News

Worried about erosion? Conserve or plant some salt marsh

By: Eric Sparks / Published: Sep 14,  2017

Salt marshes are a type of coastal wetland that are common throughout the globe. If you have driven over a bridge near the coast, you have probably seen lots of salt marsh. Among the many benefits that these ecosystems provide, such as improving water quality through filtering out pollution and providing habitat for commercially and recreationally important finfish and shellfish, erosion control and shoreline stabilization are often the most valued by waterfront property owners. In fact, scientists have conservatively estimated that coastal marshes provide over $20 billion worth of shoreline stabilization and storm protection services in the United States alone.

In coastal Mississippi and Alabama, the two most dominant salt marsh plants are black needlerush (Juncus roemerianus) and smooth cordgrass (Spartina alterniflora). Both of these plants have extensive root systems that help keep them in place along shorelines with low (e.g., bayous) to moderate (e.g., bays) wave energy. Frequent boat wakes can increase wave energy and subsequent erosion in bays and bayous, but that was covered in my last staff blog.

Living shoreline project in Perdido Key, Florida, where a temporary breakwater was installed and salt marsh (tall grass) was planted. (Photo by Eric Sparks)
Living shoreline project in Perdido Key, Florida, where a temporary breakwater was installed and salt marsh (tall grass) was planted. (Photo by Eric Sparks)

The hardy roots essentially grab and hold sediment in place and this, in turn, slows down shoreline erosion. These plants also create a dense aboveground canopy of leaves and stems that help capture sediment brought in with waves and tides (i.e., sediment deposition or accretion) and helps reduce wave energy. This resiliency of salt marshes was demonstrated by scientists in Breton Sound, Louisiana, when they found salt marsh loss to be at least 20 times less than surrounding ecosystems after both Hurricanes Katrina and Rita hit the area in 2005. Combining all of these “services” that marshes provide, you can see how they can be used to stabilize shorelines and protect against storm damage.

Wave energy is the main driver behind shoreline erosion and studies have shown that only a 30ft salt marsh buffer can reduce low to moderate wave energy by over 50 percent. What this means to a property owner is that the presence of salt marsh in front of your property essentially reduces the impact of incoming waves on upland property by at least half. Add in the increased potential to trap more sediment and the other ecosystem services provided by marshes and you can see that salt marshes are a great tool for sustainably protecting shorelines.

A salt marsh on Horn Island in Mississippi. (Photo by Eric Sparks)
A salt marsh on Horn Island in Mississippi. (Photo by Eric Sparks)

Often, salt marshes need a little help and/or protection to get established in areas with moderate wave energy. One method to providing this protection is through living shorelines projects. If installed correctly and in appropriate areas, you can think of a living shoreline project as a cheaper, more environmentally friendly, and more resilient alternative to bulkheads. The techniques used in living shorelines projects are extremely site specific, but most essentially involve the construction of a nearshore breakwater to help reduce wave energy before it hits the marsh. Depending on the site, these breakwaters can me made of temporary materials, such as COIR logs or a short board fence, or longer term materials, such as rip-rap, concrete structures, or oyster shell cages. The intention of the temporary breakwaters are that they will only persist long enough for the plants to get established or rerooted, whereas in higher wave energy environments (e.g., larger fetch of heavy boat wakes) the more permanent breakwaters may be needed for sustained shoreline protection in conjunction with the shoreward salt marsh.

If you are interested in learning more, we do offer living shorelines education workshops in Mississippi and Alabama once to twice per year. The majority of these workshops are focused on homeowners, but there are some contractor workshops being planned for the near future.

If you are interested in being placed on the email list for future living shorelines workshops or have any questions, contact me at eric.sparks@msstate.edu or 228-546-1025.

Comments

comments powered by Disqus