Impacts of climate change on lakes

October 21, 2008

Sapporo/Magdeburg. Climate change will have different effects on lakes in warmer and colder regions of the globe. This is the conclusion reached by Japanese and German researchers following studies of very deep caldera lakes in Japan. Scientists from Hokkaido University, the Hokkaido Institute of Environmental Sciences, Kagoshima University and the Helmholtz Centre for Environmental Research (UFZ) compared current measurements with measurements taken 70 years ago. This confirmed a rise in temperatures in the deep water layers of lakes in the south of Japan, while the deep water temperatures of lakes in the north remained the same. Rising temperatures can lead to changes in nutrient exchange and turnover in the water. In certain circumstances, winter circulation behaviour can be so severely affected by rising temperatures and other climatic factors that oxygen supplies to the lower depths become insufficient for many organisms, leading to an accumulation of nutrients in the deep water, say the researchers writing in Geophysical Research Letters.

Measurements from 2005 and 2007 in deep Japanese caldera lakes provide information about the distribution of dissolved nutrients in the water. There are two reasons why this chain of lakes makes an excellent research subject for providing general information about circulation under changeable climatic conditions that will be valid for lakes outside the research area. Firstly, the lakes cover a climate gradient that stretches from the south of Japan to the northern island of Hokkaido. Secondly, oxygen and nutrient exchange between the deep water and the surface in the lakes under investigation is controlled almost exclusively by temperature differences.

The researchers found that almost all of the lakes studied displayed a good distribution of the dissolved nutrients, despite their enormous depths of up to 423 metres (Lake Tazawa, Honshu). The lakes can be divided into two main depth-circulation categories based on their climatic conditions.

The researchers expect deep water temperatures of colder lakes (e.g. Lake Shikotsu, Hokkaido) to remain unchanged in warmer winters, provided the temperature rises are not excessive, while deep water temperatures in warmer lakes are likely to rise. This was confirmed by comparisons with single-point measurements from the 1930s. The scientists warn that a very steep rise in winter temperatures over the years results in water temperatures that do not fall anywhere near as low as the temperatures of the previous years and depth circulation can cease altogether (Lake Ikeda, Kyushu). In such circumstances oxygen supplies and nutrient distribution would be interrupted, which would have impacts on organisms.

Water quality in lakes is an important economic factor for tourism, water companies and fishing businesses. Together with colleagues in Australia, Canada and Spain, UFZ scientists are therefore working on numeric lake simulation models which are designed to provide predictions about water quality under altered conditions.
-end-
Publications

Boehrer, B., R. Fukuyama, and K. Chikita (2008), Stratification of very deep, thermally stratified lakes, Geophys. Res. Lett., 35, L16405, doi:10.1029/2008GL034519. http://www.agu.org/pubs/crossref/2008/2008GL034519.shtml

The research was founded by the Japan Society for the Promotion of Science (JSPS).

Boehrer, B., and M. Schultze (2008), Stratification of lakes, Rev. Geophys., 46, RG2005, doi:10.1029/2006RG000210. http://www.agu.org/pubs/crossref/2008/2006RG000210.shtml

Further Information:

Dr Bertram Boehrer
Helmholtz Centre for Environmental Research (UFZ)
Telephone: +49-391-810-9441
http://www.ufz.de/index.php?de=1830

Prof. Kazuhisa CHIKITA
Laboratory of Physical Hydrology,
Faculty of Science,
Hokkaido University
Sapporo, JAPAN
Phone: +81-11-706-2764

Links:

Stratifcation of Lakes: http://www.ufz.de/index.php?en=17114

Stirred, not shaken from: UFZ Magazine 12 (2006), page 37-39 http://www.ufz.de/data/magazin_engl_web28815.pdf

At the Helmholtz Centre for Environmental Research (UFZ) scientists research the causes and consequences of far-reaching environmental changes. They study water resources, biological diversity, the consequences of climate change and adaptation possibilities, environmental and biotechnologies, bio energy, the behaviour of chemicals in the environment and their effect on health, as well as modelling and social science issues. Their guiding research principle is supporting the sustainable use of natural resources and helping to secure these basic requirements of life over the long term under the influence of global change. The UFZ employs 900 people at its sites in Leipzig, Halle and Magdeburg. It is funded by the German government and by the states of Saxony and Saxony-Anhalt.

The Helmholtz Association helps solve major, pressing challenges facing society, science and the economy with top scientific achievements in six research areas: Energy, Earth and Environment, Health, Key Technologies, Structure of Matter, Transport and Space. With 25,700 employees in 15 research centres and an annual budget of around EUR 2.3 billion, the Helmholtz Association is Germany's largest scientific organisation. Its work follows in the tradition of the great natural scientist Hermann von Helmholtz (1821-1894).

Helmholtz Association

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