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Silent Spring - 50th Anniversary Essay Series


50 Years After Silent Spring:  Lessons Learned at Indiana’s Cane Ridge

By Dan Sparks
U.S. Fish and Wildlife Service Contaminants Specialist
Bloomington, Indiana


Least tern in flight.

Selenium from a nearby power generating station was a potential threat to the endangered Least Tern in Indiana. Duke Energy worked with the Service to remediate the contamination.

Photo by USFWS; Steve Hillebrand

Early on in her book Silent Spring, Rachel Carson laments the indiscriminate pesticide use "with little or no advance investigation of their effects on soil, water, wildlife..." and the "lack of prudent concern for the integrity of the natural world that supports life." Carson’s work, published 50 years ago this month, alerted the world to the dangers of indiscriminate use of organochlorine pesticides like DDT.


Carson’s warning of the potential for a silent spring has been widely heeded, but awareness of the problem is not always enough. For example, wet-management of fly-ash from coal-fired power plants can cause high concentrations of selenium in nearby aquatic systems, harming fish and wildlife. Although the problem was first recognized and addressed at Belews Lake North Carolina in the 1980s, wildlife managers found themselves faced with a similar, significant selenium problem in Indiana in 2008, one that threatened Indiana’s nesting population of endangered least terns.


Federally endangered least terns began nesting at Duke Energy’s Gibson Generating Station in southern Indiana in 1986. Terns nested on the center dike in Gibson Lake, the facility’s 3,000-acre cooling pond, and in later years, also nested on the ash ponds, dredge flats, landfill and surrounding roads. To protect and manage least terns at the site, Duke Energy entered into a Habitat Conservation Plan in 1999. In 2004, Cane Ridge, a part of Patoka National Wildlife Refuge near Gibson Generation Station, was created.  Cane Ridge was developed specifically to provide nesting habitat for least terns. Water feeding into the area’s wetlands came directly from Gibson Lake.


Aerial view of the tern management unit on the Cane Ridge unit of Patoka National Wildlife Refuge.

The tern management unit on the Cane Ridge unit of Patoka National Wildlife Refuge.

Photo by Tim Hayes

In 2007, Duke reported high levels of selenium at Gibson Lake and began a full-scale environmental investigation and high levels of selenium were found in water and aquatic life at Cane Ridge. Selenium concentrations in water coming into the tern unit on Cane Ridge from Gibson Lake ranged from 11 to 14 parts per billion. Recommended water quality concentration to protect fish and wildlife is less than 2 parts per billion. 


Although selenium is an essential micronutrient, excessive selenium in the diet of female birds during the period just before egg-laying results in transfer of selenium to eggs and causes severe embryo deformity and chick death.


Following discovery of elevated levels of selenium, the U.S. Fish and Wildlife Service took action to reduce selenium levels available to endangered least terns and other birds feeding on the refuge. In 2008, the Service stopped the flow of water from Gibson Lake into Cane Ridge, drew down the ponds and wetlands, removed approximately 4 tons of fish, and disked the soil on the bottom of the ponds and wetlands to redistribute selenium in the soil and reduce the surface average concentrations of selenium.


Ring billed gulls and white-fronted geese at the Cane Ridge Unit of Patoka National Wildlife Refuge.

Ring billed gulls and white-fronted geese at the Cane Ridge Unit of Patoka National Wildlife Refuge. Ducks, geese, shorebirds, and gulls are only some of the birds that use Cane Ridge.

Photo by Steve Gifford

Later that year, Patoka River National Wildlife Refuge secured $60,000 in Refuge Cleanup Funds to investigate, monitor and take additional management actions to address selenium contamination at Cane Ridge. In 2009, Duke Energy contracted the construction of a new water supply from the Wabash River directly to Cane Ridge. Each spring since then, Duke Energy has stocked 60,000 ready-to-spawn fathead minnows in the tern pool to provide a clean alternative food source in hopes of attracting least terns away from contaminated fish in Gibson Lake.


The results of these efforts have been very positive. In a little more than 2 years, almost every indicator shows that selenium concentrations have significantly declined and are nearing or below concern levels. Selenium residues are down 30 percent in forage fish, 38 percent in invertebrates and 71 percent in sediments of the Cane Ridge tern pool in sampling done in 2010.


The selenium problem at Cane Ridge developed quickly, and could have led to high levels of bird egg mortality at the site. Fortunately, the partnership between Duke Energy and the Service allowed quick action to not only solve the problem but to continue important conservation work at the site. Thanks to that partnership, Cane Ridge continues to provide excellent habitat for a wide variety of birds. An important lesson was learned; perhaps we should all be better students of history.



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Last updated: February 10, 2016