Major Coastal Environmental Issues
The committee began its work by identifying the most significant issues confronting coastal environments. This assessment was based on the collective experience of committee members as well as perspectives gained from background documents. The recently completed Regional Marine Research Plans (see Appendix C) provided the views of scientists and environmental managers from the major coastal regions of the United States. Also, the Group of Experts on the Scientific Aspects of Marine Pollution listed the most serious problems affecting the marine environment around the world (GESAMP, 1990). Some of the issues highlighted in the committee's list have been recognized for decades. The committee believes that achieving further significant progress in addressing these issues will require joint agency efforts spanning terrestrial and coastal systems. Such efforts are needed urgently and are now possible under the aegis of the Water Subcommittee.
The committee chose issues that are characterized by their wide geographic scope (e.g., are shared by many regions of the country) and that address the problems of (1) sustainable use of resources, (2) reversibility of effects, and (3) anthropogenically mediated deterioration of coastal systems:
hydrologic and hydrodynamic disruption,
exploitation of resources,
introduction of nonindigenous species,
global climate change and variability,
shoreline erosion and hazardous storms, and
pathogens and toxins affecting human health.
In this chapter the importance of each of the nine categories is described, examples are offered, and references are provided. These categories provide themes for the specific recommendations in Chapter 3 for high-priority scientific activities related to the goals of the Water Subcommittee. The committee chose to list issues overlapping those addressed by other National Science and Technology Council (NSTC) subcommittees for the sake of completeness and to highlight their relevance to improving coastal environmental quality.
Although the committee did not rank the nine categories, there was consensus among committee members that the problems associated with changes in the quantity and quality of freshwater inputs and atmospheric deposition of materials to coastal environments are of fundamental importance and are particularly relevant to the Water Subcommittee. These problems result from increases in nutrient loading from agriculture and other land-use practices, waste disposal, and fossil fuel combustion; widespread contamination by toxic materials; and changes in the delivery of freshwater and sediment to the coast.
Recommendations for high-priority science required to address these complex environmental problems should have broad applicability. For example, in the past decade, significant impacts of diffuse pollutant sources and their indirect ecosystem-level effects on coastal environmental health have been demonstrated (NRC, 1993a). This has enormous implications not only for environmental management priorities but also for how science is conducted and used to support effective management. Bearing responsibility for both water resource and coastal environmental issues, the Water Subcommittee has the opportunity to stimulate an integrated scientific approach to processes that span the land-ocean interface. Although the recommendations in this report are widely applicable, they are specifically directed to the Committee on Environment and Natural Resources Research's Water Subcommittee.
Inputs of nutrients to coastal areas from waste treatment facilities, nonpoint sources in watersheds (such as from agriculture), and the atmosphere have been increasing worldwide (Turner and Rabalais, 1991; Kennish, 1992). For example, the loading of nitrate to coastal areas of the East Coast, Gulf Coast, and Great Lakes increased 20 to 46 percent over a seven-year period ending in 1981 (Smith et al., 1987; see Figure 3). Data on riverine inputs of nitrogen from the Mississippi River (Turner and Rabalais, 1991) and rivers entering the Chesapeake Bay (Boynton et al., in press) suggest that this seven-year increase was part of a long-term trend that began with land clearing in the watershed. Total
nitrogen loading to the Chesapeake Bay increased an estimated 6-to 8-fold since the pre-colonial period, while nitrogen concentrations in the lower Mississippi River increased approximately 3-fold since the early 1960s, commensurate with increases in the use of chemical fertilizers. For both the Susquehanna (the largest river entering Chesapeake Bay) and the Mississippi rivers, there is some indication that nitrogen concentrations leveled off or declined slightly in the late 1980s, perhaps as a result of a decline in fertilizer use. Organic enrichment (eutrophication), results from an influx of excess nutrients (particularly nitrogen in the coastal zone) and their subsequent distribution and transformation (Nixon et al., 1986). Moderate inputs of nutrients can have beneficial effects because they stimulate plant production, which can lead to enhanced productivity of living resources. However, many coastal ecosystems receive excessive nutrient inputs, leading to harmful or noxious algal blooms; shifts in food chains; increased sedimentation of organic particles; and, ultimately, depletion of dissolved oxygen, particularly in bottom waters.
