Research Group for Marine Geochemistry (ICBM - MPI Bridging Group), Institute for Chemistry and Biology of the Marine Environment, Carl von Ossietzky University of Oldenburg , D-26111 Oldenburg, Germany.
Skidaway Institute of Oceanography, Department of Marine Sciences, University of Georgia , Savannah, Georgia 30602-3636, United States.
Environ Sci Technol. 2017 Dec 19;51(24):14144-14154. doi: 10.1021/acs.est.7b03713. Epub 2017 Nov 29.
Sulfidic sediments are a source of dissolved organic sulfur (DOS) to the ocean but the fate of sedimentary DOS in the oxic, sunlit water column is unknown. We hypothesized that photodegradation after discharge from the dark sedimentary environment results in DOS molecular transformation and decomposition. To test this hypothesis, sulfidic porewater from a saltmarsh was exposed to potential abiotic transformations of dissolved organic matter (DOM) in the water column. We quantitatively investigated DOM transformations via elemental analysis and molecularly via ultrahigh-resolution mass spectrometry. Our study indicated that photoreactivity is dependent on DOM elemental composition as DOS molecular formulas were more photolabile than those without sulfur. Prior to solar irradiation, of the 6451 identified molecular formulas in sulfidic porewater, 39% contained sulfur. After 29 days of irradiation, the DOS concentration was depleted from 13 to 1 μM, together with a 9% decrease in the number of DOS molecular formulas. Comparing porewater and oceanic DOS molecular formulas, solar irradiation increased the similarity due to the removal of photolabile DOS formulas not present in the ocean. In conclusion, DOS from sulfidic sediments is preferentially photolabile and solar irradiation can be a potential mechanism controlling the stability and fate of porewater DOS.
硫化物沉积物是海洋中溶解有机硫 (DOS) 的来源，但沉积 DOS 在含氧、阳光充足的水柱中的命运尚不清楚。我们假设从黑暗的沉积环境中排出后，光降解会导致 DOS 分子转化和分解。为了验证这一假设，从盐沼中提取的硫化物孔隙水被暴露于水柱中可能的非生物转化的溶解有机物 (DOM)。我们通过元素分析和超高分辨率质谱技术定量研究了 DOM 的转化。我们的研究表明，光反应性取决于 DOM 的元素组成，因为 DOS 分子公式比不含硫的分子公式更容易光解。在太阳照射之前，在硫化物孔隙水中鉴定出的 6451 个分子公式中，有 39%含有硫。经过 29 天的照射后，DOS 浓度从 13µM 降至 1µM，同时 DOS 分子公式的数量减少了 9%。比较孔隙水和海洋 DOS 分子公式，由于去除了海洋中不存在的光不稳定 DOS 公式，太阳照射增加了它们之间的相似性。总之，来自硫化物沉积物的 DOS 更容易光解，太阳照射是控制孔隙水 DOS 稳定性和命运的潜在机制。
