Seasonal dynamics of dissolved organic matter in a small tropical estuary-coastal bay continuum: distribution, transformation, flux, and global perspectives

IF 2.8 2区 生物学 Q1 MARINE & FRESHWATER BIOLOGY
Pengfei Liu, Kuan Jiang, Qi Tan, Fajin Chen, Renming Jia, Chao Wang
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Abstract

The export and transformation of riverine dissolved organic matter (DOM) at the river-sea interface are critical to understanding carbon budgets in tropical regions, yet remain underexplored in small watersheds. This study analyzed dissolved organic carbon (DOC), chromophoric (CDOM), and fluorescent DOM (FDOM) over five cruises from summer 2021 to summer 2022 in the Suixi Estuary-Zhanjiang Bay continuum, a eutrophic tropical transition zone in the northwestern South China Sea. Seasonal variations were pronounced for DOM in the continuum and two endmembers. Freshwater DOM, dominated by terrestrial organic materials, was closely tied to soil leaching and erosion, correlating with precipitation patterns. Conversely, seawater DOM, enriched in protein-like FDOM, varied with the West-Guangdong Coastal Current and its associated primary production. Linear decreases in DOM with increasing salinity indicate that conservative mixing largely shapes DOM distributions in the continuum, especially for humic-like FDOM. Non-conservative processes, including flocculation, phytoplankton production, and microbial transformation, variably alter DOM components across seasons. The Suixi River in summer contributed considerably but disproportionately to the annual DOM flux (47-59%), due to intense soil leaching processes that mobilize refractory terrigenous DOM. The deviation observed in the Suixi River’s DOC-CDOM relationship from that of global rivers, coupled with a distinctive single-peak pattern between the carbon-specific absorption coefficient and water yield in global rivers, highlights the critical role of watershed nature in influencing river-exported DOM composition. The notably high DOC and CDOM yields for the Suixi River further emphasize the importance of small, tropical rivers in shaping the estuarine and coastal carbon budget.
小型热带河口-海岸湾连续体中溶解有机质的季节动态:分布、转化、通量和全球视角
河海界面上河流溶解有机质(DOM)的输出和转化对了解热带地区的碳收支至关重要,但在小流域仍未得到充分研究。本研究分析了2021年夏季至2022年夏季在南海西北部富营养化热带过渡带——随西河口-湛江湾连续带进行的5次巡航中溶解有机碳(DOC)、显色性(CDOM)和荧光性DOM (FDOM)。DOM在连续体和两个端元中存在明显的季节变化。淡水DOM以陆生有机质为主,与土壤淋滤和侵蚀密切相关,与降水模式相关。相反,海水DOM富含蛋白样FDOM,随粤西海流及其相关初级生产而变化。DOM随盐度的增加呈线性下降,表明保守混合在很大程度上塑造了连续体中DOM的分布,特别是对于腐殖质样的FDOM。非保守过程,包括絮凝、浮游植物生产和微生物转化,会在不同季节改变DOM成分。由于强烈的土壤淋滤过程调动了难降解的陆源DOM,因此夏季的睢溪河对年DOM通量贡献较大,但不成比例(47-59%)。绥溪河的DOC-CDOM关系与全球河流的差异,以及全球河流碳比吸收系数与水量之间独特的单峰模式,凸显了流域性质在影响河流输出DOM组成中的关键作用。绥溪河显著的高DOC和CDOM产量进一步强调了小型热带河流在形成河口和沿海碳收支中的重要性。
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来源期刊
Frontiers in Marine Science
Frontiers in Marine Science Agricultural and Biological Sciences-Aquatic Science
CiteScore
5.10
自引率
16.20%
发文量
2443
审稿时长
14 weeks
期刊介绍: Frontiers in Marine Science publishes rigorously peer-reviewed research that advances our understanding of all aspects of the environment, biology, ecosystem functioning and human interactions with the oceans. Field Chief Editor Carlos M. Duarte at King Abdullah University of Science and Technology Thuwal is supported by an outstanding Editorial Board of international researchers. This multidisciplinary open-access journal is at the forefront of disseminating and communicating scientific knowledge and impactful discoveries to researchers, academics, policy makers and the public worldwide. With the human population predicted to reach 9 billion people by 2050, it is clear that traditional land resources will not suffice to meet the demand for food or energy, required to support high-quality livelihoods. As a result, the oceans are emerging as a source of untapped assets, with new innovative industries, such as aquaculture, marine biotechnology, marine energy and deep-sea mining growing rapidly under a new era characterized by rapid growth of a blue, ocean-based economy. The sustainability of the blue economy is closely dependent on our knowledge about how to mitigate the impacts of the multiple pressures on the ocean ecosystem associated with the increased scale and diversification of industry operations in the ocean and global human pressures on the environment. Therefore, Frontiers in Marine Science particularly welcomes the communication of research outcomes addressing ocean-based solutions for the emerging challenges, including improved forecasting and observational capacities, understanding biodiversity and ecosystem problems, locally and globally, effective management strategies to maintain ocean health, and an improved capacity to sustainably derive resources from the oceans.
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