Licancabur Lake

Context

Volcanic lakes in the Andes of Bolivia and Chile can be found at high altitude, some of them close to or exceeding 6,000 metres (20,000 ft). Such lakes often are poor in nutrients and exposed to strong ultraviolet radiation, partly due to high insolation and partly because their waters tend to be transparent to ultraviolet radiation. Further, the atmosphere at such altitudes is oxygen-poor.

These and other environmental properties are similar to the conditions that existed on Mars. At the end of the last ice age, the Andes became much drier. The NASA High Lakes Project has studied several such lakes.

Licancabur Lake is located on Licancabur, a notable volcano whose cone dominates the Bolivian-Chilean frontier and the surrounding region. This volcano formed in the late Pleistocene, and is potentially active. Two other lakes, Laguna Blanca and Laguna Verde, can be found at the foot of the volcano. Escalante volcano farther north also had a crater lake in 2004. The volcano was considered a holy mountain by the Atacameno people and its climbing discouraged. Nevertheless, stone buildings were found by climbers on the crater rim in 1953. Legend has it that a golden guanaco head can be found in the crater.

Physical properties

The lake was first discovered by climbers in 1953. The lake is at the bottom of the crater of Licancabur, at a depth of 46 metres (150 ft) beneath the crater rim. A low content of dissolved material renders its waters clear. It is one of the highest lakes in the world.

The lake has the shape of an ellipse, 85 metres (280 ft) long in 1953. In 2002, the lake covered a surface area of 7,000 square metres (75,000 sq ft). The lake is maximally 5.2 metres (17 ft) deep. Water levels were fairly variable between 1990-2010. It lies at an altitude of 5,900 metres (19,300 ft). Its catchment covers a surface area of 22,000 square metres (240,000 sq ft) and was probably larger before erosion of the crater set in.

Water is supplied to the lake by snowfall. The average precipitation between 2002-2007 was measured to be 118 millimetres (4.6 in). According to estimates in 1955, slightly more than half of the lake water leaves the lake through seepage and the rest through evaporation. It is possible that the lake overflowed over its southwestern rim, when the climate was wetter in the past and water depth reached 40 metres (130 ft). A channel is found there and this would explain the lack of salt deposits, and past shorelines indicate that the lake reached depths of 10–12 metres (33–39 ft).

Water temperatures range from 1.4–4.3 °C (34.5–39.7 °F). Water temperatures are highest at the shore and decrease towards the centre of the lake. At the time of its first discovery, the lake was not frozen. This contrasted with other crater lakes in the region which were usually frozen. Currently, an ice cover exists from April to September; it can reach a thickness of 80 centimetres (31 in).

Overall salt content is 1.2 grams per litre (0.19 oz/imp gal). The original discoverers of Licancabur Lake considered it to have a low salt content, given that typical salt deposits were missing. The high quantities of Al, Ca, Fe, Mg and Na in the waters of the lake compared to the quantities in springs at the foot of Licancabur may be due to prolonged water-rock interactions. Nitrite, nitrate and phosphate concentrations are small. Chloride and sulfate indicate the input of geothermal liquids into the lake, and degassing was observed in 2006, resulting in higher water temperatures in the area of the degassing. pH values of 8-4-6.9 were measured during 2002-2006.

Environmental conditions

Licancabur Lake is exposed to extreme climatic conditions, including low air pressure, strong insolation and strong temperature fluctuations. The climate at Licancabur Lake is arid and strong evaporation is prevalent.

Air temperatures at Licancabur Lake range 5 – −25 °C (41 – −13 °F) during daytime and −25 – −45 °C (−13 – −49 °F) at night. The air pressure is less than half that at sea level. Water temperatures at the lake bottom always exceed 0 °C (32 °F) though - one measurement in 1984 indicated a temperature of 6 °C (43 °F). Such warming may be caused by geothermal heat from the volcano.

Most precipitation falls during the so-called "Altiplanic winter" in summer, but winter storms also bring some water to the Licancabur region. Ultraviolet irradiation in 2003 was measured to be 89–120 watts per square metre (0.0111–0.0150 hp/sq ft). Occasionally, the Antarctic ozone hole influences the Licancabur area. The environment at Licancabur Lake has been compared to that of ancient lakes on Mars, raising interest in its lifeforms. In 2002, a weather station was placed on the shores of the lake and records weather and ultraviolet radiation data.

Biology

In 1981, archeologists discovered that Licancabur Lake hosts plankton. Despite the high ultraviolet radiation, organisms can be found in the radiation-exposed parts of the water column, including at the lake surface at noon.

Microbial mats containing cyanobacteria have been found on the lake bottom. A total dissolved carbon content of 2.44 milligrams per litre (1.41×10⁻⁶ oz/cu in) has been found in the lake. The amount of cells found in sediments of the lake increases with the depth of the sediments; archea are only present beneath 2.5 metres (8 ft 2 in).

Typical bacterial taxa are actinobacteria, bacteroidetes and betaproteobacteria. Overall, at such high lakes only a limited amount of bacterial taxa can be found. The proteobacteria and bacteroidetes-cytophaga-flavobacteria dominate the community of Licancabur Lake bacteria, something that has also been found in other lakes in similar environments in Tibet and northwest Argentina. There are more bacterial species in the lake than archean ones. Cyanobacteria are mostly taxa which display nitrogen fixing such as Calothrix, Nodularia and Nostoc. There are noticeable differences in the bacterial communities in shallow and deep waters.

Some genomic sequences retrieved from Licancabur resemble those from Salar de Ascotan, Salar de Atacama and Salar del Huasco. Cyanobacterial genomic sequences resemble these of geothermal and cold environments. Most genomic sequences isolated in Licancabur lake have less than 95% similarity to cultured species, with about 37% of all cyanobacteria observed being new species.

Coloured copepods were observed to form swarms in the lake; some in November 2006 were found at the lake surface and others hidden between rocks. Two cladoceran, two ostracod and one testate amoeba species were originally discovered in Licancabur Lake. The zooplankton species identified at Licancabur are widespread in South America, in one case reaching Antarctica.

Species that have been identified in Licancabur Lake include the cladoceran crustacean Alona altiplana, the calanoid copepod Boeckella titicacae, alternatively identified as Boeckella gracilipes, the cladoceran Daphniopsis chilensis which may be endemic to the lake, the cladoceran crustacean Pleuroxus fryeri, and the testate amoeba Scutiglypha cabrolae. One species each of a testate amoeba, a chironomid, rotifer, two species copepods and three species cladocerans have been reported in 2009. The larva of this chironomid midge is also the highest find of a chironomid midge, surpassing Tibetan specimens.

Scuba diving

In 2006, scuba divers collected samples from the lake bottom. A previous dive in 1982 by Johan Reinhard was once the highest scuba dive in the world, but as of November 2016 a dive in a lake at Ojos del Salado on 21 February 2016 occurred at even higher altitudes.