Tidal Marshes

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Tidal Marshes

• Physical Factors

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Presented By

• Maureen Harding
• Jennifer Arp

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Introduction

• Salt marshes are transitional areas between land
  and water, occurring along the intertidal shore
  of estuaries and sounds where salinity ranges
  from near ocean strength to near fresh in upriver
  marshes
• Marshes are subject to rapid changes in salinity,
  temperature and water depth
• Physical characteristics of marshes include
• Development
• Effects of salinity
• Effects of tides
• Nutrients

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Basic Definition

• Wetlands are partially or periodically submerged
  lands
• Tidal marshes are predominantly intertidal and
  have a gentle slope that allows for tidal
  flooding
• Tidal salt marshes are found along protected
  coastlines
• Plants and animals must adapt to stresses of
  salinity, periodic flooding and extremes in
  temperature

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Distribution

• Salt marshes are most frequent in the temperate
  zones and are replaced by mangroves in the
  tropics
• Most prevalent in the United States along the
  Eastern Coast from Maine to Florida and in the
  Gulf of Mexico in Louisiana and Texas

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Distribution of Salt Marshes
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Tidal Marsh Development

• Sediment builds up on a sheltered shore to above
  the highest high tide level. Build up of
  vegetation aids in continued sedimentation. As
  the level rises the area becomes fully vegetated
  with the exception of drainage channels (creeks)
  and isolated depressions (pans)
• The rate of formation is determined by the
  effectiveness of the protecting coastal feature

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Formation of a Salt Marsh
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Development

• There are two broad classifications for
  development
• Formed from reworked marine sediments on
  marine-dominated coasts
• North American Coastline
• Formed in deltaic areas where the main source of
  sediment is riverine
• South Atlantic and Gulf of Mexico

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Marine-Dominated Development

• There must be shelter to prevent erosion from
  wave action and to permit the build up of
  sediment.
• Protection can come from spits, offshore bars or
  islands
• Formation from protected bays
• Chesapeake Bay

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River Dominated Marsh Development

• Major rivers carrying large sediment loads build
  marshes into shallow estuaries or out onto the
  shallow continental shelf where there is little
  wave action
• Typically begin as freshwater marshes, but as the
  river course shifts, more ocean water comes in
• Mississippi River Delta

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River Dominated
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Types of Salt Marshes

• Most types of salt marshes must have a physical
  feature providing protection against the full
  energy of waves
• Lagoonal marshes may occur where a spit partially
  encloses a body of tidal water with only a narrow
  connection to the sea
• Beach plains are either partially protected by
  bars that are overwashed at high water or they
  are unprotected-usually narrow

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Types of Salt Marshes

• Chesapeake Bay
• Lagoonal marsh in North Carolina

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Types of Salt Marsh

• Barrier island marshes occur where a chain of
  islands provides an offshore barrier, creating
  calmer waters on the landward side.
• Estuarine marshes form on sheltered inner curves
  of estuaries or may have no physical
  barrier-shallowness of estuaries results in the
  reduction of wave energy
• Semi-natural marshes have been significantly and
  deliberately modified by man
• Artificial marshes are created by man

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Stability of Marshes

• The long-term stability of marshes is determined
  by the rates of two processes
• Sediment accretion on the marsh, which causes it
  to grow upward and expand outward
• Coastal submergence caused by rising sea level
  and marsh surface subsidence

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Physical and Chemical Variables

• Important physical and chemical variables that
  determine the structure and function of the salt
  marsh include
• Salinity of water and soil
• Tidal flooding frequency and duration
• Nutrient limitation

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Salinity

• Salinity in the marsh soil and water depend on
  several factors
• Frequency of tidal inundation
• Rainfall
• Tidal creeks and drainage slopes
• Soil texture
• Vegetation
• Depth to water table
• Fresh water inflow
• Fossil salt deposits

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Salinity

• Frequency of tidal inundation-the lower salt
  marshes retain a consistent salinity close to
  that of sea water
• Rainfall-high rainfall tends to lower salinity
  while periods of drought will increase salinity
  because of evaporation
• Tidal creeks and drainage slopes-lower salinity
  because they allow saline water to drain

