246
the earthquake occurred on February 27th, 2010, causing a partial desiccation of
the wetland that has been well documented (Valdovinos et al. 2010, 2012).
(b) On the other hand, river in this zone, with snow-rain regimes and important
slopes and discharges, are able to transport large quantities of material from the
Andean cordillera to the coast (Cienfuegos et al. 2012). In the recent past, there
have been cases where the alteration of hydrodynamic equilibria has an immediate morphological response, as that documented by Pomar (1962), which
describes the accretion of a sand beach and consolidation of lagoon Llolleo
(33°36.4′S; 71°37.4′W) nearby Maipo river mouth, whose basin represents the
northern limit of the wetlands system, after the construction of a sheltering
structure in the port of San Antonio. In other cases, a rapid recovery has been
observed, as in the case of the 8 km length sand bar in Mataquito river mouth
(34°52′S, 72°09′W), which almost completely disappeared under the combined
action of tsunami waves and the relatively large land subsidence (Lario et al.
2016; Vargas et al. 2011). This zone river mouth is located right off the rupture
zone where most of the February 2010 earthquake energy was liberated (Lay
et al. 2010). After the earth quake and tsunami, the coastal evolution of this zone
has been monitored by using field work techniques and satellite imagery
(Cienfuegos et al. 2014), evidencing that most of the original sand bar recovered in less than 18 months, even showing a rapid recovery in less than 6 months
(González et al. 2012). These examples show that changes produced by
anthropic alterations as well as tectonic and seismicity can provide conditions
for beaches accretion and dune and sandbar formation (Martínez et al. 2015;
Veas et al. 2016) that also favor consolidation of coastal wetlands. This explains
the fact that there are more than 400 coastal wetlands along the coast between
30°S and 44°S (Marquet et al. 2012), conforming a, ecological corridor for
migratory birds and other species. However, these wetlands, that are fragile
environments due to those conditions that influence their construction and
destruction, are under a growing pressure due to a persistent anthropic activity
around them: using wetlands as sink of liquid residues, receiving contamination
from agriculture products, draining wetlands to extract water or expansion of
real estate projects. Moreover, contemporary climate change represents an additional pressure, influencing the delicate equilibrium of these systems.
Besides describing a so far poorly known system, the novelty of this chapter is
based in two main aspects:
(a) To incorporate the effect of tsunamis and resilience to the discussion about
coastal wetlands. During more than 50 years after the construction of the damn
in Rapel River, the system of beaches to the north maintained an unstable equilibrium, where the coastal dunes that protected the coastal lagoon and beach
stopped receiving a continuous supply of sand. In spite of that, the material
accumulated over years was able to stay in fragile equilibrium, not showing
significant changes. However, the tsunami of 2010 swept all the coastal dunes
and removed a significant part of the sand form the beach, triggering a loss of
functionality that will be detailed next.
M. Contreras-López et al.
the earthquake occurred on February 27th, 2010, causing a partial desiccation of
the wetland that has been well documented (Valdovinos et al. 2010, 2012).
(b) On the other hand, river in this zone, with snow-rain regimes and important
slopes and discharges, are able to transport large quantities of material from the
Andean cordillera to the coast (Cienfuegos et al. 2012). In the recent past, there
have been cases where the alteration of hydrodynamic equilibria has an immediate morphological response, as that documented by Pomar (1962), which
describes the accretion of a sand beach and consolidation of lagoon Llolleo
(33°36.4′S; 71°37.4′W) nearby Maipo river mouth, whose basin represents the
northern limit of the wetlands system, after the construction of a sheltering
structure in the port of San Antonio. In other cases, a rapid recovery has been
observed, as in the case of the 8 km length sand bar in Mataquito river mouth
(34°52′S, 72°09′W), which almost completely disappeared under the combined
action of tsunami waves and the relatively large land subsidence (Lario et al.
2016; Vargas et al. 2011). This zone river mouth is located right off the rupture
zone where most of the February 2010 earthquake energy was liberated (Lay
et al. 2010). After the earth quake and tsunami, the coastal evolution of this zone
has been monitored by using field work techniques and satellite imagery
(Cienfuegos et al. 2014), evidencing that most of the original sand bar recovered in less than 18 months, even showing a rapid recovery in less than 6 months
(González et al. 2012). These examples show that changes produced by
anthropic alterations as well as tectonic and seismicity can provide conditions
for beaches accretion and dune and sandbar formation (Martínez et al. 2015;
Veas et al. 2016) that also favor consolidation of coastal wetlands. This explains
the fact that there are more than 400 coastal wetlands along the coast between
30°S and 44°S (Marquet et al. 2012), conforming a, ecological corridor for
migratory birds and other species. However, these wetlands, that are fragile
environments due to those conditions that influence their construction and
destruction, are under a growing pressure due to a persistent anthropic activity
around them: using wetlands as sink of liquid residues, receiving contamination
from agriculture products, draining wetlands to extract water or expansion of
real estate projects. Moreover, contemporary climate change represents an additional pressure, influencing the delicate equilibrium of these systems.
Besides describing a so far poorly known system, the novelty of this chapter is
based in two main aspects:
(a) To incorporate the effect of tsunamis and resilience to the discussion about
coastal wetlands. During more than 50 years after the construction of the damn
in Rapel River, the system of beaches to the north maintained an unstable equilibrium, where the coastal dunes that protected the coastal lagoon and beach
stopped receiving a continuous supply of sand. In spite of that, the material
accumulated over years was able to stay in fragile equilibrium, not showing
significant changes. However, the tsunami of 2010 swept all the coastal dunes
and removed a significant part of the sand form the beach, triggering a loss of
functionality that will be detailed next.
M. Contreras-López et al.