PoRGy is a Stella model that calculates diel dissolved O2 concentrations and O2 isotopic ratios based on a few key variables. It can be used to estimate the P:R (or P:R:G) ratio of an aquatic ecosystem. It may also be used to determine the effect of of certain variables or the combination of certain variables on diel dissolved O2 concentrations and O2 isotopic ratios. Please refer to Venkiteswaran et al. (2007, Oecologia) for more details.