Eutrophication has caused oxygen depletion (hypoxia) and even elimination of oxygen (anoxia) in such places as the Chespaeake Bay (Officer et al., 1984; D'Elia, 1987), Long Island Sound (Parker and O'Reilly, 1991), and the northern Gulf of Mexico (Rabalais et al., 1994). In addition, eutrophication can cause other undesirable impacts on marine ecosystems. Seagrass populations may decline because phytoplankton and epiphytic algae reduce the light available to seagrasses growing on the seafloor (Kemp et al., 1983; Twilley et al., 1985). Excess nutrients may increase the prevalence of algal blooms responsible for red and brown tides that are harmful to marine organisms, as well as toxic algal blooms that can injure organisms higher in the food chain, such as fish and humans (Anderson, 1989; Smayda, 1989). Also, the organic enrichment of sediments as a result of greater unconsumed primary production can cause long-term changes in benthic habitats, populations, and community structure. Changes in the biotic composition of planktonic and benthic communities as a result of nutrient enrichment and death of organisms from lack of oxygen could have important effects on biogeochemical cycles, living resources, and biodiversity.
Eutrophication has increased in many coastal regions around the world as a result of increasing inputs of nutrients from agriculture, municipal wastewater, and atmospheric deposition of fossil fuel combustion products (Nixon et al., 1986). A recent National Research Council report, Managing Wastewater in Coastal Urban Areas (NRC, 1993a), noted that more comprehensive controls of nutrient emissions, beyond urban wastewater treatment, are needed. The geographic extent and changing severity of eutrophication, the relative susceptibility of different coastal ecosystems, and the most effective nutrient control strategies are highly uncertain because appropriate monitoring and supporting research are lacking. A key factor necessary for understanding eutrophication is the ability to detect subtle interannual changes in water quality and its effect on ecosystem
structure and function. This requires long-term monitoring and research programs.
Physical modifications of habitats by either natural forces or human influence pose serious threats to coastal ecosystem integrity and these modifications are often difficult to reverse. Such modification may result from filling of intertidal or subtidal habitat; loss of tidal wetlands; submerged aquatic vegetation or coral reefs due to a decline in water quality or changes in sedimentation; or from changes in the hydrodynamics of coastal systems (discussed later in this chapter). More subtle changes, such as the increasing plastic burden on the ocean floor (Goldberg, 1994a) can also damage coastal habitats. While some of these modifications are reversible over time if the offending conditions are ameliorated (e.g., revegetation by submerged aquatic vegetation or restoration of salinity conditions), the likelihood of recovery for many modified habitats is uncertain. Modification of shallow water habitats, including coral and other reefs, wetlands, and seagrass beds, pose perhaps the greatest threat to the biological diversity of marine (NRC, in press) and other aquatic organisms and can have significant consequences on the production of resource species that depend on these habitats for shelter or food at critical life stages. Because of widespread degradation of coastal ecosystems and the extensive modification of coastal habitats, active restoration or rehabilitation may be required (NRC, 1992c).
HYDROLOGIC AND HYDRODYNAMIC DISRUPTION
Changes in water circulation to and within coastal ecosystems have created poorly understood, but perhaps important, consequences in some coastal systems. The hydrology of watersheds draining to the coast has been significantly altered as a result of landscape changes, channelization and damming, consumptive water uses, and diversion to other drainage basins. Reductions in freshwater flow due to increased use or diversion have caused problems in coastal areas of the United States (see Box 1). Conversely, increased freshwater flow or higher peak flows can result because of the increase in impervious surfaces, deforestation, and channelization of flows within flood plains.
Hydrological changes can affect not only salinity patterns and circulation within coastal systems but also the delivery of nutrients, toxicants, and sediment to the coast. The consequences of such changes in delivery rates may be profound. For example, the midwest floods of 1993 increased the dispersal of nutrients, leading to eutrophication and a major expansion of the hypoxic zone in the northern Gulf of Mexico (Rabalais et al., 1994). Reductions in sediment supply from rivers may result in increased shoreline erosion (Inman, 1976; NRC, 1990d) or deprive subsiding coastal wetlands of material needed for soil accre-
tion (Boesch et al., 1994). Conversely, an increase in the supply of fluvial sediments as a result of land clearing (e.g., Maser and Sedell, 1994) or agricultural practices may cause decreased light availability and the smothering or shoaling of benthic habitats.
