Abstract Photochemically-released dissolved organic matter (PR-DOM) from resuspended sediments is an understudied flux of dissolved organic carbon (DOC) and nutrients that has the potential to influence estuarine microbial food webs. There is currently limited knowledge on the composition, lability, and biological alterations of this material once released into the water column. This study addresses the composition and fate of PR-DOM from resuspended sediments of the Cape Fear River estuary (CFRE) in southeastern North Carolina. Six-hour irradiation released 22-44% more DOC, and PR-DOM was of a different composition and enhanced lability relative to dark controls. Irradiation led to release of humic-like DOM, indicated by increased chromophoric and fluorescent dissolved organic matter, substantial increases in the humification index, and production of oxidized higher molecular weight compounds with higher aromaticity relative to dark controls. However, DOM of lower molecular weight and reduced aromaticity was produced as well – indicated by increased spectral slope (S275-295) and decreased specific ultraviolet absorbance at 254 nm (SUVA254) relative to dark controls. This latter pool of DOM may be linked to nitrogen-(N-) and sulfur-(S-)containing compounds that were photodegraded or biologically altered during irradiation experiments. In subsequent lability incubation experiments, degradation of PR-DOM was more rapid than DOM released from dark controls, especially for marine humic-like fluorophores. Incubation of PR-DOM led to an 8-fold increase in molecular formulas that were unique to light-exposed DOM relative to unexposed DOM, the majority of which were N- and S-containing compounds. Given that coastal sediments are typically enriched in these nutrients, N- and S-containing compounds appear to influence the lability of PR-DOM from estuarine resuspended sediments. Estimated lability of photoreleased DOC from resuspension events in the CFRE is comparable to previous bioavailable DOC estimates and suggest that episodic photochemical interactions with sediments may act as a previously unrecognized source of labile DOC to bacteria and plankton in these coastal waters.

中文翻译：

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从重悬河口沉积物中光化学释放的溶解有机物的组成和不稳定性

摘要 再悬浮沉积物中光化学释放的溶解有机物 (PR-DOM) 是一种尚未得到充分研究的溶解有机碳 (DOC) 和营养物质通量，有可能影响河口微生物食物网。目前对这种材料一旦释放到水体中的成分、不稳定性和生物变化的了解有限。这项研究解决了北卡罗来纳州东南部开普菲尔河河口 (CFRE) 重新悬浮沉积物中 PR-DOM 的组成和归宿。6 小时辐照释放的 DOC 多 22-44%，PR-DOM 具有不同的成分，并且相对于黑暗对照增强了不稳定性。辐照导致类腐殖质 DOM 的释放，表现为发色和荧光溶解有机物增加，腐殖化指数显着增加，和相对于深色对照具有更高芳香性的氧化更高分子量化合物的产生。然而，也产生了较低分子量和降低的芳香性的 DOM - 相对于深色对照，光谱斜率增加 (S275-295) 和 254 nm 处的特定紫外线吸收率 (SUVA254) 降低表明。后一种 DOM 池可能与含氮 (N-) 和硫 (S-) 的化合物有关，这些化合物在辐照实验期间被光降解或生物改变。在随后的不稳定性孵化实验中，PR-DOM 的降解比黑暗对照释放的 DOM 更快，尤其是对于海洋类腐殖质荧光团。PR-DOM 的孵化导致与未暴露的 DOM 相比，暴露于光的 DOM 独有的分子式增加了 8 倍，其中大部分是含 N 和 S 的化合物。鉴于沿海沉积物通常富含这些营养物质，含 N 和 S 的化合物似乎会影响河口再悬浮沉积物中 PR-DOM 的不稳定性。CFRE 中再悬浮事件中光释放 DOC 的估计不稳定性与之前的生物可利用 DOC 估计值相当，并表明与沉积物的偶发光化学相互作用可能是这些沿海水域中细菌和浮游生物不稳定 DOC 的先前未识别来源。