MARINE HABITAT-A NATIONAL TREASURE IN DECLINE
This century has seen vast changes in the nation's coastal zone management practices, in societal views of marine habitats, and in marine habitats. The most striking changes, a consequence of several often-coincidental developments, include
a concentration of population in coastal areas approaching 50 percent of the total U.S. population and projected population growth;
a proliferation of shoreline development;
increased water-dependent recreation;
water quality degradation from the introduction of pollutants, excess nutrients, and sediments into coastal waters from nonpoint and point-sources and from soil erosion affecting upland areas;
damage to seagrass beds from degradation of water quality and from the operation of recreational and commercial vessels in shallow waters;
declining fish and shellfish stocks and harvests;
degradation of scenic and cultural assets; and
permanent habitat loss, especially coastal wetlands.
The evolution of these changes may have been gradual, but it has now reached a critical threshold if habitat losses are to be arrested and reversed. If a goal of ''no net loss" of coastal wetlands, is to be achieved, then new, and innovative measures will need to be applied.
Substantial scientific and engineering knowledge and practical experience that could be used to improve the management the nation's marine resources if these capabilities can be effectively brought to bear for this purpose. Indeed, engineers and scientists have already developed and shared expertise and technology to counter the trend of marine habitat degradation and loss to some extent, but these capabilities have not been guided by national policy or objectives. Available technology provides opportunities to protect, enhance, restore, and create marine and estuarine habitats and, subsequently, to protect some fishery resources and wildlife, including endangered species. But, existing methods do not address these issues adequately; nor do they adequately address the effects of large-scale subsidence, land use in the coastal plain, sea level rise, extensive erosion, and massive and continuous salt water intrusion into freshwater surface and groundwater systems.
This report examines the role of coastal engineering in countering these trends through the application of technology to protect and restore marine habitat (see Box 1-1 for terms used in this report). But, the issue is far greater than applying engineering capabilities to a environmentally beneficial purpose in the marine environment. A larger national strategy for protection and preservation of ecosystems is needed (NRC, 1992a). Without such a development, the underlying pressure on marine natural resources will continue.
Scope of Marine Habitat Degradation and Loss
As residential, industrial, and recreational development continues to encroach upon the ocean's edge, the sea relentlessly shapes and reshapes the coastal zone. Humankind and the land are greatly affected by this interplay (Culliton et al., 1990; NRC, 1990a; Platt et al., 1992; Williams et al., 1990). About 30 square miles of Louisiana disappear into the sea each year, depending on the estimate used, although the rate of loss is decreasing. Through this process, shallow water and intertidal marine habitat with high biological activity critical to the ecological balance is transformed into subtidal water, generally unvegetated habitat. Although deep water habitat is also important and is threatened by pollutants and not an inexhaustible resource, the more immediate and noticeable problems are the loss of critical breeding, nursery, and feeding habitats in estuarine, near shore, and intercoastal areas. The cumulative habitat losses resulting from erosion, natural subsidence, sea level rise, altered natural sediment movement caused by flood control and navigation projects, and changes in hydrology and salinity from oil and gas exploration and from episodic storms are no less certain unless local changes occur in these processes (Boesch et al., 1983; Brown and Watson, 1988; Clark, 1990; Mendelssohn, 1982; Mendelssohn et al., 1983; Turner and Cahoon, 1988).
Similar losses affect other regions as well, although on a less grand scale than in coastal Louisiana. For example, in San Francisco Bay and the Sacramento—San Joaquin
BOX 1-1 TERMS USED IN THIS REPORT
Coastal zone Coastal waters and adjacent shorelands which are strongly influenced by each other and uses of which have a direct and significant impact on coastal waters.
Creation Construction or formation of a habitat of a different type that existed before a site was disturbed or conversion of one habitat form to another. The principal differences between restoration and creation are the condition and status of the habitat acreage rather than the technologies used. Because the technology is essentially the same, creation is treated as a subset of restoration as an approach to improving marine habitat.
Enhancement Improvement of one or more of the values of an existing habitat, usually one that has been degraded or disturbed. May result in a decline of other values.
Improvement General result, if beneficial, of one or a combination of protection, enhancement, restoration, and creation initiatives.
Marine habitat Marine and estuarine habitats and contiguous shorelines within the coastal zone. These areas include marine wetlands such as tidal marshes, emergent wetlands, sea grass beds, kelp forests, and mangrove swamps. Also included are beaches, shallow inshore and near shore submerged environments, and tidal and intertidal flats. Offshore marine habitat is outside the boundaries of this assessment except for artificial reefs and offshore berms on the continental shelf.
Marine habitat management A comprehensive approach to stewardship of marine habitat including protection, enhancement, restoration, creation, and administration.
