Three case studies are presented in conclusion to provide perspective on some of the approaches to restoration ecology described above. These were chosen to illustrate the range of the ecosystems that have been involved in this subfield of ecological engineering. These case studies also include several examples of importance in the history of restoration ecology.
Saltmarshes are the dominant vegetation along low energy coastlines in the temperate zones of the world. However, because human development also is focused along these coastlines, saltmarshes have been converted to commercial and residential land uses through dredging and filling in many areas. The concern about losses of saltmarshes became even more important as their value to society began to be recognized through ecological research in the 1960s. saltmarshes are important as a source of, and nursery zone for, fish and shellfish species that are harvested for seafood, and due to their role in shoreline protection. In fact, the first major ecological valuation study was done for saltmarshes (see Chapter 8) and is a benchmark in ecological economics. Thus, because of their losses due to human development and because of the recognition of their values to society, saltmarshes became a focus of conservation and restoration along the U.S. east coast in the 1970s. saltmarshes became the first ecosystems to be restored on a large scale and the technology is now well developed (Zedler, 2001).
The history of saltmarsh restoration is particularly interesting because it involves a coevolution between dredge disposal activities conducted by the U.S. Army Corps of Engineers and planting research by ecological scientists. Perhaps without contributions from both the Corps and the scientists, the development of saltmarsh restoration might have been inhibited or might have taken a different course. This coevolution is even more remarkable because dredging and filling activities conducted by the Corps were, in part, the cause of saltmarsh losses before the coevo-lution began!
An introduction to the Corps of Engineers is useful before describing the development of saltmarsh restoration. The Corps is the largest engineering organization in the world and has been important in several aspects of ecological engineering. While the environmental record of the Corps has not been flawless, as noted in the introductory chapter of this book, major changes are under way, and in the future the Corps may become a leader in ecological engineering and in areas of environmental management. The Corps has always had a role in water management as noted by Hackney and Adams (1992) below:
It is difficult to find anyone or a single publication that presents an unbiased view of the U. S. Army Corps of Engineers and their activities in U.S. Waters. In the beginning, 16 March 1802, the Corps was devoted exclusively to military operations. As the one organized group of engineers "on call" for the U.S. government, they quickly became associated with the construction and maintenance of waterways and harbors through which the U. S. military could rapidly move ships, troops, and supplies. The lack of a national policy related to transportation and defense became obvious to many American leaders after the War of 1812 with Britain. In 1824 the U.S. Army Corps of Engineers was officially given legislative authority to participate in civil engineering projects. ... Of perhaps greatest importance was the fact that the Corps of Engineers not only undertook projects directed by the military, but planned and directed projects that were primarily related to civilian commerce. Clearing rivers of snags, building canals and roads, erecting piers and breakwaters all became part of the role of the Corps of Engineers before the Civil War.
After the Civil War both the limited accepted role of the Corps in civilian projects and the annual appropriations from Congress expanded dramatically. The Rivers and Harbors Act of 1899 further expanded the Corps of Engineers' authority by granting them regulatory authority of all construction activities in navigable waters. This not only gave them authority over individual projects, but also gave them preeminence over all other agencies and boards when it came to potentially navigable waters.
All U.S. Army Corps of Engineers activities are mandated by Congress. Although the Corps may recommend certain activities (usually after a directive from Congress for study), their activities are mostly driven by various individuals and agencies through their elected official ... Almost from the beginning civilians have had an influence in initiating what later became Corps of Engineers projects. While some projects were suggested by community-spirited individuals, many had the potential to bring large profits to individuals or certain industries. Congress, however, ultimately directs all such projects through annual appropriations. Corps of Engineer project were often used to bring jobs to an area and became pork barrel projects for elected officials.
According to some, the Corps developed a questionable record of concern about the environment starting in the 1930s through their flood control efforts along inland rivers and through their dredging and filling activities, especially along the coasts. To some extent this reputation is unfair because society as a whole in the U.S. did not generally recognize the importance of environmental values until after the first Earth Day in 1970. However, the Corps' reputation developed because they were directly responsible for destroying large areas of natural ecosystems and broadly impairing ecosystem services due to their initiatives and mandates from Congress.
The Corps' environmental record is changing and the case study of saltmarsh restoration is one example. The contribution of the Corps to saltmarsh restoration has been catalyzed by its mandate for dredge and fill activities (Murden, 1984). This is a major function as described by Hales (1995):
The U.S. Army Corps of Engineers (USACE) is involved in virtually every navigation dredging operation performed in the United States. The Corps' navigation mission entails maintenance and improvement of about 40,000 km of navigable channels serving about 400 ports, including 130 of the nation's 150 largest cities. Dredging is a significant method for achieving the Corps' navigation mission. The Corps dredges an average annual 230 million cu m of sedimentary material at an annual cost of about $400 million (US).
