The tidal sheltered waters of estuaries support unique communities of plants and animals, specially adapted for life under a wide range of conditions. Estuarine environments are incredibly productive, producing more organic matter annually than any equal-sized area of forest (including rain forests), grassland, or cropland. A wide range of habitats exists around and in estuaries, including shallow open water, tidal pools, sandy beaches, mud and sand flats, freshwater and salt marshes, rocky shores, oyster reefs, mangrove forests, river deltas, wooded swamps, and kelp and sea grass beds. Estuaries provide habitat for more than 75% of the U.S. commercial fish catch, and for 80% to 90% of the recreational fish catch.
Estuaries are very important to the economy of coastal communities and the United States. Nationwide, twenty-eight million jobs in fields as diverse as shipbuilding, tourism, commercial and recreational fishing, real estate, and other coastal industries are dependent on estuaries. Nearly 70% of the nation's population (about 180 million people) visit the coasts annually, generating $8 billion to $12 billion in revenue.
National Estuary Program
The Water Quality Act of 1987 created the National Estuary Program (NEP) as an alternative to the traditional command-and-control regulatory approaches to water quality programs. Congress recognized that in order to achieve long-term protection of living resources and water quality (the basic "fishable/swimmable" goal of the Clean Water Act), the participation of those most affected by the environmental decisions was critical. Based on the highly successful Chesapeake Bay Program (see below), with its collaborative approach to managing watersheds and estuaries, the NEP is a voluntary program.
To improve an estuary, the NEP brings together community members using a forum to establish working relationships and the trust necessary to find and implement solutions. Together, stakeholders define program goals and objectives, identify estuary problems, and design action plans to prevent or control pollution, while restoring habitats and living resources such as shellfish. This approach results in the adoption of a comprehensive conservation and management plan (CCMP) for implementation in each estuary. This integrated watershed-based, stakeholder-oriented, water resource management approach has led to some significant local environmental improvements since its founding. In 1987 the NEP consisted of six local estuary programs; as of 2005 it had grown to include twenty-eight estuaries in eighteen states and Puerto Rico.
Two examples of environmental improvement resulting from the NEP program can be found in the Leffis Key and Corpus Christi projects. The Leffis Key restoration project in Sarasota Bay, Florida, resulted in thirty acres of productive intertidal habitat being created and planted with more than 50,000 native plants and trees at a cost of $315,000. In Corpus Christi Bay, Texas, treated bio-solids were applied to a twenty-five-acre plot of aluminum mine tailings, resulting in plant growth promotion, wildlife habitat, and improved water quality. Biosolids are composed of sewage sludge that has been properly treated and processed to make a nutrient-rich material that can be safely recycled and applied as fertilizer.
Chesapeake Bay Program
The Chesapeake Bay ("the Bay") is the largest estuary in North America and one of the most productive estuaries in the world. It has a 64,000-square-mile watershed draining six states and the District of Columbia. Its watershed is home to 15.1 million people and 3,600 species of plants and animals. The Bay has 11,684 miles of shoreline and averages twenty-one feet deep, with hundreds of thousands of acres of very shallow water. It is 200 miles long and thirty-five miles wide at its widest point.
The Bay is an incredibly complex ecosystem that includes many important habitats and food webs. A food web is a complex food chain where many different species of plants and animals interact by producing food, consuming organic material, and recycling wastes. Primary producers like phytoplankton, algae, and sea grasses are eaten by small animals and fish, which then become meals for larger fish and animals. These, in turn, are eaten by birds, larger fish, and mammals.
Chesapeake Bay is a mixture of freshwater and salt-water from the Atlantic Ocean and is subject to seasonal weather. Plant and animal populations vary with changes in temperature, salinity, water clarity (light penetration), dissolved oxygen, and human impacts. Human impacts include activities such as overfishing, development, marina construction and operation, and farming. Excess nutrients, most of which comes from nonpoint sources (primarily agricultural activity and urban runoff) is the primary stressor in Chesapeake Bay. A nonpoint source is a source that is widely spread and has no fixed location.
The first estuary in the United States to be targeted for restoration and protection, the Bay is protected under its own federally mandated program, separate from the NEP. The Bay Program began in 1983 with a meeting of the governors of Maryland, Pennsylvania, and Virginia; the mayor of the District of Columbia; and the EPA administrator. These individuals signed the Chesapeake Bay Agreement committing their states and the District of Columbia to prepare plans for protecting and improving water quality and living resources in Chesapeake Bay. The Chesapeake Bay Program evolved as the institutional mechanism to restore the Bay and to meet the goals of the Chesapeake Bay Agreement. The program, which guides and coordinates multistate and multiagency activities, is the model for the NEP and has resulted in a Chesapeake Bay that is cleaner than it was in 1983.