Mitigation Measures taken to reduce adverse impacts. A regulatory approach that, in effect, permits conversion of habitat in return for compensation in the form of enhancement, restoration, or creation of other habitat.
Monitoring The collection of data to aid project planning and design and to enable evaluation of project performance.
Partial restoration Return of a degraded or altered natural area as close as possible to its condition prior to disturbance if full restoration is not feasible (Box 1-2).
Protection Use of structural and nonstructural means, including regulation, to minimize or prevent harm to existing habitats.
Restoration Return of a degraded or altered natural area or ecosystem to a close approximation of its condition prior to disturbance (Box 1-2).
SOURCES: Cairns (1988), Lewis (1990b), NRC (1992a).
River delta, intense development of shorelines and inland areas, and use and diversion of fresh water within the watershed are causing or contributing to hypersalinity subsidence and erosion problems (Bay Institute of San Francisco, 1987; EPA, 1992; Josselyn and Buchholz, 1984; McCreary et al., 1992; NRC, 1990a). Along much of the Atlantic and Gulf Coasts, engineered
BOX 1-2 THE MEANING OF RESTORATION OF MARINE HABITATS AND RELATIONSHIP TO THE SEDIMENT STREAM AND DREDGED MATERIAL
In this report, restoration is defined as the return of a marine natural area or ecosystem to a close approximation of its condition prior to disturbance. In restoration, ecological damage to the resource is repaired. Both the structure and the functions of the natural area are improved or recreated. Merely recreating the form without the functions, or the functions in an artificial configuration bearing little resemblance to a natural resource, does not constitute restoration. The goal is to emulate a natural, functioning, self-regulating system that is integrated with the ecological landscape in which it occurs.
In practical application, since ecosystems are the cumulative result of a sequence of climatological and biological events, full ecological restoration is rarely achieved. Therefore, efforts to restore habitat may necessarily consist of various measures to enhance or partially restore natural functions depending on site-specific conditions, habitat improvement objectives, and other factors. In some cases, the ecological landscape may have been so altered as to preclude a return to a predisturbed condition. In these cases, partial restoration may be feasible, recognizing that all natural functions may not be completely restored and that assisted regulation may be necessary, such as control of water and sediment flows.
Marine ecosystems typically involve dynamic forces including substantial physical energy in the form of currents and waves, local or global changes in relative mean sea level, and sediment streams that can lead to rapid changes in the characteristics of a natural area. Therefore, defining what constitutes a predisturbed condition can be problematic. In such cases, the characteristics of a natural, functioning, self-regulating system that is integrated into its ecological landscape and which emulates nearby undisturbed natural areas is an alternative frame reference.
Although use of dredged material does not constitute restoration, per se, restoration can be accomplished using dredged material in its native environment to achieve general parameters which will aid in natural marsh evolution in those locations where marine sediments would normally form essential substrates for intertidal and emergent wetlands habitat. Placing marine sediments so as to mimic natural deposition of sediment at sites where conditions otherwise favor restoration would preclude the chemical changes that occur when marine sediments are exposed to air in upland areas or in wetlands above appropriate intertidal elevations. Further, natural deposition of sediments to form intertidal flats and emergent wetlands can occur over relatively short time spans in deltas and estuaries, depending on such factors as hydraulic conditions and sediment loads. The rapid placement of suitable dredged material at appropriate locations and elevations in an estuary or delta approximates natural deposition and can be an important, but not exclusive, element of a marine habitat restoration project.
protective structures and sand replacement activities are used to try to stabilize the shorelines of otherwise dynamic and resilient barrier islands (Charlier et al., 1989; NRC, 1990a). Engineering technologies and structures maintain an increasingly tentative balance with nature in every coastal state.
Throughout the coastal zone, habitat is continually lost to human development; what remains is under constant threat of degradation or further loss (EPA, 1992). The causes of the decline in marine habitat quality and quantity may be traced to several factors. Human activities have altered natural current action and sedimentation patterns; degraded water quality by introducing excess nutrients, toxins, and sediments into coastal waters as a result of nonpoint and point-source pollutants; altered estuarine inflow and outflow patterns; and changed other physical, chemical, and biological processes. Protecting finfish and shellfish habitats is a concern, as are sedimentation starvation and excess sedimentation in deltaic and other fragile wetland systems. Scientific concern has also arisen regarding the effects of beach stabilization measures, whether physical structures or placement of beach-quality sands, on biotic communities for which beaches provide habitat. Considerations include the fate of biota in the nearshore borrow area, impacts on biota using the changed shoreline, changes in sedimentation patterns and shoreline stability beyond the project boundaries, and project stability. Sweeping changes in the policies and practices of all parties involved in marine habitat protection and enhancement are needed to arrest and reverse these trends (NRC, 1992a).
