Salt Marshes and Succession Flashcards
What are salt marshes?
Saline, vegetated wetlands dominated by herbaceous and small shrubby halophytes. Mostly coastal although extensive inland areas do exist.
What are some salt marsh characteristics?
Forms in the intertidal zone where there is a source of sediment and wave energy is low so fine sediments like silt and clay can accrete.
In the protection of barrier islands, estuaries or in shallow water environments (wave absorbing).
Elevational gradient from land to the sea
Dissected by drainage creek system
Hypersaline ponds and depressions
What are some features of salt marshes?
Hypersaline in summer and hyposaline in winter
Fine muddy clays and silts containing appreciable sand - determines drainage and aeration
Frequently flooded sediments become chemically reducing - redox potential and elevation affect the ability of plants to colonise.
Variation in adaptations to toxic reduced ions and anoxia.
How does zonation and succession change in space and time?
Occurs along an elevational gradient from land to sea.
Sediment accretion increases elevation.
Involves interplay between sediment and developing plant communities which promotes accretion e.g. some plants help stabilise the sediment surface and reduce wave energy.
How do salt marshes develop?
Tidal waters carry silt that sediments-out under calm conditions.
Initial colonist, Spartina maritima is very tolerant of low redox, stabilises the surface and traps silt, creates raised tussocks.
Drainage better and redox potential higher in raised areas.
New species, less tolerant of reducing conditions, colonise the expanding tussocks.
Tussocks merge into marsh platform leaving drainage creeks.
Marsh surface continues to accrete sediment within tidal range.
What is the stress-gradient hypothesis?
Shift in species interactions from facilitation to competition with reduced environmental stress. Sub sequential colonisations out-compete and replace previous ones.
What are the two types of sea level change?
Eustatic - increasing sea water volume, e.g. thermal expansion and melting of continental ice sheets.
Isostatic rebound - local uplift and tilting of land e.g. S.E England sinking as N.E rises after weight of ice removed.
What is coastal management realignment? (managed retreat)
Reversal of centuries of thinking, now not economical to defend all coastline.
Vulnerable areas protected by seawalls or dykes.
