Warming Bad for Life in Freshwater Lakes and Rivers

Marine and freshwater fish could one day be in trouble as ever-rising levels of carbon dioxide affect aquatic life.

The Alpine lakes of Austria are warming up.  By 2050 their surface waters could be up to 3°C warmer, according to new research in the journal Hydrobiologia.  Martin Dokulil of the Institute for Limnology at the University of Innsbruck studied data from nine lakes larger than 10km2 (3.9 sq mi).  The largest, Bodensee or Lake Constance, touches Austria’s border with Germany and Switzerland to the west; 800 kms to the east, Neusiedler See borders Germany and Hungary.  The nine lakes range from 254 to 1.8 meters maximum depth and they are vital to Austria’s tourist industry:  they play powerful roles in the Alpine ecosystem and they are of course reservoirs of water.  But the Alpine valleys are warming:  between 1980 and 1999 the region warmed at three times the global average and by 2050 the median temperatures for the region could have risen by 3.5°C.  The challenge has been to anticipate the impact of global warming on the lakes.  “The predicted changes in surface water temperatures will affect the thermal characteristics of the lakes,” says Dr Dokulil.  “Warmer water temperatures could lead to enhanced nutrient loads and affect water quality by promoting algal blooms and impairing the biological functions of aquatic organisms.  “Significant increases in summer temperatures will affect the carbon cycling in the lakes, with potential consequences on atmospheric carbon dioxide levels and the Earth’s climate.”  

Next, the fish
The Austrian research so far is concerned only with freshwater temperatures.

Peter Moyle, a biologist at the University of California Davis, has been more concerned with the freshwater fish that make their homes in, or migrate to, California’s rivers and lakes.  He and colleagues report in the journal PLOS One – the Public Library of Science – that if current climate trends continue, then 82 per cent of California’s native fish could be extinct, and their native homes colonized by invasive species.  The scientists looked at 121 native species and found that four fifths of them were likely to be driven to extinction or at least to very low numbers.  These include prized sporting fish such as the Klamath River summer steelhead and other trout, the Central Valley Chinook salmon, the Central Coast coho salmon and many others that depend on cold water.  “These fish are part of the endemic flora and fauna that makes California such a special place,” said Prof Moyle.  “As we lose these fishes, we lose their environments and are much poorer for it.”

Read more at Warming Bad for Life in Freshwater Lakes and Rivers