Data Bases • Custom Term Papers • Free Term Papers • Free Research Papers • Free Essays • Free Book Reports • Plagiarism? Links • Top 100 Term Paper Sites • Top 25 Essay Sites • Top 50 Essay Sites • Search 97,000 Papers @ DirectEssays.com • Search 101,000 Papers @ ExampleEssays.com • Search 90,000 Papers @ MegaEssays.com Free Essays • Term Paper Sites • Chuck III's Free Essays • Free College Essays • TermPaperSites.com • Free Essays • My Term Papers • Essay World • Planet Papers	Search Lots of Essays Back to Subjects - Physics Estuaries Estuaries Estuaries are bodies of water along our coasts that are formed when fresh water from rivers flows into and mixes with salt water from the ocean. In estuaries, the fresh river water is blocked from streaming into the open ocean by either surrounding mainland, peninsulas, barrier islands, or fringing salt marshes. This mixing of fresh and salt water creates a unique environment that brims with all kinds of life. The estuary gathers and holds an abundance of life-giving nutrients from the land and from the ocean. They provide a unique habitat for over 75 percent of our nation's commercial fish. This along with commercial and recreational fishing, boating and tourism provides many jobs and lots of enjoyment for those who use the area. Estuaries are important to our quality of life and our health for reasons other than jobs, healthy economies, and recreational opportunities. The local bay or sound often serves as the focal point for community life and traditions, hosting everything from harvest festivals to busy ports. They also protect water quality, are a center for research and education, and help stem the erosion of our shoreline communities. Estuaries come in all shapes and sizes and go by many different names, often known as bays, lagoons, harbors, inlets, or sounds. Estuarine environments are among the most productive on earth, creating more organic matter each year than comparably-sized areas of forest, grassland, or agricultural land. Among the cultural benefits of estuaries are recreation, scientific knowledge, education, and aesthetic values. Boating, fishing, swimming, surfing, and bird watching are just a few of the numerous recreational activities people enjoy in estuaries. These commercial activities thrive on the wealth of natural resources estuaries supply. The protected coastal waters of estuaries also support important public infrastructure, serving as harbors and ports vital for shipping, transportation, and industry. Estuaries provide us with a whole suite of resources, benefits, and services. Some of these can be measured in dollars and cents, others can not. Estuaries are an irreplaceable natural resource that must be managed carefully for the mutual benefit of all who enjoy and depend on them. Oceanographyically an estuary is "a semi enclosed coastal body of water having a free connection to the open sea and within which the sea water is measurably diluted with fresh water derviving from land drainage."1 The rive water which enters the estuary mixes to some extent with the salt water thereing and eventually flows out to the open sea in the upper layer. A corresponding in flow of sea water takes place below the upper layer. The inflow and the outflow are dynamically associated so that while an increase in river flow tends to reduce the salinity of the estuary water it also causes an increased inflow of sea water which tends to increase it, thus an approximate steady state prevails. Estuaries are classified into four types. This happens in generally shallow waters where the mixture is homogeneous from the surface to the bottom at any particular place along the estuary. The salinity increases as the distance from the head to mouth increases. This is similar to Type A in that it too has shallow water and the salinity increases with the distance from the head to the mouth. The water is in essentially two layers with the upper layer having an outward flow and is a little less saline then the deeper inward flow layer. At each position there is a mixing layer between them. The upper layer increases in salinity from near zero in the river at the head to a value close to that of the outside sea at the mouth. Depp water however is almost of uniform salinity from head to mouth. Again there is a net out flow in the upper layer and inflow in the deepwater. Here there is a very strong halocline between the upper water and deep water, particularly at the head where vertical salinity gradients of 10 to 20 %o per meter may occur in summer during the peroid of greatest river runoff. There is a vertical mixing but it results predominantly in an upward movement of salt water from below. Here the saline water intrudes from the sea as a wedge below the river water. This situation is typical of rivers of large volume transport. The salt wedge estuary has features in common with the stratified estuaries. There is a horizontal gradient of salinity at the bottom as in a slightly stratified estuaryand a pronounced vertical salinity gradient as in a highly stratified estuary. The distinction is in the lack of saline water at the surface until it reasches the sea. A feature of the stratified estuaries is that depth of the halocline (the thickness of the upper, low salinity layer) remains substantially constant from head to mouth of an estuary for a given runoff. If the estuary width does not change much, the constancy of depth of the upper layer means that the corss-sectional area of the upper layer outflow remains the same while its volume transport increases because of the entrainment of salt water from below. In consequence the speed of the ouflowing surface layer increases markedly along the estuary from head to mouth. The increase in volume and speed can be very considerable, the outflow at the mouth being as much as 10 to 20 times the volume flow of the river. Bibliography: Word Count: 918
Copyright © 1998-2008 College Term Papers, INC All Rights Reserved. DMCA Notifications and Requests