Estuaries Nutrients example essay topic

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 worlds 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 wildlife. 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 vegetation.

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 water tables, 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 estuarine 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 hasnt 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.

Bibliography

1. Phillips, Robert S. Estuaries Funk and Wagnalls New Encyclopedia. 1982.2. web.