Life on Earth is sustained by ecosystems, which vary greatly but have certain attributes in common.  This section should foster your understanding of the material covered in the text regarding the concepts of the ecosystem and why they are crucial to an understanding of many environmental issues.  

ENVIRONMENTAL ISSUE  - Can Damaged Ecosystems Be Restored? 

   In the 1960s, Lake Erie was pronounced dead, its oxygen depleted in deep waters, its surface choked by overgrowth of algae, and some of its top predators endangered.  Scientists concluded that the major cause of the destruction of the Lake Erie ecosystem was too much phophorus from municipal waste.  Through cooperation, the United States and Canada improved waste treatment in communities surrounding Lake Erie.  By 1985, the annual release of phosphorus from these sources had been reduced by 84%.

     Lake Erie is the world's twelth largest lake.  Bordered by New York, Pennsylvania, Ohio, Michigan, and the Provice of Ontario, the lake is 388 km long and covers an area of 25,690 square kilometers.  As the water quality improved with phosphorus abatement, algal growth declined and oxygen levels improved.  Populations of fish that feed on other fish rebounded, and programs to stock the lake with salmon were successful.  Despite this success, blue pike, once a commercially valuable species, may have become extinct.  Increases in potassium, sodium, and calcium, which come in runoff from developments and farms, cannot be reduced.  Development of the shoreline, including wetlands, and contamination with toxic chemicals from nearby industries continue.

   By 1991, the total phosphorus in Lake Erie had been reduced almost to the target levels set by scientists.  Oxygen depletion has decreased significantly except in the central basin, and oxygen levels are expected to continue to improve through the end of the century.  By 1993, water clarity had improved drmatically as a result of the decline in algae in the lake.  Has Lake Erie been restored to its former condition?