Bald Eagles – the Canary in the Ecosystem

This is an update on the Law of Unintended Consequences which may not have originated with Murphy, but he certainly extended the Law into new places. Basically, in any given system, anything that can go wrong will, plus a few others.

Around 1994 a Bald Eagle die-off was observed in one lake in southeast Arkansas. Within a few years, not only were eagles dying every winter in that lake, but lakes to the southeast as well. In addition, migratory waterfowl were also dying. Carcasses were sent to various wildlife labs for analysis. The eagles were poisoned with a “halogen” compound containing Bromine. (Halogens include elements such as chlorine, fluorine, bromine, and iodine.) The waterfowl had lower concentrations of bromine, and the water from the lake contained almost no bromine at all. How could this be? What was the source of bromine for these birds?

One biologist noted that the lakes with the bird and duck die-offs also had a green, invasive aquatic plant called “hydrilla.”  Even though the coots and ducks gorged on hydrilla, alas, the hydrilla didn’t seem to make the laboratory birds sick. Chickens were used as test subjects. The key turned out to be that it was only migratory birds who arrived in the fall that fell ill.

In the late summer, the lakes build up warm water at the surface and oxygen-depleted cooler water below. The hydrilla stops flourishing when the lake surface temperatures warm in late summer. The plant then begins to leak bromine compounds that it has concentrated 20-50 times greater than the surrounding lake water. But there is more.

Researchers found a new species of bacteria in the family of cyanobacteria growing on the leaves of the hydrilla plants. When the temperature stressed hydrilla started to decay, it gave off large amounts of its bromine-laden chemicals from the plant itself. The cyanobacter then used the dying hydrilla compounds as food and thereby concentrated the bromine another factor of 50. All this took place just in time for migrating eagles and waterfowl to feast on the hydrilla with bromine concentrated 1,000 fold over the lake water.

Bromine gets into groundwater partly through natural sources and largely through coal-burning power plants. It took many researchers several years to unravel the mystery. The hydrilla plants were not native to these lakes but were invading from more southern lakes because the air and water temperatures in more northern lakes was now favorable. This is a case of one thing leading to another. In this case the symbol of the strength of our nation was poisoned by our own appetite for cheap energy.

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