por The estuaries They are low-lying, poorly drained depressions 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 saltwater lagoons derived from the production of salt by human action.
In general terms, estuaries make up open swampy areas with predominantly low vegetation. They originate from the overflow of rivers or lakes onto poorly drained flat terrain or from flooding due to heavy rains.
The flora and fauna vary 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 that they are organisms adapted to ecosystems with a dominant presence of water.
The estuaries are classified within the so-called wetlands, of great importance because most of them are 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 about estuaries originally created by the action of the human being.
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General characteristics of the estuaries
Relief
The estuaries are characterized by being low-sloping flat relief depressions with insufficiently drained soils. Normally they are extensive alluvial plains, that is to say, through which runs the bed of a river that periodically floods it and its soils have low fertility.
hydroperiod
The estuaries are the product of permanent or periodic flood flows due to the overflow of rivers or lakes, or due to the effect of rain.
Hydrology
They are relatively large and shallow wetlands (less than 3 m) where water has little mobility. Generally, the surface temperature can be high due to the slight slope and shallow depth.
The water is sweet and has a low dissolved oxygen content given the amount of vegetation in relation to the volume of water. In the same way, there is abundant organic matter in suspension.
In the case of the estuaries in the south of the Iberian Peninsula, such as the Guadalquivir estuaries, they are shallow saltwater 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 wild flora and fauna typical of the coastal zone.
Vegetation
Unlike many swamps, estuaries are characterized by low vegetation, where trees are sparse or absent. A large part of the water surface is covered with submerged, floating or rooted aquatic plants and in the mainland areas mainly grasslands develop.
Flora
Grasses, sedges and families of aquatic plants such as Alismataceae, Hydrocharitaceae, Potamogetonaceae, Lemnaceae and others predominate. However, the composition of species varies depending on the geographical area.
Fauna
The fauna is diverse, also depending on the latitude, however, a typical feature is the abundance of waterfowl, especially waders. In the estuaries there are herons of various species, spoonbill birds, and also birds of prey such as eagles and hawks.
Climate
Given their nature, estuaries occur in varied climates, ranging from tropical climate conditions to Mediterranean climate.
In general, there is high solar radiation, and in the tropical estuaries the precipitation is high (above 1,600 mm per year), but markedly seasonal. The average temperature in the tropical estuaries is around 27 ºC.
examples
– Wetlands of Camaguán (Venezuela)
They are a great alluvial plain of 190.3 km2 in the plains of Venezuela, to the southwest of the Guárico state, which receives the tributaries of the Orinoco basin. Among the major rivers are the Portuguesa, the Capanaparo and the Apure.
It is a flooded wooded savannah, where the arboreal elements are dispersed with a predominance of palms and legumes.
Fauna
A great diversity of birds, among them: herons, hawks, toucans and hummingbirds. Reptiles such as the Orinoco caiman (Crocodylus intermedius), the slime (alligator crocodilus), turtles and the anaconda (Eunectes murinus).
It is also possible to find large mammals such as amphibians such as the capybara or capybara (Hydrochoerus hydrochaeris) and aquatics such as bottlenose dolphins or river dolphins (Inia geoffrensis).
Activities
A part has been dedicated to wildlife refuge and tourist activities. While other areas are devoted 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 estuary vegetation, includes mangroves along the coastline.
In total, around 200 plant species have been inventoried in the area, with the best represented families being grasses, legumes and composites. In the flooded areas there are characteristic species such as the «tule» (Typha dominguensis), which forms the so-called tulares.
– Iberá Wetlands (Argentina)
They are located in the province of Entre Ríos in Argentina, between the Paraná and Uruguay rivers in the Plata river basin. The name of Iberá comes from the Guarani: “shining waters”. Together with the Brazilian Pantanal, it forms a large continuous system that represents one of the most relevant tropical wetlands.
The Iberá marshes also continue with the Ñeembucú marshes in Paraguay, being 12,000 km2 in Argentina that when added to the Paraguayan estuaries reach 45,000 km2. The main source of water that feeds the Iberá estuaries is the region’s heavy rainfall, together with the area’s mostly flat relief.
References
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, Publishers:, pp.47-67
Lara-Lara, JR, et al. (2008). Coastal, insular and epicontinental ecosystems, in Natural Capital of Mexico, vol. I: Current knowledge of biodiversity. conabio.
Neiff, JJ (2004). Iberá… in danger? Ed. Wildlife Foundation.
Orfeo, O. (s/f) Iberá Wetlands. Origin and formation. The sparkling waters of Corrientes. The eye of the condor magazine.
Ringuelet, RA 1962. Continental aquatic ecology. EUDEBA, Buenos Aires, Argentina.