Environmental Engineering Reference
In-Depth Information
habitats "Pannonic salt steppes and marshes". Reintroduction of traditional land use, like
cattle grazing is essential to maintain the structure and species diversity of these alkali
habitats. Alkali marshes are threatened by land-use changes, amelioration, eutrophication
and fragmentation. Improper management, as regular reed harvesting also decreases the
spatial diversity of these habitats.
Keywords
: Wetland, alkali landscape, management, reed, salinity, zonation, grazing
1.
I
NTRODUCTION
Salt marshes are among the few naturally open ecosystems in Europe. They are often
species-poor communities characterised by a few salt-tolerant wetland species. The structure
and species composition of salt marshes are driven by many environmental factors, including
hydrology, salinity, nutrient- and oxygen availability and substrate type (Ranwell 1972). Salt
marshes play an important role in global nutrient cycles acting both as a sink and a source
(Doody 2008). Salt marshes are considered as important nesting and foraging habitats for
birds, especially for waders, geese, ducks and herons (Ecsedi et al. 2004).
Majority of salt marshes are typical in coastal areas, covering approximately 175,000
hectares along the Atlantic and Baltic coasts in Europe (Bakker et al. 2002). Coastal salt
marshes develop at shallow tidal coasts characterised by continuous sedimentation (Adam
1990). Elevation within the tidal range is a primary determinant of the environmental factors
that affect the distribution of vegetation types in coastal salt marshes (Davy et al. 2011).
These habitats are characterised by distinct vegetation zonation and rapid temporal dynamics.
Thus, coastal salt marshes are often chosen as model ecosystems for studying ecosystem
functions at multiple scales (Minden & Kleyer 2011). Many studies focus on ecological and
physiological adaptations of halophyte species to the extreme environmental conditions
typical in coastal salt marshes (Egan & Ungar 2000; Zia et al. 2004). Seed banks often play a
crucial role in vegetation dynamics in coastal salt marshes, since species can survive
hypersaline conditions by their long-term persistent seed banks (Chang et al. 2001). For
instance, the highest seed bank density records ever detected were found in salt marshes: in
case of
Spergularia salina
a seed density of 1,000,000 seeds/m
2
was detected by Ungar
(1991).
Compared to coastal salt marshes, much less attention was devoted to the study of
Eurasian inland salt marshes. They are characterised by lower salinity than coastal salt
marshes and their hydrology is not influenced by tidal movements. While coastal salt marshes
are characterised by a high concentration of sodium-chloride, alkali marshes have sodium-
chloride, sodium-carbonate and sodium-sulphate types. This diversity is a result of various
salt concentrations of groundwater and soil solution depending on site conditions (Dajic-
Stevanovic et al. 2008). Alkali marshes are intrazonal habitats typical for the Pannonian
biogeographical region, embedded in the matrix of alkali meadows and alkali dry grasslands
(Török et al. 2012). Alkali marshes play a crucial role in maintaining landscape-scale
heterogeneity in alkali landscapes. They provide wetland habitats for multiple taxa in the
matrix of meadows and dry grasslands and also form buffer zones around ex lege protected
sodic lakes. Alkali marshes provide nesting habitats for many protected bird species including
reed warblers (
Acrocephalus
spp.), herons (
Ardea
spp.), spoonbill (
Platalea leucorodia
), rails
