Johns Hopkins Gazette: October 10, 1994

Prof Brushes Floor of bay for Samples
By Ken Keatley

Some of the Chesapeake Bay's most telling tales lie beneath
the water itself, in the silt, sand and clay that have
settled there over thousands of years.
    Grace Brush plies those depths, extracting sediment
cores from the bottom of the bay and its tributaries. In her
Ames Hall laboratory, Dr. Brush and her team of student
researchers painstakingly examine those samples--a centimeter
at a time--and have literally unearthed information on how
the bay has evolved over time.
    Quite often, it is not a pretty picture. Dr. Brush's
trained eye has seen evidence of the hurricanes, forest
fires, floods and droughts that have ravaged the bay since it
was formed some 10,000 years ago. But Mother Nature has been
kinder than humans, who have done more damage in the 350
years since European settlers arrived than all the natural
disasters combined.
    "Changes in the bay that are man-made are just mammoth,"
said Dr. Brush, a paleobotanist who is a professor in the
De-partment of Geography and Environmental Engineering. "When
we look at the cores, we see a direct line from one core to
the next of the impact of European settlement. You literally
get a history of a watershed." 
    Time is actually frozen in her lab, where core samples--
cut into centimeter-long segments, marked according to
location and sediment depth, and tucked into plastic bags--
are maintained in large freezers, awaiting the scientist's
    To take a core sample, Dr. Brush and her assistants
drive cylindrical irrigation tubes, about 5 inches in
diameter, into the muck, sometimes using a piston-driven
vibrocorer machine to facilitate the work.
    The cores are then extruded, sealed in long plastic bags
and transported back to her lab. There, they are cut in half
lengthwise, and then sliced into centimeter-long sections for
    To get a chronology of the sample, Dr. Brush will first
examine the bottom, oldest section of the core. If she finds
ragweed pollen, an indicator of agricultural activity, she
knows the sample is no more than 300 years old. If no ragweed
is found near the bottom, the sample is carbon dated. Some of
her samples are more than 10,000 years old.
    After it has been dated, the sample is further analyzed.
In general, Dr. Brush has found that many of the most
dramatic changes--especially the decrease in bottom-dwelling
species due to lower light and oxygen levels--can be directly
attributable to settlement.
    For two decades, Dr. Brush has tested the sediment at
countless sites, from bucolic Otter Point Creek in Cecil
County to Dan's Bog, a forested swamp on a tributary of the
Anacostia River near Washington. What she routinely finds are
dramatic increases in sediment, organic nitrogen, carbon and
in certain areas sulfur in the centuries since European
settlement and the subsequent deforestation, agriculture and
urbanization of drainage areas.
    The most extreme changes have occurred since 1940, and
are proportional to the amount of land cleared and
fertilizers used.
    "Settlement has had the effect of gradually changing a
dynamic, diverse system to one that we have now: turbid and
with fewer species," said Dr. Brush. "The bay has gone from
being a system with a long food chain to one that is
bacterially driven. There has been a drastic reduction of
commercially important species such as the oyster, shad and
striped bass."
    Not only can Dr. Brush make broad conclusions based on
her analyses, she can actually "see" specific historical
events in the dark, muddy cores. 
    For instance, she analyzed a core taken from Back River
near Essex, home of a century-old sewage treatment plant.
Since about 1940, the plant has channeled its discharge water
to a nearby Bethlehem Steel plant, where it is used to cool
the equipment. Since that time, according to her analysis,
the levels of chlorophyll from algae in Back River have been
lower than they would otherwise be, because of the discharge
water being diverted from the river. However, Dr. Brush was
puzzled to see that the levels spiked higher for a brief
time, around 1950.
    "I looked at newspapers from that time, and found that
Bethlehem Steel was on strike for an entire summer then, so
more of the water went into the river during that period,"
she explained. "This work is just like solving a detective
    Dr. Brush said sediment levels have actually dropped in
recent decades, thanks to farm abandonment and soil
conservation practices. But restoring Mother Nature to the
driver's seat would require drastic societal change.
    "The ultimate cure is to manage the human population in
a way that is compatible with nature," Dr. Brush said. "If
the right kind of management plan--whatever that is--were
introduced, the system would likely change. The organisms
that live in the estuary are highly resilient. They just need
a chance to recover."
    Dr. Brush came to Hopkins in 1970 as a research
scientist, arriving with her husband, Lucien Brush, a
professor of hydraulics and hydrology. Until his death in
February, the couple frequently collaborated on research,
especially on the transport of pollen grains in lakes and
    Current projects take Dr. Brush to all parts of the bay
and the globe. She has used her core sampling technique to
examine the effect of land use on Perdido Bay in Florida, and
is now studying effects of hurricanes, as well as land use,
on certain areas in Puerto Rico. This week, she is in
Bangalore, India, at the Bioresources '94 conference
presenting papers highlighting her Chesapeake Bay findings.
    Additionally, Dr. Brush helped organize and has
contributed a chapter to a book project being orchestrated by
Philip Curtin, a Hopkins history professor, on a history of
the ecosystem of Chesapeake Bay drainage.
    But her favorite, and most exotic locale, is a fourth
floor microscope room in Ames Hall, where she can literally
see the history of the bay unfold before her eyes.
    "This is like a library, actually," she said, pointing
to tiny vials of water containing pollen and seeds. "This
work has been so interesting, so useful and such great fun."

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