River deltas store carbon in different ways in their topsoil and subsoil layers. The type of land use and soil properties affect how much carbon is stored. Wetlands have a lot of plant-based carbon in the topsoil, while subsoil contains older carbon from outside sources. Different soil layers have different textures and minerals that affect how carbon is stored. The red clay layer in the subsoil can keep both new and old carbon stable. Overall, the way land is used and the soil composition determine how much carbon is stored in river deltas.