Geomorphological modifications of shallow coastal systems may significantly affect the hydrodynamics of the coastal regime (Inman, 1976), affecting the influence of the coastal ocean on estuaries as well as the movement of materials from rivers to the sea. Such modifications may result from dredging of navigation channels, shoreline development and filling, shoreline protection (e.g., breakwaters and groins), and channelization of tidal wetlands. For example, dredging channels to facilitate shipping provides a pathway for the transport of relatively salty oceanic water into bays and estuaries and can change salinity structure, circulation, flushing, and residence times of these semi-enclosed coastal systems. Such changes can have dramatic effects on biological productivity and ecosystem structure and function (U.S. Army Corps of Engineers, 1979).
Box 1 Many Major Coastal Environmental Problems Are Linked to Inland Water Resources
Coastal environments of the United States and many other parts of the world face unprecedented changes as a result of the use and degradation of water resources. Far-reaching consequences of changes in quantity and quality of fresh water flowing to Florida Bay, San Francisco Bay, the Mississippi Delta, the Columbia River estuary, and Chesapeake Bay illustrate the problems.
Florida Bay, at the tip of the Florida peninsula, has undergone devastating changes during the last decade, including the loss of much of its submerged aquatic vegetation and the proliferation of algal blooms, some of which cause extensive mortalities of animals (Rabalais et al., 1994). Although the exact causes of ecosystem decline are unknown, they seem to be related primarily to reductions of freshwater inflow and, possibly, to nutrient enrichment of the remaining flow. This is the ultimate result of a cascade of effects of water use and drainage on the ecosystems of south Florida (including the Everglades) and Florida Bay that may, in turn, affect the coral reefs of the Florida Keys offshore.
San Francisco Bay has been greatly altered by human activity, including the filling of most of its wetlands and the introduction of many nonindigenous species (see e.g., Nichols et al., 1990). The present quality of the bay and its future are, however, influenced considerably by the decreased allocations of freshwater inflows to the bay because of increased agricultural and urban uses. This lack of foresight about the salinity requirements of the estuarine ecosystem has resulted in endangering fish species that use the delta as a spawning or nursery habitat and may have created conditions amenable to invasions by nonindigenous organisms.
Louisiana has lost over 1,500 square miles of its coastal wetlands since the 1940s as a result of extensive channelization, hydrological modification, and reduction of the freshwater and sediment flow from the Mississippi River into the
subsiding delta (Boesch et al., 1994). Confinement of the flood plains has resulted in higher peak river flows, heightening flood peaks. The protection and restoration of this important ecosystem will require ''reengineering" of freshwater and sediment flows in the delta. At the same time, increases in the flux of nutrients, particularly nitrogen, from the Mississippi River (from agricultural fertilizers and atmospheric deposition) have contributed to serious oxygen depletion over a large (>3,000 square miles) area of the continental shelf in the northern Gulf of Mexico (Turner and Rabalais, 1991). "Plumbing" decisions made far upstream for flood control or wetland restoration have consequences extending into the Gulf of Mexico.
The Columbia River estuary has been dramatically altered by an extensive hydropower and irrigation system that includes 21 major dams on the Columbia and Snake rivers and over 150 dams on smaller tributaries. Flow regulations and water withdrawals have led to suppression of annual floods, and channelization of the lower river and filling of wetlands have further changed circulation in the estuary (Sherwood et al., 1990). These have affected the timing and strength of salinity intrusion and caused sedimentation along the margins of the estuary. Many native species, such as salmonids which cannot traverse the multiple dams, have declined dramatically, while introduced species, such as American shad, have increased.
Watershed management for coastal environmental restoration is perhaps most advanced in the 64,000-square-mile Chesapeake Bay watershed. This bay suffers nutrient over enrichment from nonpoint sources (agriculture, urban development, and atmospheric sources), which causes oxygen depletion, increased turbidity, and consequent loss of submerged vegetation (D'Elia, 1987) and associated living resources. A goal of 40 percent reduction of nitrogen and phosphorous inputs is being approached by dividing this large watershed into more manageable units and through the use of sophisticated hydrodynamic, ecosystem, and landscape models that simulate the effects of changes in land management on estuarine conditions.
