Interaction of Climate Change and Acid Deposition - Climate Change Impacts on Freshwater Ecosystems - page 170

from the last 200 years, which show a strong positive correlation between pH
and mean air temperature.
Furthermore, a reduction in the extent and duration of snow cover, owing to
less precipitation and higher temperatures, means a greater exposure of rocks
and soils in the catchments, which enhances weathering processes. An analysis of
long-term chemical data for high altitude lakes in the central Italian Alps showed
an increase of solute contents in the last few years, mainly evident in lakes lying
in catchments with highly soluble rocks (Rogora et al . 2003). At these sites, the
overall effect of warming on weathering processes will be to increase ANC and
accelerate recovery of lake water from acidification.
Studies of acid-base chemistry in soils and lakes in the Bohemian Forest, Czech
Republic, indicate that warming results in decreased aluminium concentrations
in surface waters. Vesely et al . (2003) hypothesize that this may be because of the
temperature dependence of the equilibrium between inorganic Al and secondary
minerals in the soil; higher temperature pushes the equilibrium towards lower Al
concentrations. The net effect of both these processes is to increase the ANC and
decrease the toxicity of runoff from soils under increased temperature.
Modelling the combined effects of climate change
and acid deposition
Climate change and acid deposition have many connections, from the economic
activities that give rise to emissions of gases and particles to the atmosphere to
long-range transport and deposition of S and N, to their combined effects on
terrestrial ecosystems and finally to their effects on aquatic ecosystems. For all
these links, models have been used to evaluate future scenarios. A switch from
use of fossil fuels to renewable energy sources will entail both a reduction in
emissions of greenhouse gases and also a reduction in emissions of S and N
compounds. A study by Mayerhofer et al . (2001) looked at the linkages
between climate change and regional air pollution in Europe using the
Integrated Model to Assess the Global Environment (IMAGE; Netherlands
Environmental Assessment Agency (PBL) ) for climate and the Regional Air
Pollution Information and Simulation model (RAINS); International Institute
for Applied Systems Analysis (IIASA) for air pollution. One of the obvious
trade offs is that decreased emissions of S will result in fewer particles in the
atmosphere, which, in turn, will increase solar radiation inputs through
reduced cloud formation.
Climate change will also affect the transport and deposition of S and N on a
regional scale. Modelling studies in Europe using regional climate models and
chemical transport models indicate that the increased precipitation projected for
North-West Europe will entail commensurate increased N deposition (Hole et al .
2008; Hole & Enghardt 2008).
There are many processes in terrestrial ecosystems that will affect the amount
and chemical composition of runoff. The combined effects of these processes can
be quantified by the use of process-orientated biogeochemical models. MAGIC
(Cosby et al . 1985a, b, 2001) is such a model. It has been used to evaluate the