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Structure Retrieved from Lumcon

An estuary is a "partly enclosed body of water" in which river water (fresh water) mixes with ocean water (salt water) (#Encyclopedia Britannica Online). An estuary is an ecosystem that occupies the protected space between solid land and open water; visually, estuaries often represent the shift from land to ocean with the presence of a peninsula or barrier islands (#EPA, 2007), although sometimes protective borders are less-visible, like reefs. Estuaries are protected like rivers, but have tides like the open ocean (#National Ocean Service, 2006). Well-known estuaries include the San Francisco Bay, Puget Sound, Chesapeake Bay, and the New York/New Jersey Harbor (#EPA, 2007).


Estuaries are one of the most productive ecosystems in the world, home to more than two-thirds of the fish and shellfish consumed by humans. These ecosystems can also protect nearby communities from floods, as the marshes often present in estuaries are very absorbent (#National Ocean Service, 2006). Estuaries also offer a variety of cultural benefits and often played a central role in local lifestyles. Influences and artifacts from early Native Americans or European settlers still are visible in or around many estuary habitats (#National Ocean Service - Cultural Traditions, 2007). Many estuaries are also popularly visited by tourists, who utilize estuaries for swimming, boating, bird watching, and fishing, among other things (#National Ocean Service, 2006).

Estuaries also act as natural filters, although their role in this is somewhat controversial. Some plants commonly found in estuaries filter pollutants by storing the pollutants in their roots. Studies have suggested that estuaries may be able to filter some sewage without any negative effects. The sewage under consideration, though, was largely nitrogen and phosphate (#Oberrecht, 2007), the very nutrients that, in high concentrations, have been found to negatively effect the abundance of marine life (See: #Problems). Additionally, there are many harmful pollutants, notably mercury, that estuaries cannot store away (#Oberrecht, 2007).


Toxic Effects
Estuaries around the world are losing their health and productivity, due to increased human stress on the ecosystems. Hypoxia, or a lack of oxygen in the water, is an example of a natural occurrence that can be exacerbated by human activities. Fertilizer runoff, in particular nitrogen and phosphorous laden fertilizers, often leads to hypoxia and the growth of algal blooms (#Carlisle, 2000).

Without adequate levels of oxygen in the water, many organisms die. This may lead to the formation of a "dead zone," an area of the water that is no longer able to support aquatic life (#Buck, 2006). Dead zones are most common during the summer months, when runoffs from sewage treatment plants, septic systems, and fertilizers are greatest (#EPA - Too Many Nutrients, 2007). (See: #Gulf of Mexico Dead Zone). Congress specifically targeted the growing hypoxia problem with the Harmful Algal Bloom and Hypoxia Research and Control Act of 1998, an act which provided money to the [National Oceanic and Atmospheric Administration (NOAA) for researching, monitoring, educating, and managing the occurrence of hypoxia (#Buck, 2006).

Pathogens also can affect an estuary's health. Like hypoxia, pathogens can be released into an estuary through runoff from sewage treatment plants and septic systems, but can also get into the ecosystem through marina pollution and pet or wildlife waste. Pathogens have the potential to cause disease or sickness in humans, so estuaries are typically closed off from direct human use when pathogens are found to contaminate the area (#EPA - Pathogens, 2007). A well-known example of a preponderance of potentially deadly pathogens is the phenomena known as "red tide". Red tide is a condition that is caused by the domination of toxic algal blooms. While only eighty-five out of thousands of aquatic bacteria have been found to be toxic, the harmful bacteria are more likely to grow in polluted conditions. Though most algae kill their food without toxins, the toxins that the algal blooms produce can be released after they are consumed. Some of these blooms, such as the ones found in red tide, produce neurotoxins, which is bioaccumulative and can result in negative health affects in mammals allergic reactions, and renal and nervous system effects including death (#Carlisle, 2000).

Toxic chemicals also contribute to the deterioration of estuaries. In addition to contributing to hypoxia and the prevalence of pathogens, runoff can also include Pesticides, heavy metals, and other substances toxic to human and aquatic life. Toxic runoff can be primarily from one location (referred to as 'point source') or can be the accumulation of runoff from many areas (nonpoint sources, like parking lots or lawns). Aquatic life will usually be banned from human consumption if it is found to be contaminated by toxic chemicals (#EPA - Toxic Chemicals, 2007). Habitat loss is another threat to estuary productivity and health. Coastal land is highly valued, and humans often encroach on estuary habitat by allotting land to agriculture, marinas, roadways, forestry, housing, and commercial development, or destroy the estuary by damming, dredging and filling, diking, or otherwise altering the flow and landscape of the estuary (#EPA - Habitat Loss and Degradation, 2007). Such actions can have repercussions beyond the immediate welfare of the estuaries, as well. The high damage from Hurricane Katrina in New Orleans is largely thought to be due to the disappearing wetlands. For New Orleans, the solid land of estuaries and barrier islands that line the Mississippi River Delta have historically decreased the intensity of hurricanes. Because the delta has experienced heavy coastal land loss in the past few decades, however, there were many fewer miles of protection, making the impact on the city much more intense than it would have been, had there not been heavy coastal land loss (#Hirsch, 2005).

