WETLANDS: CHARACTERISTICS, FLORA, FAUNA, CLIMATE, EXAMPLES - ENVIRONMENT - 2024

The estuaries are depressions of flat relief and poor drainage that are permanently or seasonally flooded. However, the term estuary does not have a single definition and its meaning varies in different Spanish-speaking regions.

For example, in Chile the term is applied to refer to small rivers or torrents, such as the Marga-Marga estuary in Viña del Mar. While in Spain the term estuary refers to extensive shallow lagoons of salt water, derived from the production of salt by human action.

Sunset in the estuaries of Camaguán (Venezuela). Source: Tomas Rojas / CC BY-SA (https://creativecommons.org/licenses/by-sa/3.0)

In general terms, the estuaries make up open swampy areas with predominantly low vegetation. They originate from the overflowing of rivers or lakes into poorly drained flat lands or from waterlogging due to heavy rains.

The flora and fauna varies depending on the latitude at which the estuary is located, being different between a tropical estuary and a Mediterranean one. But both cases have in common the fact of organisms adapted to ecosystems with a dominant presence of water.

The estuaries are classified within the so-called wetlands, of great importance for being the majority sources of fresh water and are formed by factors of relief and soil.

This ecosystem can occur in tropical areas such as the Camaguán estuaries in the Venezuelan plains. In subtropical areas, the El Salado estuary occurs on the Pacific coast of Mexico.

The Guadalquivir estuaries in Spain are an example of an estuary in the Mediterranean region. Although in this case it is a question of estuaries originally created by the action of the human being.

General characteristics of the estuaries

Relief

The estuaries are characterized by being flat relief depressions of little slope with insufficient drainage soils. Normally they are extensive alluvial plains, that is to say through which a river runs that periodically floods it and their soil has low fertility.

Hydroperiod

The estuaries are the product of permanent or periodic flood flows due to the overflowing of rivers or lakes, or due to the effect of rains.

Hydrology

They are relatively large and shallow wetlands (less than 3 m) where water has little mobility. In general, the surface temperature can be high due to the low slope and the shallow depth.

The water is fresh and has a low content of dissolved oxygen given the amount of vegetation in relation to the volume of water. Similarly, abundant organic matter is present in suspension.

Esteros de Camaguán (Venezuela). Source: Franescobar04 / CC BY-SA (https://creativecommons.org/licenses/by-sa/3.0)

In the case of the estuaries in the south of the Iberian Peninsula, such as the Guadalquivir estuaries, these are shallow, salt-water lagoons. However, these estuaries are not strictly natural formations, since they originally arose from human action to produce salt.

When these were abandoned, they became naturalized and became a refuge for flora and fauna typical of the coastal area.

Vegetation

Unlike many swamps, estuaries are characterized by low vegetation, where trees are scarce or absent. Much of the water surface is covered by submerged, floating or rooted aquatic plants and mainly grasslands develop in the terra firme areas.

Flora

Grasses, sedges and families of aquatic plants such as Alismataceae, Hydrocharitaceae, Potamogetonaceae, Lemnaceae and others predominate. However, the species composition varies depending on the geographical area.

Fauna

The fauna is diverse, also depending on the latitude, however, a typical characteristic is the abundance of aquatic birds, especially waders. In the estuaries there are herons of various species, paddle birds, and also birds of prey such as eagles and hawks.

Weather

Given their nature, estuaries occur in varied climates, ranging from tropical to Mediterranean conditions.

In general, there is high solar radiation, and in tropical estuaries the precipitation is high (above 1,600 mm per year), but markedly seasonal. The average temperature in tropical estuaries is around 27 ºC.

Examples

- Esteros de Camaguán (Venezuela)

They are a large alluvial plain of 190.3 km ² in the plains of Venezuela, southwest of the Guárico state, which receives the tributaries of the Orinoco basin. Among the major rivers are the Portuguesa, Capanaparo and Apure.

It is a flooded wooded savanna, where the arboreal elements are scattered with a predominance of palms and legumes.

Fauna

A great diversity of birds, including: herons, hawks, toucans and hummingbirds. Reptiles such as the Orinoco caiman (Crocodylus intermedius), the slime (Caiman crocodilus), turtles and the anaconda (Eunectes murinus).

It is also possible to find large mammals such as amphibians such as the chigüire or capybara (Hydrochoerus hydrochaeris) and aquatic mammals such as the dolphin or river dolphin (Inia geoffrensis).

Activities

A part has been dedicated to wildlife refuge and tourist activities. While other areas are dedicated to rice production and fish farming.

- Estero El Salado (Mexico)

They are found in the Mexican Pacific region in the Puerto Vallarta municipality in Jalisco, made up of the plain of the Ameca River delta. The area is formally protected by the Mexican state as an Ecological Conservation Zone.

The area covers about 170 hectares and in addition to the characteristic vegetation of the estuary, it includes mangroves on the coastline.

In total, around 200 plant species have been inventoried in the area, the best represented families being grasses, legumes and composites. Characteristic species such as “tule” (Typha dominguensis), which form the so-called tulares, occur in flooded areas.

- Esteros del Iberá (Argentina)

They are located in the province of Entre Ríos in Argentina, between the Paraná and Uruguay rivers in the Río Plata basin. The name Iberá comes from the Guaraní: “waters that shine”. Together with the Pantanal of Brazil it forms a great continuous system that represents one of the most relevant tropical wetlands.

Esteros del Iberá (Argentina). Source: Joshua Stone / CC BY-SA (https://creativecommons.org/licenses/by-sa/3.0)

The Iberá estuaries also continue with the Ñeembucú estuaries in Paraguay, with 12,000 km ² in Argentina which, when added to the Paraguayan estuaries, reach 45,000 km ². The main source of water that feeds the Iberá estuaries is the region's heavy rainfall, coupled with the area's mostly flat relief.

References

1. Contreras-Rodríguez, SH, Frías-Castro, A., González-Castro, SI and Ávila-Ramírez, BO (2014). Flora and Vegetation of the El Salado estuary. In: Navarrete-Heredia, JL, Contreras-Rodríguez, SH and Guerrero-Vázquez, S., Biodiversity of the El Salado estuary, Prometeo Editores. Publisher: 2014, Editors:, pp.47-67
2. Lara-Lara, JR, et al. (2008). The coastal, insular and epicontinental ecosystems, in Natural Capital of Mexico, vol. I: Current knowledge of biodiversity. Conabio.
3. Neiff, JJ (2004). Iberá… in danger? Ed. Fundación Vida Silvestre.
4. Orfeo, O. (s / f) Esteros del Iberá. Origin and formation. The bright waters of Corrientes. The eye of the condor magazine.
5. Ringuelet, RA 1962. Continental aquatic ecology. EUDEBA, Buenos Aires, Argentina.