Coastal estuaries and adjacent continental shelf seas constitute vital global carbon reservoirs, and the sources and transformations of organic carbon in these regions are crucial to global biogeochemical cycles and climate change. This study investigated the total organic carbon (TOC), total nitrogen (TN), black carbon (BC), and their stable carbon and nitrogen isotopes (δ15NTN, δ13CTOC, δ13CBC) in the surface sediments of the Pearl River Estuary (PRE) and its adjacent northern South China Sea (NSCS) aiming to assess the impact of human activities on organic carbon dynamics in these areas. Results showed that the highest TOC concentrations occurred in the inner PRE due to intense human activities, and decreased seaward. The west side of the PRE exhibited higher TOC levels than the east side, which was attributed to differences in hydrodynamic processes and human activities. The westward flow of the Pearl River diluted water, which carried terrestrial organic matter inputs due to the influence of the Coriolis effect and intense local human activities, was a primary contributor to higher TOC levels on the west side (terrestrial source). In contrast, increased productivity and intensive mariculture activities on the east side predominated as sources of organic matter (marine source). Similar to the TOC, BC and TN sources were mainly influenced by human activities. δ15NTN distribution shows that TN in the east side of PRE mainly originated from industrial wastewater input from the Pearl River, while in the east side TN was mainly from domestic sewage discharge. Additionally, BC sources have shifted from primarily biomass combustion in the 1990s to fossil fuel emissions presently. Isotopic analysis revealed that over 70% of BC originated from fossil fuel inputs and C3 plant combustion, highlighting the significant influence of human activities in the PRE and adjacent NSCS, and underscoring the need for effective management and protection of the eco-environment in these regions.

中文翻译：

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珠江口及其邻近南海表层沉积物中有机碳和黑碳的来源分配——来自稳定碳氮同位素的见解


沿海河口和邻近的大陆架海构成了重要的全球碳库，这些地区有机碳的来源和转化对全球生物地球化学循环和气候变化至关重要。本研究调查了珠江口及其邻近的南海北部 （NSCS） 表层沉积物中的总有机碳 （TOC）、总氮 （TN）、黑碳 （BC） 及其稳定的碳和氮同位素 （δ15NTN、δ13CTOC、δ13CBC），旨在评估人类活动对这些地区有机碳动态的影响。结果表明，由于人类活动的激烈，TOC 浓度最高出现在 PRE 内部，并且向海降低。PRE 西侧的 TOC 水平高于东侧，这归因于水动力过程和人类活动的差异。由于科里奥利效应和当地强烈人类活动的影响，珠江稀释水向西流动，携带了陆地有机物输入，是导致西侧（陆地来源）TOC 水平较高的主要因素。相比之下，东部生产力的提高和集约化海水养殖活动是有机物（海洋来源）的主要来源。与 TOC 类似，BC 和 TN 来源主要受人类活动的影响。δ15NTN 分布表明，PRE 东侧的 TN 主要来源于珠江工业废水输入，而东侧的 TN 主要来自生活污水排放。此外，BC 来源已从 1990 年代的主要生物质燃烧转变为目前的化石燃料排放。 同位素分析显示，超过 70% 的 BC 来自化石燃料输入和 C3 植物燃烧，突出了人类活动对 PRE 和邻近 NSCS 的重大影响，并强调了有效管理和保护这些地区生态环境的必要性。