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A laboratory study of the presence and transformation of dissolved Mn(III) across the sediment–water interface of an anoxic freshwater body

Chen, Lei, Zhang, Junjie, Zheng, Xilai
Environmental earth sciences 2019 v.78 no.4 pp. 108
environmental factors, freshwater, laboratory experimentation, manganese, manganese oxides, organic carbon, oxygen, pH, quantitative analysis, redox potential, sediment-water interface, sediments, surface water
Dissolved Mn(III) has been verified to be an important component of Mn cycling in a natural water system. However, the existence and stability of dissolved Mn(III) and its interactions with environmental factors, such as pH, dissolved oxygen (DO), oxidation–reduction potential (ORP) and dissolved organic carbon (DOC) in freshwater body are still not clear. In this paper, the dynamic characteristics of dissolved Mn (Mndᵢₛₛ), Mn(III), pH, DO, ORP and DOC across the sediment–water interface of anoxic freshwater environment (Wangjuan Reservoir of Qingdao City) were studied through laboratory experiments. The correlations between Mndᵢₛₛ and these key environmental factors, as well as between Mn(III) and environmental factors were quantitatively analyzed. The results indicated that concentration gradient was the main driving force of Mndᵢₛₛ and Mn(III) of each layer overlying water, and there were obvious differences between the concentrations of Mndᵢₛₛ and Mn(III) of overlying and pore water. In sediment pore water, dissolved Mn(III) concentrations were as high as 9.35 mg/L and constituted up to 23% of the total dissolved Mn pool, indicating that dissolved Mn(III) could stably exist in anoxic freshwater body and mainly came from the reduction process of Mn oxides in sediment. According to data analysis results, both the concentrations of Mndᵢₛₛ and Mn(III) of pore water had significant correlations with the values of pH, ORP, and DOC of sediment pore water. The correlation coefficients of Mndᵢₛₛ with the three factors were − 0.861, − 0.882 and − 0.934, respectively, while, the correlation coefficients of Mn(III) with them were − 0.836, − 0.671 and − 0.851, respectively.