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W2 AM Chesapeake Bay Restoration (Part 1)
(BRU-1122-337227) The Long Term History of the Chesapeake Bay.
Brush, G1, 1 Johns Hopkins University, Department of Geography and Environmental, MD, USA
ABSTRACT- The history of the Chesapeake Bay since its origin some 10,000 years ago is recorded in sediments that have eroded off the land and been deposited in the estuary and tributaries. This history is retrieved from sediment cores. Preserved in the sediment are pollen grains and seeds of terrestrial and aquatic plants, diatoms, ostracods, foraminifera, mandibles of worms, charcoal, chemicals and other entities which serve as indicators of the Bay's environment and biota. During all of this time, the landscape drained by the Bay was about 90% forested. The history contained in the sediment shows the response of forests to climate change over the millennia from species such as spruce and fir present on the landscape when the Bay began to form to hemlock later as climate became warmer to the present oak-hickory-pine forests that have existed over the past 5000 years. During this time, organisms such as diatoms that lived in the estuarine waters were mostly benthic. Submerged grasses were always present. The record indicates that estuarine waters were clear and turbidity low. Dramatic changes began about 300 years ago with the beginning of European settlement. Within a relatively short period of time, the forests were removed and replaced by agricultural fields. This transformation of the landscape was followed by decreased salinity with increased runoff from a deforested landscape, high turbidity from soil erosion resulting in light limitation, increased eutrophication from fertilizers and more widespread anoxia as oxygen in the bottom waters was consumed by decaying biomass. The benthic ecosystem became very stressed, and eventually the mesohaline part of the Chesapeake Bay was converted from a rich benthic ecosystem to one that is now primarily planktonic and in many parts of the Bay heterotrophic.
Key words: Chesapeake Bay, Historical Ecology, Sediments
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