School of Environment, Tsinghua University, Beijing 100084, China.
Shenzhen Ecological and Environmental Monitoring Center of Guangdong Province, Shenzhen 518049, China.
Sci Total Environ. 2024 Nov 20;952:175855. doi: 10.1016/j.scitotenv.2024.175855. Epub 2024 Aug 28.
Highly urbanized coastal ecosystems are vital in the global carbon budget. However, there are limited researches on carbon flux gradients in these nearshore areas, considering both natural and anthropogenic influences. Through on-site measurements and field samplings during wet-to-dry season in 2023, this study investigated spatial variations and factors affecting carbon fluxes, focusing on the impacts of salinity and eutrophic status in five geographically connected coastal waters of the Guangdong-Hong Kong-Macau Greater Bay Area (GBA). By estimating carbon exchange at land-sea-air interface, dominant processes in carbon dynamics were identified as well. Results showed that partial pressure of CO (pCO) varied from 391 to 2290 μatm, and sea-air CO exchange fluxes (FCO) ranged from -3.07 to 70.07 mmol m d, indicating significant geographical distinctions among five coastal waters of the GBA. The total carbon transport from rivers to these nearshore waters was approximated at 6.44 Tg C yr, with the Pearl River (PR) contributing 99.7%, primarily in dissolved forms. Atmospheric CO release was calculated at 0.29 Tg C yr for studied five coastal waters, primarily as carbon sources, except for Dapeng Bay (DPB) as a sink. CO emissions inversely correlated with salinity, yet positively with eutrophication status, particularly in river-dominated estuaries. Moreover, CO flux decreased 23 times as eco-status shift from eutrophic to non-eutrophic. River plumes, terrestrial pollutant inputs, and economic structure were underlying drivers, influencing carbon species concentrations and fluxes. Elevated CO concentrations in eutrophic coastal waters were mainly attributed to terrestrial carbon and nutrients inputs, supporting active biological respiration and microbial decomposition. Conversely, carbon dynamics potentially depend on the balance of respiration and photosynthesis in non-eutrophic coastal waters. This study offers high geographic precision and specificity of carbon species, and provides land-sea integration insight to understand carbon dynamic mechanisms, promoting advancements in water quality management and climate mitigation.
高度城市化的沿海生态系统对全球碳预算至关重要。然而，考虑到自然和人为因素的影响，对于这些近岸地区的碳通量梯度，相关研究还很有限。本研究通过 2023 年干湿季的现场测量和实地采样，调查了碳通量的空间变化及其影响因素，重点研究了盐度和富营养化状态对粤港澳大湾区（GBA）五个地理相连的沿海海域的影响。通过估算陆海气界面的碳交换，确定了碳动力学中的主要过程。结果表明，CO 的分压（pCO）从 391 到 2290 μatm 不等，海气 CO 交换通量（FCO）从-3.07 到 70.07 mmol m d 不等，表明 GBA 五个沿海海域之间存在显著的地域差异。从河流向这些近岸海域输送的总碳量约为 6.44 Tg C yr，其中珠江（PR）贡献了 99.7%，主要以溶解形式存在。研究的五个沿海海域的大气 CO 释放量约为 0.29 Tg C yr，主要是碳源，除大鹏湾（DPB）为碳汇。CO 排放与盐度呈负相关，与富营养化状态呈正相关，特别是在河流主导的河口。此外，生态状况从富营养化转变为非富营养化时，CO 通量降低了 23 倍。河涌羽流、陆地污染物输入和经济结构是潜在的驱动因素，影响碳物质浓度和通量。富营养化沿海水域中 CO 浓度升高主要归因于陆地碳和营养物质的输入，支持了活跃的生物呼吸和微生物分解。相反，非富营养化沿海水域的碳动力学可能取决于呼吸和光合作用的平衡。本研究提供了具有高地理精度和特异性的碳物质，并提供了陆海一体化的见解，以了解碳动态机制，促进水质管理和气候缓解的进展。
