What are the trends in extent and condition of coastal waters and their effects on human health and the environment? Coastal waters are one of the nation’s most important natural resources, valued for their ecological richness as well as for the many human activities they support. As the interface between terrestrial environments and the open ocean, coastal waters encompass many unique habitats, such as estuaries, coastal wetlands, seagrass meadows, coral reefs, mangrove and kelp forests, and upwelling areas.17,18 Coastal waters support many fish species for at least part of their life cycle, offering some of the most productive fisheries habitats in the world. These waters also provide breeding habitat for 85 percent of U.S. waterfowl and other migratory birds (largely in coastal wetlands),19 and support many other organisms with high public visibility (e.g., marine mammals, corals, and sea turtles) or unique ecological significance (e.g., submerged aquatic vegetation). For humans, coastal waters provide opportunities for tourism and recreation, and they contribute to the economy through transportation, fisheries, and mining and utilities.20 Lands adjacent to the coast are highly desirable places for people to live, and represent the most densely developed areas in the nation.21 Extent and condition are two key variables in assessing coastal waters and their ability to serve ecological and human needs. The extent of coastal waters—i.e., the spatial area—is particularly important in terms of the extent of specific types of coastal waters, such as coastal wetlands or coral reefs. The condition of coastal waters reflects a group of interrelated physical, chemical, biological, and ecological attributes. For example, nutrient levels should be sufficient to support the food web but not so high as to cause eutrophication, while toxic chemical contaminants in water and sediment may pose a threat to aquatic organisms or accumulate in the food web. Of particular concern to human health are contaminants in consumable fish and shellfish. Other key aspects of condition include levels of pathogens and organisms that produce biotoxins—which may pose a risk to human health through aquatic recreation or contaminated fish and shellfish, and which may impact the environment by injuring native populations. Also important is the degree to which native plant and animal populations are healthy and their habitats intact. Many factors can affect the extent of coastal waters. For example, the extent of coastal wetlands may be influenced by natural events such as erosion or storms, or by human activities such as draining or filling wetlands for development. Natural processes can change the shape of a coastline, with wave action eroding some areas while building up sediment in others, and rivers depositing sediments at their mouth. Human stressors can alter these patterns—for example, through the construction of seawalls or barriers or through the channeling of rivers, which can lead to subsidence in coastal areas that would otherwise be naturally replenished by sediments. Changes in extent may in turn affect the condition of coastal waters. For example, beach erosion and coastal wetland loss can also affect contaminant and sediment levels, nutrient cycling, and the condition of spawning and feeding grounds for fish, shellfish, and other coastal species. The loss of some wetlands can also affect the condition of the wetlands that remain. Other stressors to the condition of coastal waters include nutrients, pathogens, and chemical contaminants, which may pose risks to ecological systems or to human health. Nutrients and pathogens occur naturally, but their abundance can be increased by human activities along the coast or in upstream watersheds that ultimately discharge to coastal waters. Major sources include urban and suburban storm water, agricultural runoff, and sewage discharge or overflows. Chemical contaminants may come from these same sources, as well as from industrial activities that discharge treated wastewaters and from atmospheric deposition of airborne pollutants. Several other stressors can affect the quality of habitat and the status of native plant and animal populations. For example, many species are sensitive to temperature and salinity, which can be influenced by changes in weather patterns or the condition of freshwater inputs. Salinity is particularly important in estuaries, where species may depend on a steady, reliable flow of fresh water. Another factor affecting the status of native communities is the presence and abundance of non-indigenous species—particularly invasive species that can kill or crowd out native populations, or otherwise alter coastal watersheds. Populations of fish, shellfish, marine mammals, and other species used by humans may also be affected by overharvesting. In many cases, stressors that affect coastal condition are interrelated. For example, excess nutrients can cause algal blooms (and subsequent decay) that result in low dissolved oxygen and reduced water clarity—the chain of events known as eutrophication. Temperature and salinity can also influence algal blooms. Some algae, such as “red tide,” produce toxins that pose risks to humans.
Posted on: Tue, 11 Mar 2014 05:28:15 +0000
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