The Long-Term History of the Chesapeake's Trophic State
The food webs of any ecosystem may shift over time, sometimes dramatically, in response to large-scale influences, whether they be climatic change, natural events such as major hurricanes, or human activities. For scientists, government agencies and citizens engaged in initiatives to restore the Chesapeake Bay, distinguishing those influences over which we may have control is critical. For example, to what degree are the observed patterns of depleted oxygen conditions in spring and summer inherent to the Bay system exacerbated by human behaviors? One way to make such determinations is to reconstruct the Bay's ecology before Colonial settlement and the onset of population growth, the clearing of forests, the widespread use of fertilizers, and the growth of urban and industrial centers. While there are no written chronicles of the Bay's ecology over the past two thousand years, Grace Brush has developed methods for reading cores of Bay sediments that contain those records. The language of those histories is planktonic organisms – the remains of diatoms, dinoflagellate cysts, copepods and other bottom-dwelling organisms. By identifying their remains, together with patterns of pollen deposition that provide an accurate dating of sediment layers in which they are found, Brush can infer the historical structure of the estuarine food web. In this project, she has been studying cores from different locations in the Bay's mainstem and tributary rivers. In one core from an upper Bay tributary, for example, she has found major changes in invertebrates, beetles, insects and seeds of larger plants. With such data, she is beginning to characterize how food webs vary during different periods in the Bay's history. The results should be invaluable for the scientific community and for decision makers who are assessing long-term trends in the Chesapeake in order to sustain the productivity of this ecosystem, including those species long associated with a healthy Bay.
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Grace Brush
The Johns Hopkins University
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