Estuaries: what are they, characteristics, types, flora and fauna

del Mino estuary

There are different types of ecosystems that mix the fresh water that comes from rivers and the salty water from the sea. The main ecosystems are the estuaries. It is a type of mixed ecosystem that mixes the fresh water from the riverbed with the salty water from the sea. Estuaries are bodies of water that are closed by the area of ​​land that forms the coast and open to the sea. Therefore, they are considered semi-closed systems.

In this article we are going to tell you about all the characteristics, importance, types, flora and fauna of estuaries.

Key features



Estuaries are ecosystems that act as a refuge for many species of animals and plants. These living beings depend on these ecosystems to survive, feeding and reproducing. The different types of estuary are classified depending on the area where the water empties. This water can end up flowing its waters in the oceans, bays, taught, lagoons, orchards or canals. The mouth of the river is mixed between the fresh water that comes from the river course with the salty water of the sea. This collision of waters of different salinity causes a high degree of turbidity.

Today estuaries are used as areas that are sometimes used for recreational, tourist and scientific uses. Among its main characteristics is that it is one of the most productive ecosystems on the planet. And it is that here large amounts of organic matter are generated where nutrients from the earth arrive that have been washed away by rivers and on the other hand nutrients arrive that have been washed away by the sea.

Being a semi-closed system there is an exchange of materials from all kinds of neighboring ecosystems. These are generally very shallow areas and this allows light to easily penetrate through the water. Thanks to these environmental conditions, the rate of photosynthesis in estuaries is quite high. All this helps a good primary production. It should also be taken into account that many of the species that consume human beings such as crustaceans, mollusks and some species of fish inhabit estuaries.

One of the capacities of the estuary is to retain large volumes of water avoiding floods. They also help prevent shoreline damage during heavy storms. For this reason, they are also very important when it comes to managing populations. On some occasions, the flow of water that comes from rivers carries more water and this causes sediments and pollutants to be renewed. Thanks to this more powerful flow of water, the water stays cleaner.

Types of estuaries

river flora and fauna

river flora and fauna

There are different types of estuaries depending on some main characteristics. Each type of estuary is determined by the result between the volume of water that comes from the river during the tide and the volume of water that comes from the tide itself. From this we can find several types of estuaries:

  • Salt wedge estuaries: It is formed when the amount of water in the river is greater than the amount of water in the sea. In this way we have a mixture with a thin transition layer between the river water at the top and the tidal water wedge at the bottom.
  • Highly stratified estuaries: In these types of estuaries, the amount of fresh water that enters is greater than that of sea water, but not in such quantity. These conditions cause the mixture of waters between the different bodies of water to end up forming a more saline upper layer since the waves make the sea water go to the upper part. When both waters mix, they form a stratified layer.
  • Slightly stratified estuaries: are those in which the river water is less voluminous than the sea water. Here the water undergoes a great salinity change in contrast to both. In the upper layer the salinity is changing and in the lower part as well. This is because the flow of the sea is quite turbulent.
  • Vertically mixed estuary: It is that type of wardrobe in which practically the volume of fresh water is insignificant with respect to the tidal volume. Here a general dominance of the costume tide predominates with homogeneous salinity. As there is hardly any water exchange, there is no change in salinity. There is also no vertical stratification in the water column.
  • Reverse estuary: It is that type of estuary where there is no water supply from the river. This is because they are in areas with a high rate of evaporation. Evaporation makes the salinity concentration much higher. In addition, due to the loss of water, it sinks due to the increase in density as it is more saline.
  • Intermittent estuaries: are those that can be of one type or another depending on the prevailing rainfall at that time. And it is that here you will find different options depending on the rainfall of each moment. If they are higher, the water carried by the riverbed will be greater.

Flora and fauna of the estuaries

Estuaries are made up of a very varied flora and fauna. Most of the plant species are of the aquatic type. The eneas, reeds and bijaos stand out. Mangrove ecosystems can be found in many estuaries. These are tree species that have a great resistance to brackish water conditions. Is it so adapted to humid soils and there are about 70 species of mangrove trees. The white, black, red and gray mangroves stand out.

Part of the vegetation that is associated with the mangrove is seagrass. You can also find areas with plains of algae and a large amount of phytoplankton. As for the fauna, there is also a great diversity of animal species. Among those that stand out is zooplankton since there is great penetration of sunlight in the water. This zooplankton is consumed by estuarine fish, including herring, sardines, anchovies, etc.

There are also large numbers of mollusks, crustaceans, mammals, birds, and some reptiles.

I hope that with this information you can learn more about estuaries and their main characteristics.

Estuaries: what are they, characteristics, types, flora and fauna

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