长江口沉积物有机碳及溶解有机质结构对外源磷输入的响应

Response of sediment organic carbon and dissolved organic matter structure to exogenous phosphorus input in the Yangtze River Estuary

采用泥(沉积物)水质量比约为1∶1、周期为56 d的室内模拟试验系统设置包括对照组在内的6个不同质量浓度的过磷酸钠试验组,研究不同水平的外源磷输入所引起的沉积物中总有机碳(Total organic carbon,TOC)含量的变化特征。同时,运用紫外-可见光吸收光谱方法研究含磷物质的加入对沉积物中溶解有机质结构变化的影响。实验结果显示:各实验组沉积物TOC含量在第56天比对照组分别减少了3.60%、7.08%、8.09%、9.33%、11.80%,表明随着外源磷输入量增加,长江口沉积物中TOC加速分解。在试验周期内,沉积物溶解有机质的腐殖化程度、芳香化程度最大值与磷的输入量呈正相关。溶解有机质分子量和芳香环结构变化幅度与外源磷的输入量呈正相关,说明外源磷输入量的增大能够加快沉积物溶解有机质的变化。随着实验时间的增加,不同磷水平溶解有机质的腐殖化程度和芳香化程度呈现先上升后下降的趋势,而溶解有机质的分子量随着时间的增加逐渐减小,其芳香环取代基上的取代基逐渐替换为更具有活性的官能团,表明沉积物有机碳含量减少过程中先生成腐殖质,随着腐殖质继续分解,其腐殖化程度降低,且腐殖化程度和芳香化程度具有同一性。

The content of total organic carbon(TOC)in the sediments of the Yangtze River Estuary will change with the input of exogenous phosphorus.An indoor simulation test system with a mud(sediment)water mass ratio of about 1:1 and a period of 56 days is adopted.Six concentration gradient test groups,including the control group,were set up to study the change characteristics of TOC content in sediments caused by different levels of exogenous phosphorus input.At the same time,UV-Vis absorption spectroscopy was used to study the effect of phosphorus containing substances on the structural changes of dissolved organic matter in sediments.The experimental results showed that the TOC content in the sediment of each experimental group decreased by 3.60%,7.08%,8.09%,9.33%and 11.80%respectively compared with the control group on the 56th day,indicating that the decomposition of TOC in the sediment of the Yangtze Estuary accelerated with the increase of exogenous phosphorus input.During the test period,the maximum humification degree and aromatization degree of dissolved organic matter in sediments were positively correlated with the input of phosphorus.The molecular weight and aromatic ring structure of dissolved organic matter are positively correlated with the input of exogenous phosphorus,indicating that the increase of exogenous phosphorus input can accelerate the change of dissolved organic matter in sediments.With the increase of test time,the humification degree and aromatization degree of dissolved organic matter with different phosphorus levels increased first,and then began to decline;The molecular weight of dissolved organic matter gradually decreases with the increase of time,and the substituents on its aromatic ring substituents are gradually replaced by more active functional groups.It shows that humus is formed during the reduction of organic carbon content in sediments.As humus continues to decompose,the degree of humification decreases,and the degree of humification is the same as that of aromatization.