DIFFUSION INHIBITION MECHANISM OF IRON AND MANGANESE BY RE- PRECIPITATION IN ANAEROBIC HYPOLIMNION OF A DAM RESERVOIR

Abstract

In the Miharu Dam Reservoir, no actual water quality problem has never occurred since initial impoundment, even though dissolved oxygen (DO) in hypolimnion reaches 0 mg/L and dissolved Fe and Mn are observed in stratification season. This study assumed precipitation process of Fe and Mn at high ORP layer in anaerobic hypolimnion based on field data, and experimentally confirmed this process. Precipitation of Fe and Mn were observed at high ORP (> 0.11V vs NHE) even if DO was 0 mg/L. Experimentally observed precipitation rate of Fe and Mn is 10³ to 10⁴ times larger than its estimated molecular diffusion rate. High ORP layer in static hypolimnion appears to take important role to prevent water quality problem in the Miharu Dam Reservoir.