Lake Tsimanampetsotsa is a moderately alkaline lake in the Toliara Province, in the southwestern part of Madagascar. It is located at around. The lake is protected within Tsimanampetsotsa National Park and it is also within a Ramsar site. The Ramsar site has a total area of, while the surface of the lake is much smaller. The name of the lake in Malagasy means "lake without dolphins". It is a sacred place for worship, ceremonies and rituals. Local taboos prevent water pollution. Swimming and the utilisation of pirogues is prohibited. Water, mud and some plants from the lake are used in traditional medicine. The lake is about 20 km long, about 2 km wide and is quite shallow. It is situated in a collapse area of the Mahfaly Plateau, in a closed evaporite basin with cliffs of Eocene marine limestone to the east and a wide strip of alluvium, capping low outcrops of limestone to the west. The area is covered by sand deposits of recent and Quaternary origin. In pre-history, there was a paleolake here complete with overland drainage. The paleolake was much greater in size and depth, as evidenced by strand lines that ring the outer edges of the basin. The water is “sodic”, highly mineralised and moderately alkaline with relatively high concentrations of ammonia and phosphate. Salt concentrations approach that found in seawater, becoming somewhat diluted during the rainy season. The lake may be directly connected to the sea, but this is a matter of conjecture that has not been verified. The eastern part of the lake receives some freshwater flow and so has consistently lower salt concentrations than the western part. The basin is shallow resulting in dramatic variation in the surface area of the lake with even small changes in water level. Water levels can drop significantly during the dry season, resulting in a broad exposed area of seasonal hypersaline flats around a shrunken lake.
Climate and Hydrology
Lake Tsimanampetsotsa is in an area with a semi-arid climate; daytime temperatures are high and precipitation low. It is in the lowest precipitation region in Madagascar, receiving only 300 mm of rain per year. In addition, rainfall amount and location is highly unpredictable; rain often falls only locally. There are no surface rivers here and the lake has no inlet or outlet. Lake levels are tied to rainfall, along with some underground flow from aquafers located further inland. There is a network of groundwater that surfaces at the foot of the Mahfaly Plateau, with three permanent springs and numerous seeps and intermittent springs. Lake levels rise with sufficient rainfall, and drop when water evaporates faster than it is being replenished.
Vegetation
Emergent plant species able to grow in the sodic water include southern cattail and flat-sedge. Glasswort is one of the few species that can tolerate extreme salinity, so it is usually found alone on highly saline sites. Other salt-tolerant species move onto the flats as the water levels recede including Salsola littoralis, Atripex perrieri, as well as some grasses and the golden leather fern. The introduced speciesbeach sheoak can be found in small stands along the east shore.
Aquatic Fauna
High phosphate concentrations, originating from erosion, are thought to be the main factor limiting the diversity of aquatic fauna. There are no fish. Invertebrates belonging to four taxonomic groups have been documented. Taxonomic richness was at its highest in April and decreased to 11 taxa in August. The eastern part of the lake had consistently more species then the western part, probably because of the consistently lower salt concentrations. The crustaceans were the most widespread species. The aquatic fauna documented in Lake Tsimanampetsotsa is as follows:
Gastropoda species : Planorbis planorbis , Georissa petiti and Potamopyrgus sp. .
Crustacea species : Grandidierella mahafalensis and Halmyrapseudes thaumastocheles.
Insects found included: flies ; beetles, including nymph of the Dytiscidae and adults of the Hydroptilidae and Elmidae families; mayflies ; bugs from 3 families ; dragonflies of the Libellulidae family and damselflies of the Coenagrionidae family.
Birds
More than 34 bird species are recorded from the lake area. Greater flamingos are at times present in large numbers and nest on the lake. Lesser flamingos have also been seen here. The lake and saline flats constitute an important habitat for many threatened water bird species, such as Madagascan plover and supports a breeding colony of Madagascan grebe .
