Hydrographic comparison of estuary and fjord Essay Example

partially enclosed, creating a transition zone between land and sea. They minimize wave action and offer protection against strong winds and waves similar to a river. Estuaries mix saltwater from the ocean with freshwater from rivers, streams, and creeks. These areas are affected by tides like the sea and are home to unique habitats such as coastlines, marshes, wetlands, barrier islands, reefs, sand or mud flats. These different ecological components make estuaries crucial areas where freshwater run-off meets the oceans.

The significant salinity gradient in estuaries is a result of the varying densities between freshwater and salt water. When there are no winds or tides, freshwater remains on the surface while seawater moves inland as a countercurrent, creating a salt-water wedge beneath the freshwater surface. This generates stronger gravitational circulation within the estuary than if only river water flowed to sea. Additionally, strong tides may lead to tidal bores - rapid increases in tidal water caused by shallows before reaching shore.

Estuaries are rarely static, with tides being the main energy source for mixing, while wind, wave motions, and river run-off can play a local role. The mixing of salt and freshwater creates brackish water that can shift seasonally and vary greatly in different areas due to river flow oscillations. During the spring-neap tide cycles, an estuary zone may transition from stratified to well-mixed. Estuaries that receive a significant amount of freshwater but have low tidal range are typically the most stratified.

Partially mixed estuaries with moderate freshwater inflow and tidal range typically have a brackish zone salinity ranging from 2 to 10 ppm, as compared to the approximately 35 ppm of salt water. Greater mixing occurs in

areas with a large tidal range and limited freshwater inflow. Coastal lagoons with extensive open waters, low freshwater input, and a small tidal range are more affected by wind mixing than tidal mixing. Freshwater exhibits considerable chemical diversity, while salt water is relatively uniform.

The estuarine nutrient cycles are affected by the chemistry of rivers, particularly with regard to essential compounds for estuarine life. Freshwater provides silicon, iron, nitrogen, and phosphorus while seawater offers sulphates and bicarbonate. Estuaries accumulate and provide access to nutrients along with sufficient light conditions that promote phytoplankton production, making them some of the most productive environments in the world.

Estuaries are known for their demanding environments and nutrient-dense waters, which tend to support comparable organisms as those in the coastal ocean. Phytoplankton and algae have developed great adaptability, with diatoms being especially significant. The vegetation found in estuaries worldwide varies from scanty grasses to dense rainforest trees. Intertidal communities that inhabit salt marshlands contain rooted plants that experience frequent flooding during high tides.

Estuaries typically contain dense communities of submerged vascular plants in shallower and partially protected areas, with these plants taking root in soft sediments. Additionally, some species migrate from offshore to reproduce in these protected environments, making estuaries significant as nursery areas for numerous species. Due to several factors, estuaries are highly productive and yield a considerably high biomass of fish and shellfish for each unit area.

Due to their importance as biological resources, estuaries require protection from harm. Geologically, there are various types of estuary mixing, including salt wedge, partially mixed, well-mixed, and fjord. These estuaries come in a range of sizes and are characterized by the salinity gradient between freshwater

and coastal marine waters at the mouth. This gradient produces diverse stratifications in different types of estuaries.

Figure 1 illustrates the salt wedge estuary, which is highly stratified due to a powerful river flow and limited mixing by tidal currents. This results in a separated freshwater layer over a distinct saltwater layer at the bottom, creating visible differences along the length of the estuary. On the other hand, the partially mixed estuary (Figure 2), such as Narragansett Bay, exhibits a salinity gradient from the mouth to the head, with corresponding differences from surface to bottom over a considerable distance.

Figure 2 illustrates a Partially Mixed Estuary, while Figure 3 shows a well-mixed estuary. The latter is mainly influenced by tidal currents rather than river flow, resulting in a mostly uniform mixing throughout its length. Although salinity varies from the source of freshwater to the mouth, there is little stratification due to minimal vertical variation.

