January 2007, Vol. 19, No.1

Waterline

Forests Prove Importance in Watersheds During Heavy Rainfall

 According to the Chesapeake Bay Program, a regional partnership dedicated to restoring the bay, June’s rainfall illustrated how impervious surfaces — paved roads, driveways, and parking lots — contribute to excess runoff into the Chesapeake Bay. At the same time, the important role forests play in reducing runoff and nutrient pollution during such rainfall became more apparent than ever, a news release from the Chesapeake Bay Program states.

When Europeans first set foot on the shores of the bay in the 17th century, they found diverse, extensive forests covering about 95% of the watershed. Today, that number has dropped to about 60% and continues to decline. Since 1982, more than 303,520 ha (750,000 ac) of forest have been lost to new development, the news release notes.

Trees hold soil in place with their deep root systems, which stabilize streambanks and reduce erosion. Forests can reduce the amount of nutrient pollution that enters the bay by retaining more than 85% of the nitrogen deposited on them from the air. Nitrogen is one of the main nutrients that pollute the bay, and scientists have made a direct connection between forestland loss and an increase in nitrogen loads to the water.

This fall the U.S. Forest Service and The Conservation Fund (Arlington, Va.) released the State of the Chesapeake Forests report, which is a guide to forest conservation efforts in the watershed. According to the news release, the report was designed to show citizens, governments, and environmental groups how best to keep forests thriving.

For more information, contact the Chesapeake Bay Program Office at (800) YOUR-BAY.

Arctic Sea Ice Diminished Rapidly in 2004 and 2005

The Arctic Ocean’s perennial sea ice, which survives the summer melt season and remains year-round, shrank abruptly by 14% between 2004 and 2005, according to a newly published study. Researchers found that the loss of perennial ice in the East Arctic Ocean, above Europe and Asia, neared 50% during that time as some of the ice moved to the West Arctic Ocean, above North America, according to an American Geophysical Union (AGU; Washington, D.C.) press release.

The overall decrease in winter Arctic perennial sea ice totaled 725,000 km2 (280,000 mi2), the release says. Perennial ice can be 3 m (10 ft) thick, or more. It was replaced in winter by new, seasonal ice, which was only about 0.3 to 2 m (1 to 7 ft) thick and more vulnerable to summer melt. The research was published in the September issue of the journal Geophysical Research Letters.

The decrease in perennial ice raises the possibility that Arctic sea ice will retreat to another record low extent this year, the researchers say. This follows four summers of very low ice cover, as observed by active and passive microwave instruments aboard the U.S. National Aeronautics and Space Administration (NASA) Quick Scatterometer (QuikSCAT) satellite, the researchers report.

A team of seven scientists led by Son Nghiem of NASA’s Jet Propulsion Laboratory (Pasadena, Calif.) used satellite data to measure the extent and distribution of perennial and seasonal sea ice in the Arctic. While the total area of all Arctic sea ice was stable in winter, the distribution of seasonal and perennial sea ice changed significantly.

Data from the National Centers for Environmental Prediction (Boulder, Colo.), suggest that winds pushed perennial ice from the East to the West Arctic Ocean and moved ice through the Fram Strait, a deep passage between Greenland and Spitsbergen, Norway. This movement of ice out of the Arctic is a different mechanism for ice shrinkage than the melting of Arctic sea ice, but it produces the same result — a reduction in the amount of perennial Arctic sea ice.

The researchers say that if the sea ice cover continues to decline, the surrounding ocean will warm, further accelerating summer ice melts and impeding fall freezeups. This longer melt season, in turn, will diminish the Arctic ice cover further.

Contact Nghiem for more information at
son.v.nghiem@jpl.nasa.gov.