NATURAL AND ANTHROPOGENIC INFLUENCES ON THE GEOCHEMISTRY OF QUATERNARY LAKE-SEDIMENTS FROM HOLZMAAV, GERMANY

The accumulation of heavy metals and trace elements has been investiga ted in a well laminated sequence of Holocene and late Pleistocene lake sediments composed of diatomaceous gyttja, tuff and silt and clay sed iments. Varve chronology of the annually deposited gyttja yielded a co ntinuous high-resolution time sequence and allowed the absolute age da ting of the sediment. Fluxes of elements remained largely uniform from the late Pleistocene into the Holocene (12 867-2 364 VT years ago; VT : varve time, years before 1950). Higher trace element and heavy metal fluxes occur from 2 322 to 862 VT years ago and reached their maxima in the uppermost sediments (< 845 VT years ago). These increasing elem ent fluxes correlate with increasing inputs of elastic material. The c hanging accumulation rates are the result of elevated soil erosion in the lake catchment caused by human settlement, deforestation and agric ultural activities. Thus disturbances of the natural geochemical cycle s of the Holzmaar region have occurred since the beginning of the Iron Age and especially since the beginning of the Middle Ages.