55
down to 60 cm (Hippensteel et al. 2000). On the contrary, analyses from Europe
show a dominant shallow infaunal behavior of foraminifera (Horton 1999; Alve and
Murray 2001), as in northern Spain where they live in the top 2 cm and do not significantly change the assemblage downcore (Cearreta et al. 2002; Leorri et al. 2008).
Moreover, the taphonomic loss of calcareous species is not relevant in northern
Spain, where foraminifera are well preserved due to the abundant supply of calcium
carbonate to the environment by regional carbonate rocks (Cearreta and Murray
2000). Hence, the paleoenvironmental interpretation of buried assemblages can be
easily performed by comparison with modern analogues.
Modern salt-marsh foraminiferal assemblages in northern Spain are dominated by
agglutinated species (Cearreta 1988, 1989; Cearreta et al. 2002; García-Artola et al.
2015). The high marsh is dominated by the agglutinated taxa Entzia macrescens and
Trochammina inflata, together with Arenoparrella mexicana, Haplophragmoides
wilberti, Miliammina fusca, and Scherochorella moniliformis as secondary forms
(Plate 2.1). In the low marsh, the agglutinated assemblage is combined with the calcareous hyaline species Ammonia tepida, Haynesina germanica, Elphidium oceanense, Elphidium williamsoni, and even the marine species Lobatula lobatula.
In northern Spain, foraminifera are very abundant in intertidal areas such as salt
marshes. Thus, the unusual absence or near absence of foraminifera detected in
some salt-marsh sedimentary records can be attributed to former agricultural activities following the graphical proof of historical aerial photographs (otherwise related
to anthropogenic environmental pollution, as in the nearby Bilbao estuary; Cearreta
et al. 2000). Foraminifera present a clear trend in response to this human intervention (Fig. 2.4): (1) extremely low numbers or absence of foraminiferal tests during
the agricultural reclamation; (2) increasing foraminiferal densities during the environmental regeneration process; and (3) abundant foraminiferal tests in the regenerated salt marsh.
We studied foraminifera retained in the sand-size fraction (see Sect. 2.4.2) under
a stereoscopic binocular microscope using reflected light. In order to accelerate the
counting process, foraminifera were concentrated by flotation in trichloroethylene
as described by Murray (1979). Foraminiferal tests were picked until a representative number of at least 300 individuals for each sample was obtained. Otherwise, all
the available tests were counted. Foraminiferal results are expressed as a percentage
(Table 2.2). In order to homogenize abundances, the number of foraminiferal tests
in 50 g of dry sediment was calculated for standardization with regional values
(Table 2.2).
2.4.2 Sand
The amount of sand in a sample is indicative of tidal influence, which declines during land reclamation (Cearreta et al. 2013). Immediately after reclamation ends,
sand-rich tidal waters invade previously occupied areas. Therefore, we observe an
increase in sand content during the regeneration process until the stabilization of the
environment arrives once the salt marsh is regenerated (Fig. 2.5).
2 Recent Agricultural Occupation and Environmental Regeneration of Salt...
down to 60 cm (Hippensteel et al. 2000). On the contrary, analyses from Europe
show a dominant shallow infaunal behavior of foraminifera (Horton 1999; Alve and
Murray 2001), as in northern Spain where they live in the top 2 cm and do not significantly change the assemblage downcore (Cearreta et al. 2002; Leorri et al. 2008).
Moreover, the taphonomic loss of calcareous species is not relevant in northern
Spain, where foraminifera are well preserved due to the abundant supply of calcium
carbonate to the environment by regional carbonate rocks (Cearreta and Murray
2000). Hence, the paleoenvironmental interpretation of buried assemblages can be
easily performed by comparison with modern analogues.
Modern salt-marsh foraminiferal assemblages in northern Spain are dominated by
agglutinated species (Cearreta 1988, 1989; Cearreta et al. 2002; García-Artola et al.
2015). The high marsh is dominated by the agglutinated taxa Entzia macrescens and
Trochammina inflata, together with Arenoparrella mexicana, Haplophragmoides
wilberti, Miliammina fusca, and Scherochorella moniliformis as secondary forms
(Plate 2.1). In the low marsh, the agglutinated assemblage is combined with the calcareous hyaline species Ammonia tepida, Haynesina germanica, Elphidium oceanense, Elphidium williamsoni, and even the marine species Lobatula lobatula.
In northern Spain, foraminifera are very abundant in intertidal areas such as salt
marshes. Thus, the unusual absence or near absence of foraminifera detected in
some salt-marsh sedimentary records can be attributed to former agricultural activities following the graphical proof of historical aerial photographs (otherwise related
to anthropogenic environmental pollution, as in the nearby Bilbao estuary; Cearreta
et al. 2000). Foraminifera present a clear trend in response to this human intervention (Fig. 2.4): (1) extremely low numbers or absence of foraminiferal tests during
the agricultural reclamation; (2) increasing foraminiferal densities during the environmental regeneration process; and (3) abundant foraminiferal tests in the regenerated salt marsh.
We studied foraminifera retained in the sand-size fraction (see Sect. 2.4.2) under
a stereoscopic binocular microscope using reflected light. In order to accelerate the
counting process, foraminifera were concentrated by flotation in trichloroethylene
as described by Murray (1979). Foraminiferal tests were picked until a representative number of at least 300 individuals for each sample was obtained. Otherwise, all
the available tests were counted. Foraminiferal results are expressed as a percentage
(Table 2.2). In order to homogenize abundances, the number of foraminiferal tests
in 50 g of dry sediment was calculated for standardization with regional values
(Table 2.2).
2.4.2 Sand
The amount of sand in a sample is indicative of tidal influence, which declines during land reclamation (Cearreta et al. 2013). Immediately after reclamation ends,
sand-rich tidal waters invade previously occupied areas. Therefore, we observe an
increase in sand content during the regeneration process until the stabilization of the
environment arrives once the salt marsh is regenerated (Fig. 2.5).
2 Recent Agricultural Occupation and Environmental Regeneration of Salt...