Add below-ground organic matter: brackish/salt marshes
Overall effectiveness category Unknown effectiveness (limited evidence)
Number of studies: 1
Background information and definitions
This action involves adding organic matter (i.e. remains or waste products of living organisms) below the ground surface, for example by mixing it into the sediment or placing it into holes. Specific substances than can be used include compost, sewage sludge, wood chips and seaweed extract.
The soil organic matter content of wetland soils may be reduced by disturbance. For example, drainage allows oxygen into the soil, whilst reprofiling removes surface layers rich in organic matter (Bruland et al. 2006). Organic matter can be an important component of wetland soils. It directly supplies nutrients to growing plants, supplies carbon and energy to soil organisms, helps bind the soil together, retains water during dry periods, and mediates soil temperature (Donahue et al. 1983; Weil & Brady 2016). Adding carbon-rich organic materials can indirectly modify nutrient availability by stimulating microbial activity, and so could help to manage invasive species where they benefit from an excess of certain nutrients (Reever Morghan & Seastedt 1999; Tilman et al. 1999; Perry et al. 2004).
To be summarized as evidence for this action, studies must evaluate the effects of adding organic matter without adding living vegetation. The organic matter should be used to help or manage existing vegetation, such as remnant patches of vegetation, or seedlings that germinate from seeds already present.
Related actions: Add surface mulch; Add below-ground organic matter to complement planting.
Bruland G.L., Richardson C.J. & Whalen S.C. (2006) Spatial variability of denitrification potential and related soil properties in created, restored, and paired natural wetlands. Wetlands, 26, 1042–1056.
Donahue R.L., Shickluna J.C. & Robertson L.S. (1983) Soils: An Introduction to Soils and Plant Growth, Fifth Edition. Prentice-Hall, Englewood Cliffs, NJ, USA.
Perry L.G., Galatowitsch S.M. & Rosen C.J. (2004) Competitive control of invasive vegetation: a native wetland sedge suppresses Phalaris arundinacea in carbon-enriched soil. Journal of Applied Ecology, 41, 151–162.
Reever Morghan K.J. & Seastedt T.R. (1999) Effects of soil nitrogen reduction on nonnative plants in restored grasslands. Restoration Ecology, 7, 51–55.
Tilman E.A., Tilman D., Crawley M.J. & Johnston A.E. (1999) Biological weed control via nutrient competition: potassium limitation of dandelions. Ecological Applications, 9, 103–111.
Weil R.R. & Brady N.C. (2016) The Nature and Properties of Soils, Fifteenth Edition. Pearson, USA.
Supporting evidence from individual studies
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