Portfolio I: Estuarine Processes
Historical Trends of Productivity
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Figure 1. Historical changes in ratio of centric to pinnate diatoms for four dated sediment cores from the Chesapeake Bay, showing the shift to predominantly planktonic centric diatoms in recent years (from studies of Brush et al.).
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Between 1988 and 1994 Grace Brush and Sherri Cooper examined stratigraphic records preserved in the sediments to reconstruct both prehistoric and historic sedimentation and water conditions of the Bay. Since initial land clearance ca. 1760, sedimentation rates have increased from ~0.02 cm.yr-1 to an average of 0.22 cm.yr-1, and total organic carbon (TOC) from 0.14 mg.cm-2.yr-1. Diatom diversity has decreased since 1760 and the centric:pinnate ratio has increased since 1940. This project verifies that Chesapeake Bay ecology has fundamentally changes since European settlement, an assumption that drives the majority of the current Bay restoration efforts. Dr. Brush received a grant in 1999 to continue this work.
