U.S. Water News Online
UPPSALA, Sweden -- A strange debilitating malady has killed hundreds of moose in southwest Sweden over the past decade, and acid rain was the catalyst for a complex chain of events leading to the disease, a Swedish scientist says.
This appears to be the first instance in which acidification has been linked to mortality in a warm-blooded wild animal.
The scientist, Adrian Frank of the Center for Metal Biology in Uppsala, said the disease was not caused directly by acid rain, but by the spreading of lime to counteract the effects of acidification on the environment.
The lime appears to have caused a toxic imbalance in concentrations of the chemical elements copper and molybdenum in the animal's livers, Frank said.
"Wetlands, lakes, fields, pastures, and to a lesser extent forest areas of this acidified region have been limed since the beginning of the 1980s," Frank said.
The spreading of lime was intensified in the second half of the decade, when the disease began occurring in the moose, Frank noted. Because the plants the moose usually eat, like blueberry bushes, have been decimated by years of acid rain, the animals altered their browsing habits, he said.
"Moose frequently browse on cultivated pastures and fields of oat and rape, all of which are heavily limed by farmers," Frank said.
When the pH level of the soil decreases because of atmospheric fallout of sulfuric and nitric acid, metals such as cadmium, zinc, and manganese are mobilized in the upper soil and their ingestion by animals grazing on plants increases, Frank said.
Molybdenum, however, becomes less soluble in an acidic environment. Raising the soil's pH or alkalinity by liming reverses the chemical behavior of cadmium and other metals, and the availability of molybdenum in plants increases. Frank said excessive molybdenum in relation to the amount of copper in a ruminant's diet can lead to copper deficiency and death.
More than 1,500 moose have died from the disease since the mid-1980s in Alvsborg County northeast of Gothenburg, one of the most acidified areas in Sweden. Power plants and factories in Europe emit sulfur dioxide that falls as acid precipitation.
The moose is found in northern areas around the world. Because moose eat a great variety of plants, they can provide information about changes in levels of both essential and nonessential metals within five years, according to researchers.
In a paper to be published by the American Chemical Society, Frank touts the moose as "a useful, fast, and sensitive monitor of environmental change."
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