Purpose

Desorption of phosphorus (P) bound to iron-containing minerals (Fe-P) is a crucial component of the eutrophication process in lakes. However, the main process and regulation mechanism of iron (Fe) and sulfur (S) on P release is little known because of a lack of in situ high-resolution data. High-resolution measurement evidence is needed to assess the availability and diffusion kinetic process of P at the water–sediment interface.

Materials and methods

Soluble reactive phosphate (SRP), ferrous ion (Fe²⁺), and sulfide (S²⁻) fluxes through the water–sediment interface in a freshwater lake were detected using the novel double-sided diffusive gradients in thin films (DGT) technique. Different P forms in solid sediment were also measured using the sequential extraction procedure. The diffusion fluxes across the water–sediment interface and dynamic diffusion parameters between solid sediment and solution were calculated using the DGT-induced fluxes in sediments and soils (DIFS) model.

Results and discussion

There was a clear decrease of the SRP_DGT, Fe²⁺_DGT, and S²⁻_DGT fluxes from ~5 cm sediment depth to the water–sediment interface. The significant positive correlation between SRP_DGT and Fe²⁺_DGT fluxes in the whole profile demonstrates that Fe-P was a vitally important source of labile P in the solution phase. The significant positive fluxes of SRP_DGT and Fe²⁺_DGT indicated upward diffusion from the sediment particle toward the overlying water. This process further indicated the desorption and resupply of SRP and Fe²⁺ from the solid sediment phase and the synergistic effect between these two parameters. In addition, a gentler decline of R curves fitted with the DIFS model was found as the sediment depths increased, which suggesting the continuous resupply process from solid phase to pore water, especially under anaerobic conditions.

Conclusions

The novel DGT technique in combination with DIFS analysis confirmed the considerable remobilization and transport capacity of labile P fractions including loosely adsorbed MgCl₂-P and reductive Fe-P. These pools can diffuse from sediment particles to the interstitial and the overlying water, and can be further assimilated by organisms in shallow lacustrine ecosystem.

中文翻译：

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高分辨率DGT技术评估水-沉积物界面中磷的有效性和扩散动力学过程

目的

与含铁矿物质（Fe-P）结合的磷（P）的解吸是湖泊富营养化过程的关键组成部分。然而，由于缺乏原位高分辨率数据，铁（Fe）和硫（S）对磷释放的主要过程和调控机制鲜为人知。需要高分辨率的测量证据来评估水-沉积物界面上磷的有效性和扩散动力学过程。

材料和方法

使用新型的薄膜双面扩散梯度（DGT）技术检测了淡水湖中穿过水-沉积物界面的可溶性反应性磷酸盐（SRP），亚铁离子（Fe ²⁺）和硫化物（S ²⁻）通量。固体沉淀物中不同的P形式也使用顺序萃取程序进行了测量。利用DGT引起的沉积物和土壤中的通量（DIFS）模型，计算了水-沉积物界面上的扩散通量以及固体沉积物和溶液之间的动态扩散参数。

结果和讨论

从约5 cm的沉积深度到水-沉积物界面，SRP _DGT，Fe ²⁺ _DGT和S ^2- _DGT通量明显减少。SRP _DGT和Fe ²⁺ _DGT通量之间的显着正相关关系表明，Fe-P是固溶相中不稳定P的至关重要的来源。SRP _DGT和Fe ²⁺ _DGT的显着正通量表明从沉积物颗粒向上覆水向上扩散。此过程进一步表明SRP和Fe ²⁺的解吸和再供应从固体沉积物相和这两个参数之间的协同作用。此外，随着沉积物深度的增加，发现符合DIFS模型的R曲线出现了较缓和的下降，这表明从固相到孔隙水的连续补给过程，尤其是在厌氧条件下。

结论

新的DGT技术与DIFS分析相结合，证实了不稳定的P部分（包括松散吸附的MgCl ₂ -P和还原性Fe-P）的相当大的迁移和转运能力。这些池可以从沉积物颗粒扩散到间隙和上覆的水中，并且可以被浅湖相湖泊生态系统中的生物进一步吸收。