For eons a natural cycle of land loss and land gain sustained the complex, dynamic ecosystem of the Mississippi River delta.

The expanse of land built from sediment deposited by the river’s floodwaters roughly balanced land lost to the natural forces of erosion and subsidence.

But by reshaping the landscape for social and economic interests, human interference in the ecosystem has upset this natural equation. No longer self-sustaining, the Louisiana coast has lost hundreds of square miles over the past century.

A biologist turns over a clump of cordgrass in a subsiding marsh to show how soil around the roots has washed away. Without roots anchored in sediment, the plant will tear free and float off, exposing a new edge of marsh to erosion.

Continued land loss threatens the economy and security of the entire nation, dependent on the region for natural resources, oil and gas infrastructure, shipping routes and storm protection. Consequently state and federal agencies have undertaken protecting and restoring Louisiana’s wetlands. The agencies rely on scientists and engineers to remedy the ecological disruption. Halting, or even reversing, the trend of land loss will depend on their success in replicating the ecosystem’s natural functions.

Causes of a Complex System’s Decline

To mimic the ways that wetlands naturally nourish and sustain themselves, restoration scientists and engineers must understand the ecosystem’s structure and functions and the reasons for their current demise. Study of the wetlands is conducted through the four broad disciplines comprising coastal science: biology, geology, hydrology and chemistry. “In the wetlands,” says Richard Neill, manager of the Plant Materials Center, Natural Resource Conservation Service (NRCS), “you can’t be a good biologist — or hydrologist or geologist or chemist — without knowing the other fields. Everything interrelates — it’s an interdependent, dynamic system.”

Scientists describe land loss in the terms of their own disciplines. Biologists point out that conversion of land to open water is directly related to the loss of vegetation. “Kill the plants and you expose the soil,” says John Jurgensen, an engineer and project manager with NRCS. “Without a root mat to hold it together, soil washes away.”

But vegetative death is part of the ancient natural cycle, contributing essential organic bulk to wetland soils. What causes plant death to outstrip plant production, undoing the age-old balance?

The success of a restoration project may be determined by comparing the structural and functional characteristics of the rebuilt wetland to those of a nearby healthy, or reference, marsh. Drawing on all disciplines of coastal science, comparisons consider factors such as species composition, the growth rate of the biomass, changes in elevation, the texture and nutrient content of soil particles, drainage regimes, and use by fish, benthic invertebrates and other animals.
Sharon Coogle, Koupal Communications

Chemists cite changes in the chemical profile of water, such as decreased nutrients or increased salinity, as causes of vegetative decline. “Every species has its range of tolerances defining where it can live, “ says Mark Hester, associate professor at the University of Louisiana at Lafayette. “As conditions change — as sea water invades freshwater marshes, say, or severe drought alters the natural soil chemistry — plants that can’t acclimate die.”

But why are conditions changing so dramatically and rapidly as to outstrip the ecosystem’s self-sustaining adaptability? Hydrologists describe effects resulting from humans intervening in waters’ flow, such as interruption of delivery of river-borne nutrients, saltwater intrusion through man-made canals into marsh interiors, or blocked drainage that causes the drowning of subsoils. Is altered hydrology responsible for the wetlands’ decline?

Throughout the history of the delta, hydrological patterns have shifted, yet the wetlands have survived. Geologists suggest subsidence underlies the current crisis. “Probably the biggest stress on plants is lack of sufficient elevation,” says Hester. “Floodwaters no longer replenish the marshes with sediment. The soil sinks and becomes waterlogged. Plants become stressed and produce less biomass for maintaining marsh elevation; plants die and the land washes away.”

Restoring Conditions for Sustainability

Understanding how coastal land loss results from interrupting natural ecosystem functions provides the framework for designing projects to restore the wetlands. Using nature as their model, scientists describe optimal conditions for a project to create, and engineers determine the best way to achieve them.

Whether killed by waterlogged soils resulting from subsidence, by increased salinity due to advancing gulf waters, or by other causes, these trees stand as evidence to an ecological change so swift, so extreme, that they were unable to survive.
Richard Neill, PMC, NRCS

“As an engineer I tend to focus on physical factors, such as wave height and energy, that influence structural choices,” says Jurgensen. “However, often my co-manager on projects is a biologist. He analyzes the project’s probable effects on the living ecosystem and recommends features, such as openings in shoreline protection to allow tidal exchange, to support functions upon which living organisms depend.”

Scientists may use healthy marshes adjacent to project areas as reference marshes to establish standards for natural features such as elevation; the type, coverage and growth rate of vegetation; the nutrient load carried in water; or the speed and direction of water currents.

“The first step is to look at what naturally is in a functioning wetland,” says Neill. “We shouldn’t fight nature. We have to figure out the reasons why a plant grows here and not 100 yards over there. It goes back to the chemical, hydrological and geological conditions that define and distinguish any single ecosystem.”

Project design incorporates information from all these coastal science disciplines. For instance, geologists may help select locations by identifying areas of greatest potential land gain. Hydrologists might calculate the frequency and depth of flow from diversions that move nutrients farthest into the wetlands. Chemists could measure the rate of organic carbon decomposition in the soil to determine the nutrient release available for plant growth.

