A robust high-resolution coupled hydrodynamic-biogeochemical model was applied to the northern Gulf of Mexico to assess the efficiency of river- and ocean-sourced ocean alkalinity enhancement (OAE). Sensitivity tests indicate that the effectiveness of OAE-induced CO₂ uptake is primarily influenced by the amount of alkalinity introduced and local wind-driven mixing, with the former determining the overall uptake and the latter affecting short-term variability. Compared to ocean-sourced OAE (direct ocean release), river-sourced OAE (elevated river alkalinity) is more effective and sustainable. River-sourced OAE has higher CO₂ uptake efficiency with reduced spatial and temporal uncertainty and greater overall CO₂ uptake. For river-sourced OAE, surface pH increases pronouncedly near the mouths of the Mississippi River. The ideal OAE implementation time includes spring, early summer, fall, and winter. Mid and late-summer implementation is not recommended due to weak mixing, which results in less alkalinity dispersal and greater pH variability. In addition, while the aragonite saturation state generally remains below 6 around the Mississippi River plume, it increases pronouncedly during mid to late summer, risking alkalinity loss due to CaCO₃ precipitation and reduced CO₂ uptake efficiency near river mouths. Scaling OAE-induced CO₂ uptake to the 25 largest rivers in the world indicates that increasing riverine alkalinity concentrations by 10% could remove 23.23 megatons of CO₂ annually, meeting 0.37%–0.61% of the 2025–2030 CO₂ removal target.

Ship Shoal has been a high-priority target sand resource for dredging activities to restore the eroding barrier islands in LA, USA. The Caminada and Raccoon Island pits were dredged on and near Ship Shoal, which resulted in a mixed texture environment with the redistribution of cohesive mud and noncohesive sand. However, there is very limited knowledge about the source and transport process of suspended muddy sediments near Ship Shoal. The objective of this study is to apply the Regional Ocean Modeling System (ROMS) model to quantify the sediment sources and relative contribution of fluvial sediments with the estuary and shelf sediments delivered to Ship Shoal. The model results showed that suspended mud from the Atchafalaya River can transport and bypass Ship Shoal. Only a minimal amount of suspended mud from the Atchafalaya River can be delivered to Ship Shoal in a one-year time scale. Additionally, suspended mud from the inner shelf could be transported cross Ship Shoal and generate a thin mud layer, which is also considered as the primary sediment source infilling the dredge pits near Ship Shoal. Two hurricanes and one tropical storm during the year 2017–2018 changed the direction of the sediment transport flux near Ship Shoal and contributed to the pit infilling (less than 10% for this specific period). Our model also captured that the bottom sediment concentration in the Raccoon Island pit was relatively higher than the one in Caminada in the same period. Suspended mud sediment from the river, inner shelf, and bay can bypass or transport and deposit in the Caminada pit and Raccoon Island pit, which showed that the Caminada pit and Raccoon Island pits would not be considered as a renewable borrow area for future sand dredging activities for coastal restoration.

Salinity variations across the Land‐Estuary‐Ocean (LEO) continuum are critical for coastal ecosystems and impact the socioeconomic benefits to local communities. However, evaluating these variations is challenging due to the complex interactions of terrestrial and oceanic processes, including river discharge, winds, tides, sea level rise, and storms. This study incorporates a salinity module into a newly developed dynamically coupled hydrological‐ocean model on the COAWST platform, which is, to the best of our knowledge, the first process‐based modeling that achieves seamless two‐way land‐ocean water and salt exchanges across the LEO continuum, facilitating simulations of landward salt input and transport. Using Hurricane Florence (2018) as a case study, we examined how various physical processes influence salinity dynamics and freshwater plume development in the Cape Fear River Estuary, North Carolina. The model simulated saltwater intrusion into freshwater wetlands upstream of the estuary and demonstrated that salinity in the estuary was initially regulated by wind‐driven water level gradients, followed by a dominant influence from significant river runoff. In the coastal ocean, runoff created a large freshwater plume that moved westward, driven by the interplay between runoff, winds, and the estuary's geomorphology. The excellent performance of the coupling approach for salinity simulation underscores the importance of the seamless transport of water and salt at the land‐ocean interface. This study demonstrates that the coupled model is a valuable tool for representing saltwater intrusion, tracking coastal pollutants, and understanding water and material exchange across the LEO continuum.

River-dominated continental shelves significantly influence coastal carbon cycling and ocean acidification due to substantial freshwater river discharge. Despite this importance, the contributions of riverine dissolved inorganic carbon (DIC), total alkalinity (TA), and nutrient loads to surface pCO2 trends remain inadequately quantified. This study employs the Regional Ocean Modelling System (ROMS) to evaluate the effects of riverine DIC, TA, and nutrient fluxes on surface pCO2 trends in the northern Gulf of Mexico/America from 2001 to 2019. A control simulation (CTR) representing historical river inputs was compared to three scenarios: no historical riverine DIC and TA flux (NRC), no historical nutrient flux (NRN), and high freshwater discharge (60% of historical levels, HRD60). Results indicated positive pCO2 trends in most nGoM regions, except for HRD60, which exhibited some negative trends. First-order Taylor series decomposition revealed that DIC is the primary contributor to increasing pCO2 trends, accounting for 50%, while TA offsets this by 31%. Sea surface temperature (SST) contributes 13%, and sea surface salinity (SSS) contributes 6%. Under the HRD60 simulation, increased freshwater discharge enhances both DIC and TA delivery, leading to spatially heterogeneous yet dampened pCO2 trends due to stronger buffering. These findings emphasize that coastal pCO2 trajectories depend on the magnitude and composition of riverine fluxes. Carbonate supplies account for 59% of total river-driven modulation of surface pCO2, with biological uptake offsetting the remaining 41%. Future climate projections must consider these nonlinear interactions to effectively assess acidification risks in river-influenced coastal regions.