Aluminum Mobilization in an Acidic Headwater Stream: Temporal Variation and Mineral Dissolution Disequilibria

Intensive sampling was performed along an elevational gradient in a headwater stream during snowmelt and storm events to study the chemical response of the stream to acidic inputs. Aluminum is an important constituent because of its toxicity to some fish species. The results indicate that aluminum concentrations during this period were not in equilibrium with a readily formed mineral phase, as has been assumed, and that the increase in aluminum concentration due to episodic depressions in pH lessened during the snowmelt. It is hypothesized that this temporal variation is caused by the depletion of a slowly forming, labile pool of aluminum in the soil.