太湖蓝藻衰亡过程对沉积物-水界面氮迁移转化影响的研究

【作者】 陈颖；

【导师】 韩睿明； 姚羽；

【作者基本信息】 南京师范大学 ， 环境科学， 2023， 硕士

【摘要】 湖泊外源氮污染得到有效控制的情况下,沉积物中内源氮的释放是影响湖泊富营养化治理成效、引发蓝藻水华的关键因素。然而,蓝藻水华衰亡过程中沉积物-水界面处氮迁移转化的机制尚不明确。基于此,本研究以太湖为研究对象,野外调查和室内模拟相结合,应用微电极技术、薄膜扩散梯度技术（Diffusive Gradients in thin-films,DGT）、膜渗析平衡技术（High-resolution peepers,HR-Peeper）和分子生物学等技术,解析太湖沉积物-水界面氮的空间分布特征,阐明各种理化指标对沉积物-水界面氮分布的影响,揭示蓝藻水华衰亡对沉积物-水界面不同形态氮迁移、转化的影响机制。主要研究发现如下:（1）野外调查表明,太湖沉积物-水界面氮浓度分布表现出很强的空间异质性,各采样点位的NH₄⁺-N、NO₃^--N和NO₂^--N平均浓度范围在3.32～13.60 mg L^-1、2.01～6.58 mg L^-1和0.031～0.108 mg L^-1之间,藻华爆发最严重的竺山湾区域沉积物NH₄⁺-N平均浓度最高,湖心区最低;而湖心区的NO₃^--N平均浓度最高,梅梁湾最低;南部沿岸区NO₂^--N平均浓度最高,贡湖湾最低,太湖南部区域的NO₂^--N平均浓度整体上要高于蓝藻爆发的北部区域。各采样点位NH₄⁺-N、NO₃^--N和NO₂^--N的扩散通量范围分别为-72.72～109.71 mg m^-2 d^-1、-40.13～34.26mg m^-2 d^-1、和-2.05～0.78 mg m^-2 d^-1,太湖沉积物主要表现为NH₄⁺-N的“源”,NO₃^--N和NO₂^--N的“汇”。（2）蓝藻水华衰亡的过程中,风浪扰动促进了沉积物-水界面的复氧和有机质的降解速度,进而促进了硝化作用和反硝化作用。在大风浪和小风浪扰动的条件下,沉积物-水界面NH₄⁺-N的扩散通量范围分别为60.44～437.21 mg m^-2 d^-1和23.56～130.30 mg m^-2 d^-1,而静态条件下鲜藻和藻粉降解过程中沉积物-水界面NH₄⁺-N的扩散通量范围分别为-75.08～127.86 mg m^-2 d^-1和-27.11～84.08 mg m^-2d^-1。扰动条件下的扩散通量远大于静态条件,因此,风浪扰动促进了氮的扩散,扰动作用越强,氮的扩散强度也越大,这会导致沉积物向上覆水中释放NH₄⁺-N增多,进而导致来年蓝藻水华的再次爆发。（3）野外调查和室内模拟实验表明,沉积物-水界面的NH₄⁺-N浓度主要表现出两种分布模式。当沉积物-水界面处出现陡峭的浓度梯度时,可能处于藻类爆发初期,藻类还没有发生大量沉降,没有藻类碎屑在沉积物-水界面处堆积,或者堆积的藻类碎屑已经分解完毕;当沉积物-水界面处出现浓度峰时,说明大量蓝藻或者其它植物碎屑在沉积物-水界面堆积,正处于分解阶段,其浓度峰越宽,说明聚积的藻类碎屑越厚。因此,沉积物-水界面处NH₄⁺-N浓度分布模式的变化可以用来指示淡水生态系统中蓝藻水华的分解程度以及富营养化水平。（4）新鲜蓝藻和干藻粉分解过程中产生的大量DOM成分没有显著的组成差异,都以类腐殖质和类蛋白质为主。这些大分子DOM在矿化过程中会释放出大量NH₄⁺-N,使得沉积物中的硝化微生物氨氧化细菌AOB占主导地位。此外添加新鲜蓝藻和藻粉的沉积物柱中,氮的浓度以及硝化和反硝化微生物没有显著性差异,说明新鲜蓝藻中的藻际微生物对氮的去除以及对沉积物中的微生物影响不显著。综上所述,蓝藻水华衰亡影响了沉积物-水界面氮的迁移转化。在风浪扰动下,沉积物的悬浮作用以及内源氮释放作用强烈,蓝藻衰亡使得沉积物氮的扩散通量增大,蓝藻的衰亡也会改变沉积物氮“源”和氮“汇”的功能。而在静态条件下,蓝藻衰亡沉降的初期沉积物-水界面缺氧,抑制硝化作用,进而间接抑制了反硝化作用,在分解后期,由于上覆水逐渐复氧,硝化和反硝化作用增强。因此,蓝藻水华在衰亡的过程中,沉积物的理化性质及微生物等因素相互作用,共同影响着氮的迁移转化。更多还原

