History book of lakes - The impact of climate, vegetation and man on lakes in the past 10,000 years

Innsbruck/Vienna (FWF) – Does man, through the felling of trees, alpine farming and atmospheric metal pollution produce a more negative effect on lakes than do natural changes, such as climate and vegetation? How long does it take until environmental protection measures actually show effect in lakes? Karin Koinig from the Institute of Zoology and Limnology at the University of Innsbruck tries to find an answer to this and similar questions by examining lake sediment cores dating back up to 14,500 years.
Within the framework of an Erwin Schrödinger Fellowship and sponsored by the Austrian Science Fund (FWF), she analyses long-term changes in the geochemistry of lakes at the Geological Institute of the University of Bern and the Institute for Environmental Geochemistry in Heidelberg.

The sediment cores are cut in thin slices and dated, serving as "history books" of a special kind.
They tell scientists about the environmental changes of the past 10,000 years. Karin Koinig measures the changes in the concentration of the geochemical elements using a special X-ray fluorescence analyser. The results are compared with palaeobotanical and mineralogical profiles.
The analysis is aimed at distinguishing between natural long-term changes in sediment geochemistry and man-induced changes. The researchers are specially interested in metal concentrations, which
in Europe have experienced an anthropogenic increase since the beginning of metal processing in the Bronze Age, and in particular since the onset of industrialisation. Koinig detected a marked
increase in the lead content of alpine lake sediments (Sägistal See, Bernese Alps) over the past 150 years, resulting from increased atmospheric deposition. In the 1970s this increase was steepest and
the lead concentrations reached the highest values. "In the top layers, however, we measured lower levels as a result of the introduction of unleaded petrol", Koinig explains. "This shows how fast environmental protection measures can show effect."
In the older sediment layers, however, changes in metal concentrations are caused by other processes: at the beginning of the Holocene the concentration of all geochemical elements, and hence also of metals, was determined by the extent and type of vegetation cover. This can be
explained by the influence of vegetation cover on erosion. Larger quantities of dust and fine particles were introduced into the lake at times, when its catchment area was only partly covered with forests. The climate-induced migration of spruce into the catchment area about 6,500 years ago resulted in denser forests and a change in particulate deposition and hence also in the geochemical composition of the sediment.
Human influence becomes visible as early as the Bronze Age: trees in the catchment area were felled in order to gain land for alpine pastures, leading to an increase in erosion and a change in the concentration of all geochemical elements in the sediment. The higher nutrient deposition as a result of alpine farming slowly showed its effect on the lake: "Sediment geochemistry suggests that the first signs of eutrophication and reduced oxygen content in the bottom water layers of the lake occurred as early as 3,000 years ago", explains Koinig. The investigation of long-term changes allows the extent of human intervention, which made itself felt even in alpine lakes more than 3,000
years ago, to be compared with natural changes. In this way the researchers intend to asses whether human impact on lakes exceeds the extent of natural fluctuations. In follow-up investigations, Koinig will also examine a lake in the Alpine foothills, whose catchment area was
subject to human settlement much earlier and where agricultural cultivation was more intense:
Koinig: "I also intend to measure natural Sr-isotopes in order to investigate changes in dust deposition or weathering sources."

Dr. Karin A. Koinig
Institute of Zoology and Limnology, University of Innsbruck
Institute of Environmental Geology, University of Heidelberg
T +49 6221 54 4809