The distinct type of estuary known as a fjord (Figure 4) has a unique geometry that is characterized by a relatively long and narrow shape with deep waters along much of its length. A defining characteristic of a fjord is a shallow water sill at the mouth that separates the deeper waters from the ocean. This can lead to poor mixing of deeper waters and can create high levels of stratification if there is enough freshwater. Figure 4 depicts a fjord-type estuary. Although present-day estuaries are young and brief coastal features from a geological perspective.

Estuaries originated in their current form during the present interglacial period. The increase in sea level over 15,000 to 5,000 years ago was approximately 120 meters (400 feet), eventually reaching

its current position. During glaciation periods when sea levels were lower, estuaries were restricted and existed on the continental slope. Extensive estuaries have only been observed during around 10-20% of the last million years when sea levels were relatively high. Unless there is an increase in sea levels, sediments from continent erosion and sand transported by tides from the continental shelf naturally fill up estuaries causing them to decrease in size. There are four main categories for identifying estuaries.

Coastal plain estuaries have the appearance of a V-shaped river channel with a floodplain and are generally less than 20 m (65 ft) deep. They were created either during the previous great sea level rise resulting from melting glaciers, or through a combination of rising sea levels and increased rainfall leading to greater flooding. Salt-marsh estuaries possess a clear drainage system but typically are not fed by rivers, making them predominantly saltwater. This type of estuary is common in areas along the Florida coastline of the United States. Compared to the salt-marsh type, lagoons have more open space, a less defined drainage system, and are often shallow.

The raised ridge known as a sand barrier is a distinctive aspect of lagoon borders, which were created due to fluvial and atmospheric erosion during the last ice age. The flooding caused by rising sea levels subsequently submerged the regions situated behind the barrier. Moreover, geological occurrences including volcanic eruptions, landslides and faulting gave rise to tectonic estuaries.

Fjords are a significant type of estuary found in both the northern and southern temperate latitudes above about 45°. They are characterized by their steep, U-shaped cross-sectional form and interior

water depths that can exceed 500 meters. Fjords typically occur in glaciated regions where valleys have been shaped by various processes, such as faulting and erosion by running water. Glacial scouring may have also played a role in their creation. As the regions occupied by these glaciers subsided, the valleys were flooded by the sea.

Examples of fjord coastlines can be found in Norway, Scotland, Greenland, Alaska, British Columbia, southern Chile, southern New Zealand and Antarctica. These coastal formations generally have a shallow mouth that deepens further inland. For instance, the Sognafjord in Norway boasts an impressive length of more than 100 miles (160 km) and reaches a depth of 4,000 feet (1,220 m). Meanwhile Loch Moran in Scotland is a typical fjord separated from the sea with a depth of 310 m/1,017 ft. Norwegian fjords are especially renowned for their natural beauty.

Fiords are characterized by extending branches and deep walls from the main body of water. In general, their mouths tend to be shallower than further inland. According to geologists, fiords are believed to have been formed through the process of glaciers carving into the coastline.

As the sea level rose, the grooves were filled with water, resulting in fjords. Some fjords started as river mouths and were eventually deepened by glaciers. Fjords can have depths exceeding 305 m (1,000 ft) below sea level and are often wider than 6 km (4 mi) and longer than 161 km (100 mi). See Figure 6 for an illustration of a fiord. (Microsoft ® Encarta ® Premium Suite 2005)

Fjords are a result of glacial carving that occurred in coastal areas where mountains were previously glaciated, creating valleys. As

temperatures increased and ice melted, rising sea levels inundated these valleys. Fjords often contain channels that align with faults in the rock beneath them, sometimes even featuring sharp turns.

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Often, the valley at the head of a fjord stretches into the mountains, and some residual glaciers may still exist. Alternatively, if no residual glacier is present, the river which flows through the valley will create a delta at the fjord's head. This delta frequently serves as an ideal location for establishing villages and farms due to the shallow threshold, great depth, and protection provided by the valley walls. Fjords naturally make excellent harbors due to these characteristics. Typically, the sole area where villages and farms are established is at the fjord's head, where a river formed a delta before entering the ocean.

