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Poopo Lake


Lake Poopo is a large saline lake located in a shallow depression in the Altiplano Mountains in Bolivia at an altitude of approximately 3,700 meters. Because the lake is long and wide (90 km by 32 km) it makes up the eastern half of the Oruro Department, a mining region in southwest Bolivia. The permanent part of the lake body covers approximately 1,000 km. The lake receives most of its water from the Desaguadero River which links Lake Poopo with Lake Titicaca at the north end of the Altiplano. Since the lake lacks any major outlet and has a mean depth of no more than 3 m, the surface area varies greatly.

The lake has been designated as a site for conservation under the Ramsar Convention.

Lake dynamics

Lake Poopo gets the majority of its water (roughly 92%) from the Desaguadero River which enters the lake at the north end. There are numerous smaller inlets along the eastern shore of the lake, many of which are dry most of the year. At times of very high water levels, Poopo is connected to the salt desert Salar de Coipasa in the west. A minor outlet also leads to Salar de Uyuni in the far south of the Altiplano, but as the lake lacks any major outlet it is classified as an endorheic basin.

When the water level of Lake Titicaca drops below 3,810 m, the flow of River Desaguadero is so low it can no longer compensate for the massive water losses due to evaporation from the surface of Lake Poopo. At this point, the lake volume begins to decrease. At its maximum in 1986, the lake had an area of 3,500 km. During the years that followed, the surface area steadily decreased until 1994 when the lake disappeared completely. The time period between 1975 and 1992 is the longest period in recent times with a continuous existence of a water body.

Lake Titicaca basin's drainage system, for the most part, is able to provide Titicaca with enough water to retain its status as a freshwater lake although its evaporation rate is so high.

Salinity and geology

The water of Lake Poopo is highly saline. The salinity is a result of the endorheic nature of the hydrological system on the Altiplano, which allows all weathered ions to remain in the system. The salinity of Lake Poopo is further enhanced by the lack of outlet, the arid climate and the high evaporation from the lake surface.

In the northern end of Lake Poopo there is a dilution with freshwater from River Desaguadero. This results in a salt gradient of higher values towards the south.

The salinity varies with water volume. During October November 2006 the salinity in the north end of the lake varied between brackish and saline . In the south end of the lake the water was classified as a brine . The water type is a 4-2 Na-(Mg)-Cl-(SO4).

Geological sources of NaCl such as halite and feldspars are present in the drainage area. These could also contribute to the salinity of Lake Poopo. The lake body is situated on top of Cenozoic deposits, consisting mainly of unconsolidated material. These sediments are the remains of extensive prehistoric lakes, which covered the Altiplano during at least five glaciation periods.

Mining and heavy metals

There is a long tradition of mining in the Poopo basin. Extraction of metals began already in the 13th century in order to support the Inca army. After the Spanish colonization in the 16th century, the mining operations became more large scale. At this point the region got its current identity as one of the mining centres of Bolivia.

The mining districts are situated at the foothills of the Cordillera Oriental along the eastern border of the Poopo basin. The economically most important minerals are Silver and tin.

Studies have shown elevated concentrations of heavy metals in surface and ground waters of the Poopo basin. These metals are naturally present in the bedrock, from which they are released through weathering processes. The mining activities in the area further contributes to the heavy metal pollution. Acid leaching from mines and mechanical processing of ore speed up the process.

The major part of the heavy metals transported to Lake Poopo seem to be immobilized in the bottom sediments. Still, concentrations of arsenic, lead and cadmium in the lake water exceed Bolivian and WHO guideline values for drinking water.

Flora and fauna

Three to four native fish species inhabit the lake: the Mauri (a Trichomycterus catfish), and the Carache and Ispi (Orestias spp.). Two exotic fish species were introduced in the 20th century; the rainbow trout (trucha) in 1942 and the silversides Odontesthes bonariensis (pejerrey) in 1955. These bigger fish are now the most commercially important species. The lake has a relatively large fish population although it declines during the years of low water when the salinity is high.

The aquatic bird life is highly diverse with a total of 34 species. Most famous are the three types of flamingos which mainly live in the shallow lagoons in the northern and eastern parts of the lake. An inventory of the bird population, made in the year 2000 in cooperation with BirdLife International, identified 6 endangered species. Among these are the Chilean flamingo and the Andean Condor.

A total of 17 superior plants and 3 species of algae have been identified in and around Lake Poopo. Due to the constant drought and flooding, the littoral zone experiences great disturbances. As a result, there is hardly any vegetation to be found on the shores of the lake.

Archaeological evidence

Archaeological investigations conducted by the San Andres University of La Paz, Bolivia, shows the influence of the Wankarani culture on the Poopo area where complex central urban areas such as villages and towns were developed that expanded into the Poopo basin during the Late Formative period, (200 B.C.E. 200 C.E.), probably in conjunction with changing patterns of agriculture. Herders and the life style of llama caravan merchants coexisted with more sedentary farmers in a harmonious system of exchange of goods and services. Other investigators examining the following period, the Early Regional Developments (aprox. 300 C.E. - 900 C.E.), shows that the size of the inhabited areas increased. The South Poopo inhabitants developed a unique style of ceramics style with triangular spirals. The Huari at the east portion of the lake displays an important Tiwanaku enclave, with ceramic styles from the core Titicaca area and surrounding styles, demonstrating the interactions between different peoples in the area.

References

Drever, James I: The Geochemistry of Natural Waters, 3rd edition, Prentice Hall, 1997.

Montes de Oca; Geografia y Recursos Naturales de Bolivia, 3rd Edition, EDOBOL, La Paz, 1997.

Rocha, O.O. (editor): Diagostico de los recursos naturales y culturales de los lagos Poopo y Uru Uru, Oruro Bolivia. Convencion RAMSAR, WCS/Bolivia, La Paz, 2002.

Troeng, B., Riera-Kilibarda C. Mapas tematicos de recursos minerales de Bolivia, Boletin del Servicio geologico de Bolivia N 7, La Paz, 1996.

External links

Master thesis about heavy metals in the rivers of the Poopo basin

Master thesis about heavy metals in Lake Poopo

Satellite images and information from NASA about Lake Poopo

Lake Titicaca, Lake Poopo, and Salar de Uyuni, Bolivia

Bolivia Drainage

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This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article Poopo Lake


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