Finding Balance Among Competing Objectives
Institutional, political, and sociological factors that have made it difficult to strike a balance among competing objectives for the use of coastal sites include:
the fragmented structure of existing management regimes and legal instruments related to marine habitat management;
fragmented and overlapping authority, complicated by competing agency objectives;
conflicting or self-serving project goals;
limited cross-training among scientific and engineering disciplines;
an incomplete scientific and engineering understanding of the functional relationships among marine habitat, marine life, and coastal processes;
an established trend of human overexploitation of coastal resources for developmental and recreational purposes; and
the lack of a holistic approach to managing end use so that the natural functions of ecosystems are not abused.
Despite these constraints, engineers working in the coastal zone and using the technologies and practices they develop can contribute to better management of
marine resources by working hand in hand with coastal scientists and policy-makers and managers on projects that benefit marine habitat. Where feasible, these capabilities can be put to use for the protection of natural marine habitats before they are degraded or lost or for after-the-fact enhancement or restoration.
THE CHALLENGE FOR COASTAL ENGINEERING
It is time to rethink the role of coastal engineering in serving both human and environmental objectives. An integrated, holistic approach that encompasses engineering practices and capabilities and understands the functions of marine ecosystems and their habitat is especially important. Engineers are faced with seemingly contradictory objectives: habitat conversion versus enhancement, restoration, and creation; traditional structural ("hard") protection, such as seawalls, versus enhanced natural ("soft") shore protection, such as beach nourishment and underwater berms; use of dredged material as a resource rather than as spoil (that is, waste by-product); economic versus ecological returns to the national welfare; and prevention of pollution versus cleanup and restoration. Through research and development, education, and the innovative application of engineering knowledge, the engineering profession has the opportunity to accommodate these competing objectives. A comprehensive understanding of engineering practices and capabilities and their relationship to the ecology of marine habitats is as important to informed decision making over habitat use as are economic considerations. A positive role for the engineering profession can be developed in cooperation with the scientific community to protect and enhance marine habitat and contribute information essential to the formation and refinement of national policy and management objectives.
Overview of Scientific and Engineering Capabilities
Although examples of successful applied engineering capabilities to accomplish environmental objectives are numerous, traditional engineering practices have not always recognized and dealt fully with the varied needs of marine habitats. New territory for the engineering profession includes methods to protect habitats, especially from contaminants, erosion, and subsidence, while preserving or retaining their natural attributes. An ecosystem approach to project design and implementation that recognizes the ecological interdependencies of marine systems is seldom applied. Further development of the potential for coastal engineering to protect, enhance, restore, and create marine habitats therefore depends in part on further collaboration between the coastal sciences and engineering.
Status of Science and Engineering
Scientists and engineers concerned with marine systems share many interests and have a wide variety of tools at their disposal. Some technology transfer has occurred, demonstrating the fact that science and engineering can be complementary. For example, marine turtles returned to historical beach nesting areas after well-timed deposition of beach-quality dredged material. Knowledge of habitat requirements, when the turtles came ashore to nest, and the capability to place beach-quality material prior to turtle arrival were required. Applied research has demonstrated that beach nourishment can be timed to accommodate environmental, stabilization, and aesthetic objectives. This measure is now widely used in Florida (Higgins and Fisher, 1993; Hodgin et al., 1993; Montague, 1993; Nelson, 1993; Nelson and Dickerson, 1988). Although there are still gaps in knowledge about turtle nesting, the approach used shows the potential benefits from cooperative application of scientific knowledge and coastal engineering technology.
Fisheries biologists and navigation project design engineers (interested in successful construction and maintenance of navigation channels) are both concerned with hydraulic and hydrologic conditions, water quality, sedimentation patterns, salinity and temperature, and other physical and chemical factors. Although discipline perspectives differ, each group is vitally interested in the effects of physical modifications to an existing system. For example, changes to an estuary's tidal prism that do not maintain hydraulic balance within the system can greatly affect sedimentation rates and salinity, benefiting either navigation, biota, both, or neither. The full potential of scientific and engineering contributions to marine habitat protection, creation, restoration, and enhancement has yet to be realized despite the advances that have been made.
Scientific Tools and Techniques
Over the past three decades, the scientific community's understanding of marine habitats has advanced greatly. Science produced monitoring, sampling, and analytical techniques that help detect and respond to problems affecting marine habitats. The rapid advances in the computation power of computers, computer modeling, and graphic representations has significantly advanced the capability to analyze, interpret, and apply the data that are collected. This understanding and monitoring capabilities have been instrumental in decision making to set environmental quality objectives (NRC, 1990b,c).
