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Surface water samples were collected from two municipally monitored sections of the Tuhai River in Liaocheng—Li Fengtao and Lao Nanzhen—and analyzed using a combination of spectroscopic techniques, including ultraviolet-visible (UV-Vis) absorption and three-dimensional excitation-emission matrix (EEM) fluorescence spectroscopy, supplemented by ultrafiltration fractionation and fluorescence-quenching experiments to comprehensively characterize dissolved organic matter (DOM). The study investigated seasonal variations in DOM composition across three molecular weight fractions (<0.7μm, 0.7μm~1kDa, and<1kDa) and explored the underlying mechanisms of DOM-Cu2+ complexation. The specific ultraviolet absorbance at 254nm (SUVA254) was significantly higher at Li Fengtao (0.33 ± 0.01) than at Lao Nanzhen (0.30 ± 0.01) (P<0.05), suggesting a higher proportion of smaller, non-aromatic molecules at the latter site. Parallel factor analysis (PARAFAC) of EEM data identified five fluorescent components, including three humic-like (C1, C2, C4) and two protein-like (C3, C5) substances, with humic-like constituents dominating at both locations. Total fluorescence intensity (Fmax) was higher at Lao Nanzhen, and dissolved organic carbon (DOC) was primarily concentrated in the <1kDa fraction at both sites. Two-dimensional correlation spectroscopy (2D-COS) analysis demonstrated that humic-like components preferentially bound to Cu2+ in the unfractionated DOM samples from both locations. However, after ultrafiltration fractionation, the binding sequence shifted, with protein-like components becoming the dominant Cu2+-binding constituents. Furthermore, high-molecular-weight fractions (excluding C1 and C4) from both sites exhibited relatively strong metal-binding capacities, as evidenced by their conditional stability constants (logKCu:(3.08 ± 0.08) to (3.62 ± 0.02)).
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| 科 Family | 属数 Number of genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) | 属 Genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) |
|---|---|---|---|---|---|---|
| 鹅膏菌科Amanitaceae | 2 | 11 | 5.26 | 鹅膏菌属 Amanita | 10 | 4.78 |
| 小菇科 Mycenaceae | 2 | 12 | 5.74 | 丝盖伞属 Inocybe | 5 | 2.39 |
| 多孔菌科 Polyporaceae | 8 | 14 | 6.70 | 蜡蘑属 Laccaria | 5 | 2.39 |
| 红菇科 Russulaceae | 3 | 23 | 11.00 | 小皮伞属 Marasmius | 6 | 2.87 |
| 小菇属 Mycena | 11 | 5.26 | ||||
| 光柄菇属 Pluteus | 5 | 2.39 | ||||
| 红菇属 Russula | 17 | 8.13 | ||||
| 栓菌属 Trametes | 5 | 2.39 |
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