What are salt marshes and why are they important?

Salt marshes are coastal wetlands, acting as a buffer between land and sea. They are found in low-lying areas that are routinely flooded and drained by tides. A recent study conservatively estimates the global coverage of salt marshes to be 90,800 km2 which is roughly the size of Portugal! This figure is likely to be much higher (up to 400,000km2).

Salt marshes in Tollesbury, Essex, UK

Marshes provide vital ecosystem services just like mangrove trees - filtering water, sequestering carbon, protecting coasts, and more!

They are also referred to as ‘tidal marshes’ or ‘coastal marshes’ and are commonly dominated by a few salt-tolerant plants like glassworts and cordgrasses. Many of these plants are not grazed on, at all, by larger animals but die off and decompose to become food for micro-organisms, which in turn become food for fish and birds.

Life in the salt marshes

Salt marshes provide essential habitats for many organisms, including mammals, birds, fish, and invertebrates, and are called a “gene pool” of diverse species. In particular, they provide important feeding and stopover habitats for migratory birds along international flyways.

Here is a pictorial representation of the diverse fauna found in the marshes –

Life in the salt marshes

Reasons for loss of salt marshes

A 2011 study quantified a 25% total loss of salt marsh coverage since the 1800’s, with an annual rate of loss between 1-2%. Some of the drivers of loss are -

  • Coastal Development: dredging and land reclamation
  • Climate Change: sea level rise and eutrophication (where water bodies with excess nutrients and minerals can result in algal blooms and low oxygen levels)
  • Pollution: agricultural and industrial run-off
  • Overfishing: changes in species distribution, sometimes leading to marsh diebacks (when the plants in salt marshes brown and die off)

A significant reduction in global loss of salt marshes was noted in a recent paper, from 1 – 2% to a rate of 0.28% per year, recorded between 2000-2019. This is equivalent to double the size of Singapore. Losses come at a price of increased carbon emissions due to the reduced capacity of carbon burial. This means that carbon is released back into the atmosphere when salt marshes or other blue carbon ecosystems are lost or degraded. 

Salt marshes in Cape Cod, USA

Three reasons why salt marshes need to be conserved

  • A Blue Carbon Sink -

    Salt marshes have the capacity to sequester carbon less than or comparable to mangroves. They store carbon in their biomass and soil. According to a 2011 paper, salt marshes are capable of sequestering between 4.8 – 87.2 Tg C every year. This is equal to removing 3-52 million diesel cars off the road for a year!

    Great uncertainties remain on quantifying the carbon sequestration potential of salt marshes, partially due to gaps in mapping the extent of salt marshes globally. This knowledge gap must be addressed through research if we want to effectively utilise salt marshes for mitigating global warming.

  • Coastal Protection -

    They provide natural buffering against coastal hazards such as storms because vegetation greatly increases friction coefficients, which reduce current flow and dissipates wave energy. In this way, salt marshes contribute to minimising the impact of storm surges and protecting shorelines against erosion and floods.

    There are also reduced economic impacts when protecting salt marshes. For example, according to the Second World Ocean Assessment (WOA) 2021, $625 million worth of damages were prevented due to the presence of salt marshes in New Jersey, USA.

  • A Natural Filter –

    Salt marshes remove contaminants, sediments and pollutants from river discharge and run-off, thereby protecting nearby areas from erosion and harmful effects. Excess nutrients are also filtered, making salt marshes useful for improving water quality.

Algonquin National Park, Canada

Did you know?

Salt marshes can be artificially created or constructed by humans! This does makes it trickier to quantify the global extent of salt marshes.

What is being done to restore salt marshes?

Over the last few decades, the value of salt marshes has been recognised, albeit disproportionately across the world. They are now being included in climate change adaptation planning as a nature-based solution (NbS).

In the San Francisco Bay, a whopping 85% of wetlands were historically lost. The Napa River Salt Marsh Restoration Project seeks to address this loss by “restoring 10,000 acres of former salt ponds, remnant sloughs, fringing marsh and levees to tidal marsh and other valuable habitats in the North Bay of San Francisco.”

This salt marsh restoration project is nearly complete and will be a necessary habitat for the revival of endangered fish and various aquatic animals. It will also be instrumental in hosting recreational activities such as fishing and birdwatching.

Salt marshes in Napa River, USA

Although the above example is a large-scale effort, most restoration projects are small, adding up to low mitigation potential, as per best case scenarios. We need bolder and larger restoration projects if we want to realistically rely on salt marshes as a solution. This can only happen if there is sufficient research to guide region-specific projects.

What can I do to protect salt marshes?

The best thing we can do is to preserve existing salt marshes while vouching for restoration projects where possible.

  • Consider limiting use of pesticides and chemical fertilisers –

    These products eventually sneak their way into our Ocean so, whether you live near tidal wetlands or not, limiting use will help reduce eutrophication and limit overall harm against aquatic species.  

  • Education is key –

    The importance of salt marshes is not widely known within the general public. Consider spreading the knowledge to protect your local community and the biodiversity it hosts.

  • Volunteer at your nearest salt marsh restoration site –

    Although not all projects are volunteer based, volunteers have been instrumental in general restoration efforts. If you live in South Carolina, USA, for example, here is a project you can support.

    Consider carving out some time to understand if there is a project that you can support locally!