216
Keywords Salt marshes • Contamination • Trace elements • Management • Invasion
• Phytoremediation • Restoration • SW Iberian Peninsula
7.1 Introduction
7.1.1 A Brief View to Coastal Marsh Ecosystems and Its
Significance for Conservation
Coastal salt marshes are complex ecosystem developing in the intertidal zone of
middle and high latitudes worldwide, regularly flooded by tides and subjected to
sedimentary dynamic of accretion. Developed within the last 8000 years (Milliman
and Emery 1968), they are characterized by harsh environmental conditions, including flooding, sedimentation, high salinity and anoxia. This abiotic matrix imposes
certain limits on organisms living in such habitats. A low vegetation type, mainly
composed by salt-tolerant species particularly adapted to this environment (halophytes), grows in salt marshes, where the majority of species are perennials, with
only few annuals, mainly pertaining to the Chenopodiaceae family (Ranwell 1972).
Vegetation is generally distributed in relatively well defined belts or bands parallel
to the tidal line, along the intertidal gradient defined by elevation, showing a typical
vertical zonation leaded by the particular abilities of the species to establish and
survive to the environmental constrains, mainly related with the degree of tidal
influence (flooding frequency and permanence timing, nutrient availability, degree
of anoxia and salinity, sedimentation rates and mechanical damage), and the associated level of accretion and soil maturation (Álvarez Rogel et al. 2001; Davy and
Costa 1992; Olff et al. 1997; Ranwell 1972; Vince and Snow 1984). Nonetheless,
biotic interactions, both positive and negative, also play a relevant role in determining plant species distribution in these systems (Bertness 1991; Castillo et al. 2008a;
Costa et al. 2003; Pennings and Callaway 1992).
Coastal salt marshes provide notable ecosystem services to society. They play a
relevant role as natural barriers to front coastal hazards such as storms, flooding and
coastal erosion, by attenuating wave energy and storing floodwaters, and so decreasing the impact of extreme events such as hurricanes and tsunamis (Costanza et al.
2008; Gedan et al. 2011; Möller et al. 2014). They act as a sponge absorbing and
sequestering nutrients, microbes and pollutants from runoff and riverine discharge,
thus improving estuarine and coastal waters quality (Gedan et al. 2009; Mitsch and
Gosselink 2007), and play a major role in the global carbon cycle by acting as carbon sinks (Chmura et al. 2003). Salt marshes are recognized for their importance in
the aquatic food web and the cycling of nutrients in coastal waters, and they are
crucial to global biodiversity maintenance, providing habitats for feeding, resting
and breeding for many bird species, both migrator y and resident (Ferns 1992; Howe
1987; Hughes 2004; Laegdsgaard 2006), as well as for juvenile fishes, crabs, and
shrimps (Shenker and Dean 1979; Zimmerman et al. 2000). The harsh environment
S.M. Vallés et al.
Keywords Salt marshes • Contamination • Trace elements • Management • Invasion
• Phytoremediation • Restoration • SW Iberian Peninsula
7.1 Introduction
7.1.1 A Brief View to Coastal Marsh Ecosystems and Its
Significance for Conservation
Coastal salt marshes are complex ecosystem developing in the intertidal zone of
middle and high latitudes worldwide, regularly flooded by tides and subjected to
sedimentary dynamic of accretion. Developed within the last 8000 years (Milliman
and Emery 1968), they are characterized by harsh environmental conditions, including flooding, sedimentation, high salinity and anoxia. This abiotic matrix imposes
certain limits on organisms living in such habitats. A low vegetation type, mainly
composed by salt-tolerant species particularly adapted to this environment (halophytes), grows in salt marshes, where the majority of species are perennials, with
only few annuals, mainly pertaining to the Chenopodiaceae family (Ranwell 1972).
Vegetation is generally distributed in relatively well defined belts or bands parallel
to the tidal line, along the intertidal gradient defined by elevation, showing a typical
vertical zonation leaded by the particular abilities of the species to establish and
survive to the environmental constrains, mainly related with the degree of tidal
influence (flooding frequency and permanence timing, nutrient availability, degree
of anoxia and salinity, sedimentation rates and mechanical damage), and the associated level of accretion and soil maturation (Álvarez Rogel et al. 2001; Davy and
Costa 1992; Olff et al. 1997; Ranwell 1972; Vince and Snow 1984). Nonetheless,
biotic interactions, both positive and negative, also play a relevant role in determining plant species distribution in these systems (Bertness 1991; Castillo et al. 2008a;
Costa et al. 2003; Pennings and Callaway 1992).
Coastal salt marshes provide notable ecosystem services to society. They play a
relevant role as natural barriers to front coastal hazards such as storms, flooding and
coastal erosion, by attenuating wave energy and storing floodwaters, and so decreasing the impact of extreme events such as hurricanes and tsunamis (Costanza et al.
2008; Gedan et al. 2011; Möller et al. 2014). They act as a sponge absorbing and
sequestering nutrients, microbes and pollutants from runoff and riverine discharge,
thus improving estuarine and coastal waters quality (Gedan et al. 2009; Mitsch and
Gosselink 2007), and play a major role in the global carbon cycle by acting as carbon sinks (Chmura et al. 2003). Salt marshes are recognized for their importance in
the aquatic food web and the cycling of nutrients in coastal waters, and they are
crucial to global biodiversity maintenance, providing habitats for feeding, resting
and breeding for many bird species, both migrator y and resident (Ferns 1992; Howe
1987; Hughes 2004; Laegdsgaard 2006), as well as for juvenile fishes, crabs, and
shrimps (Shenker and Dean 1979; Zimmerman et al. 2000). The harsh environment
S.M. Vallés et al.