Temporal dynamics and analysis of pollutant parameters in the water quality entering a reservoir dam

Assessing water quality changes across water bodies is essential for resource management and environmental protection, as variations influenced by natural and human factors help predict trends and control pollution. This study evaluates temporal trends in key physical, chemical, and biological water quality parameters from 2014 to 2024, entering the Sardasht Reservoir Dam, located in the mountainous region, in order to assess the effects of pollution, natural changes, and human activities on water quality. The data includes physical parameters (temperature, EC, TDS), chemical parameters (BOD, COD, nitrates, heavy metals like Mn and Pb), and biological parameters (total coliforms). The research applied statistical methods, including the Mann-Kendall test and Sen’s slope, to determine trends in these parameters over time. In addition to trend analysis, the study utilized box plots, violin plots, and probability density functions (PDFs) to understand the distribution and variability of water quality values. The results reveal several important trends in water quality at Sardasht Dam. COD showed a significant increasing trend (Tau = 0.224, p = 0.033), indicating rising organic pollution. Several parameters, including TDS and pH, exhibited decreasing trends, though not statistically significant. Mn levels and Temp showed increasing trends, possibly linked to environmental changes like industrial activities or climate change. Significant fluctuations in COD, NO3, and Pb suggest episodic pollution events, potentially from urban or agricultural runoff. DO, pH, and TDS displayed more consistent trends, showing stable water quality in these aspects. These results indicate the rising COD and temperature posing potential threats to water usability and ecosystem health. Elevated manganese levels may lead to sediment accumulation and water treatment challenges. The study recommends closer monitoring and management of inflows to the reservoir, particularly addressing organic pollution, temperature increases, and metal contamination to maintain water quality standards. The results emphasiz the need for strategic pollution control measures, further emphasizing the importance of long-term monitoring in this key water resource. The results show the urgent need for integrated pollution control and sustainable water management strategies to maintain water quality and support long-term reservoir operation.