Formation and mechanisms of hydroxyl radicals during the oxygenation of sediments in Lake Poyang, China.

Seasonal flooding-drought transformation process of lake sediments lead to changes of dissolved oxygen and redox conditions and the resultant generation of hydroxyl radical (HO ^• ). To date, information on HO ^• formation and its regulators in seasonal lake sediments is largely unexplored. In this study, a total of nineteen sediments were collected from Lake Poyang, China, with the formation and mechanisms of HO ^• during the oxygenation process exploring via the incubation experiments, Fe K-edge X-ray adsorption spectroscopy, ultrafiltration, and fluorescent spectroscopy. Results showed that the concentrations of HO ^• generated ranged from 3.75 ± 1.13 to 271.8 ± 22.81 μmol kg ^-1 , demonstrating high formation potential and obvious spatial heterogeneity. The yield of HO ^• formed was positively correlated with the contents of Fe(II), sedimentary organic carbon, and dissolved organic carbon, showing a general contribution of these reduced substances to HO ^• formation. Furthermore, application of Fe K-edge X-ray adsorption spectroscopy revealed the key species of sedimentary Fe-smectite for HO ^• formation due to its high peroxidase-like activity. Besides inorganic Fe(II), the sedimentary dissolved organic matters (DOMs) represented an important regulator for HO ^• formation, which contributed about 2-11% of the total HO ^• generation. Moreover, the DOM-induced formation potential was found to be highly related to the molecular weight distribution that the low molecular weight- (LMW, <1 kDa) fraction exhibited higher HO ^• formation potential than the bulk and high molecular weight- (HMW, 1 kDa-0.45 μm) counterparts. In addition, the omnipresent mineral Fe(II)-DOM interaction in sediment matrix exhibited another 2-6% of contribution to the total HO ^• production. This study highlighted the importance of contents and species of Fe(II) and DOM in manipulating the HO ^• yield, providing new insight into understanding the formation mechanisms of HO ^• in the seasonal lake sediment.
(Copyright © 2021. Published by Elsevier Ltd.)