265
occurrence of a natural phenomenon was able to neutralize the natural mechanism
of protection and dissipation of energy that El Yali wetlands system used to have.
As result of climate change, it is possible to infer that another important alteration is occurring: From El Yali River northward, the beach is oriented from SSW to
NNE and the littoral border runs parallel to the incident direction of waves from
SW, increasing the attenuation of wave energy. As the marine terrace is very wide,
it provides space to create an extended system of dunes cordons, transversal free
dunes, dunes restrained by vegetation, along with coastal dunes on depressions and
wetlands around the Albufera. However, if there is a change in the incident waves
(Fig. 8.8), the beach orientation will lose this characteristic, implying a change in
the costal morphology. This way, there is a natural experimental design: the system
was completely reset after the earthquake and tsunami 2010, there are no continuous sediment discharges since 1968 but the only occur when the dam gates are open
and consequently it is possible to know the exact moment when new sedimentary
material is delivered to the system. Finally, the direction of the incident waves is
gradually changing.
It is important to observe that sea-level raising in central Chile coasts seems to be
no relevant as threat to coastal wetlands, considering the alterations represented by
co-seismic vertical movements associated to earthquakes occurring in this region.
As observed in Table 8.2, the 1985 earthquake meant a rising of 50 cm in San
Antonio port. When comparing this elevation with the actual increment rate of the
sea-level, about 3 mm/year, it means that the earthquake made the sea-level rise to
retrogress the equivalent to 167 years. On the other hand, the descent of 35 cm during the earthquake in 2010 implied an advance equivalent to about 100 years.
Finally, besides climate change, ENSO, tsunamis and earthquakes, it must be
considered the intense anthropic pressure that seeks the accelerated conversion of
these wetland systems to real estate, agriculture and recreational systems. In central
Chile, wetlands are the subject of anthropic perturbations due to the land use (e.g.
exotic forest plantations, specific and diffuse contamination, etc.), resulting in alterations of their structure and functionality (Muñoz-Pedreros and Merino 2014).
According to Fariña et al. (2012), currently, in spite of management plans
(CONAF 2009), El Yali wetland is under a series of menaces that put its biodiversity
in risk: extraction of groundwater, deviation of water streams for agriculture or
industry, urban expansion, contamination and eutrophication of streams, lagoons
and wetlands, reduction of native vegetation by fires, agriculture, livestock and forestry activities, furtive hunters, 4WD vehicles, powered parachute disturbing birds,
and electric cables causing birds dead.
8.8 Conclusions
The natural history of the wetlands complex in El Yali basin suggests that the equilibrium of this system is sensitive to the occurrence of natural phenomena like the
tsunami in 2010, ENSO and climatic variations in general. It is expectable,
8 El Yali National Reserve: A System of Coastal Wetlands in the Southern…
occurrence of a natural phenomenon was able to neutralize the natural mechanism
of protection and dissipation of energy that El Yali wetlands system used to have.
As result of climate change, it is possible to infer that another important alteration is occurring: From El Yali River northward, the beach is oriented from SSW to
NNE and the littoral border runs parallel to the incident direction of waves from
SW, increasing the attenuation of wave energy. As the marine terrace is very wide,
it provides space to create an extended system of dunes cordons, transversal free
dunes, dunes restrained by vegetation, along with coastal dunes on depressions and
wetlands around the Albufera. However, if there is a change in the incident waves
(Fig. 8.8), the beach orientation will lose this characteristic, implying a change in
the costal morphology. This way, there is a natural experimental design: the system
was completely reset after the earthquake and tsunami 2010, there are no continuous sediment discharges since 1968 but the only occur when the dam gates are open
and consequently it is possible to know the exact moment when new sedimentary
material is delivered to the system. Finally, the direction of the incident waves is
gradually changing.
It is important to observe that sea-level raising in central Chile coasts seems to be
no relevant as threat to coastal wetlands, considering the alterations represented by
co-seismic vertical movements associated to earthquakes occurring in this region.
As observed in Table 8.2, the 1985 earthquake meant a rising of 50 cm in San
Antonio port. When comparing this elevation with the actual increment rate of the
sea-level, about 3 mm/year, it means that the earthquake made the sea-level rise to
retrogress the equivalent to 167 years. On the other hand, the descent of 35 cm during the earthquake in 2010 implied an advance equivalent to about 100 years.
Finally, besides climate change, ENSO, tsunamis and earthquakes, it must be
considered the intense anthropic pressure that seeks the accelerated conversion of
these wetland systems to real estate, agriculture and recreational systems. In central
Chile, wetlands are the subject of anthropic perturbations due to the land use (e.g.
exotic forest plantations, specific and diffuse contamination, etc.), resulting in alterations of their structure and functionality (Muñoz-Pedreros and Merino 2014).
According to Fariña et al. (2012), currently, in spite of management plans
(CONAF 2009), El Yali wetland is under a series of menaces that put its biodiversity
in risk: extraction of groundwater, deviation of water streams for agriculture or
industry, urban expansion, contamination and eutrophication of streams, lagoons
and wetlands, reduction of native vegetation by fires, agriculture, livestock and forestry activities, furtive hunters, 4WD vehicles, powered parachute disturbing birds,
and electric cables causing birds dead.
8.8 Conclusions
The natural history of the wetlands complex in El Yali basin suggests that the equilibrium of this system is sensitive to the occurrence of natural phenomena like the
tsunami in 2010, ENSO and climatic variations in general. It is expectable,
8 El Yali National Reserve: A System of Coastal Wetlands in the Southern…