Evaluation of Abandoned Huanghe Delta as an Important Carbon Source for the Chinese Marginal Seas in Recent Decades

• Published in: Journal of geophysical research. Oceans 2021-03, Vol.126 (3), p.n/a
• Main Authors: Qi, Lijun, Wu, Ying, Chen, Shenliang, Wang, Xiaona
• Format: Article
• Language: English
• Subjects: abandoned Huanghe Delta; Anthropogenic factors; Biodegradation; Carbon; Carbon budget; Carbon cycle; Carbon sources; Chinese marginal seas; Climate change; Coastal erosion; Coastal sediments; Coastal waters; Coastal zone; Deltas; Efficiency; Evaluation; Fluvial sediments; Fluxes; Geochemistry; Geophysics; Global warming; Human influences; Lignin; Marginal seas; Marine environment; Organic carbon; Organic matter; Oxidation; Oxidation resistance; Perturbation; Regional analysis; Rivers; Sea level changes; Sea level rise; Sediment; Sediment yield; Sediments; Soil erosion; terrestrial OC; Transport
• ISSN: 2169-9275; 2169-9291
• DOI: 10.1029/2020JC017125

Increasing organic carbon (OC) inputs from coastal erosion contribute to large uncertainties in carbon cycling in coastal seas. The abandoned Huanghe Delta (AHD) is a typical coastal erosion region, which transports large amounts of eroded sediments to the Chinese marginal seas (CMS, not including the South China Sea). Here we investigated the organic geochemical characteristics of sedimentary organic matter (OM) from the heavily eroded region of the AHD and estimated the OC and lignin fluxes caused by coastal erosion. The eroded sedimentary OM was characterized by low carbon loading and low lignin content with high degradation and was influenced by the Changjiang. Owing to the sharp decline in the sediment fluxes from large rivers (the Changjiang and Huanghe) since the 1990s, the total fluxes to the CMS decreased from 11.5 to 5.0 Mt/yr for OC and from 11.5 × 10−2 to 4.7 × 10−2 Mt/yr for lignin; therefore, the contribution from the coastal erosion of the AHD increased from 24% ± 8% to 56% ± 10% for OC and from 21% ± 9% to 52% ± 15% for lignin. The high proportion contributed by the AHD to the Central Yellow Sea mud area (74% ± 11%) also accounted for the high terrestrial OC burial efficiency there (69%). Considering the different nature of OM and its increasing contribution, as in this case, the significance of OC input from coastal erosion to the coastal seas is expected to overwhelm that from rivers, thereby influencing regional and even global carbon budgets and cycles, especially under the scenarios of global warming and sea level rise. Plain Language Summary Due to climate change and anthropogenic perturbations, sediment fluxes from rivers to the ocean have decreased dramatically, while the sediments yielded by coastal erosion is increasing, which needs to evaluate their impacts on organic carbon (OC) fluxes. Our study examined the geochemical characteristics of the sedimentary organic matter (OM) exported to Chinese marginal seas (CMS, excluding the South China Sea) from the abandoned Huanghe Delta (AHD), a severe coastal erosion region. Our results suggest 2.8 ± 1.0 Mt of OC is contributed annually from the AHD to CMS, which has exceeded that from the Huanghe and Changjiang rivers since the 1990s. Contrast with the terrestrial OM transported by Huanghe and Changjiang, the eroded OM from the AHD has undergone extensive alteration; therefore is more resistant to the oxidation during the transportation and may end up with higher burial efficiency in th