Wetlands export chromophoric dissolved organic matter (CDOM) to estuaries, where CDOM is removed and transformed through biotic and abiotic process, subsequently impacting nutrient cycling, light availability, ecosystem metabolism, and phytoplankton activity. We examined the bioavailability and photoreactivity of CDOM exported from four Chesapeake Bay tidal marshes across three seasons and along an estuarine salinity gradient using three incubation treatments: 14‐day microbial (MD), 7‐day combined photochemical/microbial (PB + MD), and 7‐day microbial incubation after photobleaching (MD after PB). CDOM absorption at 300 nm (a_CDOM300) and dissolved organic carbon (DOC) concentrations showed strong seasonality, with minima in winter, but CDOM quality (absorption spectral slopes, fluorescence component ratios) was less variable seasonally. PB + MD over 7 days decreased a_CDOM300 (−56.0%), humic‐like fluorescence (−67.6%), and DOC (−17.8%), but increased the spectral slope ratio S_R (=S_275–295/S_300–350) (+94.8%), suggesting a decrease in CDOM molecular weight. Photochemistry dominated the PB + MD treatment. Photoreactivity was greater during the winter and in marsh/watershed versus down‐estuary sites, likely due to less previous light exposure. Prior photobleaching increased the bioavailability of marsh‐exported CDOM, resulting in a greater loss of a_CDOM300 and DOC, and a greater increase in humic‐like fluorescence (−6.0%, −5.9%, and +18.4% change, respectively, over 7‐day MD after PB incubations, vs. −2.8%, −5.5%, and +2.6% change, respectively, over 14‐day MD incubations). CDOM exported from a marsh downstream of a major wastewater treatment plant showed the greatest photoreactivity and bioavailability. This highlights the significance of human activity on estuarine CDOM quality and biogeochemical cycles.

中文翻译：

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潮汐沼泽中发色团溶解的有机物的光化学和微生物降解

湿地将发色溶解性有机物（CDOM）出口到河口，在河口中通过生物和非生物过程将CDOM去除并转化，从而影响养分循环，光照，生态系统新陈代谢和浮游植物的活动。我们使用以下三种孵化处理方法检查了三个季节在四个季节和沿河口盐度梯度从四个切萨皮克湾潮汐沼泽输出的CDOM的生物利用度和光反应性：14天微生物（MD），7天光化学/微生物联合（PB + MD），光漂白后的7天微生物培养（PB后的MD）。在300nm处吸收CDOM（一个_CDOM300）和溶解的有机碳（DOC）浓度表现出强烈的季节性，冬季极少，但CDOM的质量（吸收光谱斜率，荧光成分比率）在季节性上变化较小。超过7天的PB + MD降低了_CDOM 300（−56.0％），类腐殖质荧光（−67.6％）和DOC（−17.8％），但增加了光谱斜率S _R（= S _275–295 / S _300–350）（+ 94.8％），表明CDOM分子量降低。光化学在PB + MD处理中占主导地位。与以前的河口地区相比，冬季和沼泽/集水区的光反应性更高。现有光漂白增加沼泽出口CDOM的生物利用度，从而导致更大的损失一个_CDOM在PB孵育7天后，腐殖质荧光增加了300和DOC，类腐殖质荧光的增加也更大（分别为-6.0％，-5.9％和+ 18.4％，而-2.8％，-5.5％和2.8％）。在14天的MD孵化中，变化分别为+ 2.6％）。从主要废水处理厂下游的沼泽地出口的CDOM显示出最大的光反应性和生物利用度。这突出了人类活动对河口CDOM质量和生物地球化学循环的重要性。