Hydrochemical and Ecological Characteristics of Hypersaline Lakes in Wau El-Namus, Sahara Southern Libya: A Baseline Assessment from 2010 Field Sampling

Abstract

Wau El-Namus, located in the Fezzan region of southwestern Libya, is a rare volcanic caldera containing inland saline lakes within a hyperarid desert environment. This study presents an environmental assessment of four sampled water bodies—Lake 1, Lake 2, Lake 3, and the Red Lake—based on original field sampling conducted in May 2010. The investigation integrated geomorphological observations with physicochemical, hydrochemical, and biological analyses to characterize this distinctive saline-lake system. The three main lakes differed in morphometry, with maximum depths of 16.6 m in Lake 1, 15.8 m in Lake 2, and 11.4 m in Lake 3. Surface waters of the main lakes were alkaline, with pH values ranging from 8.6 to 8.8 and water temperatures ranging from 23.3 to 23.7°C. Electrical conductivity values ranged from 20.5 to 52.3 mS/cm in the three main lakes and reached 126.0 mS/cm in the Red Lake. Total dissolved solids exceeded 50 g/L and reached 126 g/L in the Red Lake. Hydrochemical analysis showed strong ionic enrichment, with sodium concentrations ranging from 3.82 to 7.90 g/L in the three main lakes and reaching 48.46 g/L in the Red Lake, while chloride ranged from 1.20 to 4.40 g/L in the main lakes and reached 34.47 g/L in the Red Lake. Within Lake 1, marked spatial variation was observed, with pH ranging from 8.3 to 8.9, electrical conductivity from 18.96 to 82.60 mS/cm, chlorophyll-a from 4.31 to 130.24 mg/L, and nitrite from 0.03 to 3.55 mg/L. The lake margins were dominated by Phragmites australis, with associated occurrence of Imperata cylindrica, Tamarix aphylla, and Phoenix dactylifera. Phytoplankton analysis identified 12 taxa, mainly diatoms and cyanobacteria, while zooplankton was dominated by Artemia salina and dipteran larvae. The occurrence of Dunaliella salina was associated with the red pigmentation of the Red Lake. Bird observations included Egretta garzetta, Motacilla flava, and Himantopus himantopus, indicating that the lake system also provides localized ecological habitat within the surrounding desert. These findings show that Wau El-Namus is a hydrochemically and ecologically differentiated hypersaline lake system of considerable scientific importance in the Libyan Sahara. The study provides original field-based data on one of the most distinctive inland saline environments in North Africa and establishes a basis for future limnological, ecological, and conservation-oriented research.