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 scrutiny. 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 analysis. 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 story." 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 estuaries. 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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