50
The recovery of coastal wetlands is of great importance because these vegetated
areas act as shoreline stabilizers, protecting coastal settings from storms and floods
since these ecosystems are able to dissipate wave energy (Costanza et al. 2008; Weis
and Butler 2009; Mudd et al. 2010; Gedan et al. 2011; Shepard et al. 2011). This is
of particular interest in the current context of relative sea-level rise in northern
Spain: the analysis of the nearest Bilbao tide-gauge (Fig. 2.1) record provides a
relative sea-level rise rate of 2.98 ± 1.08 mm year
−1
for the period between 1993 and
2005; and the analysis of the longer record from the nearby tide gauge of Santander
(Fig. 2.1) provides a relative sea-level rise rate of 2.08 ± 0.33 mm year
−1
for the
period from 1943 to 2004 (Chust et al. 2009). Therefore, restoration of currently
reclaimed salt marshes by reintroducing tidal flow is nowadays gaining importance
as an adaptation strategy against ongoing sea-level rise (French 2006; Roman and
Burdick 2012).
In order to predict future coastal evolution, it is essential to understand its environmental transformation in the past. In that sense, the recovery of coastal wetlands
can be easily observed in recent regional aerial photography (Chust et al. 2007).
Aside from graphical records, it is useful to study human fingerprints preserved in
salt-marsh sediments. In fact, continuous deposition of sediment within estuaries
occurs in sheltered areas such as salt marshes. Therefore, salt marshes are considered as precise geological archives of past environmental change (Fatela et al.
2009), providing a record of natural and anthropogenic processes through time.
Hence, this chapter focuses on the identification of signals of human impact in saltmarsh sedimentary records from northern Spain. This information is of great utility
in areas where anthropogenic activities took place before aerial photography was
available.
2.2 Geomorphology of Northern Spain
The northern coast of Spain is dominated by high rocky cliffs that are constantly
being eroded by high-energy waves. Therefore, salt marshes develop in the most
protected areas within the small estuaries that make their way through the cliffs.
Regional salt marshes first formed at 3000 cal years BP, when sea level stabilized
after the Holocene marine transgression (Caballero et al. 2011; Leorri et al.
2012). Holocene sediments started to infill former river valleys at 8500 cal years
BP (Leorri and Cearreta 2004) and lie above a bedrock mainly composed of sedimentary rocks of Mesozoic-Cenozoic age (Martínez Cedrún 1984; Irabien and
Velasco 1999).
The Santoña, Plentzia and Urdaibai estuaries in northern Spain (Fig. 2.1) were
infilled during the last thousands of years and are analyzed here to identify recent
agricultural fingerprints and the later environmental regeneration. These estuaries
present the main drainage channel located on the left side, while sedimentation of
A. García-Artola et al.
The recovery of coastal wetlands is of great importance because these vegetated
areas act as shoreline stabilizers, protecting coastal settings from storms and floods
since these ecosystems are able to dissipate wave energy (Costanza et al. 2008; Weis
and Butler 2009; Mudd et al. 2010; Gedan et al. 2011; Shepard et al. 2011). This is
of particular interest in the current context of relative sea-level rise in northern
Spain: the analysis of the nearest Bilbao tide-gauge (Fig. 2.1) record provides a
relative sea-level rise rate of 2.98 ± 1.08 mm year
−1
for the period between 1993 and
2005; and the analysis of the longer record from the nearby tide gauge of Santander
(Fig. 2.1) provides a relative sea-level rise rate of 2.08 ± 0.33 mm year
−1
for the
period from 1943 to 2004 (Chust et al. 2009). Therefore, restoration of currently
reclaimed salt marshes by reintroducing tidal flow is nowadays gaining importance
as an adaptation strategy against ongoing sea-level rise (French 2006; Roman and
Burdick 2012).
In order to predict future coastal evolution, it is essential to understand its environmental transformation in the past. In that sense, the recovery of coastal wetlands
can be easily observed in recent regional aerial photography (Chust et al. 2007).
Aside from graphical records, it is useful to study human fingerprints preserved in
salt-marsh sediments. In fact, continuous deposition of sediment within estuaries
occurs in sheltered areas such as salt marshes. Therefore, salt marshes are considered as precise geological archives of past environmental change (Fatela et al.
2009), providing a record of natural and anthropogenic processes through time.
Hence, this chapter focuses on the identification of signals of human impact in saltmarsh sedimentary records from northern Spain. This information is of great utility
in areas where anthropogenic activities took place before aerial photography was
available.
2.2 Geomorphology of Northern Spain
The northern coast of Spain is dominated by high rocky cliffs that are constantly
being eroded by high-energy waves. Therefore, salt marshes develop in the most
protected areas within the small estuaries that make their way through the cliffs.
Regional salt marshes first formed at 3000 cal years BP, when sea level stabilized
after the Holocene marine transgression (Caballero et al. 2011; Leorri et al.
2012). Holocene sediments started to infill former river valleys at 8500 cal years
BP (Leorri and Cearreta 2004) and lie above a bedrock mainly composed of sedimentary rocks of Mesozoic-Cenozoic age (Martínez Cedrún 1984; Irabien and
Velasco 1999).
The Santoña, Plentzia and Urdaibai estuaries in northern Spain (Fig. 2.1) were
infilled during the last thousands of years and are analyzed here to identify recent
agricultural fingerprints and the later environmental regeneration. These estuaries
present the main drainage channel located on the left side, while sedimentation of
A. García-Artola et al.