Online first articles

This study provides the first and preliminary biogeochemical characterization of Lake Magadi, an unexplored shallow soda lake in the Songwe region of Tanzania. The lake exhibited pH, alkalinity and electrical conductivity of 10.155, 760 mEquiv and 47 mS/cm, respectively, indicating that it is among the most extreme soda lakes in the East African Rift Valley and likely worldwide. Na+ (1215 mM) predominated over Ca²⁺ and Mg²⁺ (1.40 mM and 0.42 mM, respectively), while Cl⁻ (792 mM) predominated over sulfates (13 mM). The levels of total dissolved inorganic phosphorus (2.7 mM), total dissolved nitrogen (0.51 mM) and dissolved organic carbon (7 mM) indicated a high accumulation of nutrients. The dissolved organic matter was comprised of highly humified, aromatic and large-sized moieties enriched in ¹³C, suggesting an accumulation of highly recalcitrant compounds in the water column. The detection of dissolved methane (~1 µM) indicated microbial methanogenesis was likely released into the anoxic sediments. The water column also exhibited high chlorophyll concentration (0.156 mg/L), with the planktonic primary producers dominated by Spirulina-like organisms. In summary, these preliminary results, including its extreme alkalinity, indicate a set of unique biogeochemical properties that make the lake a prime site for future ecological and biogeochemical research on extreme aquatic habitats.