Add below-ground organic matter: brackish/salt marshes

How is the evidence assessed?
  • Effectiveness
  • Certainty
  • Harms

Study locations

Key messages

  • One study evaluated the effects, on vegetation, of adding below-ground organic matter to restore or create brackish/salt marshes. The study was in the USA.




  • Individual species abundance (1 study): One replicated, randomized, controlled, before-and-after study in a salt marsh in the USA found that plots amended with alginate contained a greater density of smooth cordgrass Spartina alterniflora than unamended plots after 6–52 weeks. However, amended and unamended plots contained similar smooth cordgrass biomass when it was sampled after 52 weeks.


  • Height (1 study): One replicated, randomized, controlled, before-and-after study in a salt marsh in the USA found that amending plots with alginate had no significant effect on smooth cordgrass height in the first 16 weeks after intervention, but that amended plots contained taller smooth cordgrass than unamended plots after 28–52 weeks.

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

  1. A replicated, randomized, controlled, before-and-after study in 2007–2008 in a salt marsh in Georgia, USA (Cohen & Kern 2012) found that adding alginate generally increased the density and height, but not biomass, of smooth cordgrass Spartina alterniflora. Before intervention, plots contained 285–334 smooth cordgrass stems/0.5 m2 and plants were 53–59 cm tall. After 6–16 weeks, smooth cordgrass density was greater in plots amended with alginate (282–367 stems/0.5 m2) than in unamended plots (224–313 stems/0.5 m2). However, smooth cordgrass height did not significantly differ between treatments (amended: 65–68 cm; unamended: 60–63 cm). After 28–52 weeks, smooth cordgrass density remained greater in amended plots (135–213 stems/0.5 m2) than in unamended plots (121–164 stems/0.5 m2). Cordgrass was also significantly taller in amended plots (23–49 cm) than in unamended plots (15–35 cm). Finally, after 52 weeks, above-ground cordgrass biomass did not significantly differ between treatments (amended: 3.4 g/0.25 m2; unamended: 6.3 g/0.25 m2). Methods: In July 2007, ten 0.5-m2 plots were established in a cordgrass-dominated salt marsh. Alginate (a carbon-rich seaweed extract) was added to five plots (80 g/plot, across ten 2-cm diameter x 10-cm deep holes). In the other five plots, holes were dug but alginate was not added. Live stem density and the height of the five tallest plants were recorded immediately before intervention and biweekly afterwards. Smooth cordgrass was cut from plots after one year, then dried and weighed.

    Study and other actions tested
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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Marsh and Swamp Conservation

This Action forms part of the Action Synopsis:

Marsh and Swamp Conservation
Marsh and Swamp Conservation

Marsh and Swamp Conservation - Published 2021

Marsh and Swamp Synopsis

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