Non-Native Species
Non-native species can also contribute to the decline in productivity of an estuary as they can out-compete native species and not allow them to obtain the nutrients they need to survive. The native species are also unable to defend themselves against the non-native species because they evolved independently of the new species and have not developed the necessary mechanisms to combat the new species. Exotic species can have such an extreme effect on the functioning of the ecosystem both because they act as competitors to native species who have a similar diet, and because they often have no natural predators, allowing their proliferation (#EPA - Invasive Species, 2007). In New Orleans, for example, the exotic nutria have contributed to the poor health of estuaries because they consume marsh grass. Because they have no natural predators, their high numbers have resulted in overgrazing, a state which in turn exposes the fragile soil to eroding water (#Lousiana DWF, 2007). Exotic species can enter estuaries through passing ships or accidental release from aquariums or ornamental landscaping (#EPA -Invasive Species, 2007).

Demand for Freshwater
Another major factor influencing estuary degradation is the demand for freshwater. People's daily lives place a significant demand on freshwater, causing governments to engage in activities to ensure an adequate supply of it. Such activities, including damming, dredging, and pumping groundwater, lessen the flow of freshwater into estuaries, increasing the risk of erosion and sedimentation. This in turn can make the water too salty, which can be a detriment to many of the species that live in the estuaries (#EPA - Changes in Water Flow, 2007).

Because of the pervasive and wide-ranging problems that affect estuaries, the Environmental Protection Agency has developed the The National Estuary Program, which focuses on the restoration and effective management of major estuaries across the United States (#EPA - National Estuary Program, 2007).

Gulf of Mexico

The Gulf of Mexico Dead Zone is one of the most prominent and pervasive cases of hypoxia in the United States. Seasonally, the northern Gulf of Mexico, stretching from the Mississippi delta into northern Mexico, is essentially devoid of aquatic life, as there is not enough oxygen in the water to support survival. While this dead zone first appeared in the 1970s, the condition has increasingly worsened, expanding both in size and frequency. While the dead zone used to appear every few years, it now appears every spring, and as of 1999 spanned a total of 7,728 square miles (#Carlisle, 2000).

Structure Retrieved from NOAA


National Estuaries Day

The National Oceanic and Atmospheric Administration (NOAA) and the Environmental Protection Agency began National Estuaries Day in 1988, now annually held on the last Saturday of September. The day is dedicated to educating citizens on the importance of estuaries. In 2001, EstuaryLive, an interactive internet program, became the main focus of National Estuaries Day, and has since maintained its feature role (#National Ocean Service - National Estuaries Day, 2007).

National Estuary Program

This program focuses on enhancing and recovering estuaries throughout the United States. The National Estuary Program is an umbrella organization of twenty-eight smaller projects that focus on specific estuaries. Each individual project must develop a Comprehensive Conservation and Management Plan as a means of outlining restoration and maintenance measures (#EPA - National Estuary Program, 2007).

External Links


Buck, Eugene H. Specialist in Natural Resources Policy. Resources, Science, and Industry Division. Congressional Research Service. The Library of Congress. Marine Dead Zones: Understanding the Problem. Updated 09/20/06. Accessed 07/20/07.

Carlisle, Elizabeth. The Louisiana Environment. The Gulf of Mexico Dead Zone and Red Tides. Updated 01/05/00. Accessed 08/08/07.

Encyclopedia Britannica Online. Estuary. Updated 2007. Accessed 07/17/07.

Environmental Protection Agency. Exploring Estuaries. About Estuaries. What Challenges do our Estuaries Face? Changes in Water Flow. Updated 04/09/07. Accessed 07/20/07.

Environmental Protection Agency. Exploring Estuaries. About Estuaries. What Challenges do our Estuaries Face? Invasive Species. Updated 04/09/07. Accessed 07/20/07.

Environmental Protection Agency. Exploring Estuaries. About Estuaries. What Challenges do our Estuaries Face? Pathogens. Updated 04/09/07. Accessed 07/20/07.

Environmental Protection Agency. Exploring Estuaries. About Estuaries. What Challenges do our Estuaries Face? Too Many Nutrients. Updated 04/09/07. Accessed 07/20/07.

Environmental Protection Agency. Exploring Estuaries. About Estuaries. What Challenges do our Estuaries Face? Toxic Chemicals. Updated 04/09/07. Accessed 07/20/07.

Environmental Protection Agency. National Estuary Program . Updated 06/05/07. Accessed 06/26/07.

Environmental Protection Agency. National Estuary Program. About Estuaries. Updated 04/17/07. Accessed 07/17/07.

Environmental Protection Agency. National Estuary Program. Challenges Facing Our Estuaries. Key Management Issues. Habitat Loss and Degredation. Updated 04/17/07. Accessed 07/23/07.

Hirsh, Tim. British Broadcasting Network. Environment Correspondent in the Mississippi Delta. Katrina damage blamed on wetland loss. Updated 11/01/05. Accessed 08/08/07.

Louisiana Department of Wildlife and Fisheries. Nutria Damage. Updated 2007. Accessed 08/08/07.

Oberrecht, Kenn. The Estuary as a Pollution Trap and Filter. Accessed 08/10/07.

National Ocean Service, National Oceanic and Atmospheric Administration. About Estuaries. Updated 08/08/06. Accessed 07/17/07.

National Ocean Service, National Oceanic and Atmospheric Administration. Cultural Traditions. Updated 08/22/05. Accessed 08/10/07.

National Ocean Service, National Oceanic and Atmospheric Administration. National Estuaries Day. Updated 04/26/07. Accessed 07/17/07.

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