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. To date, information on hydroxyl radical 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 hydroxyl radical 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 hydroxyl radical 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 hydroxyl radical 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 hydroxyl radical formation. Furthermore, application of Fe K-edge X-ray adsorption spectroscopy revealed the key species of sedimentary Fe-smectite for hydroxyl radical formation due to its high peroxidase-like activity. Besides inorganic Fe(II), the sedimentary dissolved organic matters (DOMs) represented an important regulator for hydroxyl radical formation, which contributed about 2–11% of the total hydroxyl radical 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 hydroxyl radical 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 hydroxyl radical production. This study highlighted the importance of contents and species of Fe(II) and DOM in manipulating the hydroxyl radical yield, providing new insight into understanding the formation mechanisms of hydroxyl radical in the seasonal lake sediment.

DU Haiyan, CAO Yuanxin, LI Zhe et al. Water