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The Oriental Basin (Spanish ''Cuenca Oriental)'' is an endorheic basin in east-central Mexico. It covers an area of 4,958.60 square kilometers, lying in the states of Puebla, Tlaxcala, and Veracruz. 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 ecoregion covers the mountains surrounding the basin to the west, north, and east.〔"Cuenca Oriental", Comisión Nacional para el Conocimiento y Uso de la Biodiversidad. Accessed October 17, 2009. ()〕 The mountains to the north and west, including the Cofre de Perote volcano, leave the valley in a rain shadow, and the xeric shrublands of the Tehuacán Valley matorral 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.〔"Cuenca Oriental", Comisión Nacional para el Conocimiento y Uso de la Biodiversidad. Accessed October 17, 2009. ()〕 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 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''.〔Caballero, Margarita; Gloria Vilcara, Alejandro Rodríguez, Diana Juarez. "Short-term climatic change in lake sediments from lake Alchchica, Oriental, Mexico". ''Geofísica Internacional'' (2003), Vol. 42, Num. 3, pp. 529-537. ()〕 Chief towns in the basin include El Carmen Tequexquitla, Tlaxcala, 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 to the west and Puebla to the south.〔Alcocer, Javier (2003). "The future of salt lakes: the case of Mexico". Abstract, "Environmental Future of Aquatic Ecosystems," 5th International Conference on Environmental Future, 23–27 March 2003, Zurich. ()〕 ==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 dace ''(Evarra bustamantei, E. eigenmanni,'' and ''E. tlahuacensis)'' formerly native to the basin are presumed extinct since about 1970.〔Bruton, Michael N. "Have fishes had their chips? The dilemma of threatened fishes". Environmental Biology of Fishes 43: l-27, 1995.〕 The WWF-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.〔"Lerma-Chapala". Freshwater Ecoregions of the World, World Wildlife Fund and Nature Conservancy. Accessed October 18, 2009. ()〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Oriental Basin」の詳細全文を読む スポンサード リンク
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