The role of stream substrates in aluminium mobility and acid neutralization

Abstract

Acidification experiments were conducted on two streams to determine the mobilization of Al and the size of the pool of exchangeable Al associated with streambed materials during acid episodes. The first experiment demonstrated a buffering capacity of the stream 20-fold higher than that associated with the water and resulted in releases of massive amounts of Al (to 2500 μg 1 −1) at pH < 5. The source of buffering and the reservoir of Al was hypothesized to be dense growths of a liverwort. A second stream acidification and laboratory experiments confirm that mosses and liverworts in streams are important in the ion exchange of base cations and Al during acid episodes. Short-term neutralization was dominated by release of base cations by ion-exchange and long-term neutralization of H + was dominated by release of Al.