Hypoxia has occurred worldwide in coastal and marginal oceans. The redox condition has recently garnered major interest as a favorable condition for delivering sedimentary organic matter to the water column. In this study, we measured the fluorescence of fluorescent dissolved organic matter (FDOM) in brackish Lake Shihwa, Korea, in which hypoxic conditions are typically observed during summer. Especially, fluorescent intensities of the humic FDOM (FDOM_H) were relatively high during summer, with a relatively lower dissolved oxygen (DO) level, and exponentially increased with decreasing DO concentrations. The results indicated that the production of FDOM_H is associated with anaerobic processes. It was further supported by a significantly positive relationship between FDOM_H and ammonium. Based on the relatively low values of redox potential (up to 60.0 mV) and high concentration of phosphate with the low DO level, this enrichment of FDOM_H seems to be linked to the input of anoxic porewater. Using a simple schematic diagram, the contribution of FDOM_H from reducing environments is comparable to that from stream water, which is known to be a major source in coastal regions. This study highlights that the redox condition is a key factor contributing to the production of FDOM_H in coastal marine environments.

中文翻译：

---

Shihwa湖中腐殖质荧光溶解的有机物质的分布：氧化还原条件的作用

缺氧已经在世界范围内的沿海和边缘海域发生。氧化还原条件最近作为将沉积有机物输送到水柱的有利条件而引起了广泛关注。在这项研究中，我们测量了韩国咸淡湖中的荧光溶解有机物（FDOM）的荧光，在夏季通常会观察到低氧条件。特别地，在夏季，腐殖质FDOM（FDOM _H）的荧光强度相对较高，溶解氧（DO）水平相对较低，并且随着DO浓度的降低呈指数增加。结果表明，FDOM _H的产生与厌氧过程有关。FDOM _H之间的显着正相关进一步支持了这一点。和铵。基于相对较低的氧化还原电势值（高达60.0 mV）和高浓度的磷酸盐以及低的DO水平，FDOM _H的富集似乎与缺氧孔隙水的输入有关。使用简单的示意图，FDOM _H在还原性环境中的贡献与溪流水相当，溪流水是沿海地区的主要水源。这项研究强调，氧化还原条件是导致沿海海洋环境中FDOM _H产生的关键因素。