Coastal Emergent Wetlands: Restoration and Protection Strategies
Emergent wetlands in coastal Texas have tremendous ecological and economic values. Finfish, shellfish, waterbirds and other wildlife depend on marshes to survive. Coastal marsh vegetation also armors shorelines from erosion, filters pollutants, enhances water quality and promotes primary production. However, emergent wetlands in Texas have been lost due to filling, draining, dredging and dredge disposal, bulkheading and shrimp trawling. Pumping groundwater for industrial, commercial and residential uses has also contributed to rapid and alarming wetland loss – especially in localized areas around Galveston Bay. As land subsided, wetland vegetation was inundated by deep water and replaced by less productive open water habitat.
Maintaining the economic values, fish and wildlife resources, and aesthetic qualities of the Texas Coast depends on re-establishing and restoring its wetlands. The FWS Texas Coastal Program, working in close coordination with the Galveston Bay Foundation and a consortium of federal and state agencies and conservation groups, played an integral role in providing funds and technical expertise to create an inventory identifying and describing sites included in the "Habitat Conservation Blueprint: A Plan to Restore the Habitats and Heritage of Galveston Bay." Completed in 1998, the Conservation Blueprint identifies 170 specific restoration projects and commits partners to work collaboratively to restore 24,000 acres of Galveston Bay’s coastal emergent marshes and seagrass meadows by the year 2010. Recently, the Coastal Coordination Council, the governing body of the state’s Texas Coastal Management Plan, agreed to fund a habitat restoration site inventory for the entire Texas coast. The FWS Texas Coastal Program is committed to lend its expertise and support to complete this broader coastwide project, for the first step in restoring habitat is to identify and prioritize potential restoration sites.
Where sites have been identified, restoration projects are being implemented by cooperative working groups that capitalize on the capabilities of various federal and state natural resource agencies and non-governmental conservation groups. Partners typically employ the following emergent wetland restoration techniques:
The "scrape-down" technique is used to remove excess dredge material from areas that were once wetlands. By removing dredge material to the elevation of adjacent salt marsh, and then planting the area with cordgrass, emergent marshes can be re-established. Typically, channels are excavated into the dredge material to allow nutrient flow into the upper reaches of the restoration site. This method has been employed to restore approximately 60 acres along the I-45 approach to Galveston.
The "beneficial uses" technique can be employed when dredge material is available from nearby construction or maintenance projects. Until recently, dredge material has typically been transported to upland disposal sites, but many partners appreciate that dredge material can be deposited in coastal areas where fill is needed to counteract the effects of subsidence. Dredge material is usually broadcast as a wet slurry across a subsided area until the elevation is appropriate for establishing emergent marsh vegetation. Once the dredge material settles, cordgrass is planted to encourage re-vegetation with native plants. Dredge material can also be used to create and maintain islands that provide predator-free nesting for colonial waterbirds. The beneficial uses technique can provide substantial environmental benefits and may also reduce costs for industrial dredgers by eliminating expensive upland disposal fees. This method has been employed to re-establish a 6 acre marsh at Armand Bayou Nature Center in Clear Lake, a 160-acre marsh at San Jacinto in Houston, and to create nesting habitat on several central Texas coast islands. These projects have demonstrated that partnerships between conservation and business interests can be forged for the benefit of all. Therefore, interest groups have already agreed that dredge material from the upcoming Houston Ship Canal deepening and widening project will be used to re-establish more than 4,000 acres of emergent wetlands in Galveston Bay.
The "marsh terracing" technique, pioneered in Holland and successfully applied in coastal Louisiana, has been used at several sites in coastal Texas, the first project was completed in 1999. In areas where coastal subsidence has led to wetland loss, and erosion threatens to destroy remaining marsh, terraces can be constructed to reduce wind fetch, help armor the shore and establish new wetlands to provide productive fish and wildlife habitat. A marsh track hoe, specifically designed for wetland use, pushes bottom sediments into long, narrow terraces with shallow side slopes that rise 2 to 3 feet above the water. Terraces are typically constructed in a series of 200 foot open square patterns. Once constructed, terraces are planted with sprigs of cordgrass. Ultimately, cordgrass and other emergent wetland plants will grow on the terraces, and submerged aquatic vegetation will grow in the open water between the terraces This restoration method has been employed to re-establish an 83 acre marsh complex at Pierce Marsh and a 121 acre wetland complex at Galveston Island State Park.
Geotextile tubes and rock groins placed in shallow calm seas, minimize shoreline erosion and increase water clarity, allowing coastal wetland vegetation to be re-established or coastal nesting island shorelines to be stabilized. Geotextile tubes, best described as giant sand-filled socks, have an exterior plastic fiber "skin" covered with a black UV-resistant shroud. Rock groins are long, narrow mounds of rock rip-rap. Geotextile tubes and rock groins can both be effective, but rock groins last indefinitely and create living oyster reef habitat. Geotextile tubes, on the other hand, have an expected lifespan of 25 years and cannot support a living marine community. However, rock groins are three times more costly than geotubes. Geotextile tubes have been deployed offshore from Galveston Island State Park to help restore coastal wetlands, and near Shamrock and Sundown Islands to protect nesting islands. In other locations, such as Armand Bayou, brush fences, snow fences and hay bales have also been used to capture silt and minimize erosion damage on windward shorelines until marsh vegetation becomes established.
Emergent wetland vegetation planting techniques have been refined. A cordgrass nursery operated by Reliant Energy Inc., located in Baytown, Texas provides vegetation for wetland restoration sites. When cordgrass is planted at the proper elevations and on 3 foot intervals, the restoration site will generally be fully vegetated within two years. Cordgrass planting has been an important component of all emergent marsh restoration projects in Galveston Bay. Oftentimes, volunteers assist staff in completing this important, but time-consuming work.
All of these restoration techniques are relatively new and are still being refined, so collaboration, experimentation and monitoring involving many conservation-minded partners will continue, in order to determine which methods are most effective in protecting our shorelines and restoring our marshes.