Estuaries

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					         Estuaries
Tidal Potomac Teacher Training Workshop
                 June 2008
       (with thanks to Leila Hamdan)
                      Outline
   What is an estuary
   Key Features of Estuaries in general
   Examining our famous Estuary: Chesapeake Bay
     Nutrients and Pollutants
     Habitat

     Human Interaction
                 What is an Estuary?
   Webster's Dictonary
       1.) A water passage where the tide meets a river current
       2.) an arm of the sea at the lower end of a river
   Oxford Dictonary
       1.) An arm of the sea


   Classification based on the organisms present
     Classic Definition of Estuary

“ An estuary is a semi-enclosed coastal body of water
   having a free connection with the open sea and
within which the sea-water is measurably diluted with
      fresh water deriving from land drainage”

 Pritchard’s treatment of estuaries based upon the common physical characteristics
                          shared by this type of ecosystem




Cameron, W.M. and D.W. Pritchard. 1963. Estuaries. In The Sea: Ideas and Observations on Progress in
      the Study of the Seas. Volume 2. M.N. Hill (ed) 1963. Interscience Publishers, New York.
                            Types of Estuaries
       Fjords
       Bar-built estuaries
       Estuaries produced by tectonic processes
       Drowned river valleys (Chesapeake)




Pritchard, D.W. 1967. What is an Estuary: Physical viewpoint. In Estuaries. Publication # 83. AAAS, Washington, D.C.
                      Estuaries
   Interface between the land and the sea
   Due to geomorphology, climate, and
    biodiversity, each estuary is unique.
   Common names include Bays, Lagoons, or
    Sounds
   Some well known Examples:
       Chesapeake Bay, Delaware Bay, San Francisco Bay,
        Boston Harbor, Tampa Bay and Puget Sound.
               Basic Concepts: Salts
   Salinity
     Salinity is the level of salts (mainly NaCl) dissolved
      in water. It is measured in parts per thousand (‰).
     Salinity affects
         Osmosis for organisms
         Stratification (formation of pycnocline)

   Salinity often varies longitudinally, horizontally,
    and vertically in estuaries.
   This can be a challenging environment for biota.
            Review of Terms
   Anoxia/Hypoxia
   Eutrophication
   Geomorphology
   Residence Time
The Chesapeake Bay
                       Basin Morphology
Drowned River Valley:
     •V shaped profile
     •Deep main channel- shallow flanks
          •Average depth: 6m
          •Channel depth: 15m

ca. 20,000 years ago the Susquehanna              2
River carved a deep valley through PA,            4
MD and VA across the dry continent.               6 Western Shore
                                                  8                 Eastern Shore




                                               Depth
Joined by tributaries each with deep V



                                               (m)
                                                  10
shaped channel                                    12
                                                  14
ca,. 10,000 years ago, sea level rise filled      16
in old river channels and beds.                   18

Deepest portion of Chesapeake and all
tributaries located just “upstream” of
mouth.

Often a shallow sill where tributaries open
to the main-stem and where Bay opens to
ocean
                Basin Morphology
•50 rivers drain into bay
•8 major tributaries account for
majority of fresh water
delivery:
          Susquehanna 48%
          Potomac         13%
          James           12%
          Rappahannock 3%
          York             3%
          Patuxent         1%
          Choptank         1%
          Nanticoke        1%
           Circulation Patterns of the
                  Chesapeake

   Moderately stratified estuary
       Fresh water flow towards the sea
       Salt water intrusion towards land
       Opposing currents of water nearly equal in volume and
        velocity


   Distance of salt intrusion into bay depends upon season
    and volume of runoff
Salinity Distribution
in the Chesapeake
Bay During Spring



High fresh water
Runoff from snow
melt into tidal rivers
pushes higher salinity
water down Bay




Schubel, J.R. and D.W. Pritchard. 1987
    Salinity
    Distribution in the
    Chesapeake Bay
    During Autumn
    Months


  Fresh water run-off
  lessens during
  summer and autumn.
  Higher salinity waters
  surge in from the Bay
  mouth and into upper
  reaches of the Bay
  and its sub-estuaries
  (rivers).




