洞庭湖沉积物不同形态氮赋存特征及其释放风险

为了揭示湖泊沉积物中氮的空间分布特征及其释放风险,采用连续分级提取法研究了洞庭湖表层沉积物中EN(可交换态氮)、HN(酸解态氮)及NHN(非酸解态氮)的赋存特征；同时,结合BN(生物可利用态氮)的含量和释放通量的大小,探讨了各形态氮对BN的贡献及与释放通量的相关关系. 结果表明,受水动力和湖盆地形的影响,沉积物中各形态氮含量空间差异较大. 全湖w(TN)在735.91~2846.51mg/kg之间,平均值为1371.85mg/kg,东洞庭湖、西洞庭湖、南洞庭湖、洞庭湖出口w(TN)的平均值分别为1513.43、1173.14、1262.76和1363.31mg/kg. 从各形态氮含量占w(TN)的比例来看,w(HN)最高,平均占66.74%；其次是w(NHN),平均占21.46%；w(EN)最小,仅占11.80%. 东洞庭湖、西洞庭湖、南洞庭湖、洞庭湖出口w(BN)的平均值分别为189.31、170.16、152.87和139.51mg/kg,其值大小主要受w(EN)和w(HN)的影响. 东洞庭湖、西洞庭湖、南洞庭湖、洞庭湖出口沉积物中NH₄+-N释放通量的平均值分别为6.32、7.03、7.78和146.96mg/(m2·d),沉积物中NH₄+-N释放通量主要受EN控制,其中尤其受可交换态NH₄+-N的控制,而沉积物中的HN和TN尚不是影响沉积物氮释放的主要因素. 

Occurrence Characteristics and Release Risk of Nitrogen Fractions in Sediments of Dongting Lake

As the second biggest freshwater lake, Dongting Lake plays an important role in floodwater adjustment of and water supply for industry, agriculture and life in the middle and lower reaches of the Yangtze River. The serious eutrophication was presented by the inorganic nitrogen in previous studies for the Dongting Lake. However, the organic nitrogen forms and release were still not clear until now. In order to reveal the spatial distribution and the release risk of nitrogen in lake sediments, nitrogen species, including exchangeable nitrogen (EN), hydrolysable nitrogen (HN) and nonhydrolysable nitrogen (NHN) in surface sediments of Dongting Lake were studied by sequential extraction methods. Concentration and release flux of bioavailable nitrogen (BN) were further measured to evaluate the contributions of different nitrogen speciation to BN and the relationship between nitrogen speciation and release flux. Results showed the spatial variations in all nitrogen forms influenced by hydrodynamic and lake topography. The TN in the whole lake was 735.91-2846.51mg/kg, with the mean value of 1371.85mg/kg. Specifically, the mean values of TN in East Dongting Lake, West Dongting Lake, South Dongting Lake and outlet of Dongting Lake were 1513.43,3.14,2.76and 1363.31mg/kg, respectively. The HN, NHN, and EN in sediments accounted for 66.74%, 21.46%, and 11.80% of TN, respectively. The mean values of BN in East Dongting Lake, West Dongting Lake, South Dongting Lake and outlet of Dongting Lake were 189.31,0.16,2.87and 139.51mg/kg, respectively, and BN was mainly influenced by EN and HN. The releases of ammonia nitrogen in East Dongting Lake, West Dongting Lake, South Dongting Lake and outlet of Dongting Lake were 6.32,7.03,7.78and 146.96mg/(m2·d), respectively, and were mainly affected by EN, especially for the exchangeable ammonia nitrogen. While HN and TN were not the main factors influencing the nitrogen release from sediments. The results could effectively support for the construction of hydraulic engineering and water environment models of Dongting Lake.