Paleoecology is much more varied 

 than studying tree rings, but you get the 

 idea: Nature remembers. Most of nature's 

 clues to the past aren't initially obvious. The 

 history of forests, swamps and even seas is 

 entombed in ecological remnants — pollen 

 grains, chemical traces, river sediments, 

 microscopic fossils. The paleoecologist's 

 job is to scoop up these shards of the past 

 and put them back together. 



Until 1979, when Cooper's mentor, 

 Grace Brush at Johns Hopkins University, 

 traced the history of human influence on the 

 Chesapeake Bay, few marine scientists 

 believed that paleoecological methods 

 would work in estuaries. They assumed that 

 strong currents and tides would scatter 

 sediments, wear away fossils, wash pollen 

 out to sea. In the Chesapeake, Brush 

 showed that she could successfully profile 

 ecological changes dating back far earlier 

 than the first European colonists. Later, 

 Brush and Cooper teamed up to do a 

 pathbreaking study of anoxia in the 

 Chesapeake Bay, published in the journal 

 Science in 1991. 



Now Cooper is using a similar 

 approach in North Carolina. With the 

 support of the N.C. Water Resources 

 Research Institute, she has begun to 

 document the history of water quality in the 

 Neuse and Pamlico estuaries. In the summer 

 of 1 997, she collected 2 3/4- to 5-foot 

 sediment cores from seven sites. She 

 divided her samples into 2-centimeter 

 sections and dated them using lead-210, 

 cesium- 137 and radiocarbon techniques. 

 The sediments are deposited on the estuary 

 bottom a little bit every year, leaving a 

 stratigraphic record that starts with the 

 present at the top layer and goes back in 

 time through the deeper sediments. Her 

 deepest samples were laid down about 

 2,000 years ago. 



To analyze the estuarine sediments, 

 Cooper uses her full box of paleo- 

 ecologist's tools. I found several of her 

 methods ingenious. One involves collecting 

 pollen fossils preserved in the sediments. 

 Ragweed pollen is an especially interesting 

 gauge of land clearing because this native 

 plant proliferates in disturbed land. Cooper 



uses a measure- 

 ment of ragweed 

 pollen as an 

 indicator of land 

 clearing 50, 100 

 and even 1 ,000 

 years ago. 



Cooper also 

 looks for chemical 

 clues to anoxia 

 and eutrophica- 

 tion. These clues 

 include concentra- 

 tions of organic 

 carbon, nitrogen, 

 phosphorus, silica, 

 sulfur and pyritic 

 iron. Each tells 

 her something 



different about the estuaries in the past. 

 Historic levels of nitrogen and phosphorus 

 are important, for instance, because nutrient 

 enrichment is linked to the depletion of 

 oxygen in estuarine waters. High nutrient 

 levels often cause algal blooms that far 

 exceed the ecosystem's usual ability to 

 recycle them. When the unconsumed algae 

 eventually die, they sink to the bottom, 

 spurring an increase in the bacteria that help 

 them to decay. As the dead algae break 

 down, the bacteria use up the available 

 oxygen, leading to anoxic conditions for 

 other estuarine life. 



Though a relatively minor part of 

 Cooper's study, her tests for sulfur levels 

 are another good illustration of the 

 imaginative ways that these chemical traces 

 can be used to track ecological changes in 

 the Neuse and Pamlico. Estuarine sedi- 

 ments harbor anaerobic bacteria, that is, 

 bacteria that don't tolerate oxygen. Unlike 

 their oxygen-loving cousins, anaerobic 

 bacteria metabolize naturally occurring 

 sulfur, in the process changing the sulfate 

 form found in seawater to a reduced form of 

 sulfur known as sulfide. 



Being highly soluble, sulfate mixes 

 with estuarine waters and washes away. But 

 sulfides are much more likely to combine 

 with metals naturally occurring in estuarine 

 waters, and they settle into bottom sedi- 

 ments. Thus, when Cooper finds a high 



Daniel Jones, a lab technician, and Sunghea Kim, 

 a master's student at Duke University, prepare to collect 

 sediment cores from the Neuse River in July 1997. 



A research crew brings a short 

 sediment core on deck from the mouth 

 of Bath Creek The crew (from left to right) 

 are Michael Madritch, an NC State 



undergraduate; Sunghea Kim; 

 and Gary Dwyer, a Duke University 

 research scientist. 



26 AUTUMN 1998 



