Analyse et datation de profils en Pb, Cd, Cu, Zn de sédiments lacustres provenant du lac des Quatre Cantons, Suisse (bassin de Vitznau)

Abstract

Two parallel sediment cores were recovered in the Vitznau basin of Lake Lucerne, Switzerland, were analysed for % dry weight and for Pb, Cd, Cu, Zn. The dry weight and the four metal profiles show two anomalies at 12 cm and at 39 cm core depth pointing to anomalous sedimentation events. The first anomaly (at 1 2 cm) can be related to the rock fall of the Biirgenstock at Obermatt which occurred in two phases in 1963 and 1964. The second anomaly (at 39 cm) is related to the slide of the Vitznau river in 1674. The mean sedimentation rates, obtained from these two events and the dry weight profiles are S1997.1964 = 0.041 g cm-2 y1 and S,962 .674 = °-025 g cm"2 Г1- The difference in the rates is supposedly primarily due to the deposition of organic matter related to eutro- phication which started in 1954. Before 1800 the metal profiles are constant and these concentrations are considered to represent pre-industrial geochemical background concentrations: 37.9 ±1.8 mg/kg for Pb, 0.53 ±0.10 mg/kg for Cd, 33.0 ± 2.6 mg/kg for Cu, and 103.9 ±5.5 mg/kg for Zn. From 1800 up to 1950 all four metal concentrations increase exponentially and decrease from 1970 onwards to recent days. We consider these curves as related to the increasing diffusive emission of heavy metals in the environment during industrial development and the subsequent efforts of the post-industrial society to limit this pollution. Maximum measured metal concentrations increased by 3.5 (Pb), 3.8 (Cd), 1.7(Cu) and 2.0 (Zn) times relative to natural background concentrations. The relative late decrease of Pb concentration in the profiles, starting around 1975, relates to the ban of leaded gasoline in Switzerland. Actual metal concentrations are still far above the natural background levels.