221
industry have been found in the estuary tidal salt marshes as well as in areas outside
the tidal influence (Bolívar et al. 2000; El Mrabet et al. 2001; Elbaz- Poulichet et al.
2000). In addition, a phosphogypsum stack created since the 1960s is located in the
right bank of the Tinto river mouth, covering about 1200 ha of formerly salt marshes.
This dump, with an average height of 5 m and containing about 100 Mt of phosphogypsum (Bolívar et al. 2000), acts as an emission source of contaminants and releases
highly toxic pollutant such as arsenic, uranium, lead or cadmium, among others
(Pérez Lopez et al. 2010). On the other hand, long-term mining activities have
occurred in the Iberian Pyrite Belt for a long time, and wastes have been drained by
both Odiel and Tinto rivers (Elbaz-Poulichet et al. 1999; Leblanc et al. 2000; Leistel
et al. 1997; Morillo et al. 2002; Van Geen et al. 1997). In this regard, the Tinto river
ore, considered as one of the largest metal-rich sulfide deposits in the world, started
to be mined before Roman times (Van Geen et al. 1997), and metal concentrations its
basin reach higher values in comparison with the basin of the Odiel river, mainly due
to a more intensive mining activity (Elbaz- Poulichet et al. 1999).
Pollution in the Odiel and Tinto joint estuary is accompanied by very low pH
values along both rivers as consequence of the sulfuric acid production by drainage
of pyrite wastes and slags oxidation, as well as due to the metabolism of specific
bacteria. Therefore, pH of both rivers remains low (approx. 2.5 in the Tinto river and
3.0 in the Odiel river) outside the tidal influence (López-Archilla et al. 1993; Van
Geen et al. 1997). This creates a gradient of pH from very acidic sediments at the
mining area to neutral sediments (pH ca. 7) in the salt marshes down to the estuary
due to the buffering capacity of dissolved salts from seawater and dilution of the
polluted waters (Elbaz-Poulichet et al. 2001; Galán et al. 1999; Grande et al. 2003)
(Table 7.2). This sediment acidification in the estuary promotes the increase on
bioavailability of many metals, becoming toxic for plants and animals and affecting
their distribution (Heckman 1990; Vázquez et al. 2000).
The referred acidity gradient, together with changes in salinity due to tides, promotes a marked vegetation zonation along the banks of the main channel of the
Tinto river. Thus, the vegetation in the Odiel Marshes shows a typical zonation pattern of species distribution related with the elevation gradient close to the mouth of
the estuary. Species such as Zostera noltii Hornemann, Spartina maritima (Curtis)
Fernald (small cordgrass), Sarcocornia perennis (Mill.) Scott ssp. perennis
(Arthrocnemum perenne (Miller) Moss). and Salicornia ramosissima J. Woods
establish in the low marshes (Figs. 7.3 and 7.4), Sarcocornia fruticosa (L.) Scott,
Sarcocornia perennis x fruticosa (Figueroa et al., 2003), Halimione portulacoides
(L.) Aellen, Suaeda maritima L. (Dumort) and Spartina densiflora grow in middle
marshes, and Arthrocnemum macrostachyum (Moric.) Moris and Suaeda vera
Gmelin dominate high marshes (Fig. 7.5).
In contrast, only a few marsh plant species, such as S. densiflora, Typha
dominguensis (Pers.) Steudel, Phragmites australis (Cav.) Trin. and Scirpus maritimus L., are able to colonize more acidic salt marshes (pH ca. 4), where many areas
are devoid of vegetation. Acidic banks (pH ca. 2.5) free from the tidal influence are
colonized by other plant species, tolerant to certain salinity and flooding degree,
such as Juncus sp., Scirpus sp. and Tamarix sp., Cynodom dactylon L. (Pers.) or
Chaetopogon fasciculatus (Link) Hayek (Curado et al. 2010).