【Abstract】 When exogenous nitrogen pollution in lake is effectively controlled,the release of endogenous nitrogen from sediments is the key factor affecting eutrophication and causing algal blooms.Neverthless,the study on the mechanisms of the effect that the decomposition of algal blooms on nitrogen migration,transformation,and endogenous release in sediments is still insufficient.Based on this,Lake Taihu has been the object of this study.We combined field investigations and indoor simulations,applied microelectrode technique,diffuisive grandients in thin-films（DGT）technique,high-resolution peepers（HR-peeper）technique and molecular biology technique.The aims of this study were to obtain the spatial distribution characteristics of nitrogen at the sediment-water interface of Lake Taihu,clarify the influence of various physicochemical properties on nitrogen distribution at sediment-water interface,and reveal the mechanism of the decomposition of algal blooms on the migration and transformation of nitrogen at the sediment-water interface.The main conclusions are as follows:（1）The field investigation of Lake Taihu showed that the distribution of nitrogen at the sediment-water interface of Lake Taihu exhibited strong spatial heterogeneity.The average concentrations of NH₄⁺-N、NO₃^--N and NO₂^--N at all sampling sites ranged from 3.32 to 13.60 mg L^-1,2.01 to 6.58 mg L^-1 and 0.031 to 0.108 mg L^-1,respectively.The average concentrations of NH₄⁺-N in the sediment of Zhushan Bay where algal blooms outbreak was most serious was the highest,and the center of the lake was the lowest.The average concentrations of NO₃^--N at the the center of the lake was the highest,and at the Meiliang Bay was the lowest.The average concentrations of NO₂^--N at the southern coastal area was the highest,and at the Gonghu Bay was the lowest.The average concentrations of NO₂^--N at the southern area of Lake Taihu as a whole was higher than the northern area where algal blooms outbreak was most serious.The diffusive fluxes of NH₄⁺-N、NO₃^--N and NO₂^--N at all sampling sites ranged from-72.72 to 109.71 mg m^-2 d^-1,-40.13 to 34.26 mg m^-2 d^-1,and-2.05 to 0.78 mg m^-2 d^-1,respectively.The sediment at Lake Taihu is mainly the source of NH₄⁺-N,and the sink of NO₃^--N and NO₂^--N.（2）During the decomposition of algae blooms,wind and wave disturbances promote the rate of sediment-water interface reoxygenation and organic matter degradation,which in turn promotes nitrification and denitrification.Under the condition of strong and weak wind and wave disturbances,the diffusion flux of NH₄⁺-N at the sediment-water interface ranged from 60.44 to 437.21 mg m^-2 d^-1,and 23.56 to130.30 mg m^-2 d^-1,respectively.Under the condition of static,the diffusion flux of NH₄⁺-N at the sediment-water interface during the degradation of fresh algae and dead algae ranged from-75.08 to 127.86 mg m^-2 d^-1,and-27.11 to 84.08 mg m^-2 d^-1,respectively.The diffusion flux under disturbance condition is much greater than that under static condition.Therefore,wind and wave disturbances promote nitrogen diffusion,and the stronger the disturbance,the greater the intensity of nitrogen diffusion.This could lead to an increase in the release of NH₄⁺-N from the sediment into the overlying water,and ultimately results in the recurrence of algal blooms in the next year.（3）Field investigations and indoor simulations experiments have shown that the NH₄⁺-N concentration at the sediment-water interface exhibits two distribution pattern.When there is a steep concentration gradient at the sediment-water interface,it indicates that the algae bloom is in its early stage,and the algae have not yet settled in large quantities,or the accumulated algae debris at the sediment-water interface has already been decomposed.When there is a pattern with a concentration peak at the sediment-water interface,it indicated that a large amount of algal or other plant debris has accumulated at the sediment-water interface and is in the decomposition stage.The wider the concentration peak,the thicker the accumulated algal debris.Thus,the changes in NH₄⁺-N concentration patterns could be used to indicate the extent of decomposition of algal blooms and the level of eutrophication in freshwater ecosystems.（4）There is no significant differences in the composition of the large amounts of DOM produced during the decomposition of living algal and dead algal,the main components of DOM were humic and protein-like.These macromolecular DOM released large amounts of NH₄⁺-N during mineralisation,which leads to the dominance of ammonia-oxidizing bacteria（AOB）in nitrifying microorganisms in sediments.In addition,there is no significant difference in nitrogen concentration,nitrifying and denitrifying microorganisms in sediment columns with the addition of living algal and dead algal,indicating that the intercellular microorganisms in living algal have no significant effect on nitrogen removal and the microorganisms in sediments.In conclusion,the decay of algal blooms affected the migration and transformation of nitrogen at the sediment-water interface.In the case of wind and wave disturbance,sediment suspension and endogenous nitrogen release were strong.The algal blooms decay increased the diffusive flux of nitrogen,and also changed the function of sediment nitrogen sources and sinks.Under the static conditions,the initial stage of cyanobacterial decay and deposition would lead to anoxia at the sediment-water interface,which inhibited nitrification and then indirectly inhibitited denitrification.In the later stages of decomposition,nitrification and denitrification would be enhanced due to the gradual reoxygenation of the overlying water.Thus,during the decay of algal blooms,the physicochemical properties of sediments and microbial factors interacted with each other to affect the migration and transformation of nitrogen.更多还原