BIODIVERSITY: Dying Beneath the Calm Waters

By Julio Godoy Reprint | | Print |

Julio Godoy* - IPS/IFEJ

PARIS, Dec 15 2010 (IPS) - At first glance, Lake Constance, trapped between Germany, Switzerland, and Austria, looks as peaceful as ever. But under the lake’s apparently placid waters, a dramatic change is taking place – one that threatens to obliterate much of local biodiversity.

Lake Constance - what is happening deep down is not so beautiful. Credit: Institut für Seenforschung Langenargen

According to records from the Agency for Environmental Protection of Baden Wuerttemberg, the German federal state in which Lake Constance is situated, the lake’s water temperatures have been rising by 0.3 degrees Celsius per decade over the past 50 years.

This rising of water temperatures is a global phenomenon caused by climate change. A recent study, carried out by the Jet Propulsion Laboratory (JPL) at the U.S. National Aeronautics Administration, confirmed the causal link.

The JPL study, released in August, analyzed surface temperatures extracted from nighttime thermal infrared imagery for 167 large lakes distributed worldwide. The data was collected from 1985 to 2009 for the months July through September and January through March.

The authors of the study, Philipp Schneider and Simon Hook, found that nighttime surface water temperatures have been rapidly warming for the 24- year period by an average of 0.5 degrees Celsius per decade. In some lakes, temperatures rose by as much as 1.3 degrees Celsius in 10 years.

This warming process slows the cyclical exchange of water layers in the lakes. Because warm water is lighter, it tends to remain on the surface of the lake, with cooler, heavier water remaining on the bottom. But during the period of the year when surface temperatures fall, the water layers rotate and mix in a cycle that transports oxygen and other nourishing elements throughout the lakes.

Depending on the size of the lake, the exchange cycle takes place once or twice a year. “But when the surface waters are warmer and remain so longer during the year, the cyclical exchange of waters slows down or does not occur at all,” Karsten Rinke, director of the department of lakes at the German Helmholtz Centre for Environmental Research, told IPS.

For biodiversity living at the bottom of the lakes, slowing down the exchange of waters can be fatal.

“After a while, there is no more oxygen on the bottom, leading to the death of fish and other species,” Rinke said.

One example of this devastation can be seen in whitefish (Coregonidae) that hatch at the bottom of lakes. If there is no oxygen, the new generation of fish literally drowns at the moment of birth.

In addition, many living organisms time their metabolic processes to each other – fish spawn during periods when the proper fodder is available, for example.

“Many of these cycles are temperature-led,” Rinke explained. “The rising of water temperatures provokes incongruences in the habitats the species are not accustomed to.”

Another problem caused by the rising of surface water temperatures in lakes is the proliferation of algae. When surface water is too warm, algae grow at an exponential rate, covering large surfaces of the water. Algae deplete the water’s oxygen supply, aggravating the consequences caused by the slowing down of the water layers’ cyclic exchange.

“Furthermore, warmer waters attract alien species into lakes, which distort the local chain food, crow out local species, and eventually destroy the habitats,” Rinke said.

In recent years, the common basket shell, originally from South East Asia, has become endemic in German lakes, affecting the local habitats.

This is only one example of many instances where climate change is directly responsible for environmental destruction: the rising lake temperatures have consequences that are not yet fully known. What is known, though, is that biodiversity suffers as natural processes are disrupted by these environmental changes.

And water temperatures continue to rise, foreshadowing disaster for the living creatures that call Lake Constance their home.

*This story is part of a series of features on biodiversity by Inter Press Service (IPS), CGIAR/Biodiversity International, International Federation of Environmental Journalists (IFEJ), and the United Nations Environment Programme/Convention on Biological Diversity (UNEP/CBD) – all members of the Alliance of Communicators for Sustainable Development.