Add upland topsoil before/after planting non-woody plants: freshwater wetlands

Overall effectiveness category Unknown effectiveness (limited evidence)
Number of studies: 3
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How is the evidence assessed?

Effectiveness

50%
Certainty

30%
Harms

2%

Calculating overall effectiveness category

Background information and definitions

Topsoil can be a source of soil organic matter and help to improve water retention (Bruland & Richardson 2004). This might benefit wetland vegetation, particularly when creating new marshes. Topsoil may often be added to complement planting (current intervention) rather than without planting: upland soil will probably not contain seeds or fragments of marsh plants. Caution: Topsoil may contain seeds or fragments of undesirable vegetation.

Related actions: Add upland topsoil, other than to complement planting; Transplant wetland soil before/after planting.

^{Bruland G.L. & Richardson C.J. (2004) Hydrologic gradients and topsoil additions affect soil properties of Virginia created wetlands. Soil Science Society of America Journal, 68, 2069–2077.}

Study locations

Key messages

Three studies evaluated the effects, on vegetation, of adding upland topsoil to freshwater wetlands planted with emergent, non-woody plants. Two studies were in the USA and one was in Canada. One study was in a greenhouse.

VEGETATION COMMUNITY

VEGETATION ABUNDANCE

Individual species abundance (1 study): One replicated, randomized, paired, controlled study in freshwater trenches in Canada found that adding a mixture of mineral soil and peat to pots of mine tailings before planting water sedge Carex aquatilis typically increased its above-ground biomass two growing seasons later.

VEGETATION STRUCTURE

Individual plant size (2 studies): One replicated, controlled study in a greenhouse in the USA found that mixing topsoil into pots of mineral soil/compost before planting tussock sedge Carex stricta seedlings typically increased the biomass and number of shoots they developed over three months. However, one replicated, paired, controlled study in a wet meadow restoration site in the USA reported that mixing topsoil into the mineral soil/compost substrate before planting tussock sedge seedlings had no clear effect on the number of shoots they developed over two months.

OTHER

Survival (1 study): One replicated, randomized, paired, controlled study in freshwater trenches in Canada found that adding a mixture of mineral soil and peat to pots of mine tailings either increased or had no significant effect on survival of planted water sedge Carex aquatilis over two growing seasons.

About key messages

Key messages provide a descriptive index to studies we have found that test this intervention.

Studies are not directly comparable or of equal value. When making decisions based on this evidence, you should consider factors such as study size, study design, reported metrics and relevance of the study to your situation, rather than simply counting the number of studies that support a particular interpretation.

Supporting evidence from individual studies

A replicated, controlled study in 1992 in a greenhouse in Iowa, USA (van der Valk et al. 1999) found that mixing topsoil into mineral soil typically increased the number of shoots and above-ground biomass of planted tussock sedge Carex stricta seedlings, whether topsoil was the only soil amendment or was additional to other amendments. After three months, sedge seedlings planted into a mixture of topsoil and mineral soil were larger (8.8 shoots/plant; 1.6 g/plant) than seedlings planted into mineral soil only (3.3 shoots/plant; 0.6 g/plant). Adding topsoil also increased the size of sedge seedlings in four of six comparisons where it was an additional treatment (i.e. added to pots that were fertilized and/or amended with compost; see original paper for data). In the other two comparisons, topsoil did not have a significant additional effect on sedge size. Methods: In March 1992, tussock sedge seedlings (6–8 weeks old) were planted into 144 pots (probably one seedling/pot). In half of the pots, topsoil was mixed in equal parts with whatever other soil was in the pots (deeper mineral soil, sometimes mixed with compost). Some pots with and without topsoil were also fertilized. All pots were watered to saturation. In June 1992, all sedge shoots were counted, harvested, dried and weighed.
Study and other actions tested
Referenced paper
van der Valk A.G., Bremholm T.L. & Gordon E. (1999) The restoration of sedge meadows: seed viability, seed germination requirements, and seedling growth of Carex species. Wetlands, 19, 756-764.
A replicated, paired, controlled study in 1992 in a wet meadow restoration site in Iowa, USA (van der Valk et al. 1999) reported that adding topsoil to plots before planting tussock sedge Carex stricta seedlings had no clear effect on the number of shoots they developed. Two weeks after planting, sedges assigned to each treatment had a statistically similar number of shoots (4.7–5.8 shoots/plant). After two months, sedge seedlings in plots amended with topsoil had a similar number of shoots (12.2–15.5 shoots/plant) to seedlings in plots that had not been amended with topsoil (11.8–15.2 shoots/plant). This was true when topsoil was the only amendment to mineral soil plots (statistically tested), or when topsoil was an additional amendment to plots already amended with compost (not statistically tested). Methods: In June 1992, tussock sedge seedlings were planted into twelve sets of four 1-m² plots of mineral soil (topsoil had been removed). The number of seedlings/plot was not clearly reported. Fresh topsoil was rototilled into the surface of half of the plots (two plots/set). Some plots were also amended with compost.
Study and other actions tested
Referenced paper
van der Valk A.G., Bremholm T.L. & Gordon E. (1999) The restoration of sedge meadows: seed viability, seed germination requirements, and seedling growth of Carex species. Wetlands, 19, 756-764.
A replicated, randomized, paired, controlled study in 2010–2011 in six experimental wetland trenches in Alberta, Canada (Roy et al. 2014) found that adding peat/mineral soil to mine tailings did not reduce survival of planted water sedge Carex aquatilis over two growing seasons, and typically increased the biomass of surviving sedges. In two of four comparisons, pots of mine tailings mixed with peat/mineral soil supported higher sedge survival (50–67%) than pots of raw mine tailings (24–44%). There was no significant difference between treatments in the other two comparisons (peat/mineral soil: 74%; raw tailings: 54–69%). In three of four comparisons, the above-ground biomass of surviving sedges was higher in pots of mine tailings mixed with peat/mineral soil (2.1–2.8 g/trench) than in pots of raw mine tailings (1.1–1.5 g/trench). There was no significant difference between treatments in the other comparisons (peat/mineral soil: 2.2 g/trench; raw tailings: 2.2 g/trench). Methods: In June 2010, water sedges were collected from a natural marsh and randomly planted into 192 one-gallon pots (number of plants/pot not clearly reported). Half of the pots contained mine tailings amended with a mixture of peat and mineral soil (1 part tailings to 2 parts peat/mineral soil). Half of the pots contained pure mine tailings (dense sediments, low in organic matter, rich in salts and metals). The pots were placed into six experimental wetland trenches: 16 amended pots and 16 raw tailings pots/trench. Surviving plants were harvested at the end of the 2011 growing season. Biomass was dried before weighing.
Study and other actions tested
Referenced paper
Roy M.-C., Mollard F.P.O. & Foote A.L. (2014) Do peat amendments to oil sands wet sediments affect Carex aquatilis biomass for reclamation success? Journal of Environmental Management, 139, 154-163.

Please cite as:

Taylor N.G., Grillas P., Smith R.K. & Sutherland W.J. (2021) Marsh and Swamp Conservation: Global Evidence for the Effects of Interventions to Conserve Marsh and Swamp Vegetation. Conservation Evidence Series Synopses. University of Cambridge, Cambridge, UK.

Where has this evidence come from?

List of journals searched by synopsis

All the journals searched for all synopses

This Action forms part of the Action Synopsis:

Marsh and Swamp Conservation

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