Chapter 8
Estuaries and Salt Marshes
Definition of Estuaries
Define: a partially enclosed coastal embayment where fresh water and seawater meet and mix.
Geological history
Various climate conditions
Different chemical and physical conditions
Salinity gradients
Types of Estuaries
Salt – Wedge
Well – Mixed
Partially – Mixed
Reversed
1. Coastal Plain Estuary
USA:
Chesapeake Bay
mouth of Delaware and Hudson rivers
Great Britian: Cornwall and Devon
2. Tectonic Estuary
Fig 8.1 cont.
San Francisco bay
San Francisco Bay’s History
The Parts of San Francisco Bay and its Watershed
3. Semiclosed Bay or lagoon
Major Lagoons
Pamlico Sound
North Carolina Coast
Lying behind barrier beach
Outer Banks
Classification by Salinity gradient
Positive estuary or salt wedge estuary
River-dominated or stratified
Homogeneous estuaries
Marine-dominated estuaries
Neutral estuaries:
Galveston Bay, Texas and Alligator Harbor, Florida
Negative or evaporite estuaries
Seasonal or intermittent estuary
Positive and Negative estuaries
(a) Positive or salt wedge
Seawater enters along the bottom and gradually mixes with our-flowing fresh water
(b) Negative estuary
Fresh water flow is diminished or absent during part of the year
Seawater enters along the surface. Evaporation is greater than runoff, salinity increases as one move up the estuary. Hypersaline water sinks and flows out below the incoming seawater.
Change of salinity
Changes by tide level
Changes by river discharge
Point A is on the bottom and B is intertidal
B is covered by high tide, is inundated only with high-salinity water
Unaffected by low-salinity water at low tide
Point A is covered by water of different salinities at different tides
Physical Characteristics of Estuaries
Stressful environment for organisms
yes or no
Salinity fluctuation
major feature
varies because of
seasons, topography, tides, influx of fresh water
figure 8.3
time frame 6-12 hours
Coriolis effect in Northern Hemisphere towards right
figure 8.4
Eastern shore of Chesapeake Bay
opposite in Southern Hemisphere
Results of Coriolis effect
North – South orientation of CB
Deflection of the isohalines to the right in this Northern Hemisphere estuary
Circled numbers refer to salinity values in ppt
Seasonal Changes
Salinity
Due to evaporation, Freshwater flow or Both
High concentrations in upper Bay
Decrease freshwater flow
High concentration downstream, lower Bay
Increased freshwater flow
Comparison of salinity fluctuations in the water column with that interstitially in the bottom mud.
Sustrates
Sand and mud
Water held between particles
Change in salinity slower
Buffered
Organisms subject to less drastic salinity changes
Most effective in lower intertidal
Soil at higher level
Dilution during rains
Evaporation in dry weather
Estuary Substrates
Most are soft and muddy
Sediments carried from
Seawater and freshwater
Wind
Coastal lagoons
Silt suspension
Seawater ions
Particles flocculate
Muddy bottom
Sandy bottom
Deposition
Control by current
Particles size
Mouth of estuary
Catastrophic events
Massive storms
Floods
Organism mortality
East Coast
Andrews 1973
Hurricane Agnes 1972
Chesapeake Bay
Salinity reduction
Loss of organisms
Organic matter
Settled out terrestrial and marine
Rich accumulation
Habitat for bacteria
Temperature
1. Variable horizontal columns
2. Depth
3. Temperate zone rivers
4. Estuarine rivers
5. Mouth of estuary
6. Variable vertical columns
Wave Action and Currents
1. Minimal wind
2. Fetch
3. Depth of water
4. Bay’s mouth narrowness limits size of wave that enters from the ocean / sea
5. Sediment deposition
6. Currents
7. Flushing Time
Turbidity
1. Particle suspension
2. High turbidities
3. Major ecological effect
4. Severe turbidity
Oxygen
1. Ample supply of O2
2. Solubility of oxygen
3. Salt wedge estuary
4. Estuarine sediments
anoxic level ( without O2 )
The Biota of Estuaries
Three major faunal components
Freshwater
Estuaries
Marine
Some typical Estuarine
Brackish water animals with 5 – 18 psu
Typical estuarine algae
A. Estuarine Vegetation
Intertidal mud flats are inhabited by a limited number of green algae
Common genera listed on left
Often seasonally abundant
Disappear during certain times of year
B. Estuarine Plankton
* Diatoms dominate
Warmer months
High turbidity
Rapid flushing
Zooplankton
Adaptations of Estuarine Organisms
Morphological adaptations
Physiological adaptations
Behavioral adaptations
Nereis diversicolor with change in salinity
Change of salinity
Blood of the crab
Australoplax trientata
With change in salinity of the external medium
Life span of Blue Crab
Callinectes sapidus
estuaries of the Atlantic coast of United States
Ecology of Estuaries
Productivity, Organic Matter, and Food Sources
Food Webs
Plankton Cycles
Bill length of Shorebirds
Relationship to the depth of some common estuarine invertebrates
A generalized estuarine food web
The food web of a typical estuary showing some of the major aquatic trophic groupings
The distribution of salt marshes in the world
Salt Marshes
Definition and Characteristics
Environmental Characteristics
Composition and Distribution
Causes of Zonation
Productivity
Interactions and Food Webs
Areal extent of salt marshes on the Atlantic coast of the U. S.
Environmental factors influencing salt marsh vegetation
.Some dominant salt marsh emergent plants
Characteristics animals present in a salt marsh at low and high tides on the Atlantic coast of North America
Zonation in a New England Marsh
Zonation in a Southern Marsh of Atlantic coast of U. S.
Generalization zonation of a Pacific coast salt marsh based on marshes of San Francisco Bay
Alternative succession patterns in bare patches of the high marsh as a result of differing physical conditions
Change in competitive relations among marsh plants under high and low nitrogen levels.
The migration of the marsh periwinkle Littoraria irrorata up the cordgrass blades to avoid predation by blue crabs
The mutual interaction between cordgrass and mussels in a salt marsh.