Environmental fate of Nutrients in the Karun River Using the AQUATAX Model

Background: The fate of nutrients plays a crucial role in the environmental management of aquatic ecosystems. Methods: This study, performed in 2024, investigated the environmental fate of nutrients in the Karun River using the AQUATOX model. The water samples were collected from 10 locations across all seasons. Phosphate and nitrate concentrations were measured, along with dissolved oxygen (DO), electrical conductivity (EC), pH, and total suspended solids (TSS), following standard methods for the AQUATOX modeling. Two scenarios were simulated: S1 (a 15% reduction in nutrient levels) and S2 (a 15% increase). The Shannon, Simpson, Camargo, and Brillouin indices were calculated as biological indicators under these scenarios. Results: The average values of the Shannon, Simpson, Camargo, and Brillouin indices were 1.295, 0.585, 0.308, and 1.247, respectively, indicating low biodiversity and a high dominance of specific species in the Karun River ecosystem. The AQUATOX model estimated annual average phosphate and nitrate concentrations at 4.55 and 23.64 mg/L, respectively. DO and algal biomass were measured at 2.31 mg/L and 1.16 g/L. The simulation results highlighted the direct impact of nutrient fluctuations on ecosystem dynamics. In Scenario 1, the total nutrient concentration reached 223.9 mg/L, while in Scenario 2, it decreased to 32.42 mg/L. A 15% reduction in nutrient concentrations significantly improved biodiversity. Conclusion: The findings showed that variations in nutrient levels can profoundly influence biodiversity in aquatic ecosystems.