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Salinity

• Soil texture-silt and clay soils reduce drainage
  rates and retain more salt than clay soils
• Vegetation-evaporation is reduced by vegetation
  and transpiration is increased
• Depth to water table-when groundwater is close to
  the surface, salinity is lower and more stable
• Fresh water inflow-reduces salinity
• Fossil salt deposits-increase salinity in the
  root zone

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Salinity
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Salinity Distribution

• Salt wedge
• Partially mixed
• Mixed, or vertically homogenous

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Salinity of Soil

• In the lower marsh, the soil salinity is
  relatively constant and rarely exceeds that of
  the flooding water
• In the upper marsh, there is more of an influence
  from flooding and the climate
• High rainfall will reduce soil salinity
• During dry periods, evaporation increases soil
  salinity
• Sometimes to the point that a salt crust will form

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Water

• Water in tidal marshes is often brackish
• Influence of fresh water from rivers and creeks
  and salt water from ocean
• Water table is near or above the soil surface
• Influenced by ebb and flow of tides
• Little or no wave action

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Tidal Range

• Horizontal width depends on
• tidal amplitude, slope of the shore and fresh
  water
• Lower limit depends on
• depth and the duration of flooding
• mechanical effects of waves, sediment
  availability and erosional forces
• Upland side extends to the limit of flooding on
  extreme tides

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Influence of Tides

• The environmental feature which distinguishes
  coastal salt marshes from terrestrial habitats is
  tidal submergence
• Tides control
• soil salinity
• degree of water logging
• carry sediment into the marshes

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Profile of Tidal Marsh vs. Tidal Range
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Tidal Influences
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Zonation

• Salinity of water and soil determines zonation of
  plants
• Often divided into two zones
• Upper marsh (high marsh)-flooded irregularly
• At least 10 days continuous exposure
• Lower marsh (intertidal marsh)-flooded almost
  daily
• No more than 9 days continuous exposure

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Zonation
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Low Marsh
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Highmarsh
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Physical Features

• Network of drainage creeks
• Small pools or salt pans, mud barren
• Small cliffs or ridges
• Gentle slope

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Tidal Creeks

• Tidal creeks serve as
• passageways for material and energy transfer
  between the marsh and its adjacent body of water
• Salinity similar to adjacent estuary or bay
• Depth varies with tide fluctuations
• Flow in the channels is bi-directional
• As marshes mature and sediment deposition
  increases elevation, tidal creeks tend to fill in

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Tidal Creeks
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Tidal Creeks
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Pans

• Pans are bare, exposed or water-filled
  depressions in the marsh
• Sand barrens/Salt Pan-upper marsh
• Form where evaporation concentrates salts in the
  substrate, killing the rooted vegetation
• Mud barrens/Mud Flat-lower marsh
• Tend to have standing water and high salinity

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Salt Pan
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Mud Barren
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Types of Sediment

• Typically sandy sediments, though others may
  include
• Muddy sand
• Soft clay or silty mud
• Firm clayey soils

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Sedimentation

• Sedimentation-natural filtration system
• Adds organic and nutrient-rich matter to the
  marsh system
• Sediments originate from
• upland runoff
• marine reworking the coastal shelf sediments
• organic production within the marsh itself

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Sediment How it works

• Water floods over a marsh
• slows down to zero velocity
• suspended particles fall out onto marsh surface
• Tidal creek rises and overflows its banks
• coarser grained sediments drop near the stream
  edge, creating a slightly elevated streamside
  levee
• finer sediments drop out farther away from the
  creek

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Streamside Levee
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Anaerobic Soil

• When water fills in pore spaces in soils, rate at
  which oxygen can diffuse through the soil is
  reduced
• It is estimated that the diffusion of oxygen is
  10,000 slower in flooded soil than in an aqueous
  solution

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Anaerobic Soil

• Surface thin layer oxygenated soil
• Lower layers-have decreased oxygen levels
• prevents plants from carrying out normal aerobic
  root respiration
• as the oxygen concentration declines, the carbon
  dioxide concentration increases
• Peat formed
• anaerobic conditions
• high biomass-becomes trapped
• does not completely decompose
• compacted into peat

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Common Elements
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Nutrients

• Saturation of soil from the water table causes
  oxidized to reduced chemical gradients (e.g.
  sulfate to sulfide) with depth
• If soil does not have adequate oxygen, bacteria
  will use other electron acceptors for oxidation,
  which causes substances to be converted to a
  reduced state
• Excessive nutrients accelerate the process of
  eutrophication

