Burst of hydroxyl radicals in sediments derived by flooding/drought transformation process in Lake Poyang, China

摘要

Oxygenation of the reduced species has been regarded as the major source for hydroxyl radical (HO·) generation in aquatic environments. Yet, the O_2-induced formation of HO· in lake sediments during the flooding/drought transformation process remained largely unexplored. In this study, two types of sediments from Wucheng (WC) and Nanji (NJ) area in Lake Poyang, China, were collected, respectively, with the burst of HO· derived by flooding/drought transformation process exploring via the incubation experiments. Results showed that no obvious HO· can be detected for the two sediments during the flooding period, while the concentrations of HO· increased rapidly for the flooding/drought transformation process due to the enhanced dissolved oxygen contents. The highest concentrations of HO· in the surface sediment were 2.45 ± 0.19 μmol kg~(-1) for WC sediment and 0.69 ± 0.25 μmol kg~(-1) for NJ sediment, showing higher burst potential of HO· for the former. The contents of Fe(Ⅱ) in the surface sediments for WC area (589.3 ± 37.29 mg kg~(-1)) were about two times higher than those for NJ area (308.4 ± 94.01 mg kg~(-1)) during the flooding period. Oxygenation of the surface Fe(Ⅱ) contributed significantly to the burst of HO· in the flooding/drought transformation process. Moreover, the higher percentage of humic-like substances in WC sediment indicated that the dissolved humic fraction exhibited also important role in the HO· formation due to electrons transfer under redox conditions. This study highlighted the importance of reactive reduced species in manipulating the burst of HO· in lake sediment, which is essential for understanding the geochemical cycling of several major and trace elements as well as the behavior and fate of the contaminants in aquatic ecosystems.