Oriental Basin

Oriental Basin

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The Oriental Basin is an endorheic basin in east-central Mexico. It covers an area of 4,958.60 square kilometers, lying in the states of Puebla
Puebla
Puebla officially Estado Libre y Soberano de Puebla is one of the 31 states which, with the Federal District, comprise the 32 Federal Entities of Mexico. It is divided in 217 municipalities and its capital city is Puebla....

, Tlaxcala
Tlaxcala
Tlaxcala officially Estado Libre y Soberano de Tlaxcala is one of the 31 states which along with the Federal District comprise the 32 federative entities of Mexico. It is divided into 60 municipalities and its capital city is Tlaxcala....

, and Veracruz
Veracruz
Veracruz, formally Veracruz de Ignacio de la Llave officially Estado Libre y Soberano de Veracruz de Ignacio de la Llave , is one of the 31 states that, along with the Federal District, comprise the 32 federative entities of Mexico. It is divided in 212 municipalities and its capital city is...

.

The climate is temperate and subtropical, semi-arid to subhumid, with summer rains. Average annual temperature 12-16°C, and annual total precipitation is 400–800 mm. The Trans-Mexican Volcanic Belt pine-oak forests
Trans-Mexican Volcanic Belt pine-oak forests
The Trans-Mexican Volcanic Belt pine-oak forests is a subtropical coniferous forest ecoregion of the Trans-Mexican Volcanic Belt of central Mexico.-Setting:...

 ecoregion
Ecoregion
An ecoregion , sometimes called a bioregion, is an ecologically and geographically defined area that is smaller than an ecozone and larger than an ecosystem. Ecoregions cover relatively large areas of land or water, and contain characteristic, geographically distinct assemblages of natural...

 covers the mountains surrounding the basin to the west, north, and east. The mountains to the north and west, including the Cofre de Perote
Cofre de Perote
Cofre de Perote, originally Naupa-Tecutépetl , is known also as Nauhcampatépetl. Both Nahuatl names mean something like 'Place of Four Mountain' or 'Mountain of the Lord of Four Places'...

 volcano, leave the valley in a rain shadow
Rain shadow
A rain shadow is a dry area on the lee side of a mountainous area. The mountains block the passage of rain-producing weather systems, casting a "shadow" of dryness behind them. As shown by the diagram to the right, the warm moist air is "pulled" by the prevailing winds over a mountain...

, and the xeric shrublands
Deserts and xeric shrublands
Deserts and xeric shrublands is a biome characterized by, relating to, or requiring only a small amount of moisture.-Definition and occurrence:...

 of the Tehuacán Valley matorral
Tehuacán Valley matorral
The Tehuacán Valley matorral is a xeric shrubland ecoregion, within the deserts and xeric shrublands biome, in central Mexico.-Setting:The ecoregion occupies the Tehuacán and Cuicatlán valleys, covering parts of Puebla and Oaxaca states. The valleys lie in the rain shadow of the surrounding...

 ecoregion occupies the center of the basin, and extend south into the Tehuacán and Cuicatlán valleys. Vegetation includes pine-oak forests and pine-fir forests at higher elevations, with dry scrub pine forests, oak forests, juniper scrub, yucca scrub, halophytic vegetation, and grassland. It includes the Llanos de San Juan and Llanos de San Andres.

The basin contains a several shallow, mostly alkaline lakes. Two ephemeral playa lakes, Totolcinco (El Carmen or Totolcingo) and Tepeyahualco (El Salado), lie in the lowest part of the basin (2300 meters elevation), and remain dry for most of the year. The basin includes six maar
Maar
A maar is a broad, low-relief volcanic crater that is caused by a phreatomagmatic eruption, an explosion caused by groundwater coming into contact with hot lava or magma. A maar characteristically fills with water to form a relatively shallow crater lake. The name comes from the local Moselle...

 lakes, locally called axalpazcos, lying in shallow volcanic craters and sustained by underground water. A northern group of lakes – Alchichica, Quechulac, Atexcac, and La Preciosa – lie southeast of Lake Tepeyahualco, and the southern lakes, Aljojuca and San Miguel Tecuitlapa, lie southeast of Lake Totolcinco. The basin also has five dry maars, called xalapazcos.