Schubel, J.R. and D.W. Pritchard. 1987.
Circulation Pattern of Chesapeake Bay




                                        From: Schubel, J.R. and D.W. Pritchard. 1987
                   Chesapeake Bay
   Moderately Stratified Estuary
       Significant mixing of both salt and fresh water layers
       Water flushes out of the estuary at equal velocity with
        water flushing in
   RESULT:
       Residence time of water in Bay is approximately 12
        months
            What does this mean for flushing?
      Flushing of Pollutants in the
           Chesapeake Bay
   Pollutants run in, pollutants flush out?
      Not quite in the Chesapeake

      Circulation of the Chesapeake ensures that following
       the initial introduction of a pollutant, it has the
       potential to be dispersed at a much greater extent, and
       will not soon flush out
   This finding needs to be considered in all management
    decisions concerning pollution of the Bay
     Net Effect of Urbanization of CB
                Watershed


•Increased Nutrient Loading - Eutrophication
•Increased Sediment Delivery
•Toxic Chemicals
•Habitat Loss
Mixing is inhibited in an Estuary
Increased Production in the surface waters results in
            oxygen depletion at depth
       Sedimentation Sources

Sediment delivery to CB increased during urbanization of
watershed (ca 1950s) and continues today

Shading due to sediment was key factor to early decline in
SAV

Impervious surfaces (highways) increase sediment
delivery
Construction and In-stream Scouring
   Construction sites deliver substantial loadings of
    sediment, particularly when not using best
    management practices
   In stream scouring increases as watersheds
    develop and there is increased impervious area.
Sediment plumes extend well out
    into large water bodies




    Mississippi River Sediment Plume
Toxic compounds in the Chesapeake
              Bay
   Examples of toxics (current or historical) in the
    Chesapeake Bay system
     PAHs-polycyclic aromatic hydrocarbons
     PCBs-polychlorinated biphenyls

     Mercury and other metals
   Four Regions of
    Concern-areas with
    known chemical
    contaminant-related
    impacts
      James River
      Elizabeth River
      Anacostia River
      Baltimore
       Harbor/Patapsco
       River
                          Habitat Loss
Decline of Submersed Aquatic Vegetation (SAV), also known as
   aquatic macrophytes


Since the 1960s, over 50% of the SAV has disappeared from the Bay waters.

Causes:
   • Declining water quality (nutrient loading, sedimentation)
   • Disturbance of SAV beds (Hurricane Agnes-1972)
   • Alteration of shallow water habitat (epiphyte growth)

Initial decline of SAV most severe in the upper Chesapeake and western
     shore tributaries.

Today, all areas of the Bay have experienced the decline of these important
   grasses.
SAV in Gunston
     Cove

    2000 Distribution
SAV in Gunston
     Cove

    2005 Distribution
             Importance of SAV

•Provides habitat for benthic organisms (Blue
Crab) and fish populations
•Stabilizes benthic sediment
•Filters water column (settling particles)
•Oxygenates deep portions of water column
Pollutants in the Bay




