Spatial–temporal distribution of total organic carbon and its transportation in the Jiulong River Estuary

Spatial and temporal distributions of total organic carbon (TOC) in the Jiulong River Estuary (JRE) were determined using data collected during three cruises in summer 2010, autumn 2010, and spring 2011. The TOC concentration influencing factors were identified, and the export fluxes were calculated. TOC concentration ranges were 0.73–4.17 mg/L in summer, 0.90–5.32 mg/L in autumn, and 1.78–8.03 mg/L in spring, respectively. TOC concentrations of the surface water and nearshore area were higher than those of the bottom water and offshore area, respectively, and the maximum TOC content occurred in the JRE upper reaches. The TOC concentration decreased with increasing salinity and exhibited a significant positive correlation with petroleum and dissolved inorganic nitrogen (DIN), indicating the influence of terrestrial input. A weak relationship between TOC and chlorophyll-a indicated that phytoplankton was not the dominant source of TOC. TOC fluxes discharged into the JRE were 50.39 × 10 3 t/a in 2010 and 46.08 × 10 3 t/a in 2011, and those transported into the sea were 38.46 × 10 3 t/a in 2010 and 33.66 × 10 3 t/a in 2011, respectively, accounting for approximately 75% of the total estuary fluxes. This study elucidates the biogeochemical processes of estuarine organic carbon and provides a quantitative basis for the land–sea integration of carbon dioxide emission reduction and sink increase projects.