Clay and organic matter interaction in the biogeochemical genesis of alkaline soda-lake water

Abstract This controlled experimental study examines bentonite, compost, and their combination (bentonite+compost) as biogeochemical drivers in the genesis of alkaline soda-lake water. Treatments affected mineral–water reactions (including hydrolysis), ion partitioning, and nutrient cycling processes, controlling brine evolution under non-flow-through, aerated bottle conditions in the laboratory. pH ranged from 8.18 to 10.35, highest in bentonite-only treatments, while electrical conductivity peaked in bentonite+compost at 995 µS cm⁻ 1 . At the final sampling point (day 30), the bentonite+compost treatment showed the strongest Na enrichment and carbonate-system response, with Na⁺ reaching 61.64 mg L⁻ 1 and the carbonate-species signal 12.83 mg L⁻ 1 (HCO 3 − + CO 3 2 ⁻), compared with 52.53 mg L⁻ 1 Na⁺ and 7.12 mg L⁻ 1 carbonate-species signal in bentonite-only and 12.77 mg L⁻ 1 Na⁺ and 4.93 mg L⁻ 1 carbonate-species signal in compost-only. Compost-only produced the highest K⁺ (162.11 mg L⁻ 1 ), Ca 2 ⁺ (46.80 mg L⁻ 1 ), and Mg 2 ⁺ (20.39 mg L⁻ 1 ), whereas bentonite-only showed the lowest dissolved Ca 2 ⁺ (3.30 mg L⁻ 1 ) and Mg 2 ⁺ (2.26 mg L⁻ 1 ); bentonite+compost was intermediate for divalent cations (Ca 2 ⁺ 14.36 mg L⁻ 1 , Mg 2 ⁺ 5.54 mg L⁻ 1 ) and K⁺ (67.38 mg L⁻ 1 ). For conservative anions, Cl⁻ increased across treatments from bentonite-only (241.02 mg L⁻ 1 ) to compost-only (329.20 mg L⁻ 1 ) to bentonite+compost (446.78 mg L⁻ 1 ), while SO 4 2 ⁻ was lowest in bentonite+compost (5.87 mg L⁻ 1 ) relative to bentonite-only (23.71 mg L⁻ 1 ) and compost-only (29.30 mg L⁻ 1 ). Compost-treated samples showed nutrient enrichment, with TN increasing from 13.54 to 28.47 mg L⁻ 1 , TP from 7334.33 to 13475.5 mg L⁻ 1 , and TOC from 67.01 to 174.93 mg L⁻ 1 , whereas bentonite contributed minimal nutrients but maintained higher and less variable pH. Evaporation rates differed among treatments (20.77, 18.39, and 17.95 mL day⁻ 1 for compost-only, bentonite-only, and bentonite+compost, respectively). The results are interpreted primarily from the solute chemistry dataset, with solid-phase and microbial effects inferred rather than directly measured. This deeper understanding of the biogeochemical genesis of alkaline soda waters provides crucial practical insights for the effective management and ecological restoration of these unique ecosystems.