城市河流水生植物氮含量和氮同位素记录及其对水体氮污染的响应

Nitrogen Concentration and Nitrogen Isotope in Aquatic Plants of City River and Their Responses to Nitrogen Pollution in River Water

城市生产和生活活动排放大量含氮污染物到城市河流中,造成水质下降、水体富营养化。河流水生植物已被广泛用于水体氮污染的评价和去除,但目前水生植物氮利用的过程机制并不十分清楚,这阻碍了利用水生植物的氮素地球化学指标去评价河流水体氮污染状态。本研究采集西南地区流经贵阳市区的南明河河水和水生植物样本,通过分析氮浓度和同位素组成,探讨在不同水体氮浓度条件下水生植物的氮利用机制。在受城市污染的河段,水体铵根(NH4^(+))、硝酸根(NO3^(-))、溶解有机氮(DON)浓度均显著升高(n=13,p<0.05),其水生植物的总氮含量随河水无机氮含量升高而升高。但是,受城市污染河段的水生植物总氮的δ^(15)N值却无显著变化,说明除了水体氮源的δ^(15)N特征,水生植物的氮利用策略是影响其δ^(15)N记录的重要因素。在河流低氮浓度下植物主要利用水中的NO3^(-),在下游高氮浓度下植物氮利用机制较复杂,过程中会发生分馏,但具体的利用形态还无法确定。本研究揭示了水生植物氮利用策略对河流氮污染状态的响应机制和对塑造其地球化学记录的重要性,为城市河流废水氮污染评价及其植物修复措施提供基础科学依据。

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 asδ^(15) N value)of total N in aquatic plants,dissolved N(nitrate(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,δ^(15) N signatures of total N of aquatic plants could not imprintδ^(15) N 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.