Mobile Bay Essay Research Paper

Mobile Bay Essay, Research Paper

An estuary is where the river meets the sea. Life in the estuary is depending upon

salinity, which decreases from open ocean to the mouths of the inflowing rivers. As salinity

declines, the assortment of life declines, because most estuarine organisms are marine. But they

are high rich ecosystems, accounting for one-half the living matter of the world?s oceans. This

high productivity is a result of a nutrient trap formed by the interactions of tides and inflowing

rivers. Fresh water, lighter in weight than salt water, flows into the estuary on top of a wedge of

inflowing seawater, producing a countercurrent. Nutrients circulate between the upper and lower

layers; strong winds and circulating currents increase the vertical mixing. The countercurrent,

flowing against the waters that move toward the ocean, holds in the estuaries nutrients and

plankton. Nutrients in the seawater of the estuary are taken up by mudflats and salt marshes,

recirculated among the vegetation and associated animal life, and carried back to the estuary by

tidal waters. The sheltering inlets and abundant nutrients of estuaries make them nursery

grounds for a big number of birds, amphibians, and fish. Yet estuaries and salt marshes are being

destroyed continually by pollution, oil spills, and dredging and filling for industrial and

residential growth.

There are three types of estuaries. Vertically homogenous estuaries have a greater tidal

current and lesser river current. Partially mixed estuaries have an equal tidal current and equal

river current. Salt wedge estuaries have a lesser tidal current but has a greater river current.

Most estuaries face similar environmental problems and challenges. Some are over

enrichment of nutrients, pathogens contamination, toxic chemicals, alteration of freshwater

inflow, loss of habitat, declines in fish and wildlife, and introduction of new species. People

think that humans are the only reason that the number of estuaries are going down, but it is not.

There are several problems with nature that are causing problems in estuaries.

The National Estuary Program (NEP) has been trying to fix these problems. Although

environmental results are sometimes slow in coming, signs of improving environmental

conditions are already emerging from the NEP. The 28 National Estuary Programs are also

showing success in finding useful plans to manage their estuaries, securing and leveraging funds,

and improving public education and citizen participation through outreach efforts.

One problem in estuaries is the over enrichment of nutrients. Nitrogen and phosphorus

are necessary for growth of plants and animals and support a healthy aquatic ecosystem. But if

there is too much, they can contribute to fish disease, red or brown tide, algae blooms, and low

dissolved oxygen. The dissolved oxygen is 5 or 6 parts per million in healthy water. But

sometimes a condition called hypoxia occurs, and the dissolved oxygen is less than 2 parts per

million. Sources of nutrients include sewage treatment plant discharges, storm water runoff from

lawns, faulty or leaking septic systems, sediment in runoff, animal wastes, atmospheric

deposition from power plants or vehicles, and groundwater discharges. The excessive nutrients

stimulate the growth of algae. As the algae die, they decay and lower the amount of oxygen in the

water. The algae also prevent sunlight form entering the water. Fish and shellfish are deprived of

oxygen, and underwater sea grasses are deprived of light and die. Animals that used to live on

sea grasses for food or shelter will now leave the area or die. In addition to that, too much algae

growth may result in brown and red tides which have been linked to fish killed, manatee deaths

and negative impacts to scallops.

Another problem in estuaries are pathogens. Pathogens are disease causing organisms

such as viruses, bacteria, and parasites. They can cause a health threat to swimmers, surfers,

divers, and seafood consumers. Sources of pathogens are urban and agricultural runoff, waste

from boats, faulty or leaky septic systems, sewage treatment plant discharges, combined sewer

overflows, recreational vehicles or campers, illegal sewer connections, and waste from pets or


Toxic substances, like metals and pesticides are a concern in the estuarine environment.

These substances enter waterways through storm drains. They also come in through industrial

discharges, runoff from lawns, sewage treatment plants, and from atmospheric deposition.

Bottom dwelling organisms are exposed to the chemicals and may cause a risk to human health if

we consume it. As a result there may be fishery and shellfish bed closures, and consumption

advisories. Factories have dumped DDP, PCBs, and mercury into the estuaries. Now they have

banned the use of some of these toxic chemicals.

Another major problem is habitat loss and degradation. The same areas that often attract

human development also provide essential food, cover, migratory corridors, breeding / nursery

areas for coastal and marine organisms. These habitats also perform other important functions

such as water quality, flood protection, and water storage. Ecosystems can be degraded through

loss of habitat, such as the conversion of a sea grass bed to a dredged material island or through a

change of degradation in structure, function, or composition. Threats to a habitat include

conversion of open land and forest for commercial development and agriculture, forestry,

highway construction, diking, dredging, filling, and damming. All their activities may cause

increases in the runoff of sediments, nutrients, and chemicals. Excess nutrients such as nitrogen

can lead to algal blooms that deplete oxygen and block sun light, killing submerged aquatic


The introduction of a new species is another problem in estuaries. It may result in

unexpected ecological, economic, and social impacts to the environment. New species have

contributed to the termination of some native populations and drastically reduced others, altering

the food web. Over population of some introduced herbivore species has resulted in overgrazing

of wetland vegetation and the result is degradation and loss of marsh. Other impacts are the

changing of watertables, modification of nutrient cycles or soil fertility, increased erosion,

interference with navigation, agricultural irrigation, fishing, recreational boating, beach use, and

possible introduction of pathogens.

Freshwater is an increasing limited resource in many areas of the country. Changes in

natural freshwater inflow can have significant impacts on the health and distribution of plants

and wildlife. Too much or too little freshwater can affect fish spawning, shellfish survival, bird

nesting, seed development, and other activities of fish and wildlife. In addition to changing

salinity levels, inflow provides nutrients and sediments that are important for overall productivity

of the estuary.

The last major problem is the decline in fish and wildlife population. The distribution

and abundance of esturine fish and wildlife depends on factors such as light, turbidity, nutrient

availability, temperature, salinity, habitat, and food availability. Declines have resulted from

fragmentation and loss of habitats and ecosystems, pollution, decreased water quality,

overexploitation of resources, and introduced species.

The National Estuary Program hasn?t found solutions for most of these problems but have

been trying hard. They will spend $400,000 on Mobile Bay to try to protect its health.


1. Phillips, Robert S. ?Estuaries? Funk and Wagnalls New Encyclopedia. 1982.



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