EXPLOITATION OF RESOURCES
The exploitation of living and nonliving resources can affect coastal ecosystem health. From the Gulf of Mexico to Alaskan waters, there is growing concern about the large by-catch mortalities of nontarget species (often a greater mass than the harvested resource) and the effect these mortalities have on the ecosystem (NRC, 1994e). Fishing activities can affect ecosystems by depleting the prey of other species, reducing populations of top predators, or disrupting the physical habitat by fishing activities. The harvesting of sea otters for the fur trade led to a massive increase in sea urchin populations on the U.S. West Coast. In turn, urchins decimated juvenile kelp and so diminished the kelp forest. This is an excellent example of a keystone species and the impact on ecosystems that can occur when such species are removed. Likewise, the dominant species have shifted from cod and haddock to sharks and rays on the heavily fished Georges Bank (Fogerty et al., 1991). It has been hypothesized that the Chesapeake Bay
ecosystem has been drastically altered by overexploitation of filter-feeding oysters that once were widely abundant, leading to increased turbidity and decreased survival of submerged aquatic vegetation, replacement of oysters by less desirable invertebrate species, and increasing anoxia in the bay (Newell, 1988). Fishing activities such as bottom trawling also can change the physical habitat and biological structure of ecosystems significantly. Trawl fishing, for example for shrimp in the Gulf of Mexico and groundfish in the Gulf of Maine, can change the physical character of the seafloor and increase turbidity, altering the ability of native organisms to prosper in these environments (Smith and Howell, 1987; Mayer et al., 1991).
There may also be undesirable effects on ecosystems by exploitation of nonliving resources of coastal waters, including development of oil and gas resources, and the recovery of sand, gravel, and other minerals. As we now strive toward sustainable use of resources, key questions pertain not only to how natural resources can be exploited on a sustainable basis but also how the ecosystems that support these resources can be sustained in the midst of resource recovery activities.
The inputs of some toxic materials [e.g., heavy metals and dichlorodiphenyltrichloroethane (DDT)] to the coastal ocean and Great Lakes have been reduced by the United States and several developed nations, and these decreased contaminant loadings are evident in declining concentrations in organisms and the environment (O'Connor et al., 1994). However, the inputs of some other toxicants remain the same or have increased. Concerns continue regarding the bioaccumulation and ecological and human health effects of such widespread contaminants as mercury, polychlorinated biphenyls (PCBs), and polycyclic aromatic hydrocarbons (PAHs) (NRC, 1993a). In addition, it is now becoming clear that extremely low concentrations (nanomolar or less) of some organic compounds may inhibit reproductive processes in aquatic organisms by disrupting endocrine biochemistry (see Box 2). The disruption of the endocrine system of aquatic organisms extends beyond reproductive processes. Receptor binding and enzyme induction affect development, sexual maturation, gender distributions, behavior, and immune function.
It has been recognized for at least two decades that there can be synergistic and antagonistic interactions among multiple chemicals acting on aquatic organisms. For example, PAHs and PCBs can act in concert to affect marine organisms adversely (e.g., Dawe, 1991). Although research on the effects of individual chemicals can lay a foundation for understanding, the effects of multiple toxic chemicals are barely being addressed. Yet even more complex interactions among multiple stressors occur in coastal ecosystems, for example, combined effects of low oxygen concentrations, habitat changes, and the variety of toxic
Box 2 Emerging Concerns About Reproductive Process Inhibitors
There are a large number of anthropogenic compounds, many organic, that accumulate in the waters and sediments of the coastal zone and can inhibit reproductive processes of aquatic organisms. They fall in the general category of endocrine-disrupting chemicals (Colborn et al., 1993) that can interfere with reproduction and can also have effects in the early developmental stages of organisms at extremely low concentrations, nanomolar and less.
