Quantitative estimates of organic carbon contributions to the river-estuary-marine system in the Jiaozhou Bay, China

Land-ocean interactions play an important role in transporting and accumulating organic carbon (OC) in marine sediments. Understanding sources (terrestrial, marine and anthropogenic contributions) of sedimentary OC are important to better evaluate the processes controlling the OC distribution in coastal zones. In this study, we present bulk parameters of total organic carbon (TOC), total nitrogen (TN), stable carbon isotopic composition (delta C-13(org)) and biomarker contents in surface sediments from the Dagu River-estuary-marine system in the Jiaozhou Bay. Comparison between OC/N ratios and delta C-13(org) indicated significant C-4 plant contribution to the sedimentary OC, which was approximately equal to C-3 plant contribution in this study. Generally, terrestrial biomarkers contents were high in the river and showed a decreasing trend towards the estuary and inner bay. Marine biomarkers displayed opposite spatial distribution patterns with terrestrial biomarkers except for the brassicasterol that also has a terrestrial/fluvial source. The universal detection of petroleum and sewage biomarkers revealed the significant anthropogenic influence on the sedimentary OC in our study. Principal component analysis-multiple linear regression (PCA-MLR) was performed to quantitatively estimate the OC contributions in the Jiaozhou Bay, showing that anthropogenic activities contributed 77.6% and 29.9% to the sedimentary OC in Dagu River and outside the Dagu River (the estuary and the inner Bay), respectively. Further studies need to be carried out to test this approach in broader regions.

Automated summary

Land-ocean interactions are important in transporting and accumulating organic carbon in marine sediments. This study in the Jiaozhou Bay found significant contributions of terrestrial, marine, and anthropogenic sources to sedimentary organic carbon. Terrestrial biomarkers were predominant in the river, while marine biomarkers showed different distribution patterns.