Geology Reference
In-Depth Information
Fig. 8.6 Upper left : Border between a bare mudflat and
Spartina marsh at Klægfledningen in the north/eastern part
of Ho Bugt, Denmark. Upper right : Border zone between a
sandy tidal flat and the backbarrier salt marsh of Skallingen,
Denmark. Below left : Wave exposed salt marsh edge from
the northern part of Ho Bugt, Denmark. Below right : An
expanding exposed salt marsh area northwest of Ribe,
Denmark
about half a metre high and is in salt marsh areas located
in upper primary sandy parts (Fig. 8.5 lower right).
Also, ice rafting can contribute to salt marsh sedi-
mentation and topographic variations on salt marsh
surfaces. It takes place when ice fl akes containing sed-
iment from the intertidal zone are moved to rest on the
salt marsh surface and subsequently release melt out
pockets of sediment. This type of sedimentation cre-
ates an uneven salt marsh surface and is documented to
be present even in relatively mild temperate climates
(Bartholdy 1997 ; Pejrup and Andersen 2000 ) . This
process is responsible for moving large quantities of
sediment in areas characterized by cold winters (e.g.
Dionne 1984 ; van Proosdij et al. 2006a ) .
wave-induced turbulence can obstruct sedimentation
such that the deposition maximum is moved inland.
This is documented for a salt marsh area in the Bay of
Fundy (e.g. Davidson-Arnott et al. 2002 ; van Proosdij
et al. 2006b ). In contrast, for sheltered backbarrier salt
marshes, waves may be of little importance, even under
storm conditions (Bartholdy and Aagaard 2001 ) .
If expanding, lee-type salt marshes generally
develop on top of the adjacent tidal fl at either as a veg-
etation front (Fig. 8.6 , upper left, where Spartina grows
directly out over a mudfl at) or in patches of vegetation
that eventually merge to form a coherent salt marsh
(Fig. 8.6 , upper right). Wave activity forms salt marsh
cliffs at the edge of exposed salt marshes (Fig. 8.6 ,
below left), and if expanding, the salt marsh in the
active cliff area will usually be uneven and dominated
by vegetated hummocks separated by unvegetated gaps
(Fig. 8.6 , lower right). This is a result of both deposi-
tional and erosional activity. Hummocks of salt marsh
can grow with lumps of clay liberated from the salt
marsh cliff as their base, or develop from colonies of
pioneer vegetation. Between the hummocks and in
8.3.3
Exposed Salt Marsh Zones
Processes related to the zone close to the salt marsh
edge are primarily connected to wave action and can
affect the general picture described above signifi cantly.
If the salt marsh edge is heavily exposed to waves,
Search WWH ::




Custom Search