Purpose

The occurrence of harmful algae blooms has been increasing in large lakes worldwide. The mechanism of heavy metals mobilization in sediments during algae blooms is not well understood. As a major pollutant in the sediments of Taihu Lake, cobalt (Co) has been selected to study heavy metal mobilization during algae blooms.

Materials and methods

Rhizon and HR-Peeper sampling techniques have been used for in situ investigation and indoor simulation experiments to collect information on dissolved Co, manganese (Mn), and UV absorbance at 254 nm (UV₂₅₄) in sediments. Excitation–emission matrix (EEM) was combined with parallel factor (PARAFAC) to determine the change of dissolved organic matter (DOM) components during algae blooms. The chemical morphology of Co in pore water was analyzed by visual MINTEQ model. The Stern–Volmer model was used to characterize the stability of different DOM components and Co(II).

Results and discussion

Algae blooms significantly increased the dissolved Co concentration in sediments. The release of Co was closely related to DOM in the algae bloom sediments, which was reflected by the similar distribution and significant positive correlation between the dissolved Co and DOM in pore water, during both in situ and laboratory simulation algae blooms experiments. On the other hand, the saturation of oxygen in the sediment–water interface (SWI) rapidly decreased from 100 to 0% during algae blooms, resulting in high mobilization of Co and reduction of Mn oxides in sediments. This was supported by the simultaneous increase of dissolved Co and Mn and significant positive correlation between dissolved Co and Mn in the simulation aerobic–anaerobic sediments. The transformation of most Co(II) into DOM-Co(II) complexes, as calculated by the Visual MINTEQ model, further demonstrated that the mobilization of Co was mainly controlled by the DOM content in the sediments during algae blooms. Further studies revealed that tyrosine-like substance released by algae played a major role in their complexation with Co, possibly due to their relatively high content and high stability after binding Co.

Conclusion

The mobilization of Co in sediments during algae blooms was mainly controlled by DOM through complexation, reflected by the observation that dissolved Co concentration and UV₂₅₄ increased simultaneously and had significant positive correlation during in situ monitoring and indoor simulations experiments. More than 80% of dissolved Co in the pore water during algae blooms was DOM-Co complexes, supporting this conclusion. It was further observed that tyrosine-like substances played an important role in Co complexation.

中文翻译：

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藻类开花期间钴在湖泊沉积物中的迁移机理

目的

在世界范围内的大型湖泊中，有害藻华的发生率一直在上升。藻类大量繁殖期间沉积物中重金属动员的机理尚不清楚。作为太湖沉积物中的主要污染物，已选择钴（Co）来研究藻华期间的重金属动员。

材料和方法

Rhizon和HR-Peeper采样技术已用于现场调查和室内模拟实验，以收集有关沉积物中溶解的Co，锰（Mn）和254 nm（UV ₂₅₄）的UV吸收率的信息。激发-排放矩阵（EEM）与并行因子（PARAFAC）相结合，确定藻华期间溶解性有机物（DOM）组分的变化。用目测MINTEQ模型分析孔隙水中Co的化学形态。Stern-Volmer模型用于表征不同DOM成分和Co（II）的稳定性。

结果和讨论

藻类大量繁殖显着增加了沉积物中溶解的钴浓度。在原位和实验室模拟藻华实验中，藻水华沉积物中Co的释放与DOM密切相关，这反映在孔隙水中溶解的Co和DOM与溶解水之间相似的分布和显着正相关。另一方面，藻类大量繁殖期间，沉积物-水界面（SWI）中的氧饱和度从100％迅速降低至0％，从而导致Co的高迁移率和沉积物中Mn氧化物的还原。模拟需氧-厌氧沉积物中溶解态Co和Mn的同时增加以及溶解态Co和Mn之间的显着正相关为这提供了支持。大多数Co（II）转变为DOM-Co（II）配合物，视觉MINTEQ模型计算得出的结果进一步证明，藻类开花期间，Co的迁移主要受沉积物中DOM含量的控制。进一步的研究表明，藻类释放的酪氨酸样物质在与Co的络合中起主要作用，这可能是由于其含量较高且结合Co后具有较高的稳定性。

结论

在藻类开花过程中，沉积物中钴的迁移主要受DOM通过络合作用的控制，这反映在原位监测和室内模拟实验中，溶解的Co浓度和UV ₂₅₄同时增加，并且具有显着的正相关关系。在藻类开花期间，孔隙水中超过80％的溶解Co是DOM-Co络合物，支持了这一结论。进一步观察到，类似酪氨酸的物质在Co络合中起重要作用。