East Fork Poplar Creek is on the road to recovery, ecologically speaking.

So says Jim Loar, an ecologist in ORNL's Environmental Sciences Division who has spearheaded the Biological Monitoring and Abatement Program (BMAP) for the Oak Ridge Y-12 Plant. BMAP was established in 1985 so that the Y-12 Plant could receive a National Pollutant Discharge Elimination System permit for releasing effluents to East Fork Poplar Creek.

According to Loar, since 1985 the Laboratory has gathered "evidence of recovery in stream communities and in the health of individual species in East Fork Poplar Creek." The evidence includes decreasing differences in various biochemical, physiological, and other indicators of fish health between the polluted creek and several reference sites--"clean" creeks that meet acceptable water quality criteria.

When the Department of Energy revealed in 1983 that large amounts of mercury had been released to the creek from the Y-12 Plant, very few species of fish and other aquatic organisms inhabited upper and lower East Fork Poplar Creek inside the plant. Today several pollution-tolerant fish species--striped shiner, blacknose dace, central stoneroller, and redbreast sunfish--have returned to these waters.

Since 1985, ORNL researchers Jim Loar and Mike Ryon have observed more than a tenfold increase in fish abundance in East Fork Poplar Creek, just below Lake Reality at the Y-12 Plant. They have observed an increase in the number of pollution-tolerant fish species, such as striped shiners, green sunfish, and central stonerollers. "Also," says Loar, "we are seeing an increase in the number of species from 5 to 14, including such new inhabitants as northern hog suckers and snubnose darters."

Although these changes in the fish communities of East Fork Poplar Creek provide strong evidence of ecological recovery, the stream still has a way to go before it could be considered a reference creek. "For example," Loar says, "what is missing is the presence of pollution-sensitive fish species. However, a few individuals of some pollution-sensitive fish species--bigeye chub, redline darter, and greenside darter--have been observed in the creek for the first time."

Growing evidence shows that the health of fish populations in the polluted creek is improving. This improvement may be attributed to several factors: the implementation of measures to reduce the levels of mercury and chlorine in the stream and the completion of new wastewater treatment facilities since 1985.

Mercury has been discharged into the creek since the early 1950s as a result of separations of lithium isotopes at the Y-12 Plant in support of the hydrogen bomb project. Process water used at the Y-12 Plant and then released to the creek contained chlorine because its source has been the water-treatment plant that provides Oak Ridge's drinking water. Successful efforts have been made to remove chlorine from and keep mercury out of water leaving the plant for the creek.

Loar says that ORNL researchers have been measuring mercury concentrations in fish at five sampling sites along the creek. "There has been a decrease in the concentration of total mercury in redbreast sunfish at the site just below Lake Reality," he notes. "This decrease coincides in time with the draining of New Hope Pond and filling of Lake Reality at the Y-12 Plant in November 1988."

ORNL scientists have compared the health of individual redbreast sunfish from East Fork Poplar Creek, other polluted streams on the Oak Ridge Reservation, and three reference streams. They have examined indicators of nutritional status, such as fat reserves and levels of liver detoxification enzymes, which are elevated when the fish is exposed to contaminants. With the help of scientists at the University of California at Davis, they have quantified tissue abnormalities in the fish. They have even counted DNA strand breaks, a biological marker for genetic toxicity.

Statistical analyses of all these indicators show that the differences between the health of individual fish from polluted sites and the health of those from clean sites have diminished over the past several years. These changes at the molecular, physiological, and histopathological level, when coupled with those observed at the fish community level, are clearly a sign that East Fork Poplar Creek is on the road to ecological recovery.--Carolyn Krause

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