Variation in the susceptibility of humic acids from the sediments of water reservoirs to oxidation

Abstract

AbstractThe aim of this study was to determine whether, and to what extent, structures of pigment‐origin affect the susceptibility of humic acids (HAs) to oxidation, with the primary focus on derivatives of chlorophyll. The sediment samples were collected from lakes with different catchment management, and the Szczecin Lagoon, which is the estuary of the Odra River. HAs were extracted from sediments using 0.5 M NaOH solution. Sediments differed in their contents of total organic carbon (3.8–456.0 g kg−1) and total nitrogen (0.8–33.7 g kg−1). HAs extracted from sediments were characterized by the highly diverse composition of chemical elements and spectrometric properties regarding the visible‐light spectrum and ultraviolet radiation. HAs extracted from the sediments of lakes situated in the Chodzież and Wałcz Lake Districts (ChWLD) with forest catchment areas, were most susceptible to oxidation, indicating that the processes that occur during oxidation are affected by the content of pigment‐originated structures (the derivatives of chlorophyll) in the molecules of HAs. These structures are relatively resistant to oxidation, because they are present in the spectra of alkaline solutions of HAs after oxidation. The conducted studies also proved that the susceptibility of HAs of sediment origin to oxidation cannot be interpreted in the standard way applied to values obtained for soil HAs.