Environment

What Are The Differences Between A Lagoon And A Lake?

A lagoon is defined on the basis of the its presence near another larger water body from which it is separated by barrier islands or reefs.

Lagoons are generally found in the marine environment and mostly in the coastal regions (coastal lagoons), while the atoll lagoons or the oceanic lagoons are within the ocean. Lakes, on the other hand, are primarily located inland.

Lakes

Lakes refer to an area that is filled with water in a localized basin and typically surrounded by land. A lake usually has one or more rivers and streams flowing into it which feeds it and a river that drains the lake and serves as an outlet. They are found mainly inland, and they do not form part of the oceans, distinguishing them from lagoons. Natural lakes could be found in rift zones, mountainous areas, and areas where glaciation is still ongoing. Some lakes are found along the course of a mature river or in endorheic basins. There are many lakes in different parts of the world as a result of the various patterns of drainage left behind in the last ice age. Over the period of geological time scales, all lakes are temporary because they will be gradually filled with sediments or eventually spill out of the basin they are located. Several other lakes could be artificial that were constructed to serve agricultural, industrial, hydroelectric generation, recreational, or for water supply among other activities.

Lagoons

A lagoon refers to a shallow body of water which is alienated from another larger body of water like the ocean by a barrier of Island or a reef. Lagoons are divided into two types, and they are atoll lagoons and the coastal lagoons. Typically, they found in areas with gravel and mixed-sand coastlines. They are common coastal features in different parts around the world. There is always an overlap between bodies of water categorized coastal lagoons and estuaries. The word lagoon is derived from the Italian language from the word Laguna, which refers to a shallow body of water.

Depth

Lagoons are generally shallow compared to lakes. For instance, the depth of lagoons hardly exceeds 200 feet (for oceanic lagoons), and many of them are less than 65 feet deep (for coastal lagoons). The deepest lagoon is found in Comoro archipelago in Mayotte Island in the Indian Ocean and reaches a depth of 300 feet. That lagoon measures about 10 miles in width and surrounds the island creating an atoll of about 34 miles in diameter. On the other hand, lakes are generally deeper, and the world's deepest Lake is Baikal in Russia measuring 5,387 feet deep at its deepest point, and an average depth of 3,893 below sea level. Although there are lakes which are shallower than some lagoons, lakes are generally deeper compared to lagoons.

Sources Of Water

Some of the primary sources of water for lakes include runoff water carried by streams and channels from the catchment area, aquifers in groundwater channels, and artificial sources from outside the catchment area. Water output for a lake includes evaporation, ground and surface water flows, and extraction by humans. Coastal lagoons are typically parallel to the shoreline, and in most cases, they are longer than they are wide. Lagoons may not have large rivers flowing in, although there are cases where a river flows into a lagoon. For instance, Curonian Lagoon found in Russia which extends to Lithuania on the coast of the Baltic Sea has River Neman flowing into the lagoon. Such a lagoon is known as an estuarine lagoon and could be classified as a unique type of an estuary. Otherwise, the primary source of water in a lagoon is from the ocean.

Water Circulation In A Lake

Because of the unique relationship between water density and temperature, lakes often form layers known as thermoclines. These layers exhibit huge variation in temperature in relation to the depth. Typically, freshwater is denser at about 39.2 degrees Fahrenheit at sea level. Therefore, the water temperatures at the surface of the lake are different from the water temperatures at the bottom of the lake. Often during cold months in temperate zones, the water in the lake could start mixing bringing up oxygen-starved water from the depths of the lake and driving oxygen-rich water down to the bottom of the lake. In deep tropical lakes, surface water does not reach the maximum density, and therefore the water does not mix. In such lakes, the deeper layer is always starved of oxygen and often saturated with carbon dioxide or other gases such as sulfur dioxide. Unique events such as landslides or earthquakes can only cause the mixing of water bringing up the deep layers that could cause the release of trapped gasses at the bottom; an event referred to as Limnic eruption. Release of such gases could be catastrophic to the communities living around as it happened at Lake Nyos in Cameroon.

Water Circulation In A Lagoon

Lagoons are generally shallow, and there is so much activity of mixing water which depends on the size of the barrier which affects the flow of water flowing in and out of the lagoon. Some lagoons may be partially enclosed or entirely enclosed and could be classified into three types depending on how the water is exchanged with the ocean. The three types of lagoons are choked lagoons, restricted lagoons, and leaky lagoons. Choked lagoons have a narrow channel leading to the sea, and they are common in areas where the wave’s energy of the sea is relatively high. The narrow channel of the lagoon limits the waves from accessing the lagoon, and therefore, there is no much mixing of water. Lagoons such as Lagoa dos Patos in Brazil, Songkhla Lake in Thailand, and Rekawa and Mundel Lagoon in Sri Lanka are examples of choked lagoons. Restricted lagoons typically have more than one outlet to the sea, and there is water exchange leading to net transport of water to the sea. Winds play a significant role in restricted lagoons because they generate currents leading to mixing of water. Examples of restricted lagoons include Laguna de Terminos in Mexico and Uppar Lagoon in East Sri Lanka. Wide channels to the sea are the main characteristics of leaky lagoons, and there is an unhindered exchange of water as a result of fast currents. An example of a leaky lagoon is the Mississippi Sound in the US.

Classification Of Lagoons And Lakes

Lagoons are broadly categorized into two the coastal lagoons and the atoll or oceanic lagoons. The coastal lagoons can further be categorized into three, namely choked lagoons, restricted lagoons, and leaky lagoons. Lakes, on the other hand, can be classified in non-exhaustive ways.

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