Salt Marshes

Salt marshes are intertidal habitats formed by communities of salt-tolerant grasses, herbs, and low shrubs that improve overall water quality and support both marine and wildlife populations.

Found from arctic to subtropical climates, salt marshes export carbon and energy into the water column, store carbon in their root systems and sediments, and filter nutrients, pollutants and pathogens from water along global coastlines. Salt marshes also help to protect against storm damage, flooding and erosion.

Salt marsh habitats can be damaged or destroyed by human activities, including oil spills, agricultural drainage, and development. Climate change and sea level rise also threaten salt marshes, particularly if natural features or human developments prevent their landward retreat. 

Examples Of A Coastal Salt Marsh
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Which Goals Does This Affect?

Coastal Salt Marsh Food Web
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How Was It Measured?

Data on the area of salt marsh habitats for each country come from multiple sources (Bridgham et al. 2006; EEA Eionet 2008; Environment New Zealand 2007; JNCC 2004), and are generally reported in km2.  The status of salt marsh related ecosystems and approximate rates of current salt marsh loss were calculated from previous extent and current extent numbers where available.

Trend for salt marshes received a categorical score. A score of 0.5, 0, or -0.5 was given for an increasing, decreasing, or stable trend respectively. Based on the trend of the habitat, the salt marsh was also assigned a condition score. If the trend was stable or increasing, it was assigned a condition score of 1.0, and if the trend was decreasing, it was assigned a condition score of 0.5.

Like all of the habitats used in the OHI, salt marsh habitat is used as a component in calculating scores for many of the different goals. However, it is used differently depending on the goal in question. Although habitats such as salt marshes are used in calculating these goal scores, countries are not penalized for not having a certain habitat type. Calculations are based on the rank of existing habitats, as opposed to using all possible habitat types. 

Salt Marsh habitat was used as a component in calculating scores for Coastal Protection, Carbon Storage, and Biodiversity (Subgoal: Habitat). The salt marsh component is used to calculate Trend and Status in these goals, however calculations differ slightly by goal. 

What Are The Impacts?

Salt marshes diffuse the impact of storms by reducing wave heights, thereby helping to protect shoreline ecosystems against damage.

Wave heights can be reduced by up to 50% over the first 10-20m of vegetated salt marsh surface (Moller et al. 2006).

Salt marshes store carbon in their surface deposit soil.  When salt marshes are exposed to erosion or submersion, CO2 is released from these stored deposits back into the atmosphere.

The surface sediments of salt marshes can contain as much as 10-15% carbon (Savidge and Blanton 2011)  [Approx. 430 ± 30 Tg C (Chmura 2003)].

The destruction or drainage of salt marshes can lead to the subsequent invasion of nonnative species which deplete existing species and grasses beneficial to the native marine and wildlife population.

Salt marshes provide the breeding grounds for a number of species, helping to maintain coastal biodiversity in both salt and freshwater ecosystems.  
Salt marshes improve water quality by removing pathogens and pollutants from natural wastewater before they reach estuaries and coastal waters and by transporting key nutrients between water and land ecosystems.

Salt marshes are important spawning grounds for many fish species. These coastal habitats have a direct correlation to the amount of commercial fish harvested annually.

What Has Been Done?

Get More Information

Ramsar Convention on Wetlands
The Convention represents an agreement between member states to protect and preserve wetland ecosystems within a nation’s boundaries and provides a Guide for Policy Makers and Planners.

Wetlands International
This organization is committed to sustaining and restoring wetlands while protecting their biodiversity and natural resources.

Saltmarsh Management Manual (DEFRA)
DEFRA provides information, guidance, and techniques to manage, restore, and enhance salt marsh environments.


PHOTO(S): © Keith A. Ellenbogen
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