Mercury in lake affecting animals

Scientists have learned more about elevated mercury concentrations in Great Salt Lake, and a new report by the U.S. Geological Survey shows that brine shrimp and, in particular, the eared grebes that eat them are being impacted.

Exactly how much lasting damage is being done by mercury contamination will be the subject of another report due out in about nine months that will be coauthored by the U.S. Fish and Wildlife Service.

The new USGS report title is long: "Anthropogenic influences of the input of biogeochemical cycling of nutrients and mercury in Great Salt Lake, Utah, USA." It's published in this month's international journal "Applied Geochemistry."

The report's findings indicate that new pathways, such as sustained high winds, are in effect treating the lake like a mixing bowl, melding mercury present in the water with brine shrimp, where the mercury "bioaccumulates." Many bird species eat the shrimp, but USGS singles out grebes.

The grebes molt for about three to five months around fall and don't fly as a result. While on the lake shores, they dine on the contaminated shrimp. Studies of the birds during that period have revealed an increase of mercury in their livers three times the amount found at other times of the year.

"We found that the composition of isotopes found in brine shrimp change in a consistent manner over the growing season, likely reflecting a change in the type of algae that brine shrimp were eating," said Dave Naftz, the main author of the USGS report. For an e-mail request of the new USGS report, contact dlnaftz@usgs.gov.

On the phone Naftz explained how an inorganic form of mercury in the lake is actually being transformed into a toxic form. The concerns now include not just global sources of mercury pollution but also the processes that stir up or mix relatively harmless mercury with human-added mercury.

"It's not necessarily the source," Naftz said about the question of cause and effect.

Nathan Darnall, an ecologist with U.S. Fish and Wildlife Service, said mercury can cause numerous problems for birds. Those can include an impact on the neurological system, leading to less attention by adults to their eggs or a reduced responsiveness to predator alarms by ducklings, or a diminishment of their immunity, which can make disease more deadly.

But currently, there is no proof that any of those are happening.

"At this point, I am not aware of any data suggesting that any of the above examples are occurring," he said.

Even if the problems for birds are not documented, debates about the sources for mercury are ongoing.