Land-surface subsidence and erosion are the principal processes that form accommodation space in interior coastal wetlands when they are converted to open water. The relative contribution of subsidence and erosion to wetland loss can be estimated by comparing elevations and vertical offsets of stratigraphic contacts that are correlated between adjacent sediment cores. Accommodation-space measurements assume that wetland-sediment thicknesses and the elevation of stratigraphic contacts were originally nearly uniform over short horizontal distances (tens to hundreds of meters). The accommodation space attributable to erosion equals the difference in wetland-sediment thickness between wetland cores and adjacent open-water cores taken at formerly emergent wetland sites. The accommodation space attributable to subsidence equals the elevation difference of a stratigraphic marker correlated between the two cores using the wetland core as the reference standard. Together, subsidence plus erosion at an open-water core location equals the accommodation space created by land loss, which is the difference between the adjacent emergent wetland elevation and the existing water depth.