7 Handling High Soil Trace Elements Pollution: Case Study of the Odiel and Tinto…
industry have been found in the estuary tidal salt marshes as well as in areas outside
the tidal influence (Bolívar et al. 2000; El Mrabet et al. 2001; Elbaz- Poulichet et al.
2000). In addition, a phosphogypsum stack created since the 1960s is located in the
right bank of the Tinto river mouth, covering about 1200 ha of formerly salt marshes.
This dump, with an average height of 5 m and containing about 100 Mt of phosphogypsum (Bolívar et al. 2000), acts as an emission source of contaminants and releases
highly toxic pollutant such as arsenic, uranium, lead or cadmium, among others
(Pérez Lopez et al. 2010). On the other hand, long-term mining activities have
occurred in the Iberian Pyrite Belt for a long time, and wastes have been drained by
both Odiel and Tinto rivers (Elbaz-Poulichet et al. 1999; Leblanc et al. 2000; Leistel
et al. 1997; Morillo et al. 2002; Van Geen et al. 1997). In this regard, the Tinto river
ore, considered as one of the largest metal-rich sulfide deposits in the world, started
to be mined before Roman times (Van Geen et al. 1997), and metal concentrations its
basin reach higher values in comparison with the basin of the Odiel river, mainly due
to a more intensive mining activity (Elbaz- Poulichet et al. 1999).
Pollution in the Odiel and Tinto joint estuary is accompanied by very low pH
values along both rivers as consequence of the sulfuric acid production by drainage
of pyrite wastes and slags oxidation, as well as due to the metabolism of specific
bacteria. Therefore, pH of both rivers remains low (approx. 2.5 in the Tinto river and
3.0 in the Odiel river) outside the tidal influence (López-Archilla et al. 1993; Van
Geen et al. 1997). This creates a gradient of pH from very acidic sediments at the
mining area to neutral sediments (pH ca. 7) in the salt marshes down to the estuary
due to the buffering capacity of dissolved salts from seawater and dilution of the
polluted waters (Elbaz-Poulichet et al. 2001; Galán et al. 1999; Grande et al. 2003)
(Table 7.2). This sediment acidification in the estuary promotes the increase on
bioavailability of many metals, becoming toxic for plants and animals and affecting
their distribution (Heckman 1990; Vázquez et al. 2000).
The referred acidity gradient, together with changes in salinity due to tides, promotes a marked vegetation zonation along the banks of the main channel of the
Tinto river. Thus, the vegetation in the Odiel Marshes shows a typical zonation pattern of species distribution related with the elevation gradient close to the mouth of
the estuary. Species such as Zostera noltii Hornemann, Spartina maritima (Curtis)
Fernald (small cordgrass), Sarcocornia perennis (Mill.) Scott ssp. perennis
(Arthrocnemum perenne (Miller) Moss). and Salicornia ramosissima J. Woods
establish in the low marshes (Figs. 7.3 and 7.4), Sarcocornia fruticosa (L.) Scott,
Sarcocornia perennis x fruticosa (Figueroa et al., 2003), Halimione portulacoides
(L.) Aellen, Suaeda maritima L. (Dumort) and Spartina densiflora grow in middle
marshes, and Arthrocnemum macrostachyum (Moric.) Moris and Suaeda vera
Gmelin dominate high marshes (Fig. 7.5).
In contrast, only a few marsh plant species, such as S. densiflora, Typha
dominguensis (Pers.) Steudel, Phragmites australis (Cav.) Trin. and Scirpus maritimus L., are able to colonize more acidic salt marshes (pH ca. 4), where many areas
are devoid of vegetation. Acidic banks (pH ca. 2.5) free from the tidal influence are
colonized by other plant species, tolerant to certain salinity and flooding degree,
such as Juncus sp., Scirpus sp. and Tamarix sp., Cynodom dactylon L. (Pers.) or
Chaetopogon fasciculatus (Link) Hayek (Curado et al. 2010).
7 Handling High Soil Trace Elements Pollution: Case Study of the Odiel and Tinto…