Water bodies, watersheds and stormwater

Restoring our coastal wetlands

Wetland restoration examples

This series of images portrays coastal wetlands restoration projects in which the St. Johns River Water Management District has been involved.

Coastal wetlands are among the most biologically productive natural ecosystems on Earth. Unfortunately, the activities of people have diminished or eliminated these important tidal areas over the past century.

On Florida’s northeast and east-central coasts, wetlands were historically considered mosquito factories, uninviting wastelands with no inherent value. For decades, the Indian River Lagoon’s wetlands were filled, ditched and diked — mostly to control mosquito populations, with little regard for the other ecological values they provided. By the 1970s, more than 40,000 acres of coastal wetlands (approximately 75 percent of the lagoonwide total) were impounded and isolated from the lagoon. Pumping water into these isolated impoundments stopped most mosquito production, but also impacted the vegetation and many wetland functions.

In the Northern Coastal Basin, an area north of the Indian River Lagoon (Volusia, Flagler and St. Johns counties), few impoundments were built, but dragline ditching and filling with dredge spoil (soil and other materials excavated to clear waterway channels) impacted many wetland areas.

Wetland habitats provide a vast array of ecosystem functions and serve as links and buffers between terrestrial (land) and aquatic (water) ecosystems where sediment and nutrients from uplands are trapped and transformed into plant biomass (leaves, stems, and roots). They provide habitat for numerous animals (especially fish and birds), thus helping to maintain a wide diversity of plants and animals. Wetlands are a source of particulate and dissolved organic materials that nourish the adjacent waters and support estuarine fisheries production. They also moderate storm and flood damage to upland areas. All of these functions are dependent on local aquatic connections between wetlands and the estuary.

Today, the ecological value of these transitional regions between land and sea are recognized. Over the last 25 years, the St. Johns River Water Management District and others have restored or reconnected more than 33,000 acres of coastal wetland impoundments and have also begun to repair other impacts to the wetlands.

The goal of the District and its partners is to reverse the damage done to coastal wetlands so that these areas continue to return to havens for wading and shore birds and breeding areas for fish, crabs, shrimps and the plants that depend on these areas as a source of food and shelter. Several types of coastal wetland restoration have been successfully implemented.

Dragline ditching:
Good for mosquito control, devastating for wetland denizens

A historic excavation photo from Volusia County Mosquito Control.

In the 1950s and 1960s, large excavators called draglines were used to cut through the marsh. The draglines were typically mounted to small barges, which moved by pulling themselves along through ditches as they were created, and material that was excavated from the wetlands piled on either side of the created ditch. These dragline ditches are extensive networks of deep, wide ditches and spoil piles cut through historical coastal wetland habitat, severely reducing the acreage of wetlands remaining.

The purpose of the ditches was to interrupt the life cycle of saltmarsh mosquitoes by altering their breeding sites. Saltmarsh mosquitoes lay their eggs on moist soils. These eggs hatch in huge numbers when the marsh is flooded by tides or rain. Dragline ditching converts large acreages to ditch and spoil piles while altering the hydrology of the remaining wetland and providing access for mosquito-eating fish.

Dragline ditching as seen from the air.

The most extensive ditching occurred in Mosquito Lagoon (nearly 1,200 acres), though some ditching is present throughout the Indian River Lagoon and the Northern Coastal Basin. While dragline ditching effectively reduced the mosquito population in coastal wetland areas, an unintended result was a severely altered wetland ecosystem.

Impacts of dragline ditching

Widespread decreases in wetland habitats were seen with dragline ditching, with the amount of wetland habitat lost varying with the intensity of ditching. In the most extensively ditched areas, up to 80 percent of historical wetland was replaced with ditch and spoil pile. On average, half of an impacted area was ditch and spoil. This reduced ecological productivity, which in turn reduced the fish and wildlife an area could support. The valuable protection from storms that wetlands provide was also diminished.

The invasion of nonnative species is also a problem. Spoil areas are substantially higher elevations than the surrounding wetland. This elevation allows the colonization of upland plant species, including invasive nonnatives, such as Brazilian peppers. The mangroves that remain inhabit a narrow intertidal zone along the edges of spoil piles, but are often out-competed by terrestrial and exotic species on the elevated portion of the pile.

Juvenile fish habitat was lost. The wetlands lost plants, especially grasses, which are critical for providing food and shelter for fishes, crabs and shrimps. The deep water provided by the ditches allows large fish predators access to what was historically shallow water habitat utilized by small juvenile and resident fish.

Restoring dragline ditches

In this photo from Volusia County Mosquito Control, a dragline ditch is filled.

The District and its partners have developed a systematic process for restoring coastal wetlands that have been dragline ditched. Dragline ditch restoration projects require the use of an amphibious excavator. An excavator is mounted on tracked pontoons, enabling them to access submerged areas. This low-bearing weight machine (less than 2 pounds per square inch) is owned and operated by Volusia County Mosquito Control.

Vegetation is cleared from the spoil area and placed in the adjacent ditch. This process avoids burning the plants and permanently sequesters the carbon they contain. Spoil material is first moved to the side of the ditch. If additional material remains, the main ditch is narrowed. The area of the spoil pile and the newly filled ditch are carefully graded to the adjacent remaining wetland elevation. The result is that substantially more area is at coastal wetland elevation.

Fiddler crabs are the first animals to appear on the newly restored surface. This semi-terrestrial wetland native can reach very high numbers and is food for numerous other animals, such as wading and shorebirds, fish and mammals. Mangroves and other wetland plants quickly colonize the area, though it will take several years to reach full coverage.

