| Lesni Potok stream drains a forested headwater catchment in the central Czech
Republic. It was artificially acidified with hydrochloric acid (HC1) for four hours to
assess the role of stream substrate in acid-neutralisation and recovery. The pH was lowered
from 4.7 to 3.2. Desorption of Ca and Mg and desorption or solution of Al dominated
acid-neutralisation; Al mobilisation was more important later. The stream substrate
released 4,542 meq Ca, 1,184 meq Mg, and 2,329 meq Al over a 45 m long and 1 m wide stream
segment; smaller amounts of Be, Cd, Fe, and Mn were released. Adsorption of
SO42- and desorption of F‾ occurred during the
acidification phase of the experiment. The exchange reactions were rapidly reversible for
Ca, Mg and SO42-; but not symmetric as the substrate resorbed 1083,
790 and 0 meq Ca, Mg, and Al, respectively, in a 4-hour recovery period. Desorption of
SO42-; occurred during the resorption of Ca and Mg. These exchange
and dissolution reactions delay acidification, diminish the pH depression and retard
recovery from episodic acidification. The behaviour of the stream substrate-water
interaction resembles that for soil–soil water interactions. A mathematical dynamic
mass-balance based model, MASS (Modelling Acidification of Stream pediments), was
developed which simulates the adsorption and desorption of base cations during the
experiment and was successfully calibrated to the experimental data.
Keywords: Al, Ca, Mg, base cations, acid-neutralisation, stream acidification, recovery,
stream sediment, experiment, modelling, adsorption, desorption, adsorption, Czech Republic,
Lesni Potok |