Effects of Fe 2+ and Fe 3+ on Algal Proliferation in a Natural Mixed Algal Colony in Algae-Rich Raw Water in Southern China

Abstract

As a necessary micronutrient for algal growth, iron (Fe) has importanteffects on the physiological metabolism and enzymatic reactions of algae. There arevarious forms of iron in nature, and soluble iron exists mainly in two forms: Fe2+ andFe3+. In this study, a series of experiments were designed to compare the effects ofFe2+ and Fe3+ on the growth of natural mixed algal colonies and single-species coloniesof Scenedesmus quadricauda. The results show that Fe2+ and Fe3+ have different effectson the reproductive processes of these two algal populations. The optimal growthconcentration of both Fe2+ and Fe3+ for natural mixed algae is 0.3 mg/L; at that concentration,algal biomass reaches its peak, with values of 1.74 × 106 cells/L and 6.82× 105 cells/L for the two iron forms, respectively. At the same time, the average growthrates of these algae also reach their maximum, which are 0.3620 d–1 and 0.3398 d–1,respectively. The optimal growth concentrations of Fe2+ and Fe3+ for S. quadricaudaare about 0.4 mg/L. We propose that Fe2+ exhibits higher biological time-effectivenessthan Fe3+ for algal reproduction, and while Fe2+ and Fe3+ exhibit similar facilitation in thegrowth of both natural mixed algae and S. quadricauda, differences exist between theirfacilitation effects. The results of the study further suggest that problems involving ironuptake priority and inter-specific competition could arise during the reproductive processin mixed algal colonies.