Lake reclamation alters molecular-level characteristics of lacustrine dissolved organic matter – A study of nine lakes in the Yangtze Plain, China

In recent decades, the reclamation of lakes has captured 42% of the total lake area of the Yangtze Plain in China and introduced additional pressure on lacustrine water quality. While lacustrine dissolved organic matter (DOM) is critical in regulating biogeochemical processing and aquatic biodiversity, the impact of reclamation on the molecular-level characteristics of lacustrine DOM remains unexplored. Here, the DOM characteristics altered by reclamation practices in the Yangtze Plain lakes were investigated using fluorescence spectroscopy, nuclear magnetic resonance spectroscopy, and Fourier transform ion cyclotron resonance mass spectrometry. Results demonstrated that reclamation not only elevated the quantity (on average +32%) but also altered the characteristics and composition of lacustrine DOM. Compared to the natural water sites close by, reclamation sites did not significantly alter the DOM aromaticity but significantly lowered the average molecular weight and increased the biolability of DOM. The chromophoric DOM and humic-like fluorescent components were remarkably elevated, but not the protein-like fluorescent components. More lipid-like and condensed aromatic-like components were detected in the lacustrine DOM as compared to the lignin-like, carbohydrate-like, and protein-like components, which may be driven by the increased microbial processing. Overall, the significant alteration in characteristics and composition of lacustrine DOM highlights the potential impact of reclamation on the DOM biogeochemical cycle and the environmental quality in aquatic ecosystems.