Dynamics of iron movement involving colloids, bacteria, and siderophores in an aqueous alkaline environment

Abstract

Water quality used for irrigation of alkaline soils will have a significant effect on Fe addition to the plant environment. By following the distribution of Fe added to reservoir water we were able to determine the fate of inorganic Fe in an alkaline environment which contains planktonic bacteria and photosynthetic cyanobacteria. The formation of colloidal Fe was found to be dependent on pH and amount of colloid increased with incubation time. Addition of aluminum, copper, chromium and lanthinum salts greatly increased colloidal Fe formed; however, considerable quantities of Fe remained in solution even in the presence of these cations. The adsorption of Fe onto the surface of bacteria was greatly increased in the presence of aluminum, chromium, copper and lanthinum salts, while active transport into planktonic bacteria was markedly reduced by these four cations. Fe was immobilized by adsorption and active transport of cyanobacteria but release of Fe from cyanobacteria was slow. Greatest solubility of iron, suggestive of siderophore production in natural waters, occurred in reservoir waters of pH 8.5 to pH 9.3. A model reflecting the variables in this dynamic movement of Fe in reservoir waters is constructed which involves dissolved Fe, colloidal formation, planktonic bacteria and photosynthetic bacteria as variables.

Key words:

• Iron solubility
• Water quality
• Cation interactions