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Salt Marsh Habitats: When Does Mother Nature Need Help?

By: Karen Greene, Sandy Hook Habitat Conservation Division Field Office

There are few things Habitat Conservation biologists love more about their jobs than getting out on a salt marsh on a perfect late summer day:  Sunny, cool enough for a long-sleeved shirt to protect against ticks, and just windy enough to keep mosquitoes and greenhead flies at bay. This September, habitat staff from the New Jersey field office got out on one of those rare, perfect days. Along with a team of biologists from a variety of other state and federal agencies, we visited a number of salt marsh sites in Little Egg Harbor, New Jersey to see if these marshes needed some help.

Eroded shoreline along Little Egg HarborEroded shoreline in Little Egg Harbor, NJ, a potential living shoreline.

The Value of Salt Marshes

In our rush to industrialization, we filled salt marshes around the nation – they were seen as smelly nuisances that should be filled for development and to get rid of mosquitos. It wasn’t until the 1960s that we began to recognize their value as water filters, flood and erosion protection, and valuable habitat for birds, fish, and other wildlife. For example, summer flounder, striped bass, bluefish, winter flounder, and many other fish use salt marshes for food, shelter, spawning, nursery areas, and refuge from predators. Egrets and herons, along with many other birds, feed on the variety and abundance of small fish, crabs, and other animals that live in the marsh. Because these marshes are so important, both for animals and humans, we need to be careful that we do not harm them.

Two Ways to Help a Salt Marsh

On this particular day, we were looking at two ways to help stabilize a salt marsh: living shoreline projects or thin layer placement of dredged material.

Living shorelines stabilize an area using plants alone or in combination with some type of harder structure (e.g., oyster reefs or rocks). Living shorelines maintain the natural connection between the land and water and reduce erosion, while providing habitat value and enhancing coastal resilience. 

Open water and mudflats in salt marsh. Little Egg Harbor, NJ.Open water and mudflats in salt marsh, Little Egg Harbor, NJ.

Thin layer placement of dredged material raises the level of a marsh using sand and mud. Placing dredged material on top of a marsh that is sinking, losing plants, or has expanding areas of open water can help the marsh keep pace as sea levels rise. This build-up prevents the marsh from drowning. There are many challenges with using this technique since the placement of material on the marsh can smother the existing plants or create conditions that prevent plant regrowth. When considering the use of thin layer placement, we have to answer a host of questions, such as:

When to Help, and When to Leave it to Mother Nature

The Little Egg Harbor salt marshes are beautiful, with large expanses of cord grass and salt hay, two plants commonly found in East Coast salt marshes. Our site visit took us to see two locations where wind, waves, boat wakes, and other impacts have eroded the marsh shoreline. At one spot, the road was also eroding away. These areas were excellent spots to install a living shoreline using dredged material, wetlands plants, and possibly some rock along the edge, which would protect these spots from further erosion. If living shorelines are built along these marshes, it will be a win-win situation for the residents and the wetlands.

Little Egg Harbor, NJ salt marshLittle Egg Harbor, NJ salt marsh with mix of salt marsh plants and open water.

We also visited another area of salt marsh where thin layer placement of dredged material is being considered. This wetland contained a mix of salt marsh plants and small areas of open water where egrets were feeding. It was almost the picture of a perfect salt marsh – a carpet of green with creeks and open water ponds. Because there was little evidence that this marsh was sinking, the vegetation was dying or getting sparse, or that the ponds and channels were expanding, this marsh would likely be harmed by thin layer placement because the material could kill the existing plants, eliminate the ponds used by fish and birds and may increase the likelihood of undesirable plants invading the wetlands.  This area highlights the challenges of deciding which marshes need help and which do not, as well as the continuing problem of what to do with sand and muds removed from navigation channels.

At the end of the day, we headed back to our cars. After pulling off our muddy boots and stowing our gear, we were left to ponder just when does Mother Nature need our help? Because each marsh system is unique, we need to carefully plan any protection and restoration activities to make sure that we keep the beneficial functions of the wetland.