Alpine ecosystems are sensitive to the atmospheric inputs for several reasons.
They are headwater catchments where chemical weathering of the bedrock is
limited, specially in those on highly insoluble crystalline rocks, so lake and stream
waters are very diluted. Consequently their capacity of buffering any acidity coming
with precipitation is rather poor. Nutrients coming from the substrate are also
scarce. Therefore, the atmospheric supply is an important (if not the larger) fraction
of nutrient input to alpine ecosystems. Catchment soils and lake sediments are
generally highly organic. This gives them a large capacity for binding pollutants
such as trace metals and organic chemicals. In the long run, this great affinity causes
a build-up of the pollutant burden stored in soils and sediments. These are some of
the main reasons for the sensitivity of alpine systems to atmospheric chemical
loadings. They are sensitive in two senses. First, they are actually threatened by
certain atmospherically deposited chemicals that may reach levels that have ecotoxic effects or alter the natural ecosystem functioning, and constitute a conservation issue. But second, even in the cases where impacts are not severe, the signs of
the chemical inputs are easily noticeable. Inputs that, remember, respond to a global
forcing. This makes alpine ecosystems an excellent early warning system of global
environmental change.
In this chapter, I am mostly presenting a summary of the results regarding some
of the topics mentioned above obtained during almost 30 years of research in the
Pyrenees. But beyond the local interest, the results presented here are an example of
how atmospheric chemical loadings affect high mountains that also applies to other
high mountain ranges.
14.2 Surface Waters Acidification
Since the onset of the Industrial Revolution, the massive burning of fossil fuels has
caused the emission of sulphur and nitrogen oxides to the atmosphere. These oxides
acidify the atmospheric precipitation, as it was already noticed in the
mid-nineteenth century when the term “acid rain” was coined (Smith 1872). Acid
rain in its turn acidifies soils and surface waters when these receptor systems cannot
buffer the incoming acidity. In that case, deleterious effects occur. The first cases of
environmental damage caused by acid deposition were reported at the beginning of
the twentieth century. These first cases were attributed to local sources in the
vicinities of the impacted sites (Cowling 1982). But in the 1970s the effects of
long-range transport of pollutants shifted the focus to a larger scale. There was then
widespread evidence of regional acidification of surface water, affecting the most
sensitive lacustrine areas in the Northern Hemisphere: the Precambrian Shields of
Canada and Scandinavia (Gorham et al. 1986; Odén and Ahl 1979; Likens and
Bormann 1974). During the 1980s, on the basis of the scientific studies carried out
in the previous years, it was generally accepted that human emissions were producing significant acidification of fresh waters (Schindler et al. 1985) and might be
a factor contributing to forest dieback (Pitelka and Raynal 1989) on a regional scale.
14 Atmospheric Chemical Loadings in the High Mountain: Current …
327
They are headwater catchments where chemical weathering of the bedrock is
limited, specially in those on highly insoluble crystalline rocks, so lake and stream
waters are very diluted. Consequently their capacity of buffering any acidity coming
with precipitation is rather poor. Nutrients coming from the substrate are also
scarce. Therefore, the atmospheric supply is an important (if not the larger) fraction
of nutrient input to alpine ecosystems. Catchment soils and lake sediments are
generally highly organic. This gives them a large capacity for binding pollutants
such as trace metals and organic chemicals. In the long run, this great affinity causes
a build-up of the pollutant burden stored in soils and sediments. These are some of
the main reasons for the sensitivity of alpine systems to atmospheric chemical
loadings. They are sensitive in two senses. First, they are actually threatened by
certain atmospherically deposited chemicals that may reach levels that have ecotoxic effects or alter the natural ecosystem functioning, and constitute a conservation issue. But second, even in the cases where impacts are not severe, the signs of
the chemical inputs are easily noticeable. Inputs that, remember, respond to a global
forcing. This makes alpine ecosystems an excellent early warning system of global
environmental change.
In this chapter, I am mostly presenting a summary of the results regarding some
of the topics mentioned above obtained during almost 30 years of research in the
Pyrenees. But beyond the local interest, the results presented here are an example of
how atmospheric chemical loadings affect high mountains that also applies to other
high mountain ranges.
14.2 Surface Waters Acidification
Since the onset of the Industrial Revolution, the massive burning of fossil fuels has
caused the emission of sulphur and nitrogen oxides to the atmosphere. These oxides
acidify the atmospheric precipitation, as it was already noticed in the
mid-nineteenth century when the term “acid rain” was coined (Smith 1872). Acid
rain in its turn acidifies soils and surface waters when these receptor systems cannot
buffer the incoming acidity. In that case, deleterious effects occur. The first cases of
environmental damage caused by acid deposition were reported at the beginning of
the twentieth century. These first cases were attributed to local sources in the
vicinities of the impacted sites (Cowling 1982). But in the 1970s the effects of
long-range transport of pollutants shifted the focus to a larger scale. There was then
widespread evidence of regional acidification of surface water, affecting the most
sensitive lacustrine areas in the Northern Hemisphere: the Precambrian Shields of
Canada and Scandinavia (Gorham et al. 1986; Odén and Ahl 1979; Likens and
Bormann 1974). During the 1980s, on the basis of the scientific studies carried out
in the previous years, it was generally accepted that human emissions were producing significant acidification of fresh waters (Schindler et al. 1985) and might be
a factor contributing to forest dieback (Pitelka and Raynal 1989) on a regional scale.
14 Atmospheric Chemical Loadings in the High Mountain: Current …
327