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The Dongjiang River Basin was chosen as the study area to compare the nitrogen concentrations and isotopes in the river with different land uses, so as to provide a better understanding and evidence for impacts of urbanization on active nitrogen turnover. In this study, the distinct characteristics of nitrogen concentrations and isotopes were found in urbanized rivers compared to rivers with other land uses. Firstly, the nitrogen concentrations in urbanized rivers were gradually increased due to urbanization and nitrate has become a main nitrogen speciation. Secondly, based on the isotope Rayleigh fractionation model, it was found that the nitrification potential in urbanized river channels was enhanced and about 25.8% of nitrate nitrogen came from nitrification in situ. In addition, a positive correlation between ln（NO3--N）and δ15N-NO3- was recorded in urbanized rivers. Moreover, Δδ15N/Δδ18O in the dry and wet seasons were –2 and -6, respectively, indicating that the denitrification potential was weakened to provide evidence for nitrate accumulation in urbanized river channels. Likewise, a weak correlation between δ15N-PN and δ15N-NH4+ was also recorded in urbanized rivers, and the 15N enrichment factor of nitrate assimilation also differed from the theoretical value, indicating a weak assimilation of ammonia and nitrate nitrogen. Finally, more input pathways and less sink processes of nitrogen in urbanized rivers have become a key mechanism for elevated riverine nitrogen concentrations in the lower reaches of Dongjiang river.
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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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