Generation of hydrogen sulfide in the deepest part of a reservoir under anoxic water conditions

The generation of hydrogen sulfide in a reservoir can be characterized by a massive influx of organic matter, manifest thermal stratification, and an extreme anoxic state specifically at the hypolimnion layer in summer. It has been reported that in this deep layer of a thermally stratified water body, where dissolved oxygen is depleted and redox potential falls sharply below the value of zero, the prolonged oxygen-free period and negative redox potential may potentiate the production of toxic hydrogen sulfide. The main aim of this study was to simulate the varying concentration of hydrogen sulfide at the deepest part of the reservoir based on intensive monitoring of water quality parameters. A one-dimensional hydraulic ecosystem model was applied to simulate vertical distribution of dissolved oxygen (DO) continuously in time. Based on the simulated DO, the length of continuous oxygen-free state in the deepest layer was specified and then utilized to estimate the temporal changes of oxidation–reduction potential (ORP) using a polynomial regression model. Finally, a linear regression model for hydrogen sulfide was fitted from the observed ORP, based on which, the temporal changes of hydrogen sulfide concentration were modeled using the simulated ORP. The introduction of several calculations gave good simulated results of hydrogen sulfide concentration, and this approach can be considered useful for predictive and explanatory purposes in further research investigating toxic hydrogen sulfide at the hypolimnion of the reservoir.