Contents and distribution characteristics of nitrogen forms in sediments of Guizhou Lake Caohai under different water level levels

Abstract

利用分级浸取分离法，分析贵州草海湿地沉积物总氮（TN）与可转化态氮（TF-N）含量及分布特征，试图揭示水位抬升对草海湿地沉积物氮潜在释放风险的影响.结果表明，草海湿地沉积物TN含量在1.94~14.07 g/kg之间，均值为7.76 g/kg；TF-N含量较高，在1.70~7.59 g/kg之间，占TN的68.7%；不同形态氮含量依次为有机态及硫化物结合态氮（OSF-N） > 离子交换态氮（IEF-N） > 铁锰氧化态氮（IMOF-N） > 弱酸可浸取态氮（WAEF-N）；不同水位梯度下各形态氮含量变化规律不同，OSF-N、IMOF-N含量沿着水位升高呈逐渐增加趋势，IEF-N含量呈先增加后降低的趋势，WAEF-N含量变化不大；TN和总非可转化态氮（NTF-N）与有机质（SOM）含量之间呈显著正相关，可能具有相似的来源.总之，草海沉积物TF-N含量及比例较高，潜在释放风险较大，而水位抬升抑制氮的转化，促进沉积物氮积累，增加释放风险.该研究揭示了不同水位梯度下沉积物氮形态分布特征，丰富了水文条件对氮迁移转化影响的理解，为湿地生态补水工程的管理决策提供了科学依据.;Lake Caohai situated in Guizhou Province is a plateau lake. The contents and distribution characteristics of total nitrogen (TN) and transferable nitrogen (TF-N) in sediments of Lake Caohai wetland were analyzed by using the method of fractional leaching and separation, and the effect of water level uplift on the potential nitrogen release risk of sediments was revealed. The results showed that the TN content in sediments ranged from 1.94 to 14.07 g/kg, with an average of 7.76 g/kg. The content of TF-N was relatively higher (between 1.70 and 7.59 g/kg), accounting for 68.7% of TN. Nitrogen content of transformable nitrogen in different forms was organic matter-sulfide form nitrogen (OSF-N) > ion-extractable form nitrogen (IEF-N) > iron-manganese oxides form nitrogen (IMOF-N) > weak acid extractable form nitrogen (WAEF-N). Under different water level, the changeable regulation of transformable nitrogen content of each form was different. OSF-N and IMOF-N increased gradually along the water level, while IEF-N first increased and then decreased. WAEF-N did not change much. There was a significant positive correlation between TN and non-transferable nitrogen (NTF-N) and soil organic matter (SOM), which may have similar sources. Shortly, Lake Caohai sediments have higher levels of transformable nitrogen and higher risk of potential release, while elevated water levels increase the risk of nitrogen release. The study reveals the nitrogen distribution characteristics of sediments under different water level, enriches the understanding of the impact of hydrological conditions on the migration and transformation of nitrogen, and provides a scientific basis for management decision of wetland ecological replenishment projects.