Simulation of Sulfur Cycle using CE-QUAL-W2 model (Case Study of Seymareh Dam Reservoir, Iran)

In recent decades, due to the importance of water quality issues and controlling the proposed environmental damages, the study of the pollutants behavior in water bodies has also became important. Sulfur compounds are contaminating factors in water bodies which should be considered in deep water bodies such as lakes and reservoirs of dams. The most common sulfur compounds in deep water bodies are sulfate and hydrogen sulfide. Accurate prediction of the interactions between these compounds can be helpful in designing hydraulic structures and water quality management. The present study examines this context and consider how they interact with each other. The international experiences in dealing with high concentrations of sulfur compounds in the reservoirs of dams and lakes are investigated in this study. This study also examines the relationship between the physical, chemical and biological reactions of the sulfur cycle in aquatic environments. The modeling will focus on two main sulfur compounds in the water, namely sulfate and hydrogen sulfide. To simulate the water quality in the reservoirs, the CE-QUAL-W2 model, which has recently been upgraded to the simulation of the sulfur cycle, has been employed. After model setup, its calibration is performed. Another point to be noted is that the spatial and temporal distribution of sulfur compounds is influenced by reaction factors and parameters affecting the temperature, hydrodynamics and the distribution of these types of pollutants. Setting the coefficients and parameters effective in the process of biological deterioration can be caused by the behavior of sulfur compounds. The access to the field data is a challenging task in this effort. In order to reduce the error of the concentration of sulfur compounds in this research, the choice of these coefficients is based on the quantities available in valid references. Modeling the concentration of sulfur compounds in the water due to the multiplicity of factors affecting the biological and chemical reactions of the sulfur cycle in aquatic environments is essentially a difficult and challenging issue. Therefore, studying this problem in water bodies seems to be necessary. On the other hand, no studies have been conducted to identify, investigate and use numerical models to simulate the sulfur compounds (sulfate and sulfide hydrogen) in water bodies in Iran. It seems that this research can be the first tackle to resolve the uncertainties and problems associated with the sulfur cycle in aquatic structures, and to examine the behavior of this cycle in the actual reservoir of the dam in Iran. In general, the objectives of this study are classified into two general sections. First, the study of the behavior of sulfur cycle in deep water bodies, such as lakes and reservoirs of dams, playing an important role in the behavior and performance of reservoirs of dams. Then, identification and prediction of the behavior and effects induced by the sulfur compounds in a case study using CE-QUAL-W2. In fact, the behavior identification and assessment of the contaminants effects are an essential step to ensure from the proper execution of a project and method for determining, predicting, controlling and changing their effects on the entire environment, public health, and the health of ecosystems that sustain life and survival of humans. In this study, the status of the sulfur compounds is simulated in various scenarios, along with the important quality factors such as thermal stratification and dissolved oxygen distribution in the platform of a real case study (Seymareh Dam reservoir). Additionally, based on the model results and analyzing these scenarios, analyzing the time trends and predicted depth profile for probable concentrations of the sulfur compounds (sulfate and sulfide hydrogen) and analyzing the behavior sensitivity of these compounds are examined in comparison with different parameters. The results of the present study revealed: (1) a significant relationship between the dissolved oxygen status and the distribution of the sulfur compounds along the reservoir depth exists, so that the hydrogen sulfide concentration is increased as the dissolved oxygen decreases; (2) the behavior of the sulfur cycle is significantly related to the interaction of main biological agents in the sediments of the reservoir bed; (3) by increasing the sulfate concentration in the reservoir, the amount of the sulfate reduction increases and it leads to an increase in hydrogen sulfide in the reservoir; (4) considering the limited capacity of dissolution of hydrogen sulfide in water, this substance is released as bubbles from the water so that the amount of hydrogen sulfide emissions increases rapidly with increasing sulfate content in water