Urbanization: The historical cause of low oxygen conditions in European lakes

October 24, 2016 by Gisèle Bolduc, INRS
Credit: INRS

A new study shows that hypoxia, i.e. low oxygen conditions, in European lakes started in 1850, becoming more widespread after 1900, long before the use of chemical fertilizers and climate change. A Canadian and European research team has identified urban expansion as the reason for the low amounts of bioavailable oxygen in numerous European lakes in past centuries. Published in Proceedings of the National Academy of Sciences, the findings of this study directed by postdoctoral fellow Jean-Philippe Jenny and Professor Pierre Francus of INRS suggest that increased waste water pollution at the turn of the 20th century boosted the lakes' biological productivity, which in turn led to a rise in oxygen consumption.

The researchers analyzed information such as climate, land use, and lake sediment data from more than 1,500 European watersheds. For the first time, they compared reconstructions of land occupancy and land use dynamics on a continental scale to their own data of oxygen depletion over the past 300 years. This allowed them to identify urban waste, primarily phosphorus, as the factor responsible for triggering hypoxia at the bottom of lakes starting at the beginning of the 20th century.

"Accurately identifying the source of the nutrient responsible for was a real challenge because of the variations in environmental stress factors throughout the region and their interactions, as well as the reliability of long term data," explains Professor Francus of the INRS Centre Eau Terre Environnement.

"Point and diffuse sources have always contributed to nutrient supplies in lakes, but at intensities that vary in time and space," adds Jean-Philippe Jenny, now affiliated with the Max Planck Institute for Biogeochemistry in Germany. "Our results show that urban point sources of phosphorus are the dominant cause of eutrophication of European lakes during the Anthropocene."

The researchers recognize, however, that during recent decades, diffuse sources have gradually become the major cause of fresh water eutrophication in developed countries with the increase in the use of and the elimination of point sources due to the installation of waste treatment plants.

"Despite the many cleanup initiatives in the 1980s, the deepest layers in the lakes we studied still are not being reoxygenated and the hypoxia persists. This illustrates the importance of studying historical land use and the need to put long-term strategies in place to maintain and restore water quality in lakes," say the study's authors.

Explore further: Human activities trigger hypoxia in freshwaters around the globe

More information: Urban point sources of nutrients were the leading cause for the historical spread of hypoxia across European lakes, Proceedings of the National Academy of Sciences, www.pnas.org/cgi/doi/10.1073/pnas.1605480113

Related Stories

Northern lakes act as CO2 chimneys in a warming world

November 10, 2015

Many of the world's approximately 117 million lakes act as wet chimneys releasing large amounts of the greenhouse gas carbon dioxide, CO2, into the atmosphere. The most recent estimates show that CO2 emissions from the world's ...

Recommended for you

Archaeologists discover Incan tomb in Peru

February 16, 2019

Peruvian archaeologists discovered an Incan tomb in the north of the country where an elite member of the pre-Columbian empire was buried, one of the investigators announced Friday.

Where is the universe hiding its missing mass?

February 15, 2019

Astronomers have spent decades looking for something that sounds like it would be hard to miss: about a third of the "normal" matter in the Universe. New results from NASA's Chandra X-ray Observatory may have helped them ...

What rising seas mean for local economies

February 15, 2019

Impacts from climate change are not always easy to see. But for many local businesses in coastal communities across the United States, the evidence is right outside their doors—or in their parking lots.

The friendly extortioner takes it all

February 15, 2019

Cooperating with other people makes many things easier. However, competition is also a characteristic aspect of our society. In their struggle for contracts and positions, people have to be more successful than their competitors ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.