Low rainfall is good and bad for bay life

As runoff declines, salinity could rise over time

April 12, 2006|By TOM HOWELL JR.

WASHINGTON -- A lack of rainfall in the Chesapeake region this year could be a mixed blessing for the bay in coming months, scientists said.

Baltimore received 0.18 inches of rain last month, the lowest March rainfall recorded in the city since 1870, when National Weather Service records begin. Rainfall this week did little to make up for low year-to-date regional totals, which can benefit as well as harm bay life.

Low precipitation reduces pollutant runoff from land surrounding the bay, but it can also increase salinity in the bay over time, scientists said.

The Chesapeake Bay receives saltwater from the ocean at its southern end, while freshwater feeds in from watershed runoff and the Susquehanna River at the bay's north end, said Jenn Aiosa, a staff scientist with the Chesapeake Bay Foundation.

This delicate balance of fresh and salty waters is vital to bay species' survival. The balance was off-kilter last month, with a 65 percent below-average freshwater flow from streams and rivers into the bay, according to the U.S. Geological Survey. It was a record low for March and likely raised salinity levels.

High salinity enhances oyster growth and reproduction, but it also strengthens oyster diseases such as dermo and MSX, said Ken Paynter, associate professor at the University of Maryland's Center for Environmental Studies.

"It's a two-edged sword," Paynter said. Present salinity levels do not pose much danger to oysters, but if the dry spell continues, dermo will be especially virulent, Paynter said.

The dry weather's effect on life in the bay might be months away. Salinity-related changes take time because the bay is so large, Paynter said. Pennsylvania rainfall also could make up for a Maryland dry streak by carrying freshwater down the Susquehanna River and into the bay.

Weather service data, however, show Pennsylvania cities near the Susquehanna had a dry March as well. Harrisburg, the state capital situated on the river, had its second-driest March on record, with 0.68 inches of precipitation. Williamsport, located along the river's west branch, had its sixth-driest March, with 1.15 inches.

Dry weather means less runoff into the bay, which improves water clarity. This is a boon for underwater plants on which fish and crabs feed, Aiosa said. Many plants, however, especially those in upper waters, are adversely affected by the high salinity.

A decline in runoff - and thus a decline in nitrogen - will benefit crab and fish because there will be more oxygen available, said Scott Phillips, Chesapeake Bay coordinator with the U.S. Geological Survey.

It's unclear whether the old adage of "April showers" will bring relief - the forecast does not give any signal that precipitation will be above or below normal this month.

While the Chesapeake region may not be steeped in drought or see drastic salinity changes now, the Chesapeake Bay Foundation is keeping a close eye on rainfall trends, Aiosa said.

"It's sort of a little red flag," she said. "It could have an indication of what the summer may look like."

Tom Howell Jr. is a reporter for Capital News Service.

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