城市景观河道中藻华暴发对水体中DOM特征的影响

摘要

In urban landscape rivers ,algal bloom caused by excess nutrients broke out regularly in summer due to the acceptance of wastewater from different sources .The characteristics of DOM in the river water were changed because of the broken out of the algae bloom ,and thus the migration and transformation of pollutants ,which affected by DOM in the river water ,was affected as well .In this study ,the water samples before and after the algal blooms in the main stream of the Haihe River were collected to study the influence of outbreak of algae blooms on DOM in water bodies in urban landscape river .The results showed that the content of DOM in the river water increased from 26.47 to 38.20 mg · L -1 .The contents of TN ,NH+4 -N and TON in the river water were 3.1 times ,2.5 times and 4.2 times higher than those before the algal bloom broke out ,respectively ,while ,the contents of TP and NO3-- remained stable .C/N ratio decreased from 18.51 to 6.39 while N/P ratio increased from 5.69 to 20.10 .The source of DOM changed from terrestrial source mainly to aquatic source mainly and the water also showed a gradual trend to phosphorus limit .Three-dimensional fluorescence spectra showed that the composition of DOM changed from the source of complex organic matter to the source of algae organic matter .The results of UV absorbance indicated that the molecular structure of DOM was changed to be more complex .However ,the content of humus-liked in water decreased while the content of protein-liked increased .Ultrafiltration experiments were also conducted to study the molecular weight of DOM before and after algae blooms .It was found that DOM with small molecular weight had the dominates ,in which DOM with molecular weight less than 10 kD accounted for more than 80% of the total DOM .With the increase of molecular weight ,the intensity of all peaks of three-dimensional fluorescence spectra showed an increasing trend and the UV absorbance also indicated that the high molecular weight DOM might contain more aromatic compounds .The results suggested that the role of DOM should be paid attention to the eutrophication in urban landscape river water .Especially when external pollutants are controlled ,the contribution of DOM degradation to eutrophication should be fully considered .%城市景观河道由于接纳了不同来源的废水造成水体富营养化,因此在夏季经常暴发藻华.藻华暴发改变了水体中DOM的性状,进而影响到水体中污染物的迁移转化行为.本研究以天津市海河干流为例,采集藻华暴发前后水体样品,研究城市景观河道中藻华暴发对水体中DOM的影响.结果表明:藻华暴发后,水体中DOM的含量从26.47 mg·L-1增加到38.20 mg·L-1,水体中的TN,NH+4-N和TON的含量也分别为暴发前的3.1倍、2.5倍和4.2倍,但是TP和NO3--N的含量保持稳定.C/N比值从18.51降低到6.39,而N/P比值则从5.69增加到20.10.藻华暴发使得DOM的来源从以陆源为主转变为以内源为主,水体也表现出一个逐步向磷限制转变的过程.三维荧光图谱结果显示藻华暴发后,D O M的成分从较为复杂的多种来源的有机质转变为藻类为主的有机质,而紫外特征光谱结果表明藻华暴发后DOM分子结构也从简单转变为复杂,但是水体中的腐殖质物质的含量有所下降,而类蛋白物质的含量出现了上升.利用超滤装置研究藻华暴发前后水体中不同分子量的DOM特征后发现,藻华暴发前后水体中DOM都主要以小分子的DOM为主,分子量小于10 kD的DOM占到了总的DOM的80%以上,随着分子量的增大,三维荧光特征峰强度都出现了升高趋势,而紫外特征吸收光谱也表明大分子量的DOM中可能含有更多的芳香族化合物.研究结果表明,在研究城市景观河道水体富营养化过程中要注意DOM在其中的作用,尤其是当外源污染物得到控制时,要充分考虑DOM降解对富营养化的贡献.