Temporal analysis and assessment of surface water quality in the Hamoun-Hirmand basin, the impact of salinity on soil degradation and intensification of dust storm events: Evaluation of sustainable water use in irrigation and agriculture

Background and Objectives: In recent years, the quality of surface waters has deteriorated due to pollution from various sources such as agricultural runoff, industrial effluents, and municipal wastewater. These factors can alter water quality and affect the livelihoods of communities and the environment. Assessing the quality of surface waters for agricultural and irrigation purposes is essential to ensure the safety of crops, ecosystems, and human health. The use of unsuitable water for agriculture can lead to soil salinization, ecosystem degradation, desertification, and the occurrence of dust storm events. Therefore, stakeholder participation and policy interventions are essential to enforce regulations and best practices for the protection of surface water quality.
Methodology: The Hamoun-Hirmand watershed, covering an area of 63,589.6 square kilometers, is located in the southeast of Iran. This closed watershed is highly important in terms of water resources and faces challenges such as water scarcity, pollution, and threats from climate change. Efforts are underway to improve water management, protect this unique ecosystem, and ensure food security. This study monitored the quality of surface waters in this watershed with a focus on sustainable agricultural practices, aiming to protect the ecosystem, prevent desertification, and reduce dust storm events caused by human activities. For this purpose, the chemical quality of surface water in the Hamoun-Hirmand watershed was investigated at 10 hydrometric stations with quantitative (flow rate) and qualitative (physicochemical parameters) data during the years 1976 to 2016. Parameters such as flow rate, electrical conductivity (EC), total dissolved solids (TDS), acidity (pH), cations (calcium, magnesium, sodium, and potassium), anions (chloride, sulfate, and carbonate), sodium percentage, sodium adsorption ratio (SAR), and total hardness were examined. Finally, the Piper diagram was used to study the hydrochemical facies, and the Wilcox diagram was applied to assess water quality for irrigation and agricultural purposes. Using 26 years of data from two meteorological stations in Zabol and Zahak, this research examined dust storm events, identified the generating winds, and analyzed the relationship between dust storms and water salinity. The WRPlot View.8.0.2 software was employed to draw the dust rose diagrams.
Results: The study of Hamoun surface waters showed that salinity (EC and TDS) varied among stations. The dominant ions were sodium, magnesium, chloride, and sulfate. Ion concentrations increased over time due to geological, hydrological, and climatic factors of the region. Salinity was within acceptable limits in most stations except for Pol-e Shileh and Lar-Payin, but it showed an increasing trend. The droughts of 1998–2008 and 2010–2011 were associated with increased salinity. EC and TDS had a direct correlation with each other and an inverse relationship with water flow. The highest salinity values were observed in hot months with the lowest flow rates. In the upstream part of the watershed, water quality was mainly “slightly saline to saline” and suitable for irrigation and agriculture, while in the downstream part, water quality was “very saline” and mostly fell into the C4-S4 and C4-S3 classes, unsuitable for agriculture and leading to increased salt concentrations, especially sulfate and chloride anions and sodium cations. The quality of Hirmand River water declined in the Chah-Nimeh wells, probably due to irrigation, agricultural and aquaculture activities, high evaporation, and the entry of suspended sediments into the wells. The study of dust in Zahak and Zabol showed that the significant increase of dust events in specific years was associated with factors such as geographical location, climate changes, land use, and water salinity. Although water salinity played a more significant role in Zahak, other factors contributed in Zabol. Overall, the occurrence of dust storms was the result of the complex interaction of multiple environmental factors, with water salinity being one of them.
Conclusion: The Hamoun-Hirmand watershed faces water quality challenges due to both natural and human factors such as climate change, irrigation and agricultural activities, wastewater, and urbanization. These factors affect salinity, ion concentrations, and the overall health and quality of water, ultimately impacting soil and ecosystems. Continuous monitoring of water quality parameters and the adoption of water management strategies are essential to address challenges leading to ecosystem and land degradation and to ensure sustainable use of this vital resource. Conservation, efficient irrigation, and wastewater treatment can improve water quality. Therefore, further research is required to identify sources of pollution and develop comprehensive water management programs, considering the relationship between land use practices, water quality, and ecosystem health