Identification of black suspended particles in the algae-induced black bloom water column

Abstract

The black bloom phenomenon is one of the most serious problems in some hyper-eutrophic shallow lakes in China. The black colour and offensive odour were their most significant and basic physical characteristics. However,no firming evidences had been presented to explain what the black causing particles were in the black bloom water. In this research,the algae-induced black bloom was simulated and the chemical compositions of black suspended particles which were intercepted under anaerobic condition after the algae-induced black bloom simulation experiment were analyzed using multi X-ray based approaches. Scanning electron microscope-energy dispersive X-ray spectroscopy and X-ray fluorescence spectrometer analysis showed that algae residues and suspended sediment particles were the main substances and C,O,and Si were the main elements of these black particles. Compared to the check samples,black bloom suspended particles performed higher Fe and S contents. Detailed X-ray photoelectron spectroscopy analysis for Fe and S proved that Fe were mainly in the Fe( Ⅱ) form while S were mainly in S2-form and the majority of them co-existed in the form of Fe S. Therefore,in the hypoxic and anoxic black bloom water column,abundant Fe2 +and ΣS2-could co-precipitate into Fe S. These black Fe S could suspend in the water column or absorb on suspended particles,which caused the black color of the water and marked the formation of the black bloom.