三峡水库香溪河沉积物氮含量和氨氮释放特征

Total Nitrogen Content and Ammonia Nitrogen Release from Surface Sediments of Xiangxi River, Three Gorges Reservoir Region

通过分析三峡水库香溪河库湾表层沉积物的理化性质和氮素分布特征,并结合室内动力学实验,对香溪河库湾沉积物氮素的组成差异和氨氮释放动力学模型进行了探讨,分析了沉积物氨氮释放潜能。结果表明,香溪河表层沉积物中总氮(TN)含量为683.71～843.19 mg/kg,氨氮(NH^+_4-N)含量为122.77～237.85 mg/kg,硝氮(NO^-_3-N)含量为35.78～102.44 mg/kg。采用一级动力学模型模拟了氨氮释放动力学,氨氮的最大释放量为67.06～74.43 mg/kg,是长江中下游湖泊平均值的1.5倍,存在一定的释放风险;表层沉积物在起始0～5 min内快速释放,达到最大释放量的97.90%～98.41%,150 min后基本达到释放平衡。香溪河氨氮的平均释放量在水土质量比为5 000时达到最大,随后趋于平衡。相关性分析发现,最大释放量与释放潜能均与沉积物中有机质含量和粒度分布相关性不明显,这可能与香溪河的水环境特点有关。

Endogenous pollution of sediments is a primary cause of water eutrophication and receiving national and international attention.Nitrogen from sediments is released primarily in the form of NH4^+-N and continued research on NH+4-N release is necessary.In this study,we determined the distribution of different forms of nitrogen in the sediment of Xiangxi Bay and studied the kinetics of NH4^+-N release from sediment,based on sediment physical and chemical parameters.Results provide a theoretical basis for eutrophication control in the backwater area of Xiangxi River.In July 2017,sediment samples were collected at three sites:Site 1,near the mouth of the river;Site 2,near the town of Xiakou;and Site 3,Xiangxi River upstream of Xiakou.The physical and chemical parameters of the sediments were determined,including total nitrogen(TN),ammonia nitrogen(NH4^+-N),nitrate nitrogen(NO3^--N,total phosphorous(TP),pH,dissolved oxygen(DO)and temperature(T).Then the kinetics of NH4^+-N release from sediments were investigated in the laboratory.Results show that the TN content in the sediments varied from 683.71-843.19 mg/kg and followed the order,Site 2>Site 1>Site 3.The content of NH4^+-N in the sediments ranged from 122.77 to 237.85 mg/kg and followed the order,Site 3>Site 2>Site 1.The content of NO3^--N in the sediments ranged from 35.78 to 102.44 mg/kg and followed the order of Site 1>Site 3>Site 2.The release of NH4^+-N from surface sediment was well simulated by first-order kinetics.The largest release rate of NH4^+-N was 67.06-74.43 mg/kg,1.5 times the average reported for the middle and lower reaches of the Yangtze River,indicating high risk.The release of NH4^+-N occurred primarily in the first five minutes,accounting for 97.90%-98.41%of the total release,and reached equilibrium after 150 minutes.The NH4^+-N release peaked at a water to soil ratio of 5 000∶1.Correlation analysis shows that NH4^+-N release is not significantly correlated with sediment organic matter content or particle size distribution.This may be related to the particular characteristics of the Xiangxi River water environment and will be investigated in future research.