Environmental Engineering Reference
In-Depth Information
R S
R
SEDIMENT
HEIGHT
SEDIMENT
TYPE
SILTY
SANDY
A
S
a
Fig. 13.7 Graphical model of the negative biodepository spiral by which mollusc-rich and reasonably silty
sediments in the lee of a mussel bank, through the successive losses of cockles due to mechanical harvesting and
the mussel bank itself, transform into permanently sandy, highly dynamic and lower-lying intertidal flats where
even the Baltic tellin ( Macoma balthica ) is unable to maintain its population (processes as they appear to have
taken place in the western Dutch Wadden Sea in 1988-98; see Piersma et al. 2001). Note that in the absence of
human activities, the winter storms do not affect the balance of the sediments: the changes have to be started by
the (mechanical) removal of the stocks of large filter-feeding and faecal-pellet-producing bivalves (blue mussels
and/or common cockles) but can then turn into a self-perpetuating process with the additional loss of small filter-
feeders. From Piersma and Koolhaas (1997).
mussels and eelgrass could comprise a key ingredient
for restoring such intertidal flats to their original, bio-
diverse state.
delta in the European north-east of Russia (van
Eerden 2000). This river delta resembles the western
European coast before coastal engineering activities.
Present western European salt marshes seem natural
ecosystems being governed by tides, but they are more
or less affected by human activities as shown above.
The cessation of accretion works along the mainland
coasts will result in erosion of many artificial marshes
in front of the present seawalls. When the area of the
marshes is maintained, the geometric drainage patterns
may remain for centuries. Only removal of the marsh
13.6 Restoration of salt marshes
13.6.1 Setting targets
The ecological frame of reference for natural coastal
systems in western Europe might be the Pechora river
 
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