Physico-chemical water characteristics and aquatic macroinvertebrates of Lake Tsimanampesotse, south-western Madagascar

Abstract

Saline lakes are known to be amongst the most productive ecosystems in the world. Tsimanampesotse, a ‘conservation hotspot’ soda lake in southwestern Madagascar, was integrated into the Ramsar wetland network in 1998. Despite its importance for aquatic birds, knowledge of its water characteristics and aquatic biota is scarce. Water quality and aquatic invertebrates were investigated in April and August 2013 to provide baseline data in order to measure possible changes of the area in the future. Changes in water temperature (19.5–25.9 °C) and in dissolved oxygen (9.3–11.3 mg l⁻¹) were detected. The water was highly mineralised (EC > 41 000 μS cm⁻¹) and moderately alkaline (pH ~ 8.0). The maximum concentrations of ammonia and phosphate were relatively high (39.1 and 57.6 mg l⁻¹, respectively). Freshwater runoff from the plateau makes the water quality in the eastern part of the lake better than that in the west. Of the 15 taxa of macroinvertebrate assessed, the crustaceans Grandidierella mahafalensis and Apseudes thaumastocheles were dominant. Decreased water salinity in April increased the abundance and diversity of macroinvertebrates. Despite its incorporation to the protected area, Lake Tsimanampesotse is still impacted by human activities and needs supplementary preservation.

Keywords: Lake Tsimanampesotse, aquatic invertebrates, Ramsar wetland network, water quality, south-western Madagascar