BIOGEOCHEMISTRY OF ALUMINUM IN A FOREST CATCHMENT IN THE CZECH-REPUBLIC IMPACTED BY ATMOSPHERIC INPUTS OF STRONG ACIDS

The Lysina catchment in the Czech Republic was studied to investigate the biogeochemical response of Al to high loadings of acidic depositio n. The catchment supports Norway spruce plantations and is underlain b y granite and podzolic soil. Atmospheric deposition to the site was ch aracterized by high H+ and SO42+ fluxes in throughfall. The volume-wei ghted average concentration of total Al (Al-t) was 28 mu mol L(-1) in the O horizon soil solution. About 50% of Al-t in the O horizon was in the form of potentially-toxic inorganic monomeric Al (Al-i). In the E horizon, Al-t increased to 71 mu mol L(-1), and Al-i comprised 80% of Al-t. The concentration of Al-t (120 mu mol L(-1)) and the fraction o f Al-i (85%) increased in the lower mineral soil due to increases in A l-i and decreases in organic monomeric Al (Al-o). Shallow ground water was less acidic and had lower Al-t concentration (29 mu mol L(-1)). T he volume-weighted average concentration of Al-t was extremely high in stream water (60 mu mol L(-1)) with Al-i accounting for about 60% of Al-t. The major species of Al-i in stream water were fluorocomplexes ( AI-F) and aquo Al3+. Soil solutions in the root zone were undersaturat ed with respect to all Al-bearing mineral phases. However, stream wate r exhibited Al-i concentrations close to solubility with jurbanite. Ac idic waters and elevated Al concentrations reflected the limited suppl y of basic cations on the soil exchange complex and slow weathering, w hich was unable to neutralize atmospheric inputs of strong acids.