Trends in the chemistry of acidified Bohemian lakes from 1984 to 1995 : I. Major solutes

Temporal changes in major solute concentrations in six Czech Republic lakes were monitored during the period 1984-1995. Four chronically-acidic lakes had decreasing concentrations of strong-acid anions (C^sub SA^ = SO^sub 4^^sup 2-^ + NO^sup 3^^sup -^ + Cl^sup -^), at rates of 3.0 to 9.0 μeq L^sup -1^ yr^sup -1^. Decreases in SO^sub 4^^sup 2-^, NO^sub 3^^sup -^, and Cl^sup -^ (at rates up to 5.1 μeq L^sup -1^ yr^sup -1^, 3.2 μeq L^sup -1^ yr^sup -1^, and 0.6 μeq L^sup -1^ yr^sup -1^, respectively) occurred. The response to the decrease in deposition of S was rapid and annual decline of SO^sub 4^^sup 2-^ in lake water was directly proportional to SO^sub 4^^sup 2-^ concentrations in the acidified lakes. Changes in NO^sub 3^^sup -^ concentrations were modified by biological consumption within the lakes. The decline in C^sup SA^ was accompanied in the four most acidic lakes by decreases in Al^sub T^, increases in pH at rates of 0.011 to 0.016 pH yr^sup -^^sup 1^, and decreases of Ca^sup 2+^ and Mg^sup 2+^ (but not Na^sup +^) in three lakes. The acid neutralizing capacity (ANC) increased significantly in all six lakes. Increases in base cation concentrations (CB = Ca^sup 2+^ + Na^sup +^ + Mg^sup 2+^ + K^sup +^) were the principal contributing factor to ANC increases in the two lakes with positive ANC, whereas decrease in C^sub SA^ was the major factor in ANC increases in the four chronically-acidic lakes. The continued chemical recovery of these lakes depends on the uncertain trends in N deposition, the cycling of N in the lakes and their catchments, and the magnitude of the future decrease in S deposition.[PUBLICATION ABSTRACT]