Chief towns in the basin include El Carmen Tequexquitla, Tlaxcala
El Carmen Tequexquitla
El Carmen Tequexquitla is a municipality in Tlaxcala in south-eastern Mexico.-References:...

, Perote, Veracruz, and Oriental, Puebla.

Groundwater levels in the basin have been dropping in recent years because of over-exploitation for irrigation and destruction of natural recharging areas. In addition, the government is considering pumping freshwater from the Oriental basin to Mexico City
Mexico City
Mexico City is the Federal District , capital of Mexico and seat of the federal powers of the Mexican Union. It is a federal entity within Mexico which is not part of any one of the 31 Mexican states but belongs to the federation as a whole...

 to the west and Puebla
Puebla, Puebla
The city and municipality of Puebla is the capital of the state of Puebla, and one of the five most important colonial cities in Mexico. Being a planned city, it is located to the east of Mexico City and west of Mexico's main port, Veracruz, on the main route between the two.The city was founded...

 to the south.

Maar lakes


The maar lakes, or axalpazcos, of the Oriental Basin are home to a closely knit set of endemic species, one at each crater lake. Some of these include the Atherinopsid fishes Alchichica silverside (Poblana alchichica), La Preciosa silverside (P. letholepis), Chignahuapan silverside (P. ferdebueni), and Quechulac silverside (P. squamata). Three species of (Evarra bustamantei
Evarra bustamantei
Evarra eigenmanni is a species of ray-finned fish in the Cyprinidae family. It was found only in Mexico, but is now extinct....

, E. eigenmanni
Evarra eigenmanni
Evarra eigenmanni is an extinct species of ray-finned fish in the Cyprinidae family.It was found only in Mexico.-Source:* World Conservation Monitoring Centre 1996. . Downloaded on 10 July 2007....

,
and E. tlahuacensis
Evarra tlahuacensis
Evarra tlahuacensis is an extinct species of ray-finned fish in the Cyprinidae family.It was found only in Mexico.-Source:* World Conservation Monitoring Centre 1996. . Downloaded on 10 July 2007....

)
formerly native to the basin are presumed extinct since about 1970.

The WWF
World Wide Fund for Nature
The World Wide Fund for Nature is an international non-governmental organization working on issues regarding the conservation, research and restoration of the environment, formerly named the World Wildlife Fund, which remains its official name in Canada and the United States...

-Nature Conservancy system of freshwater ecoregions includes the Oriental Basin with the Valley of Mexico, Lerma River, and Lake Chapala in their Lerma-Chapala freshwater ecoregion, based on faunal similarities, especially among the Atherinopsids.

{| width="100%"
|-
|
{| width="100%" style="border:1px solid black; text-align:center" bgcolor=#99CCFF
|-
! bgcolor=#99CCFF width="34%"|lake
! bgcolor=#99CCFF width="22%"|surface area (square kilometers)
! bgcolor=#99CCFF width="22%"|volume (millions of cubic meters)
! bgcolor=#99CCFF width="22%"|maximum depth (meters)
|-
| Alchichica
|1.81 || 69.9 || 64.6
|-
| La Preciosa
| 0.78 || 16.2 || 45.5
|-
| Quechulac
| 0.50 || 10.9 || 40.0
|-
| Aljojuca
| 0.44 || 11.6 || 50.6
|-
| Atexcac
| 0.29 || 6.1 || 39.1
|-
| Tecuitlapa
| 0.26 || 0.35 || 2.5
|-
|}

Lake Alchichica


Lake Alchichica 19°25′N 97°24′W, in Tepeyahualco (municipality)
Tepeyahualco (municipality)
Tepeyahualco is a town and municipality in Puebla in south-eastern Mexico....

, Puebla
Puebla
Puebla officially Estado Libre y Soberano de Puebla is one of the 31 states which, with the Federal District, comprise the 32 Federal Entities of Mexico. It is divided in 217 municipalities and its capital city is Puebla....