The Corps must dispose of the dredge materials, which is a major challenge. Dredge material is a waste product of dredging and disposal takes place both on land and in waterways. Disposal can cause environmental impacts if a natural ecosystem is filled, making this activity a significant concern. One major solution has been the idea to use dredge material as a substrate for building new saltmarshes in restoration. In this way a waste by-product is used as a resource, which is a key principle in ecological engineering. Moreover, because disposal itself is costly, use of dredge material in saltmarsh restoration can result in money savings for the overall project.
The idea to use dredge material as a planting substrate seems to have come from a group of scientists interested in saltmarshes at North Carolina State University (Seneca et al., 1976):
In 1969, we approached the U.S. Army's Coastal Engineering Research Center, Fort Belvoir, Virginia, with the proposition that stabilization of intertidal dredged material might reduce channel maintenance costs by preventing such material from being washed back into the same channels from which it had been dredged. Further, stabilization of the material with S. alterniflora would result in salt-marsh being established and thus replace some of the surface that had been lost through dredging operations. The Coastal Engineering Research Center was receptive to our ideas and supported our efforts to explore the possibility of stabilizing dredged material in the intertidal zone and the concomitant initiation of salt-marsh.
The Corps thus supported the first research on ecological restoration of saltmarshes by the NCSU group and soon afterwards by other researchers (Johnson and McGuin-ness, 1975; Kadlec and Wentz, 1974), including Edward Garbisch as noted earlier. It is significant for understanding the nature of ecological engineering that the idea came from outside the Corps rather than from inside. The Corps might have been pioneers in this subfield of ecological engineering, but they followed the stimulus from ecologists rather than being leaders. The explanation may be that the pre-1970s Corps was made up mostly of civil engineer types with little ecological training. Ecological engineering activities such as restoration require an interdisciplinary perspective that was lacking in the pre-1970s Corps, but it emerged as a coevolution when stimulated by ecologists.
The use of dredge materials for restoration was quickly taken up by the Corps and incorporated into their operations (Kirby et al., 1975; Landin, 1986) after the coevolution began. The North Carolina State group became leaders in saltmarsh restoration research with support from the Corps, resulting in the development of a large literature and a sound technology (Broome, 1990; Broome et al., 1986, 1988; Seneca, 1974; Seneca and Broome, 1992; Seneca et al., 1975, 1976; Woodhouse and Knutson, 1982). Most of this work involved horticulture of Spartina alterniflora or, in other words, basic planting techniques for dredge materials. saltmarsh restoration evolved from this early work as a two-step process. First, an appropriate site is chosen that is protected from waves, wind, and boat wakes, and dredge materials is deposited. This step takes into account the energy signature of the site in order to avoid high-energy sites where erosion will occur. The second step is planting saltmarsh species, which is essentially horticulture with considerations of soils, nutrient levels, and plant materials. In general, this two-step process has been successful in developing saltmarsh vegetation in many locations. The technology has developed since the 1970s and now includes alternative methods of dredge disposal such as spraying (Ford et al., 1999) and use of bioengineering materials (Allen and Webb, 1993). There also has been a broadening of interest to additional aspects of ecosystem structure and function, beyond plant survival and growth, when considering the success of saltmarsh restorations (Haven et al., 1995; Moy and Levin, 1991; Niering, 1997; Zedler, 1988, 1995, 2001). Much of this work is summarized by Matthews and Minello (1994) and in the proceedings of the Hillsborough County Community College Annual Conference on coastal restoration ecology that dates to the early 1970s (see also the interesting independent research being carried out in China as described by Chung, 1989).
One of the complexities with the use of dredge materials for restoration involves the system that becomes filled to create the marsh. The ecological values of these systems are lost when they are converted to marshes. Thus, there is an environmental impact when a marsh is created with dredge material. This is usually ignored because marshes have high value and are endangered. However, problems can arise with the assumption that marshes are more valuable than the systems they replace. For example, in the Anacostia River in Washington, DC, tidal freshwater marshes are being created by the Corps dredge disposal program. Existing mud flat ecosystems are filled with dredge materials to raise the surface to an appropriate level for marsh plant growth. May (2000) showed the value of the mud flats as shorebird habitat
(Table 5.6). When the mud flats are filled, the shorebird habitat is lost because these
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