<p>Tidal wetlands efficiently sequester and store soil organic matter (SOM), including blue carbon, on century time scales. However, SOM can be highly variable in estuarine wetlands, highlighting the need to better understand the roles of environmental drivers. We examined differences in soil parameters, including carbon and nitrogen density, according to wetland type, elevation, and groundwater level, salinity, and pH at four soil depths in current and former tidal wetlands in the Pacific Northwest, USA, to assess differences between marshes, swamps, and sites with restricted tidal influence. In near-surface soils, we also investigated organic matter decomposition rates. In the top 50&#xa0;cm of soils, carbon density was similar between all wetland classes, but between 50 and 100&#xa0;cm, it was twice as high in tidal swamps as in other wetland types. In tidal sites, carbon and nitrogen density were generally not correlated with groundwater level. Elevation was typically more important than soil salinity or pH in modeled effects of environmental drivers on carbon and nitrogen density, with higher-elevation sites having higher densities. Former tidal wetlands tended to have higher bulk density, lower carbon content, and relative nitrogen enrichment than tidal wetlands, indicating soil alterations with disturbance. Short-term measurements of decomposition rates and organic matter stability varied between marshes and swamps but were not correlated with carbon density. Our results show the impacts of wetland disturbance on soil properties and highlight substantial remaining variability not explained by wetland elevation, salinity, or groundwater.</p>