Tidal transport from coastal wetlands (“outwelling”), together with riverine fluxes, provide the most important sources of terrigenous organic matter (OM) to the ocean. The flux of dissolved organic carbon (DOC) from the mangrove swamps accounts for 10% of the terrestrial DOC flux to the coastal water. This study examines the sources, distribution, and export of dissolved OM at interannual, seasonal, and diurnal bases along the estuaries located at the Sundarbans, the world’s largest deltaic mangrove and heritage site. Sampling was carried out from the riverine (Hooghly) and mangrove-dominated tidal estuaries (Saptamukhi, Thakuran, Matla), covering all three seasons (pre-monsoon, monsoon, and post-monsoon) during 2012–2017. DOC varied at a broad range, from 109 to 462 μM (n = 146), with higher concentration observed in the Hooghly (383 ± 120 μM, n = 35) than the mangrove estuaries (246 ± 82 to 266 ± 120 μM, n = 111). Non-conservative mixing of DOC along the salinity gradient attested to mangrove input, particularly in the polyhaline waters. Upper and mid estuarine zones of the mangrove estuaries showed slightly higher DOC concentration (270 ± 92 μM, n = 84, salinity range 18–25) than in the mouth (250 ± 85 μM, n = 27, salinity range 26–27), because of the dilution with marine waters having low DOC concentration and shorter water residence time downstream. Seasonally, higher DOC concentration during the post-monsoon might be linked to higher litterfall, promoting leaching of organic compounds to the water. In that connection, colored dissolved organic matter (CDOM) could be a by-product of mangrove litter leaching, and its absorption coefficient (at 350 nm) exhibited non-conservative mixing pattern at wide ranges from 2.5 to 7.6 m⁻¹ (n = 40). CDOM enrichment was observed in the surface water during the low tide when outwelling maximized. Overall, the central and eastern parts of the Indian Sundarbans showed enrichment of more terrigenous type CDOM (evident from optical proxies, e.g., S_275–295 and SUVA₂₅₄) than the western part, probably due to greater mangrove productivity in the eastern side. Flux estimates of DOM resulted in higher yield and export of mangrove-derived DOC but lower export of CDOM to the Bay of Bengal as compared to their riverine transport.

来自沿海湿地的潮汐运输（“外部”）与河流通量一起，为海洋提供了最重要的陆源有机质（OM）来源。来自红树林沼泽的溶解有机碳（DOC）通量占陆地DOC向沿海水域通量的10％。这项研究研究了世界最大的三角洲红树林和遗产地Sundarbans沿河口的年际，季节和日基上溶解的OM的来源，分布和出口。在2012-2017年期间，从河流（Hooghly）和以红树林为主的潮汐河口（Saptamukhi，Thakuran，Matla）进行了采样，涵盖了所有三个季节（季风前，季风和季风后）。DOC的变化范围很广，从109到462μM（ñ = 146），而在Hooghly（383±120μM， ñ = 35）比红树林河口（246±82至266±120μM， ñ= 111）。DOC沿盐度梯度的非保守混合证明了红树林的输入，特别是在多卤水中。红树林河口的上河口区和中河区显示DOC浓度略高（270±92μM，ñ = 84，盐度范围为18–25），而不是口腔中的盐度（250±85μM， ñ= 27，盐度范围为26-27），这是因为用低DOC浓度和较短的下游水停留时间的海水进行了稀释。在季节性上，季风后的DOC浓度较高可能与凋落物增多有关，从而促进了有机化合物向水中的浸出。在这方面，有色溶解有机物（CDOM）可能是红树林垃圾浸出的副产物，其吸收系数（在350 nm处）在2.5至7.6 m ^-1的宽范围内表现出非保守的混合模式（ñ= 40）。在潮汐最大化时，在退潮期间在地表水中观察到CDOM富集。总体而言，印度松达尔班山脉的中部和东部地区比西部地区富含更多陆源类型的CDOM（来自光学代用品，例如S _{275 – 295}和SUVA ₂₅₄），这可能是由于东部的红树林生产力更高。根据DOM的通量估算，与河流运输相比，来自红树林的DOC的产量更高，出口量更大，但向孟加拉湾的CDOM出口量却更低。