s2ary
09-09-2007, 08:46 AM
Salt Marsh Development
• Sediments are first deposited on a Mud Flat until the elevations reach Mean Sea Level
• At mean sea level Spartina alternaflora can take root and establish pioneering stands on the high spots (Low Marsh)
• Sediment and peat accumulation (accretion) increases around pioneering stands of S. alternaflora because the tall standing grasses slow the flow of water and filter out sediments.
• As Pioneering stands continue to expand distinct tidal features such as channels, rills, pools and pannes are formed. This can be readily observed at Joppa Flats in Newburyport, Massachusetts.
• Peat accretion continues around the tidal features until the intertidal marsh elevation reaches Mean High Water (High Marsh elevations)
• Once the low marsh elevation reaches high marsh elevations S. alternaflora is out competed by Disticalis spicata and S. patens. On the surface of the high marsh S. alternaflora may still be found, but only in the wetter areas such as depressions or close to the lower edges of tidal channels.
• Salt marsh surface elevations continue to accrete, but now because the marsh surface is above mean high water only 50% of the 730 tides per year flood over the marsh surface. (Irregularly Flooded Marsh) However, because the marsh surface has a vast network of rills and the salt marsh peat is porous salt water still penetrates the marshes to fertilize the grasses and carry away nutrients on each tide. This channel and rill system is vital to coastal ecology as nursery habitat for juvenile fish populations.
• The salt marsh elevation eventually reaches a dynamic equilibrium with sea level rise and its surface elevation fluctuates with the rise or fall of sea level. As the height of sea level rises organic matter and sediments build up the peat elevation. When the average height of sea level recedes the peat is oxidized more frequently allowing aerobic bacteria to decompose the organic matter in the peat and lower the average height of the marsh.
Ultimately salt marsh elevations are maintained by sea level. Marshes below this level continue to accrete peat; marshes above this level subside until a dynamic equilibrium is reached.
• Sediments are first deposited on a Mud Flat until the elevations reach Mean Sea Level
• At mean sea level Spartina alternaflora can take root and establish pioneering stands on the high spots (Low Marsh)
• Sediment and peat accumulation (accretion) increases around pioneering stands of S. alternaflora because the tall standing grasses slow the flow of water and filter out sediments.
• As Pioneering stands continue to expand distinct tidal features such as channels, rills, pools and pannes are formed. This can be readily observed at Joppa Flats in Newburyport, Massachusetts.
• Peat accretion continues around the tidal features until the intertidal marsh elevation reaches Mean High Water (High Marsh elevations)
• Once the low marsh elevation reaches high marsh elevations S. alternaflora is out competed by Disticalis spicata and S. patens. On the surface of the high marsh S. alternaflora may still be found, but only in the wetter areas such as depressions or close to the lower edges of tidal channels.
• Salt marsh surface elevations continue to accrete, but now because the marsh surface is above mean high water only 50% of the 730 tides per year flood over the marsh surface. (Irregularly Flooded Marsh) However, because the marsh surface has a vast network of rills and the salt marsh peat is porous salt water still penetrates the marshes to fertilize the grasses and carry away nutrients on each tide. This channel and rill system is vital to coastal ecology as nursery habitat for juvenile fish populations.
• The salt marsh elevation eventually reaches a dynamic equilibrium with sea level rise and its surface elevation fluctuates with the rise or fall of sea level. As the height of sea level rises organic matter and sediments build up the peat elevation. When the average height of sea level recedes the peat is oxidized more frequently allowing aerobic bacteria to decompose the organic matter in the peat and lower the average height of the marsh.
Ultimately salt marsh elevations are maintained by sea level. Marshes below this level continue to accrete peat; marshes above this level subside until a dynamic equilibrium is reached.