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Nitrogen Concentration and Nitrogen Isotope in Aquatic Plants of City River and Their Responses to Nitrogen Pollution in River Water (Vol. 49, No.3, Tot No.341 2021) TEXT SIZE: A A A

WU Yun1, LIU Xueyan1,2, HU Chaochen1

(1. Institute of Surface-Earth System Science, Tianjin University, Tianjin, 300072, China;
2. State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550081, China)

Abstract: With densely production activities in city, a large amount of pollutant has been discharged into urban rivers and deteriorated the water quality, the high nutrientient input may even cause eutrophication. Aquatic plants have been widely used into monitoring water nitrogen pollution and removing nitrogen laden water bodies. But until now, little knowledge about the nitrogen utilization of aquatic plants hinders us to precisely evaluate the river nitrogen pollution. In this study, concentrations and N isotopes (expressed as δ15N value) of total N in aquatic plants, dissolved N (NO3-, ammonium (NH4+) and dissolved organic N (DON)) in river water were investigated from upstream to sewage-polluted urban-to-downstream sections of Nanming river in Guiyang area, southwestern China in July 2016. Concentrations of dissolved N species in river water were significantly higher in polluted section than in upstream section, suggesting sewage-derived N pollution to the urban-to-downstream river sections. Aquatic plants also showed higher total N with more dissolved inorganic nitrogen in surface water. However, δ15N signatures of total N of aquatic plants could not imprint δ15N signatures of sewage N pollution. Instead, the preference for NO3- in upstream river and fractionation is accompanying with nitrogen utilization in pollution section were evidenced for aquatic plants. These results highlighted the importance of N preference in aquatic plants for shaping their N geochemical records. Physiological adjustment of N assimilation in aquatic plants should be considered in the bio-monitoring and phytoremediation of sewage N pollution.

Key words: aquatic plant; nitrogen isotope; river; sewage; nitrogen preference

EARTH AND ENVIRONMENT Vol.49, No.3, Tot No.341, 2021, Page 260-269

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