But wetland conditions are not only a complex interplay of geologic, hydrologic, biologic and chemical factors, they are also dynamic, in constant flux. Restoration projects must factor changing conditions, whether taking place within hours or over decades, into their designs.

Sea level rise is an example of a change anticipated by scientists. “With rising sea levels we expect salinity to increase in interior marshes,” says Neill, “so we’re looking for plants with greater salt tolerance to use in restoration. It might take 10 or 12 years to find and develop such a plant.”

Establishing target elevations for marshes enhanced with dredged material presents another example of how project design must consider change over time. Should the ideal height be established with the initial delivery, or should the marsh reach its target height after a few years’ subsidence? How many years should the target height be sustained? The decision influences when, and for how long, the desired plant community will flourish. When conditions are optimal, the plants will make positive contributions, such as trapping sediment and providing organic matter, that influence the lifespan of the project.

Project areas suffer changing conditions the same as do natural wetlands. Without maintenance, they are subject to decay and decline. “Although designing wetland restoration projects for self-sustainability is the ideal goal,” Hester says, “maintaining projects is as important as building them, helping to reduce costs in the long run.”

Learning from Louisiana

Although located within the state to address the state’s crisis of land loss, Louisiana’s coastal restoration projects make global contributions to science and engineering.

“For instance, our studies of brown marsh die-back assist ecologists in understanding the phenomenon in New England,” says Hester. “What we learn about the effects of climate variability in our wetlands will help people develop strategies to deal with the consequences of climate change worldwide.”

Ultimately the answers to all ecological questions reside in the field. Wetland secrets are unlikely to be revealed without dedicated researchers willing to get hot, wet, sweaty, sandy, muddy and cold.
Dr. Robert Lane, LSU

As data on the results of Louisiana’s restoration projects accumulate, the exchange of information among scientists and engineers is constant. “There’s a continuous loop between research and implementation,” says Rick Raynie, a coastal resources senior scientist with the Louisiana Department of Natural Resources. “Research suggests how a project should be built and managed. Data collected on project results indicate where uncertainties lie and point to topics requiring further research.”

“We have the opportunity in Louisiana to create a model for integrating life sciences with physical engineering and socioeconomics to deal with global issues like climate change and sea level rise,” says Hester. “This synergistic and interdisciplinary approach will be the key to success in managing and restoring coastal ecosystems worldwide.”

Wetlands Center Develops Science for Sound Restoration

Where has coastal land loss been most severe? How might global climate change threaten flora in brackish wetlands? What technology is used to collect data on migratory bird populations?

Government agencies, academicians, even the interested public ask such questions of the National Wetlands Research Center (NWRC). If an answer exists, the center is likely to locate it in its extensive print and digital library. If the answer’s not known, the question could become a research topic for the center’s ecologists, chemists, biologists, geographers and others who study threatened wetland ecosystems and investigate how to stabilize, restore and manage the coastal landscape. The center conducts research through three branches:

The Wetlands Ecology Branch focuses on the sustainable management and restoration of coastal saltwater wetlands, coastal and inland freshwater wetlands, submerged aquatic ecosystems, and coastal prairies. Research focus areas include

• accretion, subsidence and sea level rise
• coastal marsh die-back
• marsh and coastal prairie management and restoration
• global climate change
• nutrient dynamics and biogeochemical cycling
• plant community dynamics
• submerged aquatic vegetation

The Forest Ecology Branch studies the ecology and restoration of forested wetlands and uses computer modeling techniques to predict conditions under various changing circumstances. Research focus areas include

• physical, chemical and biological functions of forested wetlands
• conservation genetics
• dendroecology
• fire science
• reforestation and restoration methodologies

From marine sea grasses to bottomland hardwoods in forested wetlands, NWRC scientists conduct field and laboratory research to provide the ecological knowledge and insight necessary for making sound decisions about vital wetland resources.
NWRC

The Spatial Analysis Branch uses computerized analysis techniques and state-of-the art technology to provide the spatial data necessary for making informed decisions about natural resource management. Research focus areas include

• ecosystem analysis
• environmental electronics engineering
• geographic information systems (GIS)
• GIS-based ecosystem assessment and modeling
• photo interpretation and cartography
• population ecology
• remote sensing

Administered under the Department of the Interior as an agency of the U.S. Geological Survey, NWRC employs about 80 scientists working at the center’s facility in Lafayette, Louisiana, at two field stations in Texas and Louisiana, and at a project office in Florida. Founded in 1975 as the National Coastal Ecosystems Team, the center mapped coastal Louisiana land loss and played a leadership role in raising awareness about the extent of the problem of wetland loss.

“Every CWPPRA project incorporates analyses of historical wetland changes into its planning,” says Greg Steyer, an ecologist at NWRC and co-chair of the CWPPRA Monitoring Workgroup. “By addressing key scientific uncertainties, the center’s investigations increase the likely success of our efforts to restore a degrading environment.”

Learn more about the National Wetlands Research Center by visiting its Web site at www.nwrc.usgs.gov.

In addition to providing offices and laboratories for the center’s research scientists, NWRC’s facility in Lafayette, Louisiana houses the center’s library and information center, which provides services to manage, store, retrieve, translate and present scientific information.
NWRC