Science recognizes the importance of a holistic approach to understanding the interrelationships of species and how they function to consume and change the chemical composition of wastes such as sewage, buffer the system against shock, and secure the health and reproductive capacities of species forming the ecosystem. This recognition requires an understanding of the chemical and physical
characteristics of the environment that promote the success of or harm to the species. Density-dependent interactions as well as the effects of density-independent factors such as temperature, light, heat, precipitation, wave actions, and pollutants of various types, must also be understood. Understanding the geology, hydrology, and chemical characteristics (such as salinity) of the system enables description of physical and chemical processes that are important in determining sensitive land forms, sediment transport regimes, and the quality of sediment and water. Understanding the formation of substrates in estuaries and the material composing them is not fully developed. Likewise, the effects of organic matter and contaminants such as pesticides in substrates as they pertain to restoration of natural functions in and performance of habitat restoration projects are not thoroughly understood and are a concern. This is an important consideration because the substrates are the foundation materials for marine habitats. Nevertheless, the holistic approach is an integrated one that enables human activities to fortify rather than destroy fragile and complex coastal ecosystems.
National concerns about the relationship of human activities and natural marine systems involve economic and social sciences, as well as natural sciences. Assessment of economic and social values of natural marine systems is marked by controversy because of uncertainties in scientific knowledge about the functioning of marine ecosystems and the contribution of marine habitat to commercial fisheries, recreational activities, and other activities. These factors make it difficult to establish economic values of marine habitat in natural uses. Economic sciences can be employed to assess the costs and benefits of alternate uses, residential development, for example (Bell, 1989; Costanza and Wainger, 1990; Smith, 1990). The social sciences can address the range of variables and help identify interested parties whose participation in planning and implementation is needed to ensure project acceptability and success, examine social attitudes and changes, and address quality-of-life issues (Caldwell, 1991; Davos, 1988; Dwivedi, 1988; Hickman and Cocklin, 1992; McCreary et al., 1992). The disparity in the ability to quantify the value of marine habitat as a natural resource places these attributes at a disadvantage when determining their fate—whether they should be preserved and improved or converted.
Coastal Engineering Tools and Techniques
Various engineering disciplines, including civil, hydraulic, sediment, geotechnical, environmental, biological, mechanical, and sanitary engineering, are involved in coastal zone projects. All are experienced with project design, implementation, evaluation, equipment, and structures. Their experience contributes to an understanding of and methods to prepare construction plans, documents, and cost estimates; evaluate and recommend contractor engagements; and develop and implement project monitoring techniques and performance evaluations.
A substantial body of engineering knowledge and tools has been developed and applied in the coastal zone to design, construct, and maintain waterways and port facilities; protect and stabilize shorelines, entrances, and channels; control flooding and lessen storm-driven energy; improve water quality and lessen pollution; monitor, calibrate, analyze, and adjust physical aspects of hydraulic and sediment systems; and lessen or mitigate the environmental impacts of water-related projects. Over the past three decades, various diagnostic procedures have been developed for examining coastal processes and impacts of structures and other restorative measures. These procedures rely on field and laboratory studies and advanced mathematical modeling. These same techniques are then extended for prediction of anticipated impacts. Laboratory capabilities include physical scale models and wave tanks. Advances in coastal engineering capabilities are regularly published in the proceedings of national and international conferences, handbooks, and professional journals and magazines. Engineering techniques developed by the USACE are usually well documented in official reports which are generally accessible to practitioners.
A great many coastal engineering projects involve the transport and placement of dredged sediment and sands (Bruun, 1989a,b; Dyer, 1986; Herbich, 1990, 1991, 1992a; NRC, 1983a, 1983b, 1985d, 1987b, 1989b; Vanoni, 1975). The use of dredged material to restore or create marine habitats is an accepted practice in many world ports and estuaries, some in the United States, as discussed in this report. Herbich (1992b) and the Permanent International Association of Navigation Congresses (PIANC, 1989, 1992a) describe dredging technologies and practices, including the constructive use of dredged material to support environmental objectives. The environmental benefits of dredged material have sometimes been learned by accident. For example, practitioners learned that artificial islands created with dredged material from operations to maintain shipping channels often provide a primary habitat for sea birds and wading birds and a refuge for species displaced from other sites by human activity. Eroded natural islands can be restored for these purposes. Such habitats are now being routinely designed and constructed (Landin, 1992b; James F. Parnell, personal communication, December 13, 1990). Successful habitat protection, enhancement, restoration, and creation programs, as elements of coastal engineering works, are growing in number and significance, but interdisciplinary principles of natural resource management are not fully utilized.