Add lime or similar chemicals before/after planting non-woody plants: brackish/saline wetlands

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

Effectiveness

28%
Certainty

30%
Harms

23%

Calculating overall effectiveness category

Background information and definitions

This action involves adding chemicals – such as lime (CaO or Ca(OH)₂), limestone (CaCO₃), magnesium oxide (MgO), fly ash (residue from burning coal) and biochar (a type of charcoal) – to areas planted with marsh or swamp vegetation. These calcium and/or magnesium-rich chemicals may reduce acidity and modify nutrient availability (Weil & Brady 2016), potentially increasing plant survival or growth.

Related actions: Add lime or similar chemicals to wetlands, other than to complement planting.

^{Weil R.R. & Brady N.C. (2016) The Nature and Properties of Soils, Fifteenth Edition. Pearson, USA.}

Study locations

Key messages

Three studies evaluated the effects, on vegetation, of adding neutralizing chemicals to brackish/saline wetlands planted with emergent, non-woody plants. Two studies were in Canada. One study was in the USA. One study was in a greenhouse.

VEGETATION COMMUNITY

VEGETATION ABUNDANCE

Characteristic plant abundance (1 study): One replicated, paired, controlled, before-and-after study in salt-contaminated bogs in Canada reported that liming reduced the above-ground biomass of planted salt marsh vegetation after one year.
Individual species abundance (2 studies): One controlled study in former borrow pits in the USA found that limed and unlimed plots supported similar biomass of a planted herb species after 1–2 growing seasons. In contrast, one replicated, randomized, paired, controlled study in salt-contaminated peat in Canada found that limed pots supported lower biomass of two sown herb species than unlimed pots, after four months.

VEGETATION STRUCTURE

OTHER

Germination/emergence (1 study): One replicated, randomized, paired, controlled study in salt-contaminated peat in Canada found that for each of two sown herb species, germination rates were similar in limed and unlimed pots.

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 controlled study in 1980–1981 on reprofiled borrow pits in North Carolina, USA (Broome et al. 1982) found that liming had no significant effect on the biomass of planted smooth cordgrass Spartina alterniflora. Limed and unlimed plots supported statistically similar above-ground cordgrass biomass in seven of seven comparisons after one growing season (limed: 7–172 g/m²; unlimed: 6–100 g/m²) and in one of one comparisons after two growing seasons (limed: 2,380 g/m²; unlimed: 1,804 g/m²). The result was the same when lime was applied to fertilized or unfertilized plots, and at two different lime doses (see original paper). Methods: In June 1980, wild-harvested smooth cordgrass plants were planted into coastal land that had been reprofiled (to 6–43 cm above mean sea level; salinity <20 ppt) after excavation of sediment for construction. The site was dry during planting but rewetted after. Some plants were limed after planting (dolomitic limestone; 2,240–4,500 kg/ha) whilst others were not limed. The study does not clearly report the experimental design (including number of plants and plots). In October 1980 and 1981, living cordgrass was cut from 0.25-m² quadrats then dried and weighed.
Study and other actions tested
Referenced paper
Broome S.W., Seneca E.D. & Woodhouse W.W. (1982) Establishing brackish marshes on graded upland sites in North Carolina. Wetlands, 2, 152-178.
A replicated, paired, controlled, before-and-after study in 2011–2012 in two salt-contaminated bogs in New Brunswick, Canada (Emond et al. 2016) found that liming reduced the biomass of planted salt marsh vegetation. After one year, limed plots supported a lower above-ground biomass of planted vegetation (26 g/m²) than unlimed plots (42 g/m²). This result is not based on an assessment of statistical significance. Methods: In summer 2011, eighty 9-m² plots were established (in four blocks of 20) on bare, salt-contaminated peat (0.5–1.4 ppt). Sixty-four of the plots were planted with vegetation (chaffy sedge, prairie cordgrass, or mixed salt marsh plant fragments). Half of the plots were limed (18 g in planting holes; increasing soil pH to 3.8). The other half were not (soil pH 3.5). Some limed and unlimed plots were also fertilized. In July 2012, vegetation was cut from a 250-cm² quadrat in each plot, then dried and weighed.
Study and other actions tested
Referenced paper
Emond C., Lapointe L., Hugron S. & Rochefort L. (2016) Reintroduction of salt marsh vegetation and phosphorus fertilisation improve plant colonisation on seawater-contaminated cutover bogs. Mires and Peat, 18, Article-17.
A replicated, randomized, paired, controlled study in 2011–2012 in a greenhouse in New Brunswick, Canada (Emond et al. 2016) found that liming had no significant effect on seed germination rate of two salt marsh herbs, but reduced the height of transplants of one species and reduced the above-ground biomass of both. For both species, a statistically similar number of seeds germinated over two months in limed and unlimed pots (data not reported). After four months, chaffy sedge Carex paleacea transplants were shorter in limed than unlimed pots, whilst prairie cordgrass Spartina pectinata height did not significantly differ between limed and unlimed plots (data not reported). However, above-ground biomass of transplants was significantly lower for limed than unlimed chaffy sedge (high lime: 30; low lime: 50; no lime: 87 g/m²) and significantly lower for heavily limed than unlimed prairie cordgrass (high lime: 31; low lime: 54; no lime: 69 g/m²). Methods: In October 2011, five pots of salt-contaminated peat were planted per treatment: sedge or cordgrass, with no lime (pH 3.8), low lime (2.5 kg/m³; pH 4.7) or high lime (7.5 kg/m³; pH 6.2). Pots were kept in five groups, each containing one pot of each treatment. Seeds and transplants were kept in the dark at 4°C for three months before planting. Seeds were also kept in brackish water for two weeks before sowing. Seed germination was recorded after two months. After four months, all transplants were measured, cut, dried and weighed.
Study and other actions tested
Referenced paper
Emond C., Lapointe L., Hugron S. & Rochefort L. (2016) Reintroduction of salt marsh vegetation and phosphorus fertilisation improve plant colonisation on seawater-contaminated cutover bogs. Mires and Peat, 18, Article-17.

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

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This Action forms part of the Action Synopsis:

Marsh and Swamp Conservation

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