       Low DO
 Chesapeake Bay
Lecture 2 – Living
   Resources
      HNRS 228
      Spring 2006
               Chesapeake Bay
           Important Living Resources
   Shellfish (Invertebrates)
       American oyster
       Blue crab
   Fish
       American shad
       Striped bass
       Menhaden
                     American Oyster
   The “trademark” species of the bay
    from the 1600’s to the 1960’s
   A bivalve mollusc
   Larva is planktonic and spends first
    few weeks of life drifting in the
    currents
   When it reaches the size of the
    head of a pin, it settles to the
    bottom and attaches to a hard
    surface and is called “spat”
   The spat grows larger and in the
    process extends the size of its shell
                     American Oyster
   Oysters pump water through their
    shell and as the water passes over
    their gills, plankton (microscopic
    plants and animals) are filtered out
   The plankton provides the food for
    the oyster
   In the process the oyster clears the
    water and makes it easier for SAV
    (submersed aquatic vegetation) to
    grow
   Population levels in the 1930’s
    were calculated to filter the entire
    volume of the Bay in 2-3 days.
                  American Oyster
   Oyster shell also forms the
    major hard surface substrate
    in the bay
   Oyster “reefs” were once so
    common that they caused
    ship wrecks
   Oyster reefs provide essential
    habitat for new oysters and
    for other estuarine organisms
                American Oyster
What Happened?
     Over-harvesting: not only
      depleted the stock of live
      oysters, but also wrecked
      the reefs
     Algal blooms and toxic
      chemicals
     Siltation from the land
     Parasites (protozoans)
                         Blue Crab
   The most important
    commercial species in the bay
    now
   A crustacean, crabs have an
    exoskeleton or shell
   As they grow, they must molt
    or shed their shell
   It takes the new shell a few
    days to harden. In the interim
    they are “soft shell” clams
                        Blue Crab
   Crabs spawn in the ocean just outside the Chesapeake Bay
   The larvae and young crabs move up into the estuary and some
    even into the tidal rivers where they spend most of their life
    cycle
   Mating occurs and the gravid (with eggs) females move back
    through the estuary and into the ocean
                            Blue Crab
   How are they doing?
       Harvests increased in the
        1980’s as watermen shifted
        from oysters to crabs and
        demand for crab from
        consumers increased
       However, by 2000 harvests had
        declined, not because effort or
        demand had declined, but
        because the resource was
        becoming more scarce
       This could signal a problem for
        the blue crab
            Striped Bass (Rockfish)
   Striped bass is the most
    sought-after fish in the
    Chesapeake Bay
   They can grow to a length of
    nearly 5 ft and reach 100 lbs
   They are valued by
    recreational fisherman for
    their size, fighting ability, and
    their taste
             Striped Bass (Rockfish)

   The striped bass is an
    semianadromous fish
   That means that it spawns in tidal
    freshwater
   This occurs in May and early June
   The eggs are fertilized and hatch in
    open water where they are subject
    to predation even by oysters
   The small larvae are unable to
    swim and are moved by currents
            Striped Bass (Rockfish)

   By later in the summer, they reach
    juvenile stage and can swim
   At this time they move back down
    into the estuary and even into the
    open ocean
   By age 3-4 they reach sexual
    maturity and can return to spawn
   They can return multiple times
    Striped Bass (Rockfish)
   How are they doing?
        Striped bass landings remained steady
         through mid-1970’s
        But by mid-1980’s landings had decreased
         markedly
   1985 The Atlantic Striped Bass
    Conservation Act
        requires that states implement a 55% harvest
         reduction
        states respond by placing a moratorium on
         the taking of striped bass
   Bass recover quickly
        Limited fishing is resumed and by 1997
         landings reach a new record
   Lingering issues
        Bass have started showing signs of a new
         disease (mycobacteriosis)
        Also water quality continues to decline and
         food supplies (menhaden) are being heavily
         exploited by humans
                              Menhaden
   Menhaden are small fish that serve
    as forage (food) for the larger game
    fish like striped bass (max 7.3
    inches long)
   Native americans called menhaden
    “munnawhateaug” which means
    “fertilizer”
   These were probably this fish that
    were planted in the mounds used
    to grow corn
   Today these fish are heavily
    exploited for fish meal, fish oil, and
    bait
                            Menhaden
   Menhaden spawn from March to
    May and Sept to Oct in the bay
    proper
   The larvae live as plankton in the
    open water and grow rapidly
   During winter they migrate out of
    the bay and stay off North Carolina
    before returning to the bay in the
    early spring
   Menhaden, like oysters, feed
    heavily on phytoplankton and
    zooplankton
                             Menhaden
   Huge amounts of menhaden are
    harvested each year from the
    midAtlantic region
   Harvests have declined from the
    600,000 mt range in the late 1950’s
    to current levels below 200,000 mt
   Menhaden probably benefited
    from the oyster decline, but fishing
    pressure has increased
   Some have begun to question
    whether the decline in menhaden
    due to human fishing may be
    limiting the food for fish such as
    striped bass
                      Lessons Learned
   Human resource utilization tends to focus on a single species
    until it is reduced beyond it’s sustainability
       First oysters and shad, then striped bass, then crabs and now, maybe
        menhaden?
       Some species can spring back quickly (striped bass), others may require
        much longer, more intervention or never? (oyster)
       Exploitation of one species has an effect on others:
            Oyster overfishing may have release menhaden
            Oyster disappearance resulted in more exploitation of crabs and their
             overfishing
   More and longer data are needed to fully understand human
    impacts vs. those of climatic and other environmental cycles and
    changes