Spectroscopic characterization of dissolved organic matter from macroalgae Ulva pertusa decomposition and its binding behaviors with Cu(II).

Dissolved organic matter (DOM) from macroalgae is regarded a crucial source of autochthonous DOM in coastal ocean. In the present study, the characteristics of DOM from the macroalgae Ulva pertusa decomposition (U. pertusa-DOM) and its binding behaviors with Cu(II) using multiple spectroscopic techniques and chemometric analyses. The labile U. pertusa-DOM could be consumed and transformed by microorganisms. The absorption spectroscopic descriptors indicate that the hydrophobicity, aromaticity, and molecular weight of the U. pertusa-DOM increase during the 27-day incubation period. Fluorescence excitation-emission matrix spectroscopy combined with parallel factor analysis suggests that the relative abundance of the protein-like component (C1) (96.10-84.96%) sequentially decreases, whereas the humic-like components (C2) (2.16-9.73%) and (C3) (1.75-5.31%) in the U. pertusa-DOM increase with the U. pertusa decomposition. The Cu(II) binding properties of the U. pertusa-DOM are dependent on the decomposition time. The order of the conditional stability constant (logKM) is C2 > C1 > C3. The complexation capacity (f) of C1 is higher than those of C2 and C3 at a specific time. Synchronous fluorescence spectroscopy coupled with two-dimensional correlation spectroscopy reveals that the microbial degradation could accelerate the Cu(II) binding to humic-like fractions in the U. pertusa-DOM. These findings will help us better understand the biogeochemical behaviors of macroalgal DOM and heavy metal in coastal ecosystems.