The first problems with reproductive process inhibitors in the marine environment involved the DDT family of compounds, which nearly decimated some bird populations in the 1960s and 1970s. Tributyltin (TBT) provides a more recent example of reproductive process inhibitors. TBT is probably the most effective antifouling agent that has ever been developed. However, after extensive use on pleasure craft in marinas of the Bay of Archachon in France, the substance nearly wiped out the oyster industry in the mid-1980s (Goldberg, 1986). TBT leached from painted ships into the marina waters where it quickly came into contact with oysters cultured nearby. Later, the causal relationship between body burden of TBT and oyster morbidity was well established. TBT has also been shown to cause female gastropods to develop male sexual organs and become effectively sterile. TBT affected a variety of other marine organisms, so that marinas with large numbers of recreational craft suffered dramatic losses of indigenous flora and fauna.
chemicals. Understanding these interactions poses an urgent challenge for science to improve coastal environmental quality.
Thus, despite the reductions in risks from some toxic chemicals, the effects of other compounds, which have not been reduced or which induce toxic effects at extremely low levels, remain of concern. In addition, even though water column concentrations of toxicants are low, contaminated sediments in many coastal areas can continue to release toxic chemicals to the overlying water column due to natural resuspension or dredging (NRC, 1989), affecting organisms living in or near the sediments (Dawe, 1991).
INTRODUCTION OF NONINDIGENOUS SPECIES
In some coastal environments, nonindigenous species have been introduced by human activities and have established populations that have had major ecological consequences. The proliferation of the zebra mussel in the Great Lakes (Nalepa and Schloesser, 1993) has received the most attention, but other introductions have produced similar consequences. For example, most of the dominant species of benthic invertebrates in San Francisco Bay are nonindigenous (Nichols, 1979), and the filter-feeding activities of the Chinese clam Potamocor-
bula amurensis have eliminated summer phytoplankton blooms in the northern portions of the bay (Warner and Hollibaugh, 1993). Diseases that are ravaging populations of oysters in Chesapeake Bay may have been introduced with oysters transplanted from other regions; likewise, organisms transported for aquaculture and recreational fishing purposes in the past have been the source of many species introductions. Transport of organisms in the ballast water of ships is a major and growing source of introductions of nonindigenous species (Carlton and Geller, 1993). Consequences to coastal ecosystems include loss of biodiversity by elimination of indigenous species (NRC, in press), alteration of trophic dynamics, degradation of habitats, and diminution of fisheries productivity.
GLOBAL CLIMATE CHANGE AND VARIABILITY
In addition to contemporary pressures from human influences, coastal ecosystems are susceptible to global climate change. Global sea level rise could accelerate from a variety of factors (Misdorp et al., 1990; Wigley and Raper, 1992), rising by as much as three to 10 meters. Local sea level changes (from subsidence of coastal areas from freshwater withdrawal, erosion, movements of Earth's crust, and thermal expansion of seawater (Roemmich, 1992) could add to global effects (Stewart et al., 1990). Regardless of their source, sea level rises cause significant shoreline inundation, overstepping of barrier islands, loss of intertidal wetlands, and increased salinization of coastal embayments.
Of all the potential effects of global climate change on coastal environments, the effects of sea level rise have received perhaps the most attention, but other effects of climate change may be even more important. These include the potential for increased tropical storm intensity and frequency; changes in precipitation patterns and river flow; changes in seawater temperature range and seasonality; alteration of coastal currents and upwelling (Bakun, 1990; van Geen et al., 1992), which affect temperature, nutrient supply, and larval transport; and modification of intermediate-scale weather patterns that affect winds, currents, and rainfall. The effects of decadal-scale climate variations on biotic communities and ecosystem productivity produced by the El Niño-Southern Oscillation along the Southern California coast (Tegner and Dayton, 1987) and on estuarine salinity and the prevalence of oyster diseases in the Gulf of Mexico (Powell et al., 1992) demonstrate the potential significance of long-term climate changes.