, is ecologically unique, with stromatolite
Stromatolite
Stromatolites or stromatoliths are layered accretionary structures formed in shallow water by the trapping, binding and cementation of sedimentary grains by biofilms of microorganisms, especially cyanobacteria ....

 deposits and a high degree of endemism. The biota has adapted to extreme conditions characterized by high ionic concentrations of water and poor nutrient content.

Lake Alchichica is the largest of the maar lakes, lying at an elevation of 2320 meters. It is Mexico's deepest natural lake, with a maximum depth of 64 meters, and a mean depth of 38.6 meters. The lake has an area of 1.81 square kilometers. It is both saline and alkaline (pH 8.7-9.2).

The dominant stromatolite species are the spongy type Enthophysalis atrata, Enthophysalis sp. Calothrix cf. Parletina and Calothrix sp. and the columnar stromatolites Enthophysalis lithophyla and Nitzchia sp. In the deep parts of the lake, abundant cladophores develop on the spongy stromatolites, with many cyanobacterial epiphytes Chamaesiphon halophilus, Heteroleibleinia profunda, Mantellum rubrum and Xenococcus candelariae. 23 genera of phytoplankton have been found: fourteen genera of Chrysophyta
Chrysophyta
Chrysophyta is a term used to refer to certain heterokonts.It can be used to refer to:* golden algae* golden algae and diatoms together....

, five of Cyanophyta and four of Chlorophyta
Chlorophyta
Chlorophyta is a division of green algae, informally called chlorophytes. The name is used in two very different senses so that care is needed to determine the use by a particular author...

. The dominant species throughout the year are Agmenellum sp., Amphora sp., Chaetoceros similis, Coscinodiscus sp., Cyclotella striata, Nodularia spumigena, Stephanodiscus niagarae and Synechocystis sp. The best represented species best of vascular plants in the axalpazcos are rooted emergent hydrophytes Eleocharis montevidensis
Eleocharis montevidensis
Eleocharis montevidensis is a species of spikesedge known by the common name sand spikerush. It is a widespread coastal plant native to the Americas, ranging from North Carolina south to Argentina, where it grows in moist, sandy spots in many habitat types, including lakes, riverbanks, wet...

, Juncus andicola, J. mexicanus
Juncus mexicanus
Juncus mexicanus is a species of rush known by the common name Mexican rush. It is native to the southwestern quadrant of the United States and parts of Mexico and Central and South America...

, Phragmites australis, Scirpus californicus
and Typha domingensis
Typha domingensis
Typha domingensis Pers., also known as Southern Cattail or Cumbungi, is a perennial herbaceous plant of genus Typha.It is found throughout temperate and tropical regions worldwide...

, the submerged rooted hydrophytes Cyperus laevigatus
Cyperus laevigatus
Cyperus laevigatus is a species of sedge known by the common name smooth flatsedge.-Distribution:It is native to most continents and grows in wet areas, especially in brackish water, wet alkaline soils, mineral-rich hot springs, and other moist saline and alkaline habitat...

, Potamogeton pectinatus
Potamogeton pectinatus
Stuckenia pectinata , commonly called fennel pondweed or sago pondweed, and sometimes called ribbon weed....

and Ruppia maritima
Ruppia maritima
Ruppia maritima is a species of aquatic plant known by the common name wigeongrass. Despite its Latin name, it is not a marine plant; is perhaps best described as a salt-tolerant freshwater species.-Distribution:...

, and the free-floating hydrophyte Lemna gibba
Lemna gibba
Lemna gibba is a species of Lemna with distribution in temperate areas in Europe, including Britain, to the Himalayas, Africa, South America and North America....

.

Animals endemic to Lake Alchichica include the Taylor's Salamander
Taylor's Salamander
Taylor's salamander, Ambystoma taylori, is a neotenic salamander species from Puebla, Mexico.Taylor's salamander is found only in Laguna Alchichica, a high-altitude crater lake 24 miles southwest of Perote, Puebla, Mexico. It was described in 1982 by Brandon, Maruska, and Rumph, and named for...

 (Ambystoma taylori), the fish Poblana alchichica (Alchichica silverside, Charal de Alchichica), and the isopod Caecidotea williamsi.