温度对湖湾沉积物垂向氮吸附特征影响的研究

Effect of Temperature on Vertical Nitrogen Adsorption Characteristics of Sediments in Lake Bay

沉积物中氮是上覆水体营养盐的主要来源之一,垂向各层沉积物对上覆水体中氮含量的贡献不同,温度对各层沉积物氮释放影响较大。该研究在调查藻型湖湾上覆水和沉积物氮素空间分布的基础上,开展温度对沉积物垂向氮吸附特征的影响研究,揭示微生物群落在此过程中的响应。结果显示,研究区域水体总氮最高可达2.85 mg/L,沉积物表层总氮含量最高,在958.23~1 123.54 mg/kg之间。沉积物吸附动力学结果表明,沉积物对氨氮的吸附主要发生在前2 h,不同温度下平衡吸附量(Q_(e))随温度的降低而增大(15℃时Q_(e)均值为0.68 mg/g)。吸附等温实验结果表明,沉积物对氨氮的理论最大吸附量(Q_(max))为3.13~32.25 mg/g,其中在25℃下,底层沉积物Q_(max)最高可达32.25 mg/g。表层沉积物氨氮的平衡吸附浓度(ENC_(0))均高于上覆水中氨氮浓度,达0.22~2.78 mg/L,中、底层沉积物ENC_(0)均小于0.17 mg/L,低于间隙水氨氮浓度,表明表层沉积物中氨氮有向上覆水释放的风险,中、底层沉积物氨氮释放风险较小。此外,微生物群落结构分析显示,沉积物表层比中、底层含有更多脱氮功能微生物(变形菌门中的类固醇杆菌属)优势菌落;冗余分析结果显示叶绿素a含量是影响微生物群落丰度的重要因素之一。

Nitrogen in sediments is one of the main sources of nutrients in the overlying water. Contributions of vertical sediments to nitrogen content in the overlying water are different, and temperature has a great influence on nitrogen release in sediments of each layer. Based on the investigation of the spatial distribution of nitrogen in overlying water and sediment of algal bay, this study evaluated the effect of temperature on sediment vertical nitrogen adsorption characteristics, and revealed the response of microbial community in this process. The results show that the total nitrogen in the water was up to 2.85 mg/L,and the total nitrogen content in the sediment range from 958.23 to 1 123.54 mg/kg. The results of sediment adsorption kinetics at selected research sites show that the adsorption of ammonia nitrogen mainly occurred in the first 2 h, and the equilibrium adsorption capacity(Qe) increased with the decrease of temperature at different temperatures(the average Qeat 15 ℃ was0.68 mg/g). The results of adsorption isotherm experiment show that the theoretical maximum adsorption capacity(Q_(max)) of sediments for ammonia nitrogen is 3.13~32.25 mg/g, and the Q_(max) of bottom sediments is 32.25 mg/g at 25 ℃. The equilibrium adsorption concentration(ENC_(0)) of ammonia nitrogen in surface sediments is higher than that in overlying water, reaching 0.22~2.78 mg/L, while ENC_(0)in middle and bottom sediments is lower than that in interstitial water(0.17 mg/L), indicating that ammonia nitrogen in surface sediments has a risk of release to overlying water. The middle and bottom sediments have little risk of ammonia nitrogen release. In addition, the analysis of microbial community structure show that there are more dominant colonies of denitrification functional microorganisms(Sterobacilli in Proteobacteria) in the surface layer of sediment than in the middle and bottom layer. RDA shows the content of chlorophyll-a is one of the important factors affecting the abundance of microbial community.