235
the minimization or elimination the existing impacts and perturbations. Regarding soil
contamination by trace elements, phytoremediation has become a main green technology in recent years, due to its notable efficiency in terms of costs and efficacious
(Montpetit and Lachapelle 2016). General soft management actions regarding the
rehabilitation of contaminated soils by trace elements have preferentially tried to stabilize pollutant in the soil rather than extract them. Nonetheless, phytoextraction has
received increasing attention since the discovery of hyperaccumulator plants, able to
phytoextract and accumulate high levels of particular metals in their above-ground
biomass (Vamerali et al. 2010). In such a dynamic ecosystem as salt marshes, phytoextraction would be limited to the use of herbaceous native species, particularly
selected to each specific pollutant and objective. Additional desirable characteristics
that these species should present are fast grow and high biomass production, extended
root system for exploring large soil volumes, good tolerance to high concentrations of
metals, high translocation factor and easy management (Vamerali et al. 2010). Such
species should ideally avoid biomass (leaves) release along their life cycle, since polluted biomass circulating through marshes channels and even littoral sea currents
would easily enter the food chain. On top of all, further biomass management should
be planned, regarding harvesting and safe storage of polluted biomass. All this brings
to the idea that management of polluted salt marshes needs for the design of particular
actions adapted to each case.
In the case of the salt marshes in the Odiel and Tinto joint estuary, other two main
threats are identified in addition to soil contamination: the invasion by the alien
Spartina densiflora and erosion of marsh channels. A local restoration project has
resulted in a rapid recovery of the native prairies of low tidal marshes, dominated by
S. maritima, becoming a promising tool to phytostabilize eroding areas in European
marshes (Curado et al. 2012). These prairies seem to stop the advance of the S. densiflora invasion and prevent erosion. In this regard, extensive S. maritima plantations in the lower marshes along the protected area would be desirable. Plantations
in other upper areas with other native species need to be further studied, although a
relation of suitable native species for soil contamination phytoremediation in
European salt marshes is available at present. Although further research concerning
plant establishment and biomass production and limitations is still necessary, also
the use of stem cuttings of certain species, such as Halimione portulacoides
(Cambrollé et al. 2016), provides a cost-efficient way to accelerate the phytoremediaton process.
On the other hand, some protected areas of the Odiel and Tinto marshes are
invaded by the alien S. densiflora. In this regard, and in contrast to generalized criteria, it seems that maintaining the S. densiflora prairies in areas where it has become
dominant is a better option than removing them, since the latter action would lead
to an important release of presently stabilized pollutants. A solution could be related
with getting ready neutral sediment salt marshes using Spartina maritima and
Sarcocornia perennis plantations, which have already been tested as a successful
methodology for ecological restoration in polluted sediments in the same estuary
(Castillo and Figueroa 2009). The most complicated step would be to restore those
polluted areas where Spartina densiflora tussocks would be eliminated. They should
7 Handling High Soil Trace Elements Pollution: Case Study of the Odiel and Tinto…
the minimization or elimination the existing impacts and perturbations. Regarding soil
contamination by trace elements, phytoremediation has become a main green technology in recent years, due to its notable efficiency in terms of costs and efficacious
(Montpetit and Lachapelle 2016). General soft management actions regarding the
rehabilitation of contaminated soils by trace elements have preferentially tried to stabilize pollutant in the soil rather than extract them. Nonetheless, phytoextraction has
received increasing attention since the discovery of hyperaccumulator plants, able to
phytoextract and accumulate high levels of particular metals in their above-ground
biomass (Vamerali et al. 2010). In such a dynamic ecosystem as salt marshes, phytoextraction would be limited to the use of herbaceous native species, particularly
selected to each specific pollutant and objective. Additional desirable characteristics
that these species should present are fast grow and high biomass production, extended
root system for exploring large soil volumes, good tolerance to high concentrations of
metals, high translocation factor and easy management (Vamerali et al. 2010). Such
species should ideally avoid biomass (leaves) release along their life cycle, since polluted biomass circulating through marshes channels and even littoral sea currents
would easily enter the food chain. On top of all, further biomass management should
be planned, regarding harvesting and safe storage of polluted biomass. All this brings
to the idea that management of polluted salt marshes needs for the design of particular
actions adapted to each case.
In the case of the salt marshes in the Odiel and Tinto joint estuary, other two main
threats are identified in addition to soil contamination: the invasion by the alien
Spartina densiflora and erosion of marsh channels. A local restoration project has
resulted in a rapid recovery of the native prairies of low tidal marshes, dominated by
S. maritima, becoming a promising tool to phytostabilize eroding areas in European
marshes (Curado et al. 2012). These prairies seem to stop the advance of the S. densiflora invasion and prevent erosion. In this regard, extensive S. maritima plantations in the lower marshes along the protected area would be desirable. Plantations
in other upper areas with other native species need to be further studied, although a
relation of suitable native species for soil contamination phytoremediation in
European salt marshes is available at present. Although further research concerning
plant establishment and biomass production and limitations is still necessary, also
the use of stem cuttings of certain species, such as Halimione portulacoides
(Cambrollé et al. 2016), provides a cost-efficient way to accelerate the phytoremediaton process.
On the other hand, some protected areas of the Odiel and Tinto marshes are
invaded by the alien S. densiflora. In this regard, and in contrast to generalized criteria, it seems that maintaining the S. densiflora prairies in areas where it has become
dominant is a better option than removing them, since the latter action would lead
to an important release of presently stabilized pollutants. A solution could be related
with getting ready neutral sediment salt marshes using Spartina maritima and
Sarcocornia perennis plantations, which have already been tested as a successful
methodology for ecological restoration in polluted sediments in the same estuary
(Castillo and Figueroa 2009). The most complicated step would be to restore those
polluted areas where Spartina densiflora tussocks would be eliminated. They should
7 Handling High Soil Trace Elements Pollution: Case Study of the Odiel and Tinto…