Iron and Manganese Assessment in Surface and Under Profile Sediment of Water Dam and His Under-Catchment Area: Case of Okpara dam in Benin, West Africa

Abstract

: Iron and manganese concentrations vary highly and seasonally into the water of Okpara dam. Their values were related the geochemistry of the under-catchment area and its bank. Almost all soil and rock in high degradation state sampled on the catchment and bank of this dam show – concentrations’ values less or too higher than the sampled sediments in which concern iron and manganese. Iron is steal the most abundant metal whatever it is the soil or - rock analyzed. The dam bank rock metal profile showed a metal leaching more from the top to down profile. The under-profile sediment shows iron diffusion from the most anoxic layer to the less anoxic layers. The underground waters sampled from the catchment have express acidic behavior despite the neutral pH state of rivers water. The same acidity remains more in the sediment. Manganese is more concentrated (0.25 to 4.54 mg/L) in underground waters than iron (less than 2 mg/l). The sediment of the dam is the probable source of water column iron and manganese provider through physic-biogeochemical processes.