Impact of Riverine Source Rocks on Estuarine POC Flux: A Modeling Study

This study utilized the term 'POC output' to refer to the flux of particulate organic carbon at a depth of 100 meters. Compared to the control group, the input of riverine source rocks significantly increased the annual POC flux in the estuarine area. Specifically, the total annual POC output in all estuarine areas increased by 3.6% to 9.0%. When the riverine source rocks were input at high concentrations and only acted in the estuary (HF scenario), the total POC output in the estuarine area increased the most, with an increase of 9.0%. For each individual estuary, most of the annual POC output increased between 10% and 60%, with some even increasing by more than 80%, but a few estuaries showed a decrease in POC output. When the riverine source rocks spread outward from the sea surface, the increase in total annual POC output in the estuarine area was very similar to the scenario where the rocks only affected the estuarine area, with an increase of 3.5% for the LF-SD-SurfaceForcing scenario, which was close to the 3.6% increase for the LF scenario, and an increase of 8.9% for both the HF-SD-SurfaceForcing scenario and the HF-LD-SurfaceForcing scenario, which was close to the 9.0% increase for the HF scenario. When the riverine source rocks spread outward to the sea shelf and slope, even though the concentration of rocks in the estuarine area was the same as in the scenarios where they did not spread outward (LF and HF), the increase in annual POC output was significantly smaller. The annual average increase in POC output for the LF-SD-LateralForcing-FuncI and LF-SD-LateralForcing-FuncII scenarios was 1.6% and 1.5%, respectively, which was lower than the 3.6% increase for the LF scenario, whereas the annual POC output for the HF-SD-LateralForcing-FuncI, HF-SD-LateralForcing-FuncII, and HF-SD-LateralForcing-FuncIII scenarios were all close to 6.0%, which was lower than the 9.0% increase for the HF scenario. As the depth increased, the impact of riverine source rocks on POC flux in the estuarine area became more significant, and the results from all sensitive experimental groups showed that the increase in POC flux significantly increased with depth, reaching an increase of 19.2% to 83.5% at a depth of 1000 meters, indicating that the riverine source rocks significantly increased the transfer of POC from the estuarine area to deeper layers (Table 2). When the riverine source rocks spread outward from the sea shelf and slope, the variation in mid-upper layer POC flux at the same depth in the water column where the estuary was located was always significantly smaller than the simulation results for scenarios where the rocks only affected the estuarine area or spread outward from the sea surface.