231
foliosa, native from the Atlantic Coast of North America, but little was known about
the possibilities of ecological restoration and phytoremediation using S. maritima.
A novel ecological restoration project was carried out in the Odiel Marshes from
November 2006 to January 2007. Previous to the restoration works, the sediments
of the low marshes where S. maritima was planted were polluted with metals (Van
Geen et al. 1997) and an area was also polluted by an historic oil deposit due to oil
spills from neighboring industries. In addition, the alien Spartina densiflora was
actively invading these degraded marshes and had already occupied more than
2.01 ha. On top of all, one location exposed to high energy waves and currents was
suffering high erosion rates, evidenced by detachment of substrate blocks from an
erosive bank (Castillo et al. 2002).
The approach was supported by previous results obtained in different studies that
enabled the development of a suitable methodology to restore these salt marshes
using S. maritima:
Firstly, a transplant experiment was used to investigate the means by which physical and chemical factors determined lower distribution limits of native S. maritima
and invasive S. densiflora along the intertidal gradient. Neither species survived for
a year at elevation lower than 1.04 m relative to SHZ. The lower distribution limit
was +1.41 m SHZ for S. maritima and +1.46 m SHZ for S. densiflora. Moreover,
tiller growth rates of both species increased with elevation, but that of S. densiflora
was more sensitive to low elevations (Castillo et al. 2000). This study was very useful to understand the elevations where S. maritima had to be transplanted.
At the same time, the role of S. maritima and Sarcocornia perennis. ssp. perennis
on the ecological succession was analyzed. S. maritima colonization of low-lying
mud flats promotes sediment accretion sufficiently to ameliorate stressful conditions related with sediment anoxia, facilitating the colonization of S. perennis. This
halophyte becomes increasingly dominant as accretion progress, until Spartina is
virtually eliminated from all but the expanding edges of its own tussocks (Castellanos
et al. 1994, 1998). Later on the succession, S. perennis facilitates the in situ formation and the colonization of its hybrid Sarcocornia perennis x fruticosa as a result of
pollen flow from high-marsh Sarcocornia fruticosa to the stigmas of the established
dominant S. perennis. Succession might therefore be genetically facilitated
(Figueroa et al. 2003). These studies enabled us to know how restored salt marshes
using S. maritima and S. perennis would evolve over time.
On the other hand, the shoot height of S. maritima was also study since this species
tend to exhibit a wide range of phenotypes, often with short and tall growth forms. Our
results showed that height variation in S. maritima appears mainly to be a result of
phenotypic plasticity, with hypoxic sediments stimulating stem growth (Castillo et al.
2005). The discovery of this highly plastic growth form of S. maritima showed that
there was no need to select specific clumps from natural populations for transplant
since every populations showed similar heights in a common environment.
The role of S. maritima and S. densiflora on the establishment of salt marsh
ecological zonation were also studied in areas where both cordgrass species are
dominant. S. densiflora invaded the upper areas of the marsh at the centre of the
circular tussocks of S. maritima, where above-ground biomass of S. maritima
7 Handling High Soil Trace Elements Pollution: Case Study of the Odiel and Tinto…
foliosa, native from the Atlantic Coast of North America, but little was known about
the possibilities of ecological restoration and phytoremediation using S. maritima.
A novel ecological restoration project was carried out in the Odiel Marshes from
November 2006 to January 2007. Previous to the restoration works, the sediments
of the low marshes where S. maritima was planted were polluted with metals (Van
Geen et al. 1997) and an area was also polluted by an historic oil deposit due to oil
spills from neighboring industries. In addition, the alien Spartina densiflora was
actively invading these degraded marshes and had already occupied more than
2.01 ha. On top of all, one location exposed to high energy waves and currents was
suffering high erosion rates, evidenced by detachment of substrate blocks from an
erosive bank (Castillo et al. 2002).
The approach was supported by previous results obtained in different studies that
enabled the development of a suitable methodology to restore these salt marshes
using S. maritima:
Firstly, a transplant experiment was used to investigate the means by which physical and chemical factors determined lower distribution limits of native S. maritima
and invasive S. densiflora along the intertidal gradient. Neither species survived for
a year at elevation lower than 1.04 m relative to SHZ. The lower distribution limit
was +1.41 m SHZ for S. maritima and +1.46 m SHZ for S. densiflora. Moreover,
tiller growth rates of both species increased with elevation, but that of S. densiflora
was more sensitive to low elevations (Castillo et al. 2000). This study was very useful to understand the elevations where S. maritima had to be transplanted.
At the same time, the role of S. maritima and Sarcocornia perennis. ssp. perennis
on the ecological succession was analyzed. S. maritima colonization of low-lying
mud flats promotes sediment accretion sufficiently to ameliorate stressful conditions related with sediment anoxia, facilitating the colonization of S. perennis. This
halophyte becomes increasingly dominant as accretion progress, until Spartina is
virtually eliminated from all but the expanding edges of its own tussocks (Castellanos
et al. 1994, 1998). Later on the succession, S. perennis facilitates the in situ formation and the colonization of its hybrid Sarcocornia perennis x fruticosa as a result of
pollen flow from high-marsh Sarcocornia fruticosa to the stigmas of the established
dominant S. perennis. Succession might therefore be genetically facilitated
(Figueroa et al. 2003). These studies enabled us to know how restored salt marshes
using S. maritima and S. perennis would evolve over time.
On the other hand, the shoot height of S. maritima was also study since this species
tend to exhibit a wide range of phenotypes, often with short and tall growth forms. Our
results showed that height variation in S. maritima appears mainly to be a result of
phenotypic plasticity, with hypoxic sediments stimulating stem growth (Castillo et al.
2005). The discovery of this highly plastic growth form of S. maritima showed that
there was no need to select specific clumps from natural populations for transplant
since every populations showed similar heights in a common environment.
The role of S. maritima and S. densiflora on the establishment of salt marsh
ecological zonation were also studied in areas where both cordgrass species are
dominant. S. densiflora invaded the upper areas of the marsh at the centre of the
circular tussocks of S. maritima, where above-ground biomass of S. maritima
7 Handling High Soil Trace Elements Pollution: Case Study of the Odiel and Tinto…