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This paper revealed the spatial and temporal distribution and source characteristics of dissolved organic nitrogen (DON) in the watershed through the joint analysis of water quality indicators, three-dimensional fluorescence spectroscopy (3DEEM) and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). The results showed that the proportion of DON concentration to total dissolved nitrogen concentration in all counties of the watershed in all seasons ranged from 15% to 20%. The overall DON level was low, while the DON/TN ratios in the main stream sections of the two downstream counties were significantly higher than those in the upstream. 3DEEM showed that DOM was dominated by humus of terrestrial origin, and the activity of the protein-like fractions was enhanced in summer and autumn. The fluorescence index indicated that agricultural input dominated the exogenous pollution. FT-ICR MS detected that nitrogenous organic matter was dominated by lignin-like substances. The input of Yellow Water (YH) elevated the percentage of condensed aromatics downstream by 11.4%. The lower amount of nitrogenous organic matter in the water body in summer compared with autumn at Gaojiaxie Village (G9) revealed the influence of land-source humus input. The transformation of dissolved organic nitrogen in the Fen River basin was synergistically driven by exogenous inputs, biodegradation and photolysis, which formed the characteristics of DON sources under the action of multiple mechanisms. The study suggested that priority should be given to the control of tributary inputs of difficult-to-degrade organics to enhance the effectiveness of management.
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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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