Monday, March 20, 2006

Global Warming and Riverine Ecosystems

Even a small degree of global warming will have large effects on ecosystems, and ultimately on us. Take, for example, the rivers in upstate New York and New England, where reduced ice cover is changing the life along the river.

Lilliputian wildflowers will soon line the Hudson's banks. In what are known as riverside ice meadows, an ancient cycle of ice formation and melting gives rise to swamp candles, ladies'-tresses, wood lilies and other rare, diminutive flowers.

In New York's Adirondack Mountains, ice that forms on the river in winter is pushed onto its banks in spring; there it scours the sloping cobble shores, keeping them free of shrubs and small trees and leaving space for wildflowers to sprout in fragile, arctic-like ice meadows.

But the future for these floral pixies, which depend on late-melting river ice, is bleak. The number of days of ice on northeastern rivers has declined significantly in recent winters, said hydrologist Glenn Hodgkins of the U.S. Geological Survey (USGS) Maine Water Science Center in Augusta.

The trend could spell disaster for the ice meadows. It also signals trouble ahead for endangered Atlantic salmon and other fish, for wetlands plants and animals, and for Northern economies, all of which are sustained by winters with icy rivers.

If the pattern continues, say scientists, only in Currier and Ives prints will ice skaters twirl across frozen New England rivers.

"Northeastern rivers have 20 fewer days of ice cover each winter now than they did in 1936," said Hodgkins, who said the total now averages 92 days. "A lot of that decrease has occurred since the 1960s."

Like so many other environmental problems, changes due to global warming will have an impact on us.

"Lack of ice on rivers severely affects fish, especially anadromous fish like endangered Atlantic salmon," said Trial, a biologist at the Maine Atlantic Salmon Commission in Bangor. "Ice cover insulates rivers and streams, protecting young salmon from cold. Without that cover, the salmon are also more susceptible to predators." Bald eagles, for example, are able to snare their piscine prey only from open water.

Atlantic salmon are in peril for several reasons, but scientists Terry Prowse and Joseph Culp of the National Hydrology Research Center of Environment Canada in Saskatoon, say lack of river ice has the potential to kill large numbers of salmon eggs, as well as juvenile and adult fish.

The most difficult winter situation for salmon and other fish, biologists say, is on-again, off-again ice cover: rivers that freeze over one week and then are open the next.

If the salmon population dies off - along with reductions of other fish populations - there is going to be a lot less for people to eat.

Photo of Ladies Tresses Orchid by Gary M. Stolz / USFWS.