🧪 Aquatic zinc speciation modeling across the Inhulets River (September 2025) highlights why total metal concentrations fail to reflect true ecotoxicity: ☝️ Key Hydrogeochemical Trends: 🔹 Free aqua-ion (Zn²⁺): Dominates at most stations (57–64%). This fraction is the most bioavailable and drives aquatic toxicity. 🔹 Carbonate complex (ZnCO₃⁰): Secondary background form (18–24%), facilitating conservative transit migration. 🔹 Sulfate complex (ZnSO₄⁰): Consistently 6–11% due to elevated background sulfate mineralization. 🔹 Shift at Sample Point 6_1 (pH 8.66): Alkaline buffering radically alters speciation—free Zn²⁺ drops to 32%, while ZnCO₃⁰ becomes dominant (49%) alongside rising ZnOH⁺ (8%). Methodology: ⚙️ Speciation: PHREEQC (Thermoddem database) ⚙️ Pipeline & Dataviz: R (tidyverse, ggplot2) ⚙️ Minor species (<0.5%) aggregated into "Other" (Інші форми). #Hydrogeochemistry #PHREEQC #RStats #WaterQuality #EnvironmentalDataScience #InhuletsRiver #KryvyiRih #Geochemistry #OpenScience #Mining #IronOreMining