Assessing Water Quality in Rivers Flowing into the Caspian Sea in term of pollution using Water Quality Indices and Remote Sensing indices

Abstract

Abstract Ensuring the water quality of the rivers flowing into the Caspian Sea is crucial for preserving the delicate ecosystem and safeguarding the environmental health of the region. In this study, objectives encompassed determining water quality using various indices, creating zoning maps through ordinary kriging to identify contamination locations, employing Principal Component Analysis (PCA) to identify crucial parameters, and establishing the relationship between water quality indices and spectral reflections. The results revealed significant variations in pollution levels across the studied rivers. The Haraz River exhibited the highest chemical pollution (chemical Water quality index (WQI: 0.87), while the Talar River demonstrated the highest physical WQI (6.36) and overall water pollution (6.53). Additionally, the Babolroud River registered the highest pollution in the Dissolved Oxygen Deficit Index (DODI) (84.12) and Dissolved Oxygen Saturation (Dosat) (7.45), while the Talar River topped Domeasured (18), and both the Talar and Haraz rivers were identified as the most polluted based on the Pollution Load Index (PLI) (26.21) and Eutrophication Index (EI) (120.68), respectively. Utilizing the PCA method highlighted the pivotal role of the chemical WQI (-0.932 and − 0.896) in assessing water quality in the Babolroud and Talar Rivers, while the Dosat index (0.943) emerged as crucial for accurate evaluation of the Haraz River. Further analysis of the relationship between water quality and remote sensing indices revealed the pronounced association of unveiled the Modified Normalized Difference Water Index (MNDWI) index pronounced association with chemical WQI in the Talar River (coefficient: -0.705) and the robust correlation between Dosat and the MNDWI in the Haraz River (correlation rate: -0.824). Conversely, the Talar River exhibited a direct correlation between the chemical WQI and BSI (correlation level: 0.827), indicative of increased turbidity.