Two important habitat alterations in Chesapeake Bay are the focus of intense restoration efforts. They are restoration of the once-extensive beds of submerged aquatic vegetation and oysters. Oyster reefs (oyster bars) play an important ecological role in the Bay. Oysters cluster together to grow upward and outward, creating a hard surface on the Bay's bottom and a three-dimensional structure used as habitat by many species. The hard oyster shell surfaces provide places of attachment for many sessile (not moving, permanently attached) species, including oyster larvae. They also provide habitat for worms, snails, and other invertebrates as well as food and protection for small fish and crabs. Many species of ducks find food on and around the oyster bars during the winter months.
Oysters have declined in Chesapeake Bay because of introduced oyster diseases, harvest pressure and use of harvesting techniques that have flattened the large three-dimensional reefs, silting, and other pollution. Oyster populations are at or below the level of being naturally sustaining. The loss of oyster populations and their reef habitats has had important consequences for the oysters, as well as many other Bay species.
Both Maryland and Virginia have large-scale federally and state funded programs underway to artificially create reefs with oyster shell and other materials such as fly ash, rock, concrete, and other recycled materials. Oyster sanctuaries (areas off-limits to harvest) are being established as brood-stock areas to enhance the oysters' ability to maintain self-sustaining populations through natural recruitment (the ability of a population to reproduce and replace animals lost). In addition, private organizations such as the Oyster Recovery Partnership, the Chesapeake Bay Foundation, and the Tidewater Oyster Gardening Association are using volunteers to grow and plant millions of small oysters in the sanctuaries and other restored areas.
Submerged Aquatic Vegetation
Sea grasses—or submerged aquatic vegetation (SAV)—are very important in the productivity and habitat of estuaries. These grasses are vascular plants that grow completely underwater and have special adaptations to help them survive in the aquatic environment. A vascular plant is one that takes nutrients in through its roots and transports them through its roots and stems to all parts of the plant. SAV plays an important ecological role by:
- Providing food and habitat for waterfowl, fish, shell-fish, crustaceans, and other invertebrates, as well as nursery habitat for the juveniles of many species, which hide from predators among the swaying fronds
- Producing oxygen in the water column through photosynthesis
- Filtering and trapping silt that can cloud the water and bury bottom-dwelling organisms such as oysters
- Protecting shorelines from erosion by retarding wave action
- Removing excess nutrients that could cause the growth of undesirable algae in the surrounding waters
The species of SAV in an estuary change in response to the salinity. Tidal fresh SAV species require a salinity of 0 to 0.5 ppt. Oligohaline (slightly brackish) species require 0.5 to 5 ppt. Mesohaline (moderately brackish) require 5 to 18 ppt, while polyhaline (high salinity) species require 18 to 30 ppt. Upstream activities, such as dam construction or water diversions, can radically alter freshwater flow into an estuary, changing the downstream salinity and thus the composition of SAV.
The health of SAV is a good indication of the health of an estuary. The single most important factor in SAV growth and survival is the amount of light that reaches the plants. When the amount of light is too low, the SAV can no longer photosynthesize and produce enough energy and food to grow. The amount of light reaching SAV is affected by turbidity, algae, epiphytes (microbes that attach to SAV leaf surface), and nutrients present in the water column. Significant reduction in SAV is a sign that an estuary is experiencing considerable stress. Reduction in SAV has been linked to decline in important fish, crab, shrimp, and waterfowl species.
Chesapeake Bay has experienced significant SAV decline. According to the Chesapeake Bay Program, up to 200,000 acres of SAV may have grown in the area historically, but by 1984 that number had shrunk to 38,000 acres. In some areas, the grasses are returning naturally. In other areas, large-scale SAV monitoring and planting activities are being undertaken to try to reverse the decline. According to an article in the April 2003 issue of the EPA's Coastlines newsletter ("Submerged Aquatic Vegetation Being Restored in Chesapeake Bay"), in 1992 the Chesapeake Bay Program helped to develop an initial Bay-wide goal of having 114,000 acres of SAV, reflecting the total SAV area that existed between 1971 and 1990. Since annual Bay-wide surveys began in 1985, SAV has substantially increased in many areas. According to the report 2001 Distribution of Submerged Aquatic Vegetation in Chesapeake Bay and Coastal Bays (Robert J. Orth and David J. Wilcox, Gloucester Point, VA: Virginia Institute of Marine Science, December 2002), in 2001 total SAV acreage in the Bay set a new record—77,855 acres.
Similarly, the Gulf of Mexico experienced a dramatic SAV decline during the second half of the twentieth century, documented in a number of studies conducted throughout the region. The National Wetlands Research Center reported in "Seagrasses in Northern Gulf of Mexico: An Ecosystem in Trouble" (June 2000) that sea grass acreage in bays and estuaries of the northern Gulf had declined between 12% and 66%. In addition, the sea grasses are changing in species composition, densities, and distribution. Many scientists believe that Gulf of Mexico SAV decline is directly related to nutrient enrichment and hypoxia (lack of oxygen).
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