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Nutrients

• Nitrogen is often the limiting factor of growth
  of vegetation
• The near anaerobic conditions of the marsh soil
  prevent the buildup of nitrate
• Ammonium nitrogen is the primary form available

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Nitrogen Availability
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Nutrients

• Phosphorus accumulates in high concentrations and
  does not appear to limit growth
• Iron is also available in high concentrations

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Nutrients

• Sulfur is present in high concentrations in
  seawater
• In the anoxic marsh soil, it is reduced to
  sulfide
• Hydrogen sulfide
• rotten egg odor
• When sulfides are exposed to the air
• they can be reoxidized to sulfate forming
  sulfuric acid
• which will lower the pH of the soil

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Human Impact
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Human Impact

• A major impact-ditching for mosquito control
• Began with the spread of malaria during the Civil
  war
• Wetlands were drained to prevent transmission of
  malaria by mosquitoes
• After malaria was controlled, the practice
  continued targeting nuisance mosquitoes by hand
  dug ditches to drain marsh surface waters
• Had a long term effect on plants, animals and
  environment

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Mosquito Ditches
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Human Impacts

• Over half of the original salt marshes in the
  United States have been destroyed
• Examples of alterations to the marshes include
• Draining, dredging and filling in of wetlands
• Modification of the hydrologic regime
• Highway construction
• Mining and mineral extraction
• Water pollution

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Human Impacts

• Along the coastline-major wetland loss for urban
  and industrial development
• Canals, ditches, and levees are created for
• Flood control-canals designed to carry off
  floodwaters (normal drainage is slow)
• Navigation and transportation-larger than
  drainage canals and used for water transportation
  (Intracoastal waterway)
• Industrial activity-dredged to obtain access to a
  site within the marsh for development or mining

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Human Impacts

• Highway construction
• areas are isolated and no longer affected by the
  tides resulting in decreased circulation and
  increased nutrient retention, leading to
  eutrophication
• Mining and mineral extraction-peat, phosphate,
  withdrawal of water
• Water pollution-natural filter to remove
  sediments and toxins from the water
• Excessive pollutants can overburden the cleansing
  capabilities of marshes
• Pollutants can come from air, local and upstream
  runoff, and agricultural waste

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Jump in for a swim
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Environmental Uses
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Hope for the Future

• Destruction of the salt marshes has been
  minimized due to federal and state laws
• Tidal Wetland Act
• Regulation of point-source pollution from large
  plants
• Wetland restoration and creation programs
• More public awareness of the importance of these
  areas for plant and animal life

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The salt marsh is the most productive ecosystem
known.  Grasses, algae, and phyto-plankton can
produce up to 10 tons of organic matter per acre
per year. Because more organic matter is
produced than is used by salt marsh inhabitants,
this community is continually exporting
nutrients enriching the surrounding estuary. 
The importance of the salt marsh to marine
ecosystems cannot be overemphasized.   Janet
McMahon in  Forests, Fields, and Estuaries  A
Guide to the Natural Communities of Josephine
Newman Sanctuary

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References

• http//camel2.conncoll.edu/ccrec/greennet/arbo/pub
  lications/34/FRAME.HTM
• http//home.earthlink.net/zephyr 3d/enviro.html
• http//lily.mip.berkely.edu/wetlands/estuarin.html
  
• http//omp.gso.uri.edu.discovery/Saltmarsh/smtrip2
  9.htm
• http//water.dnr.state.sc.us/marine/pub/seascience
  /dynamic.html
• http//www.journey.sunyb.edu/longis/flaxpond.html
  http//www.theadvocate.com/lockwood/miss4.htm
• http//www.toymania.com/news/news8_98.shtml
• http//www.tramline.com/tours/salt/tourlaunch2htm

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References Cont.

• Adam, Paul. 1990. Saltmarsh Ecology. Cambridge
  University Press, Cambridge, UK.
• Long, SP., CF. Mason. 1983. Saltmarsh Ecology.
  Blackie and Son Limited, Bishopbrigss, Glasgow.
• Mitsch,Wm.J, James G.Gosselink. 1993. Wetlands.
  Van Nostrand Reinhold, New York, NY.