observed at different scales on the Iberian Peninsula (Galán et al. 2001; De Castro
et al. 2005). The precipitation shows a general decreasing pattern, being more
pronounced in the western part than in the east. This pattern is consistent with the
overall declining trend in the south of the Iberian Peninsula (Rodrigo et al. 1999;
Ruiz-Sinoga et al. 2010).
All these changes in climate have implications for the dynamics of snow cover.
Satellite information from MODIS (Moderate Resolution Imaging
Spectroradiometer) for the period 2000–2014 have indicated a decrease in
snow-cover duration over 79% of Sierra Nevada. There was a trend towards a delay in
the date of the first snowfall and a trend towards earlier melting dates. The change has
been more pronounced in magnitude at the summits than in the lowland areas (Bonet
et al. 2016). For instance, above 3000 m a.s.l., the duration of snow cover decreased
by an average of three days in the last 14 years. A significant recent decline in snow
duration has also been reported from other mountain regions of Europe (Scherrer et al.
2004; Moreno-Rodríguez 2005; Marty 2008; Nikolova et al. 2013).
16.9.3 Biotic Responses to Land-Use and Climate Change
Mountain lakes as integrated ecological sensors
The combination of old studies and resampling of the same localities can help to
integrate short-term data into long-term datasets (Müller et al. 2010). These long-term
datasets can be used to evaluate spatiotemporal changes and trends in biological
communities and their relation to drivers of global change, such as land use or climate
in mountain regions. For example, an exhaustive review of the research on alpine lakes
of Sierra Nevada from 1975 to the present has identified the role of these ecosystems as
sentinels of change (Villar-Argaiz and Bullejos 2016; Medina-Sánchez et al. 2016).
Unlike other European mountain lakes, the geographic location and geological history
of Sierra Nevada cause high-mountain lakes to be exposed simultaneously to several
environmental stressors: climatic anomalies (temperature and precipitation), UV radiation, aerosol deposition, and allochthonous nutrient input. High transparency, low
nutrient content, and narrow temperature ranges found in high-mountain lakes qualifies
them as sentinels of global change (Medina-Sánchez et al. 2016; Villar-Argaiz and
Bullejos 2016). However, especially the great simplicity of their biological communities helps us to assess their impact on ecosystem functioning, as well as the evolution
of organisms that inhabit them. Long-term monitoring of the population dynamics of
pelagic plankton in the Laguna de la Caldera, the largest alpine lake of Sierra Nevada,
indicates that phytoplankton has increased in parallel with the increase in the intensity
and frequency of atmospheric aerosols (Villar-Argaiz and Bullejos 2016). These results
suggest that allochthonous nutrients associated with Saharan intrusions have a fertilizing effect that stimulates the growth of algal biomass. These patterns are consistent
with previous studies indicating that the Saharan depositions are important sources
of nutrients, especially Phosphorus (Morales-Baquero et al. 2006), encouraging
16 Monitoring Global Change in High Mountains
401
et al. 2005). The precipitation shows a general decreasing pattern, being more
pronounced in the western part than in the east. This pattern is consistent with the
overall declining trend in the south of the Iberian Peninsula (Rodrigo et al. 1999;
Ruiz-Sinoga et al. 2010).
All these changes in climate have implications for the dynamics of snow cover.
Satellite information from MODIS (Moderate Resolution Imaging
Spectroradiometer) for the period 2000–2014 have indicated a decrease in
snow-cover duration over 79% of Sierra Nevada. There was a trend towards a delay in
the date of the first snowfall and a trend towards earlier melting dates. The change has
been more pronounced in magnitude at the summits than in the lowland areas (Bonet
et al. 2016). For instance, above 3000 m a.s.l., the duration of snow cover decreased
by an average of three days in the last 14 years. A significant recent decline in snow
duration has also been reported from other mountain regions of Europe (Scherrer et al.
2004; Moreno-Rodríguez 2005; Marty 2008; Nikolova et al. 2013).
16.9.3 Biotic Responses to Land-Use and Climate Change
Mountain lakes as integrated ecological sensors
The combination of old studies and resampling of the same localities can help to
integrate short-term data into long-term datasets (Müller et al. 2010). These long-term
datasets can be used to evaluate spatiotemporal changes and trends in biological
communities and their relation to drivers of global change, such as land use or climate
in mountain regions. For example, an exhaustive review of the research on alpine lakes
of Sierra Nevada from 1975 to the present has identified the role of these ecosystems as
sentinels of change (Villar-Argaiz and Bullejos 2016; Medina-Sánchez et al. 2016).
Unlike other European mountain lakes, the geographic location and geological history
of Sierra Nevada cause high-mountain lakes to be exposed simultaneously to several
environmental stressors: climatic anomalies (temperature and precipitation), UV radiation, aerosol deposition, and allochthonous nutrient input. High transparency, low
nutrient content, and narrow temperature ranges found in high-mountain lakes qualifies
them as sentinels of global change (Medina-Sánchez et al. 2016; Villar-Argaiz and
Bullejos 2016). However, especially the great simplicity of their biological communities helps us to assess their impact on ecosystem functioning, as well as the evolution
of organisms that inhabit them. Long-term monitoring of the population dynamics of
pelagic plankton in the Laguna de la Caldera, the largest alpine lake of Sierra Nevada,
indicates that phytoplankton has increased in parallel with the increase in the intensity
and frequency of atmospheric aerosols (Villar-Argaiz and Bullejos 2016). These results
suggest that allochthonous nutrients associated with Saharan intrusions have a fertilizing effect that stimulates the growth of algal biomass. These patterns are consistent
with previous studies indicating that the Saharan depositions are important sources
of nutrients, especially Phosphorus (Morales-Baquero et al. 2006), encouraging
16 Monitoring Global Change in High Mountains
401