Scientists study rising water level in Chesapeake
Bay
Copyright 1999 Associated Press
January 8, 1999
The level of water in the Chesapeake Bay is rising twice as
fast as the
worldwide average sea level increase, and scientists are taking a
closer look
into the phenomenon.
The bay's water level is increasing a little more than an
inch per decade in
the middle portions of the 200-mile
waterway. The rate is even higher at the bay's mouth, where tide
gauges show
the increase is about 1.6 inches per decade.
Water levels are almost 4 feet higher now than at the time
of the Jamestown
settlement in 1607, said Curtis Larsen, a geologist with the U.S.
Geological
Survey, which is examining the sea level rise.
"It's an eye-opener," Larsen said Thursday.
The cause is in dispute,
but
global warming appears to be a factor, he said.
Sediment cores drilled by the Virginia Institute of Marine
Science about 25
years ago showed the long-term rate of increase was about a
half-inch per year
until the 1600s, when it began to accelerate.
"That
means this is by and large a long-term natural process, but we also
think
there's clearly a man-induced component," Larsen said.
"If all the computer models we're looking at are correct, we
can attribute some
part of the increase to
global warming."
The geological survey began drilling
core samples from the Patuxtent River shoreline near Solomons
Island, Md., last
month to compare with the earlier VIMS data taken along the York
and
Rappahannock rivers, Larsen said.
The survey is also examining other areas, including
Westmoreland County marshes
in Popes Creek for evidence of
changes in the earth's crust that are causing shorelines to sink.
A broad band
of tidal marshes in Popes Creek has disappeared in the past 30
years.
Larsen said a combination of rising sea level and land
subsidence in the
Chesapeake Bay region appears to be accelerating
shoreline erosion.
The erosion is turning some marshes into pollution sources,
a significant role
reversal since marsh vegetation is often credited with filtering
water and
capturing sediments, nutrients and other impurities.
But rich beds of underwater grasses that provide crucial
hiding places for baby
crabs and fish in Tangier Sound are smothering in sediment washed
from the
rapidly disappearing Blackwater Wildlife Refuge marshes in
Maryland.
"What washes out from the undercut banks of the
marshes is very fine sediments" that shade the grasses from
the sun and cause them to die, said John Page
Williams, a naturalist with the
Chesapeake Bay Foundation.
Larsen said the geological survey hopes to drill the core
samples it needs by
the end of this year and begin studying the findings in 2000.
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