The main factors affecting water circulation in a fjord are the sill created by the terminal moraine and river flow. If sills are taller or longer, they can act as hydraulic controls and prevent ocean water intrusion. The deep inner basin of many fjords may have anoxic sea water due to infrequent replenishment with new ocean water, which occurs only once a year. Flushing out deep water frequency depends on tides, winds, river flow, and ocean density. It's worth noting that in 2000 some of the world's largest coral reefs were found at the bottom of Norwegian fjords.

Across Norway, coral reefs have been found in fjords, from the north to the south. These reefs play a critical role in supporting marine life and greatly contribute to the abundance of fish along the Norwegian coastline. Trondheimsfjord houses Norway's shallowest reef, which is 39m

(128ft) deep. The inhabitants of these reefs comprise plankton, coral, anemones, fish, sharks and other species that have adapted to thrive in the intense water pressure and darkness commonly found in deep sea environments.

Although both New Zealand's fjords and estuaries are habitats for deep sea corals, they have distinct differences. Fjords feature steep, parallel walls that extend below the water surface and numerous branches with similar shapes. Estuaries, on the other hand, sit at river mouths where fresh water meets nearshore saline water creating a transitional zone between freshwater and saltwater ecosystems. They often coexist alongside additional coastal environments like salt marshes, mudflats, beaches, and bogs. The salinity of the water in estuaries is heavily influenced by tides. Interestingly enough, a layer of dark fresh water found at the top of New Zealand's fjords creates an optimal environment for deep sea corals to thrive in shallower depths than usual.

Brackish water is formed when freshwater and saltwater mix during incoming tides. Fjords are the deepest type of estuary, with distinct water properties compared to classic estuaries. Although there is a brackish surface layer and deeper saline layer like other estuaries, circulation of deep water in fjords depends on factors such as sill depth, tidal mixing, and frequency of oceanic water flushing. In eastern Canada, deep water renewal mainly happens internally during winter.

The following are references containing links with and their contents:

ReferencesBellNET©, (1997) BellNET Webmaster http://bellnetweb. brc. tamus. edu/evaluati. htm
Gulf of Maine Aquarium (1998) http://octopus.

The website http://www.gma.org/katahdin/estuary.html, (Microsoft ® Encarta ® Premium Suite (2005)), and the National Ocean Service and National Oceanic and Atmospheric Administration at http://estuaries are all sources of information

about estuaries. © 1993-2004 Microsoft Corporation. All rights reserved.

The website address for estuaries can be found at http://www.estuaries.gov/estuaries.html, which is also referenced by Pritchard in their work. The information is presented within .The physical viewpoint of estuaries was discussed by W. in 1967. The information can be found on pages 3-5 in G.H.

Estuaries, edited by Lauf and published by A. A. A. S.

Washington, D.C. Publication Number 83.

The content is derived from two sources: the webpage http://en.wikipedia.org/wiki/Estuary and The Columbia Encyclopedia, Sixth Edition. 2001-05.The content within the states that the 6th Edition of The Columbia Encyclopedia, which is under the copyright of Columbia University Press from 2001-05, has information on estuaries. The source for this information can be found at http://www.bartleby.com/65/es/estuary.html.The National Estuary Program provided by the U.S. Environmental Protection Agency can be accessed at http://www.epa.gov/owow/estuaries/about1.htm. The program is attributed to S. Stilling.The book "Ecology: theories and applications" is in its 2nd edition and was published in 1998 by Prentice Hall, Inc. It can be found in London, UK and contains page numbers.The website "http://www.glf.dfo-mpo" belongs to Fisheries and Oceans, Canada and was established in 1997.

Visit gc.ca/sci-sci/bysea-enmer/fjords-e.html for more information.