Sediments and sedimentary history of Lake Attersee (Salzkammergut, Austria)

Abstract

Attersee represents a good example of a lake situated in the Northern forelands of the Northern Calcareous Alps and influenced by different sediment-supplying processes during the postglacial. Several compounds, of different origin, form the sediments of the basin. Clastics which are mainly composed of dolomites derive from the Northern Calcareous Alps. Clastic input of organic and inorganic particles is accomplished by rivers and landslides. They are responsible for the main input of siliciclasts like quartz, feldspar and mica. A high proportion of the sediment results from autochthonous biogenic carbonate precipitation. In the shallow sublittoral areas of the northern part of the lake benthic decalcification caused by encrusting macroand micro-phytes is dominant, while in the southern and central parts of the lake epilimnetic decalcification caused by the blooming of phytoplancton is more important during summer. The total biogenic calcium carbonate production reaches about 11 000 to 12 000 metric tons a year.

Nutrients and residues of cyanophytes (Oscillatoria rubescens) deriving from the eutrophic lake Mondsee were washed into lake Attersee by the Mondseeache. High amount of phosphorus in the sediments of the southern basin depicts local eutrophication in the mouth area of the Mondseeache. The average sedimentation rate in lake Attersee can be determined by different dating methods. Sedimentation rates increased during the last 110 years from 1 mm a year to 1.8–2 mm a year as a result of human activities. Five main phases in the postglacial sedimentary history can be recognized: Würm moraines and finely banded varves (before 13 000 B.P.), the early Attersee stage (from 13 000 B.P. up to 1200 B.P.), and the later Attersee stage after the Bavarian colonization (from 1 200 B.P. on). Using heavy metal and isotope analyses the sedimentary history can be reconstructed in more detail for the last 100 years.