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in salt marshes to living beings imply a high level of specialization of the marsh
species of fauna and flora, which contributes to the ecological value and vulnerability of these ecosystems. In addition, salt marshes have a recognized geomorphological, historical, scenic, cultural and socio-economic interest, and they are important
locations for nature tourism and recreation, education and research.
At present, it is estimated that less than 50% of the world’s original wetlands,
among which are the saltmarshes, remain, showing a current loss of 1–2% per year
(Bridgham et al. 2006; Mitsch and Gosselink 2007). Salt marshes are seriously
threatened by both natural and human-induced drives, and changes in land use and
land take, alteration of coastal hydrology, effects associated to climate change
(increases in atmospheric CO 2 , global warming, increases in storms intensity and
sea level rise), biological invasions, eutrophication and pollution by trace elements
from urban, industrial and mining areas have been identified as the main hazards for
salt marsh conservation (Curado et al. 2010; Deegan et al. 2012; Gedan et al. 2009).
7.1.2 Soil Contamination in Coastal Salt Marshes
Coastal marshes are highly vulnerable to contamination by trace elements due to
their location at the river mouths (Beeftink 1977; Williams et al. 1994), particularly
in those cases where mining and industrial areas exist close to estuaries or upstream
their associated rivers, since both nutrients and contaminants are transported through
river systems. In addition, rivers and salt marshes pollution by trace elements is
increasing in extent and number of affected areas (Handa and Jefferies 2000).
The capacity of trace elements to be transferred between soil phases under particular soil conditions is one of the main factors driving their behavior and bioavailability
in each specific case. In particular, marsh sediments are characterized by fine size of
grain, mainly composed by silt and clay, with a high capacity for adherence and retention of trace elements. In addition, both pH and redox potential are relevant drivers for
trace elements solubility and thus bioavailability in this environment. It can be generalized that, in well-aerated (oxidizing) acidic soils, several trace metals (particularly
cadmium and zinc) are easily mobile and available to plants, while metals are substantially less available in poorly aerated (reducing) neutral or alkaline soils (KabataPendias 2004). In this regard, marsh sediments are considered a sink for trace elements.
Very high metals concentrations in a reduced state may be contained in the anoxic
zone, although they show a reduced bioavailability in comparison with oxidized soils
of terrestrial systems (Kabata-Pendias 2004; Weis and Weis 2004). Nevertheless,
acidification of sediments promoted by pollution from mining activities as well as by
terestrialisation of marshes and accumulation of organic matter in the development of
ecological succession favors the bioavailability of trace elements. In addition, plant
species able to withstand high metal concentrations in soil are also able to influence
the trace element mobility through their accumulation in their tissues or their immobilization in their rhizosphere, as it is further described in this chapter. On top of all,
salt marshes are usually under other types of pressures, including human use. As a
7 Handling High Soil Trace Elements Pollution: Case Study of the Odiel and Tinto…
in salt marshes to living beings imply a high level of specialization of the marsh
species of fauna and flora, which contributes to the ecological value and vulnerability of these ecosystems. In addition, salt marshes have a recognized geomorphological, historical, scenic, cultural and socio-economic interest, and they are important
locations for nature tourism and recreation, education and research.
At present, it is estimated that less than 50% of the world’s original wetlands,
among which are the saltmarshes, remain, showing a current loss of 1–2% per year
(Bridgham et al. 2006; Mitsch and Gosselink 2007). Salt marshes are seriously
threatened by both natural and human-induced drives, and changes in land use and
land take, alteration of coastal hydrology, effects associated to climate change
(increases in atmospheric CO 2 , global warming, increases in storms intensity and
sea level rise), biological invasions, eutrophication and pollution by trace elements
from urban, industrial and mining areas have been identified as the main hazards for
salt marsh conservation (Curado et al. 2010; Deegan et al. 2012; Gedan et al. 2009).
7.1.2 Soil Contamination in Coastal Salt Marshes
Coastal marshes are highly vulnerable to contamination by trace elements due to
their location at the river mouths (Beeftink 1977; Williams et al. 1994), particularly
in those cases where mining and industrial areas exist close to estuaries or upstream
their associated rivers, since both nutrients and contaminants are transported through
river systems. In addition, rivers and salt marshes pollution by trace elements is
increasing in extent and number of affected areas (Handa and Jefferies 2000).
The capacity of trace elements to be transferred between soil phases under particular soil conditions is one of the main factors driving their behavior and bioavailability
in each specific case. In particular, marsh sediments are characterized by fine size of
grain, mainly composed by silt and clay, with a high capacity for adherence and retention of trace elements. In addition, both pH and redox potential are relevant drivers for
trace elements solubility and thus bioavailability in this environment. It can be generalized that, in well-aerated (oxidizing) acidic soils, several trace metals (particularly
cadmium and zinc) are easily mobile and available to plants, while metals are substantially less available in poorly aerated (reducing) neutral or alkaline soils (KabataPendias 2004). In this regard, marsh sediments are considered a sink for trace elements.
Very high metals concentrations in a reduced state may be contained in the anoxic
zone, although they show a reduced bioavailability in comparison with oxidized soils
of terrestrial systems (Kabata-Pendias 2004; Weis and Weis 2004). Nevertheless,
acidification of sediments promoted by pollution from mining activities as well as by
terestrialisation of marshes and accumulation of organic matter in the development of
ecological succession favors the bioavailability of trace elements. In addition, plant
species able to withstand high metal concentrations in soil are also able to influence
the trace element mobility through their accumulation in their tissues or their immobilization in their rhizosphere, as it is further described in this chapter. On top of all,
salt marshes are usually under other types of pressures, including human use. As a
7 Handling High Soil Trace Elements Pollution: Case Study of the Odiel and Tinto…