The current restoration effort is a collaboration with U.S. Fish and Wildlife Service, Florida Fish and Wildlife Conservation Commission, the District, Volusia County Mosquito Control and the public land owner/managers of impacted wetlands in Volusia County. These partners include Canaveral National Seashore, Mosquito Lagoon Aquatic Preserve, and several state parks. The majority of the funding comes from the National Coastal Wetland Conservation Grants Program.

Dragline ditches restoration benefits

Ditches are less visible in this recently restored coastal wetland.

Through early 2010, approximately 305 acres of impacted wetlands have been restored in Mosquito Lagoon, returning approximately 120 acres to wetland elevation. Restored wetlands provide more space for wading and shore birds and greater production of fishes, crabs and shrimps and the plants they depend upon. Restored wetlands can produce about 50 pounds of resident fish per acre per year.

Wetland plants recruit to the restored surface quickly. Early colonizers include black mangroves, sea purslane and glasswort. Plants left on site and from neighboring wetlands provide recruits to the restored areas within months or years.

The restored wetland area and the relic shallow ditches are a perfect combination for fish productivity. The high levels of resident fish production from the restored wetlands during the high-water periods of the year and the shallow water access provided to juveniles of large fisheries species is a recipe for great fishing into the future.

As the marshes are restored, mosquitoes might be expected to return. However, the small relic ditches that remain after restoration prevent mosquitoes from breeding. In fact, mosquito breeding has not increased in any of the previous project areas over the last eight years.

How quickly do marshes recover from the damaging effects of human manipulation? Experts are working with the University of Central Florida to find out. Sites restored over the past several years are being monitored to determine how quickly native vegetation returns and provides wetland functions.

Mosquito impoundments

Mosquito impoundments were designed to manage mosquito production by isolating wetlands from the Indian River Lagoon and flooding them with the use of wells or pumps. They were constructed with heavy machinery that was used to dig a “borrow ditch.” This sediment was piled on the outer edge of the marsh to create a dike, which isolated the interior wetland from the rest of the estuary.

The problem: Impoundments devastated wetland functions and destroyed wetland vegetation. Negative impacts of the impoundments included:

• Widespread changes throughout plant and animal communities in approximately 75 percent of wetland habitat of the lagoon.
• Invasion of nonnative plants along the dike surface, primarily Brazilian pepper trees.
• Decreased connectivity between the wetlands and the lagoon, which hindered the movement of fish and invertebrates that normally use the wetlands for breeding, feeding and refuge from predators.

A dragline ditch from ground level, as shown in this photo from Volusia County Mosquito Control.

The Reconnection Solution: Scientific research held the key for the first big steps in reestablishing wetland functions. Research conducted in the late 1950s and 1960s had demonstrated that most mosquito production could be halted by flooding the impoundments only during the summer mosquito breeding season. Subsequent work in the 1970s and 1980s documented the value of reconnecting isolated impoundments to the lagoon via culverts. The culverts, when left open during the non-breeding season (September though May), allowed vast numbers of fish, shrimp and crabs to regain access to their historical wetland nursery and feeding grounds. Wetland vegetation also benefited from this change. This seasonal mosquito control method became known as rotational impoundment management, or RIM. The demonstrated advantages of RIM implementation led to the inclusion of impoundment reconnection as a priority element of the lagoon program.

Full impoundment restoration: Nearly 50 percent of impounded wetland acreage is within the Kennedy Space Center/Merritt Island National Wildlife Refuge complex. Though initially constructed for mosquito control, the impoundments there have been managed to benefit migratory birds (primarily ducks). Where mosquito control and wildlife management are not a priority, impoundments have been selected for full restoration. As part of a comprehensive collaborative effort, the Refuge, with District support, developed site-specific restoration plans to implement its Comprehensive Conservation Plan objectives. The site plans, that included impoundment dike removal/shoreline restoration, were combined into a Refuge-wide state and federal permit application that included more than 18 miles of dike enclosing approximately 1,100 acres of coastal wetland. Full restoration of all 18 miles would return more than 120 acres to wetland elevation while enhancing the hydrologic connectivity of the interior wetlands.

With permits in hand, work on these impoundments began, but the District was only able to fund a few miles of dike restoration per year. However, with new funding from a National Oceanic and Atmospheric Administration (NOAA) Recovery Act grant, work has been accelerated and expanded.

Dredge spoil removal

From the 1880s through 1950s, significant navigation channel dredging activities were undertaken to create and maintain what is now northeast Florida’s section of the current Intracoastal Waterway. In many areas, the channel was cut through pristine wetlands, depositing large amounts of spoil beside the new channel and filling more than 1,400 acres of this important estuarine nursery habitat in the District’s Northern Coastal Basin.

In some cases, restoration involves recreating a healthy, productive saltmarsh and tidal creek habitat, and enhancing tidal connection to the estuary of adjacent isolated saltmarsh. Work generally includes clearing vegetation from the site, excavating and disposing of spoil material, grading the site to match existing elevations in adjacent wetlands and re-vegetating the restored surface with species similar to those occurring in surrounding marshes.

An excellent example of this type of restoration is found at North Peninsula State Park in Volusia County. Here, the District and its partners are restoring 30 acres of dredge spoil-filled historic salt marsh. This project will increase tidal connection of approximately 30 additional acres of salt marsh, which were isolated by spoil deposition. This project is fund through a NOAA Recovery Act grant.

For more information about the District’s involvement in coastal wetlands restoration projects, contact Ron Brockmeyer at (386) 329‑4495 or rbrockme@sjrwmd.com.

Posted on 6-28-2010