Physicochemical Characterization of Pond Waters in the Kanem Region, Republic of Chad

The physicochemical properties of ten water samples from ponds in the Kanem region and a sample from the southern part of Lake Chad were analyzed. Surface water samples were collected in October 2007. The following parameters were determined: temperature, pH, electrical conductivity, the major ions (Ion Chromatography), SiO2 and HCO3 - (UV-visible Spectrophotometer) and trace elements (Li, Rb, Cs, Be, Sr, Ba, Al, V, Cr, Mn, Co, Ni, Cu, Zn, Mo, Ag, Cd, Sn, Pb, Bi, As, Sb, U) (ICP-MS). Based on pH the waters are neutral or alkaline. The waters exhibited low, medium, and high salt enrichments based on conductivity. Compared to Lake Chad, the concentrations of major ions vary significantly. Salinity, defined by Total Dissolved Solids, ranged from fresh, brackish, and saline to brine waters. Water chemistry is predominantly influenced by the evaporation-crystallization process. In the Piper and Chadha diagrams, the pond waters are mainly of the Na-HCO3 type. Trace element concentrations are either enriched or depleted compared to Lake Chad and resemble those of soda or saline lakes. Occasionally elevated concentrations of As (0.20–0.70 mg/L) could impact the quality of harvested spirulina from the Kanem ponds.