Chemical properties of an acidified humic headwater lake with respect to reducing acidic depositions and expected climate change

During the hydrological years 1989 and 1990, water analyses of the dystrophic mountain cirque Lake Huzenbach and the precipitation within its watershed were performed. Periods of droughts which are supposed to be induced by climate change as well as acidic pulses modify the chemical composition of lake water. Snow melt and heavy rains cause flash floods in lake inflows which are controlled by subsurface-flow. One of the inflows exhibits extremely low pH values pH_min = 3.66], high concentrations for aluminium Al_max = 1.10 mg l^-1], dissolved organic carbon DOC_max = 30.7 mg l^-1], and sulfate SO_4max = 9.08 mg l^-1]. Organic and inorganic acids are both likely to contribute to the acidity of these surface waters. During baseflow conditions, groundwater springs still show slightly positive alkalinity values as well as increased pH values up to about 6.0. Since 1985 lake surface samples demonstrate an increasing tendency towards pH values higher than 5.0 during dry summer periods. Positive alkalinity values occur in the hypolimnion during anoxic conditions.