EUTROPHICATION

IB Environmental Systems and Societies © by Lorne J. Young, published by TEACHINGpoint 2 Eutrophication is the natural process of the aging of a body of water over time. As more nutrients enter the body of water and more organisms live and die and add their organic molecules to the decaying and recycling process, bodies of water evolve from an oligotrophic (clear, deep, cold, nutrient poor, few organisms, small, simple food chains, high oxygen content) to eutrophic (turbid, shallow, warm, nutrient rich, complex food webs (which then become reduced as the process goes so far as to become detrimental to life), low oxygen content).

IB Environmental Systems and Societies © by Lorne J. Young, published by TEACHINGpoint 3 Even though eutrophication is a natural process it can be accelerated greatly by human activities such as increasing levels of nitrates and phosphates from detergents, sewage and fertilizers from agricultural runoff.

IB Environmental Systems and Societies © by Lorne J. Young, published by TEACHINGpoint 4 The “ death ” of Lake Erie in the mid 1960 ’ s is a classic example of eutrophication as a direct result of man ’ s dumping of huge amounts of detergents and fertilizers into the lake over a relatively short period of time.

IB Environmental Systems and Societies © by Lorne J. Young, published by TEACHINGpoint 5 Aerial view of Lake 227 circa 1975, showing the many marker floats used for intensively studying this small, experimentally fertilized lake.

IB Environmental Systems and Societies © by Lorne J. Young, published by TEACHINGpoint 6 Aerial view of Lake 227 in Note the bright green colour caused by algae stimulated by the experimental addition of phosphorus for the 26th consecutive year. Lake 305 in the background is unfertilized.

IB Environmental Systems and Societies © by Lorne J. Young, published by TEACHINGpoint 7 ELA Lake 226 was the site of a visually spectacular experiment. The lake was divided into two approximately equal portions using a plastic divider curtain. Carbon and nitrogen were added to one half of the lake, while carbon, nitrogen and phosphorus were added to the other half. For eight consecutive years, the side receiving phosphorus developed eutrophic algal blooms, while the side receiving only carbon and nitrogen did not (see photo, below). However, after only two years, this experiment convinced even the skeptics that phosphorus is the key nutrient. A multi- billion dollar phosphate control program was soon instituted within the St. Lawrence Great Lakes Basin. Legislation to control phosphates in sewage, and to remove phosphates from laundry detergents, was part of this program.

IB Environmental Systems and Societies © by Lorne J. Young, published by TEACHINGpoint 8 View from above Lake 226 divider curtain in August The bright green colour results from bluegreen algae (Cyanobacteria), which are growing on phosphorus added to the near side of the curtain.