Remove surface soil/sediment: brackish/salt marshes
Overall effectiveness category Unknown effectiveness (limited evidence)
Number of studies: 1
Background information and definitions
Surface soil/sediment – and any vegetation on it – could be removed to create a new bare surface for plants to colonize. This new surface may have fewer nutrients and pollutants, have no undesirable seed bank, and have a looser surface. Soil/sediment removal can also make a site wetter, by bringing the surface closer to the water table, increasing the frequency/duration of tidal flooding, or increasing the water depth in an already flooded site. This action may be particularly useful in naturally dynamic habitats that have been artificially stabilized, mimicking disturbances that would create bare soil/sediment.
Caution: Heavy machinery is usually needed for this action. Heavy vehicles can churn and compress wetland soils (Campbell et al. 2002). Stripping topsoil can have counter-intuitive effects, such as increasing ammonium concentrations because nitrifying bacteria, which break down ammonia, are removed with the soil (Dorland 2004). It may remove seeds of desirable species, and can be expensive.
Related actions: Raise water level to restore degraded marshes; Raise water level to restore/create marshes from other land uses; Reprofile/relandscape; Bury surface soil/sediment; Disturb soil/sediment surface without removing material; Transplant or replace wetland soil; Remove surface soil/sediment before planting.
Campbell D.A., Cole C.A. & Brooks R.P. (2002) A comparison of created and natural wetlands in Pennsylvania, USA. Wetlands Ecology and Management, 10, 41–49.
Dorland E. (2004) Ecological restoration of wet heaths and matgrass swards: bottlenecks and solutions. PhD Thesis, Utrecht University, The Netherlands.
Supporting evidence from individual studies
A study in 1997–1999 aiming to create a brackish marsh on coastal farmland in the Netherlands (Bakker et al. 2002) reported that an area from which topsoil was removed was colonized by farmland weeds and some plant species characteristic of brackish marshes. Two years after topsoil removal, 23 plant species were recorded in the study area. The most abundant taxa were mostly farmland weeds/generalists, such as chamomile Matricaria recutita (in 97% of quadrats), sow thistle Sonchus oleraceus (76%) and meadow grass Poa annua (61%). Taxa characteristic of brackish marshes included rushes Juncus spp. (in 97% of quadrats), sea aster Aster tripolium (7%) and alkali bulrush Scirpus maritimus (5%). The study does not define a full list of characteristic species. Methods: In 1997, a 30 cm layer of topsoil was stripped from an area of coastal farmland (Emmapolder). Not all topsoil was completely removed from the site: some was stored in rows on site, and so provided a source of farmland weed seeds. Brackish groundwater naturally seeped towards the ground surface. In 1999, vegetation was surveyed in an unplanted area of the site, next to a pool (100 quadrats, each 0.4 m2).Study and other actions tested