Rooting out sources of pollution Forest study: Trees can yield heavy runoff to bay, after periodic defoliation.

December 21, 1997

PEOPLE SNICKERED years ago when Ronald Reagan blamed trees for causing air pollution. While his intention may have been devious, the former president had it partly right: trees do give off hydrocarbon emissions that can contribute to smog.

Now comes Keith Eshleman of the University of Maryland's Appalachian Environmental Laboratory who suggests that sporadic pollution of the bay (and, perhaps, the eruption of harmful algae and fish-killing organisms) may be linked to natural cycles of forests.

Actually, Mr. Eshleman found that periodic attacks by hungry gypsy moth caterpillars can cause polluting nitrogen runoff from forestland to soar 50 times normal, with adverse effect on the watershed.

With a new federal grant, he is studying the natural "background" levels of forest runoff into the estuary system and the changes that can affect water quality.

Forests, which cover 60 percent of the bay watershed, are normally good protectors against nutrient runoff, fixing nitrogen and other minerals in plants and soil. They account for little of the 230 million pounds of nitrogen entering the bay each year.

But heavy defoliation by gypsy moth caterpillars, which stripped 12 percent of the state's forests bare in 1990, can cause serious spikes in nutrient runoff, which in turn feeds excessive algae growth that can kill bay fish and degrade waters.

Other disturbances, such as clear-cutting by man and over-browsing of trees by too many deer, also can significantly increase pollutant runoff.

Knowing background levels of normal forest nutrient runoff, and their variations, can enable scientists and policy-makers to better determine and regulate human-caused pollution runoff, such as fertilizer from farms and lawns.

The workings of a natural system are not simple. Nature mysteriously produces changes that are not always understandable by or agreeable to humans. Studying those mysteries can help us to beneficially manage our own conduct in the ecosystem.

Pub Date: 12/21/97

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