Fighting Climate Change with Coastal Saltmarsh

Saltmarshes are ecosystems that thrive in brackish, or salty water. They cover an area of over 500 million hectares worldwide and provide a natural buffer against flooding, erosion, and storm surge during hurricanes. This is one reason why they are important not only to the environment but also for human safety. However this ecosystem has been declining rapidly because it can’t keep up with climate change impacts like sea level rise and increased precipitation due to global warming.

We’ve known for a long time that salt marshes are effective buffers to climate change impacts like sea level rise and increased precipitation. However, they struggle to keep up with the faster rates of these changes that we’re now experiencing because their vegetation is slow growing and they can’t recover quickly enough.

This has prompted many scientists to work on helping restore salt marshes that have been degraded by human impacts, such as coastal development and invasive species. However, it has been suggested that we might get even better results if we focused on the restoration of bigger patches of marshland.

This review paper was published in Trends in Ecology and Evolution . We talked with lead author Dr. Wei Du from the University of Maryland Center for Environmental Science about his work.

Wei – Our study was to review all published studies on salt marsh restoration and assess whether or not we could achieve ecological benefits by restoring larger patches of salt marsh instead of smaller ones. We also wanted to examine what types of individuals are best suited for large scale restoration, which is still a question that needs to be answered.

In most cases, smaller-scale salt marsh restoration schemes have only met with limited success because they don’t consider the spatial arrangement or size of restored habitat in relation to tidal range. If water levels at the site are not periodically allowed to drop during low tide, then plant species like cordgrass just can’t survive.

In addition, if you don’t consider the size of restored habitat patches in relation to tidal range you will not be able to increase habitat area or connectivity very much because most animals need a lot more space than plants do.

Allison – So what did your review tell you about environmental benefits and how they scale-up with patch size?

Wei – We found that there were often large improvements in biodiversity and ecosystem functioning when we restored larger patches. For example, by restoring about 1% of a salt marsh within a tidal range of 10 m, the habitat area could be increased up to some 18%. With higher tidal ranges you could see larger increases in habitat area.

Of course, just because you restore an additional 18% of salt marsh within the same tidal range if your original restoration was 1%, it doesn’t necessarily mean that you will also increase the benefits by 18%. For example, this might only result in a doubling of benefits with regards to water purification and coastal protection.

These are estimates though, because the results are very site specific and depend on many environmental factors. To give you an idea of what this means in practice, if we restored 1% of salt marsh within a tidal range of 10 m, it would be roughly equivalent to protecting 8-20 km2 shoreline from sea level rise. If we restored 1% of salt marsh within a tidal range of 20 m, this would be equivalent to protecting 50-100 km2 shoreline from sea level rise.

Allison – How do the size and arrangement of restored habitat influence restoration outcomes?

Wei – We think that these factors are linked because larger patches are expected to have increased connectivity and higher rates of gene flow, which in turn increases individual fitness and species persistence. In other words, those species that require large intact habitats will be better off if we restore larger patches because the overall area would be much bigger and more animals would have access to them through connectivity.