Total 689 866
Total 689 866
Note: The numbers are totals for 36 observations per year.
Source: Adapted from May, P. I. 2000. Proceedings of the Annual Ecosystems Restoration and Creation Conference. Hillsborough Community College, Plant City, FL.
species need open, exposed sediments rather than vegetated marshes to meet their life needs. Because shorebirds may be more endangered than the marshes, the wetland creation project may be generating less environmental value than if no action was taken and the mud flats were preserved. Perhaps a more in-depth analysis is needed in cases such as this one concerning marsh restoration through dredge disposal.
The Corps of Engineers has upgraded its ecological capabilities over time in response to critics and due to the need for a broader environmental awareness. One example is the multimillion dollar Corps wetland research program which started in 1990. However, there is still a civil engineering emphasis (see, for example, Palermo, 1992) which, in part, is appropriate and important in restoration work. It will be interesting to observe if and how the Corps responds to the growing paradigm of ecological engineering. Although Corps projects in saltmarsh restoration generally have been successful, this kind of ecosystem naturally has a low complexity relative to other ecosystems. Corps efforts at restoring the more complex tidal freshwater marshes have not been as successful (see the discussion of Kenilworth Marsh earlier in this chapter). Questions remain about the ability of the Corps to combine ecology and engineering. Does the military administration of the Corps inhibit interdisciplinary thinking needed for ecological engineering? Is the ecosystem too complex for the traditional civil engineering approaches of the Corps? The hope is that both the field of ecological engineering and the U.S. Army Corps of Engineers will benefit from future collaborations such as those between the dredge disposal program and saltmarsh ecologists in the early 1970s.
A final consideration about saltmarsh restoration involves the secular sea level rise that is presently occurring along global coastlines. Sea level rise causes an encroachment of the flooded tidal lands on the adjacent uplands and submergence of existing coastal ecosystems. If coastal wetlands can grow both upward and in an inland direction, they may be able to avoid submergence. However, if coastal wetlands are restricted in area and/or cannot match sea level rise by vertical accretion, then a loss of these ecosystems will occur. This situation has been discussed for mangrove ecosystems (Ellison and Stoddart, 1991; Field, 1995; Woodroffe, 1990), and Rabenhorst (1997) has called for a new approach to understanding coastal marshes in relation to sea level rise, which he terms the chrono-continuum. saltmarsh restorations are also susceptible to this problem. Thus, sea level rise may submerge and therefore destroy restored saltmarshes as quickly as they are created in some areas (J. Court Stevenson, personal communication; see also Stevenson et al., 2000). This issue will complicate the restoration of saltmarshes in the future (Christian et al., 2000).
Artificial reefs are structures of human origin used in aquatic ecosystems to increase fish production. Informed design is employed in the construction and placement of these devices, relying on both conventional and ecological engineering. These artificial reefs come to resemble natural reefs in both ecological structure and function, and can even generate more fish production than their natural analogs under certain circumstances.
A great number of different designs have been tried in both marine and fresh-waters. Fish aggregating devices are usually included under the topic of artificial reefs, although they either are suspended in the water column or floated at the surface to attract pelagic fishes. More commonly, artificial reefs refer to structures that rest on the bottom substrate and attract benthic fishes, similar to natural oyster or coral reefs.
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