SHORELINE EROSION AND HAZARDOUS STORMS
The coastal zone presents risks as well as benefits to those who populate or visit the shore and those who work or recreate in coastal areas. Although weather forecasting and public education now prevent the massive loss of life that previously occurred as a result of hurricanes and other coastal storms, more accurate and reliable forecasting and reporting of present conditions would help
prevent continuing loss of life and property and reduce adverse effects on coastal economies. Beaches buffer coastal land and habitats from assault by the ocean and lakes, providing the most effective means of preventing coastal erosion and habitat destruction. The principal source of sediment to the coastline is from rivers and streams (Komar, 1976); thus, changes in land use and stream hydrology can affect the supply of sediments to beaches and, consequently, shoreline erosion (Inman, 1976; Kuhn and Shepard, 1983).
Shoreline erosion is also influenced by coastal processes resulting in offshore and alongshore transport of sediments. Changing patterns in coastal storm climate can change the direction of sediment transport by altering the intensity and direction of waves incident to a beach. For example, over the last century the alongshore direction of net sediment transport in the Southern California Bight has been southwest because of the prevailing wave approach from the northwest as a result of storms off Alaska (Inman and Frautshy, 1966). The coastal storm climate was much different in the early 1880s, however, with a prevailing wave approach from the southwest from storms off Baja California (Dana, 1969). This change has altered sediment movement and the resulting nature of the coastline (Shepard and Kuhn, 1983). Shoreline erosion and hazardous storms are affected in a complex manner by land-use decisions and climate change and, conversely, can greatly affect coastal environmental quality. Studies of global climate change and improvements in the predictability of climate variability (see previous section) are crucial for predicting and mitigating the impacts of shoreline erosion and hazardous storms.
PATHOGENS AND TOXINS AFFECTING HUMAN HEALTH
Human health may be at risk as a result of exposure to toxicants or pathogens in coastal waters or the consumption of undercooked or raw seafood harvested from those waters (IOM, 1991; NRC, 1993a). Coastal population growth has resulted in the increasing flux of pathogens (viruses, bacteria, and parasites) to coastal waters, primarily from sewage outfalls (Alderslade, 1991). There are two public health issues involved: (1) the induction of illness through exposures of recreational swimmers, divers, and boaters to pathogens and (2) the consumption of undercooked or raw seafoods (primarily bivalve molluscs) that have accumulated pathogens or toxin-bearing algae from the environmental waters.
There are few national, state, or local monitoring programs for pathogens or toxic materials, particularly to maintain human health. Although use of the fecal coliform test to judge the suitability of coastal waters for swimming and shellfish harvest has provided a significant level of protection (i.e., there have been few serious outbreaks of waterborne diseases), illness and an occasional death still result from human pathogens in coastal waters. For example, the Norwalk virus is responsible for one-half of the epidemic occurrences of nonbacterial gastroenteritis in the United States (Goldberg, 1994b).
In the case of toxic phytoplankton, coastal monitoring occurs on a local basis, often by local health departments, as well as by the Food and Drug Administration. Seafood safety is an issue emerging as a significant concern to the nation (IOM, 1991). Paralytic, diarrhetic, neurotoxic, and amnesic shellfish poisonings are all caused by biotoxins accumulated from algae. Outbreaks of poisoning due to domoic acid and various neurotoxins accumulated by shellfish and fish have occurred several times in the past few years, possibly due to the increasing incidence of harmful algal blooms (Anderson, 1989; Hallegraff, 1993).
THE ECOSYSTEM PERSPECTIVE
The emerging and widespread environmental threats discussed above pose new challenges to environmental policy, management, and science, requiring different approaches than those used for past coastal problems, such as point-source discharges of industrial or municipal effluents, coastal land use, direct habitat destruction, and oil spills. These issues have not been eliminated, although some of their effects are relatively well understood, and significant advances have been made in their management in several developed countries, including the United States. Concern is shifting from issues amenable to single-factor risk assessment to approaches involving multiple- stressor (e.g., combined effects of chemical contaminant and low oxygen) risk assessments and indirect, cascading (Carpenter et al., 1985), and scale-related effects on living resources. Understanding such coastal problems requires approaches that focus on ecosystems, populations of organisms, and communities of species. There is now greater concern about the response of ecosystems to the effects of exploitation of resources, nutrient enrichment (as opposed to direct organic loadings), and the indirect effects of human activities on coastal habitats (see Box 1). The development of initiatives to solve these problems will require more flexibility from the scientific community, universities, and funding agencies to promote interdisciplinary science.