The effect of anthropogenic impoundment on dissolved organic matter characteristics and copper binding affinity: Insights from fluorescence spectroscopy.

Excitation-emission matrix fluorescence spectroscopy combined with parallel factor analysis (EEM-PARAFAC) and two-dimensional correlation spectroscopy (2D-COS) were applied to evaluate the effects of anthropogenic impoundment on the characteristics of dissolved organic matter (DOM) and its heavy metal binding affinity. Three field-sampling cruises conducted in Hongze Lake from 2015 to 2016 were classified as early impoundment and late impoundment cruises according to the hydrological conditions. Five fluorescence components were derived from EEM-PARAFAC, including three humic-like components (C1C3) and two protein-like components (C4 and C5). The results show a higher dissolved organic carbon concentration, humification degree, molecular size, and level of terrestrial humic-like substances (C1C3) for early impoundment DOM compared with late impoundment DOM, which were derived from the relatively high inflow discharges present before impoundment. Meanwhile, the relatively high autochthonous contribution and level of protein-like substances found in late impoundment DOM suggested that anthropogenic impoundment can influence the DOM composition in Hongze Lake. Increases in the binding affinities (log Km) of humic-like substances (C1 and C3) and decreases in the log Km of tryptophan-like substances (C4) were observed during the impoundment period. Additionally, 2D-COS results suggested that the preferential Cu(II) binding ligands in early and late impoundment DOM were tryptophan- (C4) and humic-like (C1) substances, respectively. These results indicated that impoundment-derived DOM composition alteration can decrease the bioavailability and toxicity of Cu in Hongze Lake. The results reported here will improve the understanding of DOM and heavy metal cycling in impoundment lakes.