What New England Marshes Can Teach Us About Coastal Louisiana Restoration

10.17.2017 | In Science
By John Andrew Nyman, PhD, Professor, LSU School of Renewable Natural Resources

I’ve studied coastal wetland restoration in Louisiana since the 1990s and have visited with landowners and managers who want to slow wetland loss and build new land across the coast, from Lake Sabine to Slidell. I’ve also studied coastal wetland management and restoration outside Louisiana, by reading articles and attending conferences, but until recently, I’d only visited a handful of sites.

This summer, I traveled to New England to participate in the workshop “Tidal Marsh Restoration: A Traveling Course from Rhode Island to Maine.” While there, I quickly learned that Louisiana and New England face similar challenges related to sea level rise and land loss, and that both areas can learn from each other about ways to combat that loss and restore their coasts.

Water draining at low tide through a tidal restriction on the West Branch of the Pleasant River at Addison, Maine.

Coastal Similarities

While in New England, I visited 12 tidal marsh restoration sites in Rhode Island, Massachusetts, New Hampshire and Maine. As in much of Louisiana, the marshes I visited naturally receive both fresh and salt water. Also similarly, these New England marshes were dominated by Spartina alterniflora (cordgrass), Spartina patens (another cordgrass species) or Phragmites australis (common reed).

As in Louisiana, the people know and love their New England marshes. But it is a different landscape with its own unique issues. In southeast Louisiana, human activity has reduced natural river inflow to coastal marshes. In southwest, human activity has increased saltwater tidal influence, also known as tidal inflow, into low-salinity marshes.

Therefore, two important tactics for restoring Louisiana’s coast include increasing freshwater river inputs and decreasing saltwater tidal inputs. But the same is not true for New England marshes.

Coastal Differences

In New England, human activity has reduced saltwater tidal inflow into high-salinity marshes. Coastal restoration therefore generally involves restoring tidal action into such marshes, while the opposite is true in Louisiana.

Another difference is that increasing tidal action generally increases salinity as well as drainage in New England marshes. In Louisiana, however, increasing tidal action generally increases salinity without increasing drainage. The greater tidal range in the New England marshes (5-15 feet) as opposed to Louisiana (6 inches) is the reason for this difference, but I’m unsure how much of this is related to differences in the duration that the marsh surface is flooded or the differences in the depth of water at low tides. 

Water held during low tide upstream of a tidal restriction on the West Branch of the Pleasant River at Addison, Maine.

Common Reed

Another difference is the greater abundance of the European variety of common reed in New England. In New England, the European variety is a problem plant that dominates many coastal wetlands because of roadways that restrict tidal flow and lower salinity. In coastal Louisiana, common reed rarely dominates large areas and even where it does dominate, the Gulf and Delta varieties are plentiful, and the European reed is relatively rare.

In most of Louisiana, common reed occupies a minor part of the landscape and is valued for nesting habitat, it ability to trap sediment, withstand erosion and offset subsidence with peat. It is especially valuable in the Bird’s Foot Delta at the end of the Mississippi River where it armors the river passes and dominates extensive areas at the ends of the passes that serve as a buffer between the Gulf of Mexico and freshwater, herbaceous wetlands closer to the main channel.  

New England’s Solution for Louisiana’s Common Reed

The newly recognized dieback of common reed in Louisiana, possibly due to an invasive insect, may cause the European variety to be desired in Louisiana’s Bird’s Foot Delta. Preliminary observations suggest that the European variety resists the dieback, but it currently accounts for little of the reed in the area. It is unfortunate but unavoidable that these differences in reed between coastal Louisiana and much of the Atlantic Coast complicate communicating the desirability of common reed in the Bird’s Foot Delta.

Common reed (Phragmites australis), often called Roseau Cane is dying throughout coastal Louisiana. The photo above was taken in the Bird’s Foot Delta. It shows less robust species such as elephant ear (Colocasia esculenta) and irises (Iris sp.) replacing common reed on natural levees of river passes where water is shallower. In the more extensive deeper waters, no other plant is able to survive as the common reed becomes thinner and shorter as it re-sprouts after successive dieback events.

Last month, I traveled to Washington, D.C. to assist Louisiana’s delegation with a briefing on Capitol Hill, explaining to other delegations and agency staff why Louisiana is concerned that dieback of common reed is a threat to wetlands in the Bird’s Foot Delta.  Wetlands in the Bird’s Foot Delta are used by numerous resident and migratory fish and wildlife and also hinder water flow from the navigation channel, which reduces the costs of dredging and thus benefits farmers, coal miners, and the people who consume their products. If other solutions cannot be found, planting the European variety of common reed on the river passes might become desirable. 

Land loss is a global issue, and it is one that cannot be solved by one method alone. In the rapidly changing environment that we live in, it is important to learn from our coastal neighbors about new methods for creating a sustainable environment. In the face of rising seas and stronger storms, we must consider new adaptation strategies if we want to maintain our invaluable coastal landscape for generations to come.


For more info on common reed, listen to our recent Podcast with Dr. Nyman.