| The RAIN and CLIMEX experiments at
Risdalsheia, southernmost Norway, together cover 17 years (1984-2000) of whole-catchment
manipulation of acid deposition and climate. A 1200 m2 roof
placed over the forest canopy at KIM catchment excluded about 80% of ambient
acid deposition; clean rain was sprinkled under the roof. A
climate change treatment (3.7°C increase in air temperature and increase in air
carbon dioxide concentrations to 560 ppmv) was superimposed on
the clean rain treatment for four years (1995-1998). Sea-salt inputs and temperature
are climate-related factors that influence water chemistry and can confound
long-term trends caused by changes in deposition of sulphur
and nitrogen. The RAIN and CLIMEX experiments at Risdalsheia provided direct
experimental data that allow quantitative assessment of
these factors. Run-off chemistry responded rapidly to the decreased acid
deposition. Sulphate concentrations decreased by 50% within three
years; nitrate and ammonium concentrations decreased to new steady-state levels
within the first year. Acid neutralising capacity increased
and hydrogen ion and inorganic aluminium decreased. Similar recovery from
acidification was also observed at the reference catchment,
ROLF, in response to the general 50% reduction in sulphate deposition over
southern Norway in the late 1980s and 1990s. Variations in
sea-salt deposition caused large variations in run-off chemistry at the
reference catchment ROLF and the year-to-year noise in acid
neutralising capacity was as large as the overall trend over the period. These
variations were absent at KIM catchment because the sea-salt inputs
were held constant over the entire 17 years of the clean rain treatment. The
climate change experiment at KIM catchment resulted in
increased leaching of inorganic nitrogen, probably due to increased
mineralisation and nitrification rates in the soils.
Keywords: acid deposition, global change, water, soil, catchment, experiment, Norway. |