Estuaries are characterized by interactions between freshwater from rivers and saltwater from the ocean, which drives high ecosystem productivity and dynamic carbon and nutrient cycling. Estuaries can act as a filter on river inputs of nitrogen (N) and other nutrients to the ocean and can greatly reduce the amount of N that moves from rivers to the ocean. Estuarine wetlands sequester carbon (C) at high rates due to rapid vegetation growth fueled by abundant water and nutrients combined with waterlogged sediment conditions that slow decomposition. Estuarine wetlands can also be significant sources of greenhouse gases such as methane and nitrous oxide. However, estuaries and estuarine wetlands are not currently represented in Earth System Models (ESMs) such as the Energy Exascale Earth System Model (E3SM). By omitting estuarine wetland processes, models likely overestimate N inputs from rivers to the coastal ocean and underestimate C sequestration and greenhouse gas emissions in coastal regions. This research aims to understand the current and future role of estuarine wetlands in coastal C and N cycling at scales from the estuary landscape to the continental coast by simulating estuarine wetland processes in the E3SM Land Model. Model improvements will include developing chemical and biological interactions in wetland sediments and introducing salt marsh and mangrove vegetation types. Model developments will be evaluated using observational data from existing coastal wetland field sites along the Pacific, Atlantic, and Gulf of Mexico coasts of the United States. This research will enable quantitative estimates of N removal, C sequestration, and greenhouse gas emissions from estuarine wetlands at estuary to continental scales and improve predictions of coastal C and N cycling responses to changes in wetland area, river flows, and sea levels.