# **Ecosystem Trends and Response:Chesapeake Bay**

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##       Index of Subjects    

          The Nation's Largest Estuary        
          Critical Issues for Ecosystem Management and Restoration        
          Recent Trends in Dissolved Oxygen and SAV:  Attribution of          Cause        
          USGS Project to Study Ecosystem Response        

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##         The Nation's Largest Estuary      

      The Chesapeake Bay, the Nation's largest estuary, has experienced      serious environmental degradation during the past century.      Symptoms of degradation are large declines in sea grass acreage      and in finfish and shellfish (oysters and crab) populations,      seasonal depletions in dissolved oxygen, and increases in      sedimentation.  These environmental changes raised serious concern      in the 1970's because they threatened major commercial and      recreational activities by damaging key habitats and reducing      water quality necessary for bay species to survive and reproduce.      Most scientists attribute these changes, at least indirectly, to      ecological stress due to human activities, especially land use      changes in the bay watershed related to deforestation,      agriculture, use of fertilizers, and more recently, urbanization,      pollution, and sewage.  Future stress on bay ecosystems will      potentially worsen, as the Chesapeake Bay Commission predicts that      the population in the bay watershed will swell to 17.4 million by      the year 2020.    

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###       Map of the Chesapeake Bay.    

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##         Critical Issues for Ecosystem Management and Restoration      

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###       Scientist collecting sediment cores from a marsh in the bay.    

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      Another critical problem in the Chesapeake Bay is sedimentation.      Over the last 100 years, the net deposition of sediment that      entered the Maryland portion of the bay was 155 million metric      tons.  Scientists believe that sedimentation rates have increased      since colonial time due to land use changes and have been      disruptive to the health of the bay; sediment can cloud the water      so much that SAV cannot survive.    

      Responding to these environmental problems, members of the      Chesapeake Bay Program (a regional partnership among the States of      Maryland, Pennsylvania, and Virginia; the District of Columbia;      the Chesapeake Bay Commission; and the Environmental Protection      Agency) have developed bay-wide efforts to monitor water quality      and biotic resources in order to assess the bay's ecological      health on a regular basis and to produce computer models to      predict watershed quality and ecosystem response to nutrient      loading.  The bay program modeling studies were used to establish      a goal of a 40% reduction from 1985 levels of nutrient input into      the bay by the year 2000.  Biotic resource management plans have      also been developed to restore and preserve key species for      commercial use and recreation.    

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###       Scientists collecting sediment cores from the bay.    

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##         Recent Trends in Dissolved Oxygen and SAV:  Attribution of Cause      

      Despite the extensive bay restoration effort, large gaps exist in      our understanding of the bay ecosystem.  Certain trends in      discharge, oxygen, and SAV underscore our need to better      understand the bay ecosystem as a whole.    

      Extreme fluctuations in interannual freshwater discharge entering      the bay, are the result of changing precipitation and climatic      patterns over the last few decades and have become acute during      the last 5 years.  Trend data show a clear and significant      influence of discharge on the total nutrients entering the bay and      on bay salinities, which in turn influence how bay phytoplankton      utilize the nutrients and lead to low oxygen levels.  Climatic      factors may, in fact, play a larger role in controlling bay      environmental health and determining recent trends in water      quality than previously realized; for example, the drought years      of the 1950's and 60's caused low tributary discharge into the      bay.    

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###       Graph of Historical Changes in River Flow Entering Chesapeake Bay.    

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      Since restoration efforts began in the early 1980's, SAV surveys      have indicated that grasses have begun to return to several      tributaries of the bay.  In theory, this reflected a response to      the improved water quality.  However, there were areas where SAV      did not return despite an improvement in water quality in 1994 and      1995.  This continued absence of SAV concerns scientists and      resource managers, in part because SAV provides key habitat for      young blue crabs.  The bay provides 50% of the Nation's total blue      crab harvest, and the bay crab harvest was worth $126.6 million in      1993, according to the National Marine Fisheries Service.    

      What do recent trends in discharge, anoxia, sea grasses, and              blue crabs            mean?  Are they caused by habitat change, overharvesting, or      natural mortality related to long-term, external climatic factors?      These questions remind us of how complex the bay ecosystem is and      of how little we know about the relations among individual      species, their environment, and climate.  They also illustrate how      difficult it is for scientists to separate natural versus      human-induced effects on critical species and their habitats based      solely on monitoring.  Detection of a trend can be easy,      attribution of cause is much more difficult.  While events like      these can not yet be predicted by water-quality or ecosystem      models, the effects of past events can be studied in Chesapeake      Bay history archived in its sediments.    

##         U.S. Geological Survey Project to Study Ecosystem Response      

      The U.S.  Geological Survey (USGS) Chesapeake Ecosystem Response      Project is designed to improve our under-standing of large-scale      environmental changes that influence water quality and living      resources in the Chesapeake Bay.  In particular, project workers      will investigate the links among changes in climate,      precipitation, discharge, salinity and dissolved oxygen over      interannual, decadal, century-scale periods.  To do this, USGS      scientists and other researchers from the University of Maryland,      the Maryland Geological Survey, and the Virginia Institute of      Marine Science are collaborating to study the bay's sediments,      which capture the history of its water, plants, and animals during      the period before monitoring began in the 1980's.  Using ecosystem              "indicators" (microfossils)            and geochemical data preserved in the bay's sediment and      historical and reconstructed discharge data, members of the      Chesapeake Ecosystem Response Project will reconstruct trends and      response in the bay since 1950 and will determine the natural      conditions in the bay over the last few millenia, including      periods prior to 17th-18th century colonial agriculture and      19th-20th century industrialization and urbanization.  In the next      5 years, the USGS will lead a multi-institution research program      to carry out integrated coring, sedimentological, environmental,      and ecological investigations of the Chesapeake Bay ecosystem.      Trends in oxygen, nitrogen, and phosphorus levels, phytoplankton,      benthic invertebrates, sedimentation, and biodiversity will be      studied with emphasis on separating natural versus human causes of      and responses to extreme events.    

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####       For more information contact:      U.S.  Geological Survey      12201 National Center      MS 955      Reston, VA 20192      703-648-5280    

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