Climate change as a confounding factor in reversibility of acidification: RAIN and CLIMEX projects

摘要

The RAIN and CLIMEX experiments atRisdalsheia, southernmost Norway, together cover 17 years (1984-2000) of whole-catchmentmanipulation of acid deposition and climate. A 1200 m2 roofplaced over the forest canopy at KIM catchment excluded about 80% of ambientacid deposition; clean rain was sprinkled under the roof. Aclimate change treatment (3.7°C increase in air temperature and increase in aircarbon dioxide concentrations to 560 ppmv) was superimposed onthe clean rain treatment for four years (1995-1998). Sea-salt inputs and temperatureare climate-related factors that influence water chemistry and can confoundlong-term trends caused by changes in deposition of sulphurand nitrogen. The RAIN and CLIMEX experiments at Risdalsheia provided directexperimental data that allow quantitative assessment ofthese factors. Run-off chemistry responded rapidly to the decreased aciddeposition. Sulphate concentrations decreased by 50% within threeyears; nitrate and ammonium concentrations decreased to new steady-state levelswithin the first year. Acid neutralising capacity increasedand hydrogen ion and inorganic aluminium decreased. Similar recovery fromacidification was also observed at the reference catchment,ROLF, in response to the general 50% reduction in sulphate deposition oversouthern Norway in the late 1980s and 1990s. Variations insea-salt deposition caused large variations in run-off chemistry at thereference catchment ROLF and the year-to-year noise in acidneutralising capacity was as large as the overall trend over the period. Thesevariations were absent at KIM catchment because the sea-salt inputswere held constant over the entire 17 years of the clean rain treatment. Theclimate change experiment at KIM catchment resulted inincreased leaching of inorganic nitrogen, probably due to increasedmineralisation and nitrification rates in the soils. style="line-height: 20px;">Keywords: acid deposition, global change